73 results on '"Gai, W."'
Search Results
2. A preliminary design of the collinear dielectric wakefield accelerator.
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Zholents, A., Gai, W., Doran, S., Lindberg, R., Power, J.G., Strelnikov, N., Sun, Y., Trakhtenberg, E., Vasserman, I., Jing, C., Kanareykin, A., Li, Y., Gao, Q., Shchegolkov, D.Y., and Simakov, E.I.
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COLLINEAR reactions , *DIELECTRIC materials , *LASER plasma accelerators , *PARTICLE beam bunching , *CHARGE exchange - Abstract
A preliminary design of the multi-meter long collinear dielectric wakefield accelerator that achieves a highly efficient transfer of the drive bunch energy to the wakefields and to the witness bunch is considered. It is made from ~0.5 m long accelerator modules containing a vacuum chamber with dielectric-lined walls, a quadrupole wiggler, an rf coupler, and BPM assembly. The single bunch breakup instability is a major limiting factor for accelerator efficiency, and the BNS damping is applied to obtain the stable multi-meter long propagation of a drive bunch. Numerical simulations using a 6D particle tracking computer code are performed and tolerances to various errors are defined. [ABSTRACT FROM AUTHOR]
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- 2016
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3. Using an Emittance Exchange Scheme for High Harmonic Generation by Free-Electron Lasers.
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Jiang, B., Gai, W., Liu, W., and Power, J. G.
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BEAM emittance (Nuclear physics) , *FREE electron lasers , *SECOND harmonic generation , *ELECTRON beams , *WAVELENGTHS , *ENERGY bands , *SYNCHROTRON radiation - Abstract
We propose combining a transverse-to-longitudinal emittance exchange beam line and a conventional modulator to generate high harmonics with short-wavelength free-electron lasers. The key point of this scheme is the use of a multi-slit mask to create a transverse-shaped beam. In an emittance exchange beam line, the transverse-shaped bunch will produce a longitudinal-shaped one, resulting in separated energy bands. The modulator that follows this step will generate micro-bunches containing high harmonics. A coherent synchrotron radiation effect is also considered in this paper; compared to the two-modulator scheme, the method investigated here is more flexible and can be used to relax the coherent synchrotron radiation effect. [ABSTRACT FROM AUTHOR]
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- 2010
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4. Beam dynamics simulations of the transverse-to-longitudinal emittance exchange proof-of-principle experiment at the Argonne Wakefield Accelerator.
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Rihaoui, M., Gai, W., K.-J.-Kim, Piot, P., Power, J. G., and Sun, Y.-E.
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BEAM dynamics , *COMPUTER simulation , *MATERIALS testing , *ELECTRON accelerators , *LASER manipulation (Nuclear physics) , *ELECTRONIC equipment - Abstract
Transverse-to-longitudinal emittance exchange has promising applications in various advanced acceleration and light source concepts. A proof-of-principle experiment to demonstrate this phase space manipulation method is currently being planned at the Argonne Wakefield Accelerator. The experiment focuses on exchanging a low longitudinal emittance with a high transverse horizontal emittance and also incorporates room for possible parametric studies e.g. using an incoming flat beam with tunable horizontal emittance. In this paper, we present realistic start-to-end beam dynamics simulation of the scheme, explore the limitations of this phase space exchange. [ABSTRACT FROM AUTHOR]
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- 2009
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5. Observation of transverse space charge effects in a mutli-beamlet electron bunch produced in a photo-emission electron source.
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Rihaoui, M., Gai, W., Piot, P., Power, J. G., and Yusof, Z.
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SPACE charge , *PHOTOEMISSION , *ELECTRON emission , *ELECTRON beams , *ELECTRON optics , *PARTICLES (Nuclear physics) - Abstract
A “multiple beamlet” experiment aimed at investigating the transverse space charge effect was recently conducted at the Argonne Wakefield Accelerator. The experiment generated a symmetric pattern of 5 beamlets on the photocathode of the RF gun with the drive laser. We explored the evolution of the thereby produced 5 MeV, space-charge dominated electron beamlets in the 2 m drift following the RF photocathode gun for various external focusing. Two important effects were observed and benchmarked using the particle-in-cell beam dynamics code Impact-T. In this paper, we present our experimental observation and their benchmarking with Impact-T. [ABSTRACT FROM AUTHOR]
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- 2009
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6. Development of Dielectric-Based High Gradient Accelerating Structures.
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Jing, C., Gai, W., Konecny, R., Power, J., Liu, W., Gold, S. H., Kinkead, A. K., Kanareykin, A., and Kazakov, S.
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DIELECTRIC waveguides , *ACCELERATION potential , *LINEAR accelerators , *PHOTOMULTIPLIERS , *IMPEDANCE matching , *RADIO frequency - Abstract
High gradient accelerating structures using dielectric-lined circular waveguides have been developed for a number of years at Argonne National Laboratory. In this article, we first report the experimental results of high power rf testing on the quartz based Dielectric-Loaded Accelerating (DLA) structure carried out on Feb. 2006 at the Naval Research Laboratory. The motivation for this experiment is to test the multipactor effect on different materials under high power and high vacuum condition. Up to 12 MW pulsed rf went through the tube without breakdown. Multipactor appeared during the experiment but with different features compared to other materials like alumina. Photomultiplier Tube (PMT) measurements were introduced into the experiment for the first time to observe the light emission time and intensity. In the second part of this paper, ways to achieve higher gradient for DLA structures are proposed: 1) smaller ID and longitudinal gap free DLA structures to reduce multipactor and obtain higher gradient; 2) new coaxial type coupler to avoid dielectric gap and improve impedance matching; 3) double layered DLA structure to reduce rf loss and enhance shunt impedance as well. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]
- Published
- 2006
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7. Dielectric Loaded Wakefield Structures for RF Power Generation.
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Conde, M. E., Gai, W., Jing, C., Konecny, R., Liu, W., Power, J. G., Wang, H., and Yusof, Z.
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ELECTRIC power production , *DIELECTRIC devices , *ELECTRON beams , *CORDIERITE , *ACCELERATION (Mechanics) , *WAVEGUIDES , *OSCILLOSCOPES , *PHYSICS - Abstract
A 15 GHz dielectric loaded wakefield structure has been used to extract energy from a 13 MeV electron beam. Short electron bunches (13 ps FWHM) of up to 43 nC traversed the structure, generating an accelerating field of ∼23 MV/m. The structure consists of a cylindrical ceramic tube (cordierite) with a dielectric constant of 5, inner and outer radii of 5 mm and 7.49 mm, respectively. The 102 mm long dielectric cylinder is inserted into a cylindrical copper waveguide. Short metallic cylinders, with the same inner and outer radii as the ceramic, are inserted on both ends of the copper waveguide, making it a standing wave structure. A field probe present near the outer edge of the dielectric samples the RF field generated by the electron bunches. This signal is then sent to a mixer circuit, where the 15 GHz signal is down converted to 5 GHz and sent to an oscilloscope. We present measurements made with single electron bunches and also with two bunches separated by 1.5 ns. As a next step in these experiments, another structure, with an output coupler, has been designed and is presently being fabricated. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]
- Published
- 2006
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8. Experimental Study of Multipactor Suppression in a Dielectric-Loaded Accelerating Structure.
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Power, J. G., Gai, W., Gold, S. H., Kinkead, A. K., Konecny, R., Jing, C., and Liu, W.
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PARTICLE accelerators , *PARTICLE acceleration , *ACCELERATION (Mechanics) , *DIELECTRIC devices , *ALUMINUM oxide , *PHYSICS - Abstract
High power tests are currently being conducted on RF-driven dielectric-loaded accelerating (DLA) structures to determine their viability as traveling-wave accelerators. These tests are a collaborative effort between Argonne National Laboratory (ANL) and the Naval Research Laboratory (NRL). In a previous high power test, single-surface multipactor was reported to be capable of absorbing more than half of the RF power incident on an alumina-based DLA structure. In this paper, we report on the most recent set of high power tests that are attempting to further understand multipactor and eventually suppress it. Several methods were employed to suppress multipactor including: the use of a magnetic field; a TIN surface coating; and a different dielectric material (Magnesium-Calcium-Titanate based). The effectiveness of these three methods are presented and discussed in the paper. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]
- Published
- 2004
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9. Transformer Ratio Enhancement for Structure-Based Wakefield Acceleration.
