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In radiation therapy, x-ray dose must be precisely sculpted to the tumor, while simultaneously avoiding surrounding organs at risk. This requires modulation of x-ray intensity in space and/or time. Typically, this is achieved using a multi leaf collimator (MLC)-a complex mechatronic device comprising over one hundred individually powered tungsten 'leaves' that move in or out of the radiation field as required. Here, an all-electronic x-ray collimation concept with no moving parts is presented, termed "SPHINX": Scanning Pencil-beam High-speed Intensity-modulated X-ray source. SPHINX utilizes a spatially distributed bremsstrahlung target and collimator array in conjunction with magnetic scanning of a high energy electron beam to generate a plurality of small x-ray "beamlets."A simulation framework was developed in Topas Monte Carlo incorporating a phase space electron source, transport through user defined magnetic fields, bremsstrahlung x-ray production, transport through a SPHINX collimator, and dose in water. This framework was completely parametric, meaning a simulation could be built and run for any supplied geometric parameters. This functionality was coupled with Bayesian optimization to find the best parameter set based on an objective function which included terms to maximize dose rate for a user defined beamlet width while constraining inter-channel cross talk and electron contamination. Designs for beamlet widths of 5, 7, and 10 mmThe optimized 5-, 7-, and 10-mm models had beamlet widths of 5.1 , 7.2 , and 10.1 mmBayesian optimization was coupled with Monte Carlo modeling to generate SPHINX geometries for various beamlet widths. A complete Monte Carlo simulation for one of these designs was developed, including electron beam transport of all beamlets through scanning magnets, x-ray production and collimation, and dose in water. These results demonstrate that SPHINX is a promising candidate for sculpting radiation dose with no moving parts, and has the potential to vastly improve both the speed and robustness of radiotherapy delivery. A multi-beam SPHINX system may be a candidate for delivering magavoltage FLASH RT in humans.

A novel four-port circulator is presented which uses an inline ferromagnetic element to allow for transmission or reflection depending on the sense of the incident circularly polarized wave. This configuration has been shown to reduce the dependency on ferrite anisotropy and support higher power, low rf loss, operation. An analytic analysis of this device is presented alongside corroborating cold test data of the first prototype. High-power operation was performed at 2.856 GHz, with input power levels up to 8 MW for $3.5~\mu \text{s}$ in a pressurized nitrogen environment. The results from this research not only demonstrate ability to eliminate the use of greenhouse insulators, such as SF6, but also provide conceptual groundwork for a new class of ultrahigh power (50 MW+) nonreciprocal networks including circulators, isolators, phase shifters, and rf switches.

Linacs for high-energy physics, as well as for industry and medicine, require accelerating structures which are compact, robust, and cost-effective. Small foot-print linacs require high-accelerating gradients. Currently, stable-operating gradients, exceeding $100\text{ }\text{ }\mathrm{MV}/\mathrm{m}$, have been demonstrated at SLAC National Accelerator Laboratory, CERN, and KEK at X-band frequencies. Recent experiments show that accelerating cavities made out of hard copper alloys achieve better high-gradient performance as compared with soft copper cavities. In the scope of a decade-long collaboration between SLAC, INFN-Frascati, and KEK on the development of innovative high-gradient structures, this particular study focuses on the technological developments directed to show the viability of novel welding techniques. Two novel X-band accelerating structures, made out of hard copper, were fabricated at INFN-Frascati by means of clamping and welding. One cavity was welded with the electron beam and the other one with the tungsten inert gas welding process. In the technological development of the construction methods of high-gradient accelerating structures, high-power testing is a critical step for the verification of their viability. Here, we present the outcome of this step---the results of the high-power rf tests of these two structures. These tests include the measurements of the breakdown rate probability used to characterize the behavior of vacuum rf breakdowns, one of the major factors limiting the operating accelerating gradients. The electron beam welded structure demonstrated accelerating gradients of $90\text{ }\text{ }\mathrm{MV}/\mathrm{m}$ at a breakdown rate of ${10}^{\ensuremath{-}3}/(\mathrm{pulse}\text{ }\mathrm{meter})$ using a shaped pulse with a 150 ns flat part. Nevertheless, it did not achieve its ultimate performance because of arcing in the mode launcher power coupler. On the other hand, the tungsten inert gas welded structure reached its ultimate performance and operated at about a $150\text{ }\text{ }\mathrm{MV}/\mathrm{m}$ gradient at a breakdown rate of ${10}^{\ensuremath{-}3}/(\mathrm{pulse}\text{ }\mathrm{meter})$ using a shaped pulse with a 150 ns flat part. The results of both experiments show that welding, a robust, and low-cost alternative to brazing or diffusion bonding, is viable for high-gradient operation. This approach enables the construction of multicell standing and traveling-wave accelerating structures.