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Kanareykin, A., Gai, W., Power, J. G., and Schoessow, P.
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PARTICLE accelerators , *PARTICLE acceleration , *ACCELERATION (Mechanics) , *ELECTRON beams , *PARTICLE beams , *PHYSICS - Abstract
A limiting factor in the efficiency of wakefield accelerators is the fact that the transformer ratio R, the parameter that characterizes the energy transfer efficiency from the accelerating structure to the accelerated electron beam, is less than 2 for most technologically realizable beam-structure configurations. We are planning an experiment to study transformer ratio enhancement in a 13.625 GHz dielectric wakefield structure driven by a ramped bunch train. In this paper we present an experimental program for the demonstration of this Enhanced Transformer Ratio Dielectric Wakefield Accelerator (ETR-DWA). © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]
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- 2004
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10. A Tunable Dielectric Wakefield Accelerating Structure.
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Kanareykin, A., Gai, W., Power, J., Sheinman, E., and Altmark, A.
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DIELECTRICS , *FERROELECTRICITY - Abstract
We present a method to vary the resonant frequency of a dielectric loaded structure (driven either by the wakefield of a beam or an external rf source). It consists of a thin layer of a ferroelectric material backing a layer of conventional ceramic. A DC bias voltage is used to vary the permittivity of the ferroelectric layer and thus rune the overall frequency of the accelerating structure. In this paper, a detailed model is given for this device and an experimental test is proposed. Employing this scheme would compensate for frequency shifts in the accelerating structure caused by ceramic waveguide machining tolerances and dielectric constant heterogeneity. We have identified a suitable material for this application: a BST ferroelectric-oxides compound with a dielectric constant of 300-500. A tuning range of (2-4)% could be achieved for a (11-13) GHz dielectric accelerating structure. [ABSTRACT FROM AUTHOR]
- Published
- 2002
11. Summary report of the Working Group on electromagnetic structure-based acceleration concepts.
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Colby, E. R. and Gai, W.
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PARTICLE accelerators , *MICROWAVES , *DIELECTRICS , *WAVEGUIDES - Abstract
Significant progress in both the study of new acceleration structures and in the production and experimental testing of a variety of structures has taken place since the last Conference. Staging of laser accelerator sections and acceleration of particles by a microwave inverse FEL was demonstrated for the first time, fabrication of 92 GHz structures compatible with high power was demonstrated, new experimental results on dielectric based acceleration concept were presented, and detailed analysis of a new accelerator scheme, the inverted medium accelerator, was discussed. Novel structure development continued apace, with twisted waveguide structures, resonantly driven dielectric wakefield accelerators, and evanescent-mode capillary guide laser accelerators all being introduced. Power sources present and future and their impact on structure development were examined together with the need for renewed vigor in studying rf breakdown at higher frequencies. The needs and potential applications for table top radiation sources were discussed, with the expectation that development efforts in this area would directly impact the design of a future collider. [ABSTRACT FROM AUTHOR]
- Published
- 2001
12. Transformer ratio enhancement using a ramped bunch train in a collinear wakefield accelerator.
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Power, J. G., Gai, W., and Kanareykin, A.
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ELECTRIC transformers , *LINEAR accelerators - Abstract
We present a practical method for achieving a transformer ratio (R) greater than 2 with any collinear wakefield accelerator — i.e. with either plasma or structure based wakefield accelerators. It is known that the transformer ratio cannot generally be greater than 2 for a symmetric drive bunch in a collinear wakefield accelerator. However, using a ramped bunch train (RBT) where a train of n electron drive bunches, with increasing ('ramping') charge, one can achieve R = 2n after the bunch train. We believe this method is feasible from an engineering standpoint using existing technology and an experiment to be preformed at the Argonne Wakefield Accelerator (AWA) is planned. [ABSTRACT FROM AUTHOR]
- Published
- 2001
13. X-band dielectric loaded traveling-wave acceleration structure.
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Zou, P., Gai, W., Konecny, R., Sun, X., and Wong, T.
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ACCELERATION waves , *PARTICLE acceleration , *DIELECTRICS - Abstract
We report on the construction, numerical modeling and experimental testing of a traveling-wave acceleration structure based on a dielectric-lined circular waveguide. This type of structure has similar acceleration properties to disk-loaded metal slow wave structures but with some distinct advantages in terms of simplicity of fabrication, suppression of parasitic wakefield effects, and having no dark current. Efficient coupling of external RF power to the cylindrical dielectric waveguide is a technical challenge, particularly to structures loaded with very high dielectric constant materials. We have designed and constructed an 11.4GHz structure loaded with ceramic with dielectric constant of 20, to be powered by an external RF power source. High efficiency RF coupling has been achieved using a combination of a tapered dielectric end section and a carefully adjusted coupling slot. Bench tests using a network analyzer have demonstrated a power coupling efficiency in excess of 95% with bandwidth of 30 MHz, and vacuum tests have also shown that this dielectric loaded structure can be operated in an ultra-high vacuum environment. Thus, this work provides a necessary basis for construction of an accelerator using this kind of structure. We have also simulated the parameters of this structure using MAFIA. Within the limits of the approximations used, the results are in agreement with the bench measurements. [ABSTRACT FROM AUTHOR]
- Published
- 2001
14. Short-pulse dielectric two-beam acceleration.
- Author
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GAI, W., POWER, J. G., and JING, C.
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PARTICLE acceleration , *DIELECTRICS , *ELECTRON beams , *ULTRASHORT laser pulses , *RADIO frequency , *PARAMETER estimation - Abstract
We are exploring a new parameter space of the two-beam acceleration (TBA) scheme based on an ultra-short (~20 ns) rf pulse in a dielectric TBA. All two-beam accelerators (TBAs) use an electron drive beam to generate high-power rf in a decelerator and extract this power to drive an accelerating structure to high gradient. Typically, the rf pulse is on the order of hundreds of ns or greater in order to maintain good rf-to-beam efficiency. However, recent scaling arguments show that the rf breakdown threshold improves with decreasing rf pulse length, so it desirable to find a way to run at short-pulse length with good efficiency. In this paper, we discuss how we chose the design parameters of a short-pulse TBA for a TeV linear collider module. We then present plans for an experimental program to demonstrate TBA at Argonne wakefield accelerator (AWA) facility including high-power rf generation, high-gradient acceleration, and staging. [ABSTRACT FROM PUBLISHER]
- Published
- 2012
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15. RECENT STRUCTURE BASED HIGH GRADIENT WAKEFIELD EXPERIMENTS AT ARGONNE.
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GAI, W., CONDE, M. E., GAO, F., JING, C., KONECNY, R., LIU, W., POWER, J. G., WANG, H., and YUSOF, Z.
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DIELECTRIC devices , *DIELECTRICS , *ELECTRON beams , *ELECTRON optics , *PARTICLES (Nuclear physics) , *PHYSICS - Abstract
Dielectric structures promise to support high field, especially for short wakefield pulses produced by a high charged electron beam traveling in a dielectric tube. To push the gradient higher, we have tested two structures using recent upgraded Argonne wakefield accelerator facility that capable of producing up to 100 nC charge and bunch length of < 13ps (FWHM). Here we report on the experiment results that more than 80 nC beam passes through a 14 GHz dielectric loaded wakefield structure that produced an accelerating field of ~ 45 MV/m. The two structures consist of a cylindrical ceramic tube (cordierite) with a dielectric constant of 5, inner and outer radii of 5 mm and 7.49 mm, respectively, and with length of 102 mm and 23 mm long. We present measurements made with single electron bunches and also with two bunches separated by 1.5 ns. As a next step in these experiments, another structure, with an output coupler, has been designed and is presently being fabricated. [ABSTRACT FROM AUTHOR]
- Published
- 2007
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16. High-Power RF Tests on X-Band Dielectric-Loaded Accelerating Structures.
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Chunguang Jing, Gai, W., Power, J. G., Konecny, R., Gold, Steven H., Liu, W., and Kinkead, Allen K.