Pluridirectional high-energy agile scanning electronic radiotherapy (PHASER) is next-generation medical linac technology for ultra-rapid highly conformal image-guided radiation, fast enough to "freeze" physiological motion, affording improved accuracy, precision, and potentially superior FLASH radiobiological therapeutic index. Designed for compactness, economy, and clinical efficiency, it is also intended to address barriers to global access to curative radiotherapy.

Finite element representations of Maxwell's equations pose unusual challenges inherent to the variational representation of the `curl-curl' equation for the fields. We present a variational formulation based on classical field theory. Borrowing from QED, we modify the Lagrangian by adding an implicit gauge-fixing term. Our formulation, in the language of differential geometry, shows that conventional edge elements should be replaced by the simpler nodal elements for time-harmonic problems. We demonstrate how this formulation, adhering to the deeper underlying symmetries of the four-dimensional covariant field description, provides a highly general, robust numerical framework., Comment: 13 pages, 16 figures

A new variational theory is presented for beam loading in microwave cavities. The beam--field interaction is formulated as a dynamical interaction whose stationarity according to Hamilton's principle will naturally lead to steady-state solutions that indicate how a cavity's resonant frequency, $Q$ and optimal coupling coefficient will detune as a result of the beam loading. A driven cavity Lagrangian is derived from first principles, including the effects of cavity wall losses, input power and beam interaction. The general formulation is applied to a typical klystron input cavity to predict the appropriate detuning parameters required to maximize the gain (or modulation depth) in the average Lorentz factor boost, $\langle \Delta\gamma \rangle$. Numerical examples are presented, showing agreement with the general detuning trends previously observed in the literature. The developed formulation carries several advantages for beam-loaded cavity structures. It provides a self-consistent model for the dynamical (nonlinear) beam--field interaction, a procedure for maximizing gain under beam-loading conditions, and a useful set of parameters to guide cavity-shape optimization during the design of beam-loaded systems. Enhanced clarity of the physical picture underlying the problem seems to be gained using this approach, allowing straightforward inclusion or exclusion of different field configurations in the calculation and expressing the final results in terms of measurable quantities. Two field configurations are discussed for the klystron input cavity, using finite magnetic confinement or no confinement at all. Formulating the problem in a language that is directly accessible to the powerful techniques found in Hamiltonian dynamics and canonical transformations may potentially carry an additional advantage in terms of analytical computational gains, under suitable conditions., Comment: 18 pages, 6 figures (2nd version: corrected typos and notation; added one more example in Section V). To appear in Physical Review Applied

We report the recent measurement of high gradient and rf breakdown rates (BDRs) in a millimeter-wave accelerating cavity powered by a megawatt gyrotron. The cavity is powered by 10 nanoseconds rf pulses, chopped from 3 microsecond gyrotron pulses using a laser-driven silicon switch. The highest achieved accelerating gradient is 230 MV/m corresponding to a peak surface electric field of 520 MV/m after processing the cavity with more than 105 pulses. The initial BDR is about 10−3[1/pulse] and it has not reached a steady state yet. We expect the BDR to further decrease after extended running time.

We are developing a high-gradient, THz-driven electron gun. THz-frequency accelerator structures can enable the development of compact, bright, and efficient particle sources. Our two cell standing-wave gun is powered by a 110 GHz gyrotron and will produce 350 keV electrons with 500 k $W$ of input power. The field emission cathode is a copper tip located in the first cell. High power measurements will include diagnostics to measure the energy spread, charge, and size of the resulting bunch.

SLAC is pursuing high efficiency, low cost RF source designs that are suitable for mass production, in order to enable the next generation of linear accelerators. These efforts have driven the development of compact linac systems with integrated modulators, klystrons, and accelerator structures, based on a modular, low voltage klystron topology. There is substantial demand for compact linacs for X-ray radiography with security applications, and for new radiation therapy machines that reduce treatment times by orders of magnitude and may yield beneficial biological effects. In this presentation, details and challenges for these new compact accelerator systems and the corresponding RF sources are discussed.

In this work, we investigated the delivery of a clinically acceptable pediatric whole brain radiotherapy plan at FLASH dose rates using two lateral opposing 40-MeV electron beams produced by a practically realizable linear accelerator system. The EGSnrc Monte Carlo software modules, BEAMnrc and DOSXYZnrc, were used to generate whole brain radiotherapy plans for a pediatric patient using two lateral opposing 40-MeV electron beams. Electron beam phase space files were simulated using a model of a diverging beam with a diameter of 10 cm at 50 cm SAD (defined at brain midline). The electron beams were collimated using a 10-cm-thick block composed of 5 cm of aluminum oxide and 5 cm of tungsten. For comparison, a 6-MV photon plan was calculated with the Varian AAA algorithm. Electron beam parameters were based on a novel linear accelerator designed for the PHASER system and powered by a commercial 6-MW klystron. Calculations of the linear accelerator’s performance indicated an average beam current of at least 6.25 μA, providing a dose rate of 115 Gy/s at isocenter, high enough for cognition-sparing FLASH effects. The electron plan was less homogenous with a homogeneity index of 0.133 compared to the photon plan’s index of 0.087. Overall, the dosimetric characteristics of the 40-MeV electron plan were suitable for treatment. In conclusion, Monte Carlo simulations performed in this work indicate that two lateral opposing 40-MeV electron beams can be used for pediatric whole brain irradiation at FLASH dose rates of >115 Gy/s and serve as motivation for a practical clinical FLASH radiotherapy system, which can be implemented in the near future.

We present a topology for linear accelerators (linacs) in which the power is distributed to the cavities through a waveguide with periodic apertures that guarantees the correct phases and amplitudes along the structure length. Unlike conventional traveling and standing-wave linacs, the presented topology allows the cavity shapes to be designed without the constraints applied to the coupling between cells to transfer power from one cell to the next. Therefore, the topology permits more degrees of freedom for the optimization of individual cavity shapes in comparison with conventional linacs. The cavity shapes can be optimized for power consumption and efficiency, and/or the manipulation of the surface fields for high gradient operation. This topology also provides a possibility for low-temperature manufacturing techniques that prevent the annealing of the material during typical brazing processes; hence, the material could retain its original properties such as hardness. We present a design and an experimental demonstration of this linac.

In the field of beam physics, two frontier topics have taken center stage due to their potential to enable new approaches to discovery in a wide swath of science. These areas are: advanced, high gradient acceleration techniques, and x-ray free electron lasers (XFELs). Further, there is intense interest in the marriage of these two fields, with the goal of producing a very compact XFEL. In this context, recent advances in high gradient radio-frequency cryogenic copper structure research have opened the door to the use of surface electric fields between 250 and 500 MV/m. Such an approach is foreseen to enable a new generation of photoinjectors with six-dimensional beam brightness beyond the current state-of-the-art by well over an order of magnitude. This advance is an essential ingredient enabling an ultra-compact XFEL (UC-XFEL). In addition, one may accelerate these bright beams to GeV scale in less than 10 meters. Such an injector, when combined with inverse free electron laser-based bunching techniques can produce multi-kA beams with unprecedented beam quality, quantified by ~50 nm-rad normalized emittances. These beams, when injected into innovative, short-period (1-10 mm) undulators uniquely enable UC-XFELs having footprints consistent with university-scale laboratories. We describe the architecture and predicted performance of this novel light source, which promises photon production per pulse of a few percent of existing XFEL sources. We review implementation issues including collective beam effects, compact x-ray optics systems, and other relevant technical challenges. To illustrate the potential of such a light source to fundamentally change the current paradigm of XFELs with their limited access, we examine possible applications in biology, chemistry, materials, atomic physics, industry, and medicine which may profit from this new model of performing XFEL science., 80 pages, 24 figures

This paper reviews the current state-of-the-art in understanding the phenomena of ultra-high vacuum radio-frequency (rf) breakdown in accelerating structures and the efforts to improve stable operation of the structures at accelerating gradients above 100 MV/m. Numerous studies have been conducted recently with the goal of understanding the dependence of the achievable accelerating gradients and breakdown rates on the frequency of operations, the geometry of the structure, material and method of fabrication, and operational temperature. Tests have been conducted with single standing wave accelerator cells as well as with the multi-cell traveling wave structures. Notable theoretical effort was directed at understanding the physical mechanisms of the rf breakdown and its statistical behavior. The achievements presented in this paper are the result of the large continuous self-sustaining collaboration of multiple research institutions in the United States and worldwide.