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DIELECTRICS , *RADIO frequency , *ELECTRIC breakdown , *ELECTRIC fields , *ELECTROMAGNETIC fields - Abstract
A joint Argonne National Laboratory (ANL)/Naval Research Laboratory (NRL) program is under way to investigate X-band dielectric-loaded accelerating (DLA) structures, using high-power 11.424-GHz radiation from the NRL Magnicon Facility. DLA structures offer the potential of a simple, inexpensive alternative to copper disk-loaded structures for use in high-gradient radio-frequency (RF) linear accelerators. A central purpose of our high-power test program is to find the RF breakdown limits of these structures. In this paper, we summarize the most recent tests results for two DLA structures loaded with different ceramics: alumina and MgxCa1-xTiO3 (MCT). No RF breakdown has been observed up to 5 MW of drive power (equivalent to 8 MV/m accelerating gradient), but multipactor was observed to absorb a large fraction of the incident microwave power. The latest experimental results on suppression of multipactor using a TiN coating on the inner surface of the dielectric are reported. Although we did not observe dielectric breakdown in the structure, breakdown did occur at the ceramic joint, where the electric field is greatly enhanced. Lastly, the MCT structure showed significantly less multipactor for the same level RF field. [ABSTRACT FROM AUTHOR]
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- 2005
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17. Localization of α-, β-, and γ-synuclein during neuronal development and alterations associated with the neuronal response to axonal trauma
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Quilty, M.C., Gai, W-P., Pountney, D.L., West, A.K., and Vickers, J.C.
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NEURODEGENERATION , *NEURONS - Abstract
Genetic and protein studies have indicated abnormalities in α-synuclein in neurodegenerative diseases. However, the developmental localization and cellular role of synuclein isoforms is contentious. We investigated the cellular localization of α-, β-, and γ-synuclein in developing cultured rat neurons and following axonal transection of relatively mature neurons, a model that disrupts the axonal cytoskeleton and results in regenerative sprouting. Cortical neurons were grown up to 21 days in vitro (DIV). Axon bundles at 21 DIV were transected and cellular changes examined at 4 and 24 h post-injury. Immunohistochemistry demonstrated that α- and β-synuclein were localized to cellular cytosol and growth cones at 3DIV, with accumulating puncta-like labeling within axons and growth cones by 10-21DIV. In contrast, γ-synuclein immunoreactivity was limited at all time points. By 21DIV, α- and β-synuclein were present in the same neurons but largely in separate subregions, only 26% of puncta contained both α- and β-synuclein immunoreactivity. Less than 20% of α-, β-, and pan-synuclein immunoreactive puncta directly colocalized to synaptophysin profiles at 10DIV, decreasing to 10% at 21DIV. Both α- and β-synuclein accumulated substantially within damaged axons at 21DIV and were localized to cytoskeletal abnormalities. At latter time points post-injury, α- and β-synuclein immunoreactive puncta were localized to growth cone-like structures in regenerating neurites. This study shows that α- and β-synuclein have a precise localization within cortical neurons and are generally nonoverlapping in their distribution within individual neurons. In addition, synuclein proteins accumulate rapidly in damaged axons and may have a role in regenerative sprouting. [Copyright &y& Elsevier]
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- 2003
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18. α-Synuclein Immunoisolation of Glial Inclusions from Multiple System Atrophy Brain Tissue Reveals Multiprotein Components.
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Gai, W. P., Power, J. H. T., Blumbergs, P. C., Culvenor, J. G., and Jensen, P. H.
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PROTEINS , *SYNAPSES , *PARKINSON'S disease , *BRAIN - Abstract
Abstract: Immunohistochemical studies have shown that oligodendroglial inclusions in multiple system atrophy contain alpha-synuclein, a synaptic protein also found in Lewy bodies in Parkinson's disease. We have now used density gradient enrichment and an anti-alpha-synuclein immunomagnetic technique to isolate pure and morphologically intact oligodendroglial inclusions from brain white matter of patients dying with multiple system atrophy. Filamentous inclusion structures were obtained only from multiple system atrophy tissue, but not from normal brain tissues, or from multiple system atrophy tissue processed without anti-alpha-synuclein antibody. We confirmed the purity and morphology of isolated inclusions by electron microscopy. The inclusions comprised multiple protein bands after separation by polyacrylamide gel electrophoresis. Immunoblotting demonstrated that these proteins included alpha-synuclein, alpha B-crystallin, tubulins, ubiquitin, and prominent, possibly truncated alpha-synuclein species as high-molecular-weight aggregates. Our study provides the first biochemical evidence that oligodendroglial inclusion filaments consist of multiple protein components, suggesting that these inclusions may form as a result of multiprotein interactions with alpha-synuclein. Key Words: alpha-Synuclein--Multiple system atrophy--Neural inclusion--Parkinson's disease--Neurodegeneration. J. Neurochem. 73,... [ABSTRACT FROM AUTHOR]
- Published
- 1999
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19. Observation of wakefield generation in left-handed band of metamaterial-loaded waveguide.
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Antipov, S., Spentzouris, L., Gai, W., Conde, M., Franchini, F., Konecny, R., Liu, W., Power, J. G., Yusof, Z., and Jing, C.
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METAMATERIALS , *WAVEGUIDES , *CHERENKOV radiation , *ELECTRON beams , *DETECTORS - Abstract
We report on a design of a TM-mode based metamaterial-loaded waveguide. Network analyzer measurements demonstrated a left-handed propagation region for the TM11 mode at around 10 GHz. A beamline experiment was performed with the metamaterial-loaded waveguide. In this experiment, a 6 MeV electron beam passes through the waveguide and generates a wakefield via the Cherenkov radiation mechanism. We detected a signal in the left-handed frequency band at 10 GHz. This is an indirect demonstration of reverse Cherenkov radiation as predicted in the work of Veselago [Sov. Phys. Usp. 10, 509 (1968)] and discussed in the works of Lu et al. [Opt. Express 11, 723 (2003)], Averkov and Yakovenko [Phys. Rev. B 72, 205110 (2005)], and Tyukhtin et al. [IEEE, Proceedings of the PAC, 2007 (unpublished), pp. 4156–4158]. Cherenkov radiation in artificially constructed materials [metamaterials (MTMs)] can provide unusual engineered features that can be advantageous for particle detector design. [ABSTRACT FROM AUTHOR]
- Published
- 2008
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20. High power radio frequency generation by relativistic beams in dielectric structures.
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Schoessow, P., Conde, M.E., Gai, W., Konecny, R., Power, J., and Simpson, J.
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DIELECTRIC devices , *ELECTROMAGNETIC waves - Abstract
Presents a study which examined the interaction of a high current relativistic beam with dielectric loaded waveguides, as a source of electromagnetic radiation. Information on the availability of radio frequency photocathode for generating high current beams; Details on the dielectric device measurements; Discussion and summary of the study.
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- 1998
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21. Multiple-system atrophy: a new alpha-synuclein disease?
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Gai, W. P., Power, J.H.T., Blumbergs, P.C., Blessing, W.W., and Power, J H
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NEUROMUSCULAR diseases , *CONFOCAL microscopy , *MUSCULAR atrophy , *BRAIN stem , *CELLS , *COMPARATIVE studies , *DEMENTIA , *DYES & dyeing , *RESEARCH methodology , *MEDICAL cooperation , *MOTOR neuron diseases , *NERVE tissue proteins , *NEURODEGENERATION , *NEURONS , *PARKINSON'S disease , *PHOSPHOPROTEINS , *RESEARCH , *SILVER , *EVALUATION research - Abstract
Reports on studies conducted on multiple-system atrophy. Multiple-system atrophy a neurodegenerative disease involving various combinations of parkinsonism, ataxia, and other symptoms; Tests run on samples of brain tissue; Use of confocal microscopy and double-staining for alpha-synuclein.
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- 1998
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22. Rotenone and elevated extracellular potassium concentration induce cell-specific fibrillation of α-synuclein in axons of cholinergic enteric neurons in the guinea-pig ileum.
- Author
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Sharrad, D. F., Chen, B. N., Gai, W. P., Vaikath, N., El‐Agnaf, O. M., and Brookes, S. J. H.
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ROTENONE , *SYNUCLEINS , *AXONS , *NEURONS , *PARKINSON'S disease - Abstract
Background Parkinson's disease is a progressive neurodegenerative disorder that results in the widespread loss of select classes of neurons throughout the nervous system. The pathological hallmarks of Parkinson's disease are Lewy bodies and neurites, of which α-synuclein fibrils are the major component. α-Synuclein aggregation has been reported in the gut of Parkinson's disease patients, even up to a decade before motor symptoms, and similar observations have been made in animal models of disease. However, unlike the central nervous system, the nature of α-synuclein species that form these aggregates and the classes of neurons affected in the gut are unclear. We have previously reported selective expression of α-synuclein in cholinergic neurons in the gut ( J Comp Neurol. 2013; 521:657), suggesting they may be particularly vulnerable to degeneration in Parkinson's disease. Methods In this study, we used immunohistochemistry to detect α-synuclein oligomers and fibrils via conformation-specific antibodies after rotenone treatment or prolonged exposure to high [K+] in ex vivo segments of guinea-pig ileum maintained in organotypic culture. Key Results Rotenone and prolonged raising of [K+] caused accumulation of α-synuclein fibrils in the axons of cholinergic enteric neurons. This took place in a time- and, in the case of rotenone, concentration-dependent manner. Rotenone also caused selective necrosis, indicated by increased cellular autofluorescence, of cholinergic enteric neurons, labeled by Ch AT-immunoreactivity, also in a concentration-dependent manner. Conclusions & Inferences To our knowledge, this is the first report of rotenone causing selective loss of a neurochemical class in the enteric nervous system. Cholinergic enteric neurons may be particularly susceptible to Lewy pathology and degeneration in Parkinson's disease. [ABSTRACT FROM AUTHOR]
- Published
- 2017
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23. Construction and testing of an 11.4 GHz dielectric structure based traveling wave accelerator.
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Zou, P., Gai, W., Konecny, R., Sun, X., Wong, T., and Kanareykin, A.
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DIELECTRICS , *TRAVELING-wave tubes , *RADIO frequency , *SCIENTIFIC apparatus & instruments - Abstract
We report on the design, numerical modeling, and experimental testing of a cylindrical dielectric loaded traveling wave structure for charged particle beam acceleration. This type of structure has similar accelerating properties to disk-loaded metal slow wave structures but with some distinct advantages in terms of simplicity of fabrication and suppression of parasitic wakefield effects. Efficient coupling of external rf power to the cylindrical dielectric waveguide is a technical challenge, particularly with structures of very high dielectric constant ε. We have designed and constructed an X-band structure loaded with a permittivity ε=20 dielectric to be powered by an external rf power source. We have attained high efficiency broadband rf coupling by using a combination of a tapered dielectric end section and a carefully adjusted coupling slot. Bench testing using a network analyzer has demonstrated a power coupling efficiency in excess of 95% with bandwidth of 30 MHz, thus providing a necessary basis for construction of an accelerator using this device. We have also simulated the parameters of this structure using a finite difference time domain electromagnetic solver. Within the limits of the approximations used, the results are in reasonable agreement with the bench measurements. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]
- Published
- 2000
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24. Improved risk stratification of nasopharyngeal cancer by targeted sequencing of Epstein–Barr virus DNA in post-treatment plasma.
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Chan, D.C.T., Lam, W.K.J., Hui, E.P., Ma, B.B.Y., Chan, C.M.L., Lee, V.C.T., Cheng, S.H., Gai, W., Jiang, P., Wong, K.C.W., Mo, F., Zee, B., King, A.D., Le, Q.T., Chan, A.T.C., Chan, K.C.A., and Lo, Y.M.D.
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NASOPHARYNX cancer , *EPSTEIN-Barr virus , *DNA viruses , *WHOLE genome sequencing , *SOMATIC mutation , *DNA sequencing - Abstract
Quantitative measurement of plasma Epstein–Barr virus (EBV) DNA by real-time PCR at the end of primary treatment is a robust prognostic marker for nasopharyngeal carcinoma (NPC) patients. However, up to 40% of patients who would later develop disease recurrence had undetectable post-treatment plasma EBV DNA. Targeted sequencing for the entire EBV genome potentially allows a more comprehensive and unbiased detection of plasma EBV DNA and enables the use of other parameters such as fragment size as biomarkers. Hence, we explored if plasma EBV DNA sequencing might allow more accurate prognostication of NPC patients. Plasma samples collected from 769 patients with stage IIB-IVB NPC at 6-8 weeks after radiotherapy were analysed using targeted sequencing for EBV DNA. The sensitivities of the PCR-based analysis, at a cut-off of any detectable levels of plasma EBV DNA, for prediction of local and distant recurrences were 42.3% and 85.3%, respectively. The sequencing-based analysis (involving quantitation and size profiling) achieved better performance for both local and distant recurrences than PCR. Using a cut-off of the proportion of plasma EBV DNA deduced by sequencing at 0.01%, the sensitivities of the sequencing-based analysis for local and distant recurrences were 88.5% and 97.1%, with the resultant negative predictive values of 99.1% and 99.4%, respectively. Among patients with undetectable EBV DNA on quantitative PCR, sequencing could further define a subgroup that enjoyed superior survival outcomes based on the proportion of plasma EBV DNA, with a 5-year progression-free survival (PFS) approaching 90%. On multivariate analysis, sequencing-based quantitative level of plasma EBV DNA was the independent prognostic factor with the highest hazard ratio for prediction of overall survival and PFS. NPC prognostication using post-treatment plasma EBV DNA could be enhanced through sequencing. • PCR-based analysis of plasma EBV DNA has limited sensitivity in predicting recurrences of NPC. • Sequencing analysis of post-treatment plasma EBV DNA improves the sensitivity for both local and distant relapses of NPC. • Sequencing analysis of post-treatment plasma EBV DNA could better stratify the mortality risk of NPC patients than PCR. [ABSTRACT FROM AUTHOR]
- Published
- 2022
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25. Photocathode emission studies: Dark current and Schottky-enabled photo-electrons in a high-field RF gun.
- Author
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Chen, H., Du, Y., Gai, W., Grudiev, A., Hua, J., Huang, W., Power, J., Wisniewski, E. E., Wuensch, W., Tang, C., Yan, L., and You, Y.
- Subjects
- *
PHOTOCATHODES , *DARK currents (Electric) , *PHOTOELECTRONS , *RADIO frequency modulation , *SCHOTTKY barrier , *COPPER electrodes - Abstract
We report on dark current and Schottky-enabled photoemission from a copper photocathode surface. Field-emitted dark current is a major gradient-limiting factor in RF cavities. Field emission is generally attributed to geometrical projections on the bulk surface whose field enhancement factor (β) and the emitting area (Ae) can be extracted from the Fowler-Nordheim (FN) plot. Measurements were made at Tsinghua S-band RF gun facility in two separate experiments. Using the traditional FN formula for RF fields we discovered that field enhancement factor (β) alone cannot explain the full data set. Instead, we found that a low work function at some sites is required. In addition, surface analysis of the cathode after the experiment shows that geometric β indicated would be < 10. Thus we conclude that low work function sites with a small β are responsible for dark current emission and subsequent breakdown in high-gradient structures. The origin of these sites is unclear but could be due to defects or impurities. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
26. Design and Analysis of a Single-Shot Longitudinal Phase Space Measurement Diagnostics at the Argonne Wakefield Accelerator.
- Author
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Rihaoui, M., Mihalcea, D., Gai, W., Piot, P., and Power, J. G.
- Subjects
- *
LONGITUDINAL method , *PHASE space , *PARTICLE accelerators , *MAGNETIC dipoles , *COMPUTER simulation , *CORIOLIS force - Abstract
A single-shot longitudinal phase space diagnostics is currently being assembled at the Argonne Wakefield Accelerator (AWA). The diagnostics consists of mapping the longitudinal phase space coordinates to the transverse position space plane using a beamline that incorporates two magnetic dipoles arranged as a dogleg followed by an rf deflecting cavity. The deflecting cavity streaks the beam vertically while the dipole magnets bend horizontally. In this paper, we analyze analytically and via numerical simulations the performances of such diagnostics and their limitations. Simulations done in IMPACT-T shows good reconstruction of the longitudinal phase space. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
27. 7.8 GHz High Power Generation And Extraction With A Dielectric-loaded Waveguide.
- Author
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Gao, F., Conde, M. E., Gai, W., Jing, C., Konecny, R., Liu, W., Power, J. G., Wong, T., and Yusof, Z.