Large arrays of cryogenic sensors for various imaging applications ranging across x-ray, gamma-ray, Cosmic Microwave Background (CMB), mm/sub-mm, as well as particle detection increasingly rely on superconducting microresonators for high multiplexing factors. These microresonators take the form of microwave SQUIDs that couple to Transition-Edge Sensors (TES) or Microwave Kinetic Inductance Detectors (MKIDs). In principle, such arrays can be read out with vastly scalable software-defined radio using suitable FPGAs, ADCs and DACs. In this work, we share plans and show initial results for SLAC Microresonator Radio Frequency (SMuRF) electronics, a next-generation control and readout system for superconducting microresonators. SMuRF electronics are unique in their implementation of specialized algorithms for closed-loop tone tracking, which consists of fast feedback and feedforward to each resonator's excitation parameters based on transmission measurements. Closed-loop tone tracking enables improved system linearity, a significant increase in sensor count per readout line, and the possibility of overcoupled resonator designs for enhanced dynamic range. Low-bandwidth prototype electronics were used to demonstrate closed-loop tone tracking on twelve 300-kHz-wide microwave SQUID resonators, spaced at $\sim$6 MHz with center frequencies $\sim$5-6 GHz. We achieve multi-kHz tracking bandwidth and demonstrate that the noise floor of the electronics is subdominant to the noise intrinsic in the multiplexer., 7 pages, 5 figures, Submitted to the Journal of Low Temperature Physics (Proceedings of the 17th International Workshop on Low Temperature Detectors)

Recent studies of rf breakdown physics in cryogenic copper X-band accelerating structures have shown a dramatic increase in the operating gradient while maintaining low breakdown rates. The TOPGUN project, a collaboration between UCLA, SLAC, and INFN, will use this improvement in gradient to create an ultra-high brightness cryogenic normal conducting photoinjector [16] . The brightness is expected to be higher by a factor of 25 relative to the LCLS photogun [9] . This improvement in the brightness will lead to increased performance of X-Ray free electron lasers (FELs) and ultrafast electron diffraction devices [16] . We present the rf design for this S-band photogun, which will be a drop-in replacement for the current LCLS photogun.

This paper explores the physics of vacuum rf breakdowns in high gradient mm-wave accelerating structures. We performed a series of experiments with 100 GHz and 200 GHz metallic accelerating structures, at the Facility for Advanced Accelerator Experimental Tests (FACET) at the SLAC National Accelerator Laboratory. This paper presents the experimental results of rf tests of 100 GHz travelling-wave accelerating structures, made of hard copper-silver alloy. The results are compared with pure hard copper structures. The rf fields were excited by the FACET ultra-relativistic electron beam. The accelerating structures have open geometries, 10 cm long, composed of two halves separated by a variable gap. The rf frequency of the fundamental accelerating mode depends on the gap size and can be changed from 90 GHz to 140 GHz. The measured frequency and pulse length are consistent with our simulations. When the beam travels off-axis, a deflecting field is induced in addition to the decelerating longitudinal field. We measured the deflecting forces by observing the displacement of the electron bunch and used this measurement to verify the expected accelerating gradient. We present the first quantitative measurement of rf breakdown rates in 100 GHz copper-silver accelerating structure, which was 10 −3 per pulse, with peak electric field of 0.42 GV/m, an accelerating gradient of 127 MV/m, at a pulse length of 2.3 ns. The goal of our studies is to understand the physics of gradient limitations in order to increase the energy reach of future accelerators.

We report initial high-gradient testing results of a 110 GHz single-cell standing wave accelerating cavity powered by a 1 MW gyrotron. The cavity is fed with 10 ns, 100s of kilowatt pulses, and achieved a field gradient up to 225 MV/m. We also report the observation of rf breakdowns and cavity processing for $\lt /p\gt \gt 10 ^{5}$ pulses.

Copper is critical to the manufacturing of vacuum electronic devices due to its high electrical and thermal conductivities. It enables high RF performance while maintaining low thermal losses. Copper is also responsible for some of the challenges: RF power output is often limited by the strength of copper and RF breakdown is induced by copper transformation at the vacuum surface. Recent advances in understanding of RF interaction with copper offer insight into its limitations and how they may be mitigated. Emerging manufacturing technologies, such as electron beam melting of copper, can be employed to achieve a stronger copper state in the RF structures, opening opportunities for higher power and more compact vacuum electronics. As copper focused additive manufacturing evolves, strengthening mechanisms can be incorporated into the material to produce desired material properties locally, further enhancing performance capabilities of vacuum devices.

Recent studies of the performance of radio-frequency (rf) copper cavities operated at cryogenic temperatures have shown a dramatic increase in the maximum achievable surface electric field. We propose to exploit this development to enable a new generation of photoinjectors operated at cryogenic temperatures that may attain, through enhancement of the launch field at the photocathode