- Subjects
- *
EXTRACTION apparatus , *MATERIALS testing , *DIELECTRIC devices , *RADIO frequency , *WAVEGUIDES , *FREQUENCIES of oscillating systems , *ELECTRONIC equipment - Abstract
In this paper, we present updated results on power extraction testing of a 7.8 GHz dielectric loaded waveguide power extractor using both high charge single bunches and bunch trains. We have generated a 1.7 ns radio frequency (rf) pulse with 30 MW of power with a single 66 nC electron bunch. Then we have generated a pulse train of electron beam for rf generation of 10 ns and 22 ns rf pulses. [ABSTRACT FROM AUTHOR]
- Published
- 2009
- Full Text
- View/download PDF
28. Development of a Compact Dielectric-Loaded Test Accelerator at 11.4 GHz.
- Author
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Gold, S. H., Kinkead, A. K., Gai, W., Power, J. G., Konecny, R., Jing, C., and Fliflet, A. W.
- Subjects
- *
DIELECTRIC devices , *ELECTRON accelerators , *MATERIALS testing , *ACCELERATION (Mechanics) , *ELECTRONIC equipment - Abstract
This paper presents a progress report on the development of a dielectric-loaded test accelerator in the Magnicon Facility at the Naval Research Laboratory (NRL). The accelerator will be powered by an 11.4-GHz magnicon amplifier that provides up to 25 MW of output power in a ∼250-ns pulse at up to 10 Hz. The accelerator includes a 5-MeV electron injector originally developed at the Tsinghua University in Beijing, China, and can incorporate dielectric-loaded accelerating (DLA) structures of up to 0.5 m in length. The DLA structures are being developed by Argonne National Laboratory and Euclid Techlabs, and shorter test structures fabricated from a variety of dielectric materials have undergone rf testing at NRL at accelerating gradients up to 15 MV/m. The first stage of the accelerator, including the 5-MeV injector, has recently begun operation, and initial operation of the complete dielectric-loaded test accelerator, including injector, DLA test structure, and spectrometer, should take place within the next year. [ABSTRACT FROM AUTHOR]
- Published
- 2009
- Full Text
- View/download PDF
29. Update on the Development of Externally Powered Dielectric-Loaded Accelerating Structures.
- Author
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Jing, C., Kanareykin, A., Gai, W., Konecny, R., Power, J. G., Liu, W., Gold, S. H., and Kinkead, A. K.
- Subjects
- *
DIELECTRIC devices , *RADIO frequency , *ACCELERATION (Mechanics) , *MATERIALS testing , *TECHNOLOGICAL innovations , *ELECTRONIC equipment - Abstract
We report on recent progress in a program to develop an RF-driven Dielectric-Loaded Accelerating (DLA) structure, capable of supporting high gradient acceleration. Previous high power tests revealed that the earlier DLA structures suffered from multipactor and arcing at the dielectric joint. A few new DLA structures have been designed to alleviate this limitation including the coaxial coupler based DLA structure and the clamped DLA structure. These structures were recently fabricated and high power tested at the NRL X-band Magnicon facility. Results show the multipactor can be reduced by the TiN coating on the dielectric surface. Gradient of 15 MV/m has also been tested without dielectric breakdown in the test of the clamped DLA structure. Detailed results are reported, and future plans discussed. [ABSTRACT FROM AUTHOR]
- Published
- 2009
- Full Text
- View/download PDF
30. Observation of Wakefield Generation in Left-Handed Band of Metamaterial-Loaded Waveguide.
- Author
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Antipov, S., Liu, W., Gai, W., Power, J. G., and Spentzouris, L.
- Subjects
- *
WAVEGUIDES , *ELECTRON beams , *CHERENKOV radiation , *ELECTRON optics , *ELECTRICAL conductors , *PARTICLES (Nuclear physics) - Abstract
We report on a design of a TM-mode based metamaterial-loaded waveguide. Network analyzer measurements demonstrated a left-handed propagation region for the TM11 mode at around 10 GHz. A beamline experiment was performed with the metamaterial-loaded waveguide. In this experiment, a 6 MeV electron beam passes through the waveguide and generates a wakefield, via the Cherenkov radiation mechanism. We detected a signal in the left-handed frequency band at 10 GHz. This is an indirect demonstration of reverse Cherenkov radiation as discussed in several papers. Cherenkov radiation in artificially constructed materials (metamaterials, MTM) can provide unusual, engineered features that can be advantageous for particle detector design. [ABSTRACT FROM AUTHOR]
- Published
- 2009
- Full Text
- View/download PDF
31. Left-Handed Structures for Accelerator Applications.
- Author
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Antipov, S., Liu, W., Gai, W., Power, J. G., and Spentzouris, L.
- Subjects
- *
PARTICLE accelerators , *DISPERSION (Chemistry) , *WAVEGUIDES , *ELECTROMAGNETIC waves , *FREQUENCY spectra , *COMPUTER simulation - Abstract
Metamaterials are artificial periodic structures made of small elements and designed to obtain specific electromagnetic properties. As long as the periodicity and the size of the elements are much smaller than the wavelength of interest, an artificial structure can be described by a permittivity and permeability, just like natural materials. When the permittivity and permeability are simultaneously negative in some frequency range, the metamaterial is called double negative or left-handed and has some unusual properties. Left-handed metamaterials (LHM) have potential applications in active and passive devices at millimeter waves and at much higher frequencies. Waveguides loaded with metamaterials are of interest because the metamaterials can change the dispersion relation of the waveguide significantly. Slow backward waves can be produced in a LHM-loaded waveguide without corrugations. The dispersion relation of a LHM-loaded waveguide has several interesting frequency bands which are described. Left-handed structures can be employed at X-band accelerators to suppress wakefields. In this paper we present theoretical studies and computer modeling of waveguides loaded with 2D anisotropic metamaterials, dispersion relations for LHM-loaded waveguides, and describe current efforts toward designing a left-handed accelerator. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]
- Published
- 2006
- Full Text
- View/download PDF
32. High Power rf Test on X-band MgxCa1-xTiO3 Based Dielectric-Loaded Accelerating Structure.
- Author
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Jing, C., Konecny, R., Gai, W., Gold, S. H., Power, J. G., Kinkead, A. K., and Liu, W.
- Subjects
- *
PARTICLE accelerators , *PARTICLE acceleration , *ACCELERATION (Mechanics) , *DIELECTRIC devices , *DIELECTRICS , *PHYSICS - Abstract
In this paper, we report experimental results on a series of high-power rf tests for dielectric-loaded accelerating (DLA) structures using a high power X-band Magnicon at the Naval Research Laboratory. The dielectric material loaded into this DLA structure is a commonly used high-Q ceramic, MgxCa1-xTiO3 (MCT), with a dielectric constant of 20. The purpose of these experiments is to study high-power phenomena in the DLA structure. Two important phenomena have been observed during these experiments. First, multipactor effects are strongly dependent on the dielectric material used in the DLA structure. In this case, the multipactor-induced power absorption threshold and trend to higher power differ when MCT is used instead of alumina. Second, although we did not observe dielectric breakdown in the bulk dielectric, breakdown occurred at the butt-joint between adjacent dielectric sections in the MCT structure. This occurs because of manufacturing imperfections of the joint that cause large, local field enhancements. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]
- Published
- 2004
- Full Text
- View/download PDF
33. Beam Dynamics and Performance of a 15.6 GHz Ceramic High Power RF Generator.
- Author
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Smirnov, A. V., Yu, D., Gai, W., and Wang, H.
- Subjects
- *
BEAM dynamics , *PARTICLE beams , *PARTICLES (Nuclear physics) , *WAVES (Physics) , *LINEAR accelerators , *PHYSICS - Abstract
Beam dynamics estimations of a 15.6GHz ceramic RF power generator have been performed for an experiment planned at the upgraded AWA facility at ANL. Theoretical maximum peak power that can be generated exceeds 100–150 MW. Analytical and numerical calculations address the following issues: 50A+ heavy beam loading in linac, slow-wave structures, coupler and damper; beam breakup and dipole mode suppression, end-to-end beam transport, and generated RF waveform and spectrum. Comparison is made with an earlier 21GHz experiment in a DULY/CERN/ANL collaboration. © 2004 American Institute of Physics [ABSTRACT FROM AUTHOR]
- Published
- 2004
- Full Text
- View/download PDF
34. Experimental measurements of wakefields in a multimode, dielectric structure driven by a train of electron bunches.
- Author
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Power, J. G., Conde, M. E., Gai, W., Kanareyken, A., Konecny, R., and Schoessow, P.
- Subjects
- *
PARTICLE acceleration , *ELECTRONS , *DIELECTRIC waveguides - Abstract
We report on the experimental results of a new wakefield acceleration scheme. The multibunch driven, multimode, dielectric wakefield accelerator was demonstrated at the Argonne Wakefield Accelerator (AWA). In this experiment, a bunch train of 4, 5 nC electron bunches, separated by 760 ps, was passed through a 60 cm long dielectric-lined cylindrical waveguide. The separation was chosen to match the net acceleration wavelength of the multimode structure. By carefully measuring the energy spectrum of the 4 beams after they passed through the waveguide, we demonstrated that the wakefield is indeed enhanced by a train of periodically spaced electron bunches. The analysis of the multimode structure driven by a bunch train was done by a trivial extension to the existing theory since we are operating in the linear regime. This work represents the first experimental demonstration of this concept and also shows that multibunch operation of wakefield accelerators is worthy of further investigation. [ABSTRACT FROM AUTHOR]
- Published
- 2001
35. Multi-Nanosecond High Power Pulse Generation at 7.8 GHz With a Dielectric-Loaded Power Extractor.
- Author
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Gao, F., Conde, M. E., Gai, W., Jing, C., Konecny, R. S., Liu, W., Power, J. G., Wong, T., and Yusof, Z.
- Subjects
- *
PARTICLE accelerators , *ELECTRON optics , *ELECTRON beams , *PARTICLES (Nuclear physics) , *PARTICLE beams , *CYCLOTRON waves , *ELECTRON bombardment conductivity , *RECIRCULATING electron accelerators , *WAVEGUIDES - Abstract
Power extraction from charged particle beams is a prospective way to develop future high power radio frequency (RF) sources. We have designed and tested a 7.8 GHz power extractor based on a dielectric-loaded waveguide. Building upon earlier work on single electron bunch tests, 10 ns and 22 ns megawatt-level RF pulses have been generated with trains consisting of 16 electron bunches each, by using a laser splitting-recombination scheme. In addition, 44 MW of peak power has been generated with a train consisting 4 electron bunches. Behaviors of higher-order-modes are also explored. [ABSTRACT FROM AUTHOR]
- Published
- 2009
- Full Text
- View/download PDF
36. Double-negative metamaterial research for accelerator applications
- Author
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Antipov, S., Spentzouris, L., Gai, W., Liu, W., and Power, J.G.
- Subjects
- *
PARTICLE accelerators , *NUCLEAR physics , *NUCLEAR energy , *DISPERSION relations - Abstract
Abstract: Material properties are central to the design of particle accelerators. One area of advanced accelerator research is to investigate novel materials and structures and their potential use in extending capabilities of accelerator components. Within the past decade a new type of artificially constructed material having the unique property of simultaneously negative permittivity and permeability has been realized, and is under intense investigation, primarily by the optical physics and microwave engineering communities [C.M. Soukoulis, Science 315 (2007) 47; D.R. Smith, J.B. Pendry, M.C.K. Wiltshire, Science 305 (2004) 788; J.B. Pendry, A.J. Holden, W.J. Stewart, I. Youngs, Phys. Rev. Lett. 76 (1996) 4773]. Although they are typically constructed of arrays of discrete cells, as long as the condition that the wavelength of applied radiation is significantly greater than the cell dimensions is met, the material mimics a continuous medium and can be described with the bulk properties of permittivity, , and permeability, . When the permittivity and permeability are simultaneously negative in some frequency range, the metamaterial is called double negative (DNM) or left-handed (LHM) and has unusual properties, such as a negative index of refraction. An investigation of these materials in the context of accelerators is being carried out by IIT and the Argonne Wakefield Accelerator Facility [S. Antipov, W. Liu, W. Gai, J. Power, L. Spentzouris, AIP Conf. Proc. 877 (2006); S. Antipov, W. Liu, J. Power, L. Spentzouris, Design, Fabrication, and Testing of Left-Handed Metamaterial, Wakefield Notes at Argonne Wakefield Accelerator, http://www.hep.anl.gov/awa/wfnotes/wf229.pdf ]. Waveguides loaded with metamaterials are of interest because the DNM can change the dispersion relation of the waveguide significantly. For example, slow backward waves can be produced in a DNM-loaded waveguide without having corrugations. This article begins with a brief introduction of known design principles for realizing a DNM [J.B. Pendry, A.J. Holden, W.J. Stewart, I. Youngs, Phys. Rev. Lett. 76 (1996) 4773; D.R. Smith, et al., Phys. Rev. Lett. 84 (2000) 4184; J.B. Pendry, A.J. Holden, D.J. Robbins, W.J. Stewart, IEEE Trans. Microwave Theory Tech. 47 (1999) 2075], along with a description of the experimental verification of the basic DNM properties of our designs. We then present our waveguide analysis, starting with the case of a waveguide loaded with a truly continuous medium that is dispersive and anisotropic. We show that the dispersion relation of a waveguide with frequency regions of negative and negative has several interesting frequency bands. While a DNM approximates a continuous medium, it is still made up of discrete elements. We discuss some implications of the discrete nature of the material for the behavior of a loaded waveguide, particularly at frequencies below the cutoff frequency of the waveguide. We conclude by describing our experimental program at present and in the near future. This includes testing the excitation of TM modes in a DNM loaded waveguide in the interesting frequency bands, both on the bench and from particle beam excitation. [Copyright &y& Elsevier]
- Published
- 2007
- Full Text
- View/download PDF
37. Alpha-synuclein is upregulated in neurones in response to chronic oxidative stress and is associated with neuroprotection
- Author
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Quilty, M.C., King, A.E., Gai, W-P., Pountney, D.L., West, A.K., Vickers, J.C., and Dickson, T.C.
- Subjects
- *
OXIDATIVE stress , *NEURONS , *PARKINSON'S disease , *BRAIN diseases - Abstract
Abstract: Chronic oxidative stress has been linked to the neurodegenerative changes characteristic of Parkinson’s disease, particularly alpha-synuclein accumulation and aggregation. However, it remains contentious whether these alpha-synuclein changes are cytotoxic or neuroprotective. The current study utilised long-term primary neural culture techniques with antioxidant free media to study the cellular response to chronic oxidative stress. Cells maintained in antioxidant free media were exquisitely more vulnerable to acute exposure to hydrogen peroxide, yet exposure of up to 10 days in antioxidant free media did not lead to morphological alterations in neurones or glia. However, a subpopulation of neurones demonstrated a significant increase in the level of alpha-synuclein expressed within the cell body and at synaptic sites. This subset of neurones was also more resistant to apoptotic changes following exposure to antioxidant free media relative to other neurones. These data indicate that increased alpha-synuclein content is associated with neuroprotection from relatively low levels of oxidative stress. [Copyright &y& Elsevier]
- Published
- 2006
- Full Text
- View/download PDF
38. Mode analysis of a multilayered dielectric-loaded accelerating structure
- Author
-
Jing, Chunguang, Liu, W.M., Gai, W., Power, J.G., and Wong, Thomas
- Subjects
- *
WAVEGUIDES , *ELECTRIC equipment , *VIBRATION (Mechanics) , *WAVES (Physics) - Abstract
Abstract: In this paper we evaluate a cylindrical metallic waveguide lined with multiple layers of dielectric for use as a slow-wave microwave accelerating structure. A general analysis of this traveling wave, multilayered, dielectric-loaded accelerating structure is presented including field solutions for both the TM (acceleration) modes and HEM (parasitic) modes. Furthermore, we present a recursive design procedure for choosing the layer thicknesses, calculation of the standard accelerator figures of merit such as the quality factor Q and shunt impedance per unit length r, and an easy to implement method for damping the HEM modes. Most importantly, it is shown that this multilayered DLA structure has a dramatically improved attenuation compared to the conventional single-layered dielectric-loaded structure while maintaining comparable shunt impedance. As a numerical example, we compare an 11.424GHz multilayered structure using 4 layers and an 11.424GHz conventional single-layered structure. [Copyright &y& Elsevier]
- Published
- 2005
- Full Text
- View/download PDF
39. Idiopathic Parkinson's disease: possible routes by which vulnerable neuronal types may be subject to neuroinvasion by an unknown pathogen.
- Author
-
Braak, H., Rüb, U., Gai, W. P., and Del Tredici, K.
- Subjects
- *
PARKINSON'S disease , *NEUROLOGICAL disorders , *BRAIN diseases , *NEUROLOGY , *NEUROTROPHIC functions , *NEUROPHYSIOLOGY - Abstract
Summary. The progressive, neurodegenerative process underlying idiopathic Parkinson's disease is associated with the formation of proteinaceous inclusion bodies that involve a few susceptible neuronal types of the human nervous system. In the lower brain stem, the process begins in the dorsal motor nucleus of the vagus nerve and advances from there essentially upwards through susceptible regions of the medulla oblongata, pontine tegmentum, midbrain, and basal forebrain until it reaches the cerebral cortex. With time, multiple components of the autonomic, limbic, and motor systems become severely impaired. All of the vulnerable subcortical grays and cortical areas are closely interconnected. Incidental cases of idiopathic Parkinson's disease may show involvement of both the enteric nervous system and the dorsal motor nucleus of the vagus nerve. This observation, combined with the working hypothesis that the stereotypic topographic expansion pattern of the lesions may resemble that of a falling row of dominos, prompts the question whether the disorder might originate outside of the central nervous system, caused by a yet unidentified pathogen that is capable of passing the mucosal barrier of the gastrointestinal tract and, via postganglionic enteric neurons, entering the central nervous system along unmyelinated praeganglionic fibers generated from the visceromotor projection cells of the vagus nerve. By way of retrograde axonal and transneuronal transport, such a causative pathogen could reach selectively vulnerable subcortical nuclei and, unimpeded, gain access to the cerebral cortex. The here hypothesized mechanism offers one possible explanation for the sequential and apparently uninterrupted manner in which vulnerable brain regions, subcortical grays and cortical areas become involved in idiopathic Parkinson's disease. [ABSTRACT FROM AUTHOR]
- Published
- 2003
- Full Text
- View/download PDF
40. Wakefield generation in metamaterial-loaded waveguides.
- Author
-
Antipov, S., Spentzouris, L., Liu, W., Gai, W., and Power, J. G.
- Subjects
- *
WAVEGUIDES , *CHERENKOV radiation , *PERMEABILITY , *DISPERSION (Chemistry) , *NUCLEAR physics , *METAMATERIALS - Abstract
Metamaterials (MTMs) are artificial structures made of periodic elements and are designed to obtain specific electromagnetic properties. As long as the periodicity and the size of the elements are much smaller than the wavelength of interest, an artificial structure can be assigned a permittivity and permeability, just like natural materials. Metamaterials can be customized to have the permittivity and permeability desired for a particular application. When the permittivity and permeability are made simultaneously negative in some frequency range, the metamaterial is called double-negative or left-handed and has some unusual properties. For example, Cherenkov radiation (CR) in a left-handed metamaterial is backward; radiated energy propagates in the opposite direction to particle velocity. This property can be used to improve the design of particle detectors. Waveguides loaded with metamaterials are of interest because the metamaterials can change the dispersion relation of the waveguide significantly. Slow backward waves, for example, can be produced in a MTM-loaded waveguide without corrugations. In this paper we present theoretical studies of waveguides loaded with an anisotropic and dispersive medium (metamaterial). The dispersion relation of a MTM-loaded waveguide has several interesting frequency bands which are described. We present a universal method to simulate wakefield (CR) generation in a waveguide loaded with a dispersive and anisotropic medium. This method allows simulation of different waveguide cross sections, any transverse beam distribution, and any physical dispersion, of the medium. The method is benchmarked against simple cases, which can be theoretically calculated. Results show excellent agreement. [ABSTRACT FROM AUTHOR]
- Published
- 2007
- Full Text
- View/download PDF
41. Electron acceleration through two successive electron beam driven wakefield acceleration stages.
- Author
-
Jing, C., Antipov, S., Conde, M., Gai, W., Ha, G., Liu, W., Neveu, N., Power, J.G., Qiu, J., Shi, J., Wang, D., and Wisniewski, E.
- Subjects
- *
ELECTRON accelerators , *ELECTRON beams , *ACCELERATION (Mechanics) , *POSITRONIUM , *LAW of large numbers - Abstract
Structure based wakefield acceleration may provide a viable approach for accelerating sufficiently large numbers of electrons and positrons at the high gradient needed to meet the luminosity, efficiency, and cost requirements of a future linear collider. An important step in proving its viability is the demonstration of acceleration in multiple stages. Here we show the results of the first experimental demonstration of staged two beam wakefield acceleration, conducted at the Argonne Wakefield Accelerator Facility (AWA), in which a 0.5 nC electron bunch gained equal amounts of energy in two stages ( ∼ 2.4 MeV per stage, corresponding to an average acceleration gradient of ∼ 70 MeV/m). Meanwhile 150MeV/m of acceleration in a single stage has been achieved. The demonstration experiment should be scalable to staged-acceleration at gradients of the order of 200 to 300 MeV/m. Such a development would considerably reduce both the cost and footprint of both a future high-energy physics (HEP) collider, as well as future X-ray light sources. [ABSTRACT FROM AUTHOR]
- Published
- 2018
- Full Text
- View/download PDF
42. High Power RF Generation at W-band Based on Wakefield Excited by Electron Bunch Train.
- Author
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Wang, D., Antipov, S., Conde, M., Doran, S., Gai, W., Jing, C., Liu, W., Power, J., Qiu, J., Wisniewski, E., Schegolkov, D., and Simakov, J.
- Subjects
- *
RADIO frequency , *ENERGY bands , *ELECTRONIC excitation , *PARTICLE beam bunching , *ELECTRON accelerators - Abstract
We present the planned experiment on high power RF generation at W-band, based on the coherent wakefield from the metallic periodic structure of 91 GHz, excited by intense charged bunch train at the Argonne Wakefield Accelerator (AWA) facility. The output RF peak power is expected to be ~100 MW and the electrical field gradient can reach up to 400 MV/m, with RF pulse duration adjustable from few ns to 30 ns when excited by the bunch train of 75 MeV, with 5~10 nC charge in a single bunch and up to 32 sub bunches in total. We report the design and bench test result of the W-band structure, introduce the basic theoretical background of RF generation excited by bunch train and numerical simulation results from CST wakefield solver, which agree well with the analysis. We also design the RF measurement setup, with an 8th harmonic mixer to measure the frequency and a small witness beam to measure the wakefield in the structure. All prepared work goes well and we will perform this experiment in the near future. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
43. Field Emission Study using an L-band Photocathode Gun.
- Author
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Shao, J. H., Antipov, S., Baryshev, S. V., Chen, H. B., Conde, M. E., Doran, D. S., Gai, W., Jing, C., Liu, W., Power, J. G., Qiu, J. Q., Shi, J. R., Wang, F. Y., Whiteford, C., Wisniewski, E., and Xiao, L. L.
- Subjects
- *
FIELD emission , *ENERGY bands , *PHOTOCATHODES , *DARK currents (Electric) , *PARTICLE dynamics analysis - Abstract
Field emission is strongly coupled to the breakdown problem. A series of experiments is being carried out at Argonne Wakefield Accelerator Facility (AWA) using an L-band photocathode gun. Cathodes with different shapes have been tested and a dark current imaging system has been set up. Initial experiment results are presented. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
44. High energy electron radiography system design and simulation study of beam angle-position correlation and aperture effect on the images.
- Author
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Zhao, Quantang, Cao, S.C., Liu, M., Sheng, X.K., Wang, Y.R., Zong, Y., Zhang, X.M., Jing, Y., Cheng, R., Zhao, Y.T., Zhang, Z.M., Du, Y.C., and Gai, W.
- Subjects
- *
RADIOGRAPHY , *HIGH energy electron diffraction , *COMPUTER simulation , *OPTICAL apertures , *IMAGE analysis , *QUADRUPOLES - Abstract
A beam line dedicated to high-energy electron radiography experimental research with linear achromat and imaging lens systems has been designed. The field of view requirement on the target and the beam angle-position correlation correction can be achieved by fine-tuning the fields of the quadrupoles used in the achromat in combination with already existing six quadrupoles before the achromat. The radiography system is designed by fully considering the space limitation of the laboratory and the beam diagnostics devices. Two kinds of imaging lens system, a quadruplet and an octuplet system are integrated into one beam line with the same object plane and image plane but with different magnification factor. The beam angle-position correlation on the target required by the imaging lens system and the aperture effect on the images are studied with particle tracking simulation. It is shown that the aperture position is also correlated to the beam angle-position on the target. With matched beam on the target, corresponding aperture position and suitable aperture radius, clear pictures can be imaged by both lens systems. The aperture is very important for the imaging. The details of the beam optical requirements, optimized parameters and the simulation results are presented. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
45. Complete multipactor suppression in an X-band dielectric-loaded accelerating structure.
- Author
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Jing, C., Gold, S. H., Fischer, Richard, and Gai, W.
- Subjects
- *
ELECTRONIC band structure , *DIELECTRIC-loaded antennas , *MAGNETIC fields , *MAGNETIC field effects , *ELECTROMAGNETISM - Abstract
Multipactor is a major issue limiting the gradient of rf-driven Dielectric-Loaded Accelerating (DLA) structures. Theoretical models have predicted that an axial magnetic field applied to DLA structures may completely block the multipactor discharge. However, previous attempts to demonstrate this magnetic field effect in an X-band traveling-wave DLA structure were inconclusive, due to the axial variation of the applied magnetic field, and showed only partial suppression of the multipactor loading [Jing et al., Appl. Phys. Lett. 103, 213503 (2013)]. The present experiment has been performed under improved conditions with a uniform axial magnetic field extending along the length of an X-band standing-wave DLA structure. Multipactor loading began to be continuously reduced starting from 3.5kG applied magnetic field and was completely suppressed at ~8 kG. Dependence of multipactor suppression on the rf gradient inside the DLA structure was also measured. [ABSTRACT FROM AUTHOR]
- Published
- 2016
- Full Text
- View/download PDF
46. RF breakdown test of diamond-loaded resonator for high gradient wakefield accelerator applications.
- Author
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Antipov, S.P., Baryshev, S.V., Butler, J.E., Jing, C., Kanareykin, A.D., Schoessow, P., Conde, M., Gai, W., Power, J.G., and Stoupin, S.
- Subjects
- *
RADIO frequency , *ELECTRIC breakdown , *ELECTRIC currents , *MECHANICAL loads , *X-ray topography - Abstract
Dielectric-loaded accelerating structures (DLAs) for wakefield applications are an alternative to conventional corrugated metal structures. These structures have simple geometry, scale up to THz frequencies, and feature higher breakdown threshold. Diamond has been proposed as a loading material for DLAs due to a number of its unique thermal, microwave, and electrical properties. In this paper we report results of a wakefield breakdown test of a single crystal diamond resonator. A large, 72 nC, charge beam with 2.5 mm length, 8.6 kA peak current was transmitted through a diamond-loaded parallel plate resonator, and induced a standing wave with a 70 MV/m electric field strength. One of the diamond plates had a laser cut, 20 μm wide and 200 μm deep groove, that provided an additional ~ 5-fold field enhancement at edges of the groove resulting in an electric gradient as high as 0.3 GV/m on the surface of the groove. SEM and x-ray topography analyses before and after the test did not reveal any structural damage to the diamond resonator plates. This corroborates further promotion of diamond for high gradient wakefield acceleration at high repetition rates. [ABSTRACT FROM AUTHOR]
- Published
- 2015
- Full Text
- View/download PDF
47. Start-to-end beam dynamics simulation of double triangular current profile generation in Argonne Wakefield Accelerator.
- Author
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Ha, G., Power, J., Kim, S. H., Gai, W., Kim, K.-J., Cho, M. H., and Namkung, W.
- Subjects
- *
BEAM dynamics , *SIMULATION methods & models , *TRIANGULARIZATION (Mathematics) , *PARAMETER estimation , *ELECTRIC currents , *ELECTRON accelerators - Abstract
Double triangular current profile (DT) gives a high transformer ratio which is the determining factor of the performance of collinear wakefield accelerator. This current profile can be generated using the emittance exchange (EEX) beam line. Argonne Wakefield Accelerator (AWA) facility plans to generate DT using the EEX beam line. We conducted start-to-end simulation for the AWA beam line using PARMELA code. Also, we discuss requirements of beam parameters for the generation of DT. [ABSTRACT FROM AUTHOR]
- Published
- 2012
- Full Text
- View/download PDF
48. Development of a Dielectric-Loaded Accelerator Test Facility Based on an X-Band Magnicon Amplifier.
- Author
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Gold, S. H., Kinkead, A. K., Gai, W., Power, J. G., Konecny, R., Jing, C., Tantawi, S. G., Nantista, C. D., Hu, Y., Du, X., Tang, C., Lin, Y., Bruce, R. W., Bruce, R. L., Fliflet, A. W., and Lewis III, D.
- Subjects
- *
TESTING laboratories , *OPTICAL amplifiers , *ELECTRONIC amplifiers , *DIELECTRIC amplifiers , *ELECTRONS , *PHYSICS - Abstract
The Naval Research Laboratory (NRL) and Argonne National Laboratory (ANL), in collaboration with the Stanford Linear Accelerator Center (SLAC), are developing a dielectric-loaded accelerator (DLA) test facility powered by the 11.424-GHz magnicon amplifier that was developed jointly by NRL and Omega-P, Inc. Thus far, DLA structures developed by ANL have been tested at the NRL Magnicon Facility without injected electrons, including tests of alumina and magnesium calcium titanate structures at gradients up to ∼8 MV/m. The next step is to inject electrons in order to build a compact DLA test accelerator. The Accelerator Laboratory of Tsinghua University in Beijing, China has developed a 5-MeV electron injector for the accelerator, and SLAC is developing a means to combine the two magnicon output arms, and to drive the injector and an accelerator section with separate control of the power ratio and relative phase. Also, RWBruce Associates, working with NRL, is developing a means to join ceramic tubes to produce long accelerating sections using a microwave brazing process. The installation and commissioning of the first dielectric-loaded test accelerator, including injector, DLA structure, and spectrometer, should take place within the next year. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]
- Published
- 2006
- Full Text
- View/download PDF
49. Dielectric-Based Wakefield Power Extractor.
- Author
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Jing, C., Gao, F., Kanareykin, A., Schoessow, P., Antipov, S., Gai, W., Conde, M., Liu, W., Power, J. G., Konecny, R., and Yusof, Z.
- Subjects
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DIELECTRICS , *PARTICLE accelerators , *PROTOTYPES , *PARTICLE beams , *ENERGY bands , *NANOSTRUCTURED materials - Abstract
In the Two Beam Accelerator (TBA), wakefield power extractors which extract high power RF from a high current beam are used to power high gradient accelerating structures. A dielectric-based Wakefield Power Extractor (DWPE) is one option in addition to the metallic structures considered previously, like the CLIC PETS (Power Extraction and Transfer Structure). 7.8 GHz and 26 GHz DWPE prototypes have been successfully built and tested at the Argonne Wakefield Accelerator (AWA) facility. We are currently designing an X-band version for a potential application with the CLIC beam. In this article, we report on test results of the 26 GHz DWPE and the preliminary design of the X-band structure. Future plan and possible difficulties in the development of DWPEs are also discussed. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
50. Beam Dynamics Simulation Platform and Studies of Beam Breakup in Dielectric Wakefield Structures.
- Author
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Schoessow, P., Kanareykin, A., Jing, C., Kustov, A., Altmark, A., and Gai, W.
- Subjects
- *
BEAM dynamics , *SIMULATION methods & models , *DIELECTRICS , *NUCLEAR structure , *GREEN'S functions , *PARTICLE beams , *MICROCLUSTERS , *GRID computing - Abstract
A particle-Green's function beam dynamics code (BBU-3000) to study beam breakup effects is incorporated into a parallel computing framework based on the Boinc software environment, and supports both task farming on a heterogeneous cluster and local grid computing. User access to the platform is through a web browser. [ABSTRACT FROM AUTHOR]
- Published
- 2010
- Full Text
- View/download PDF
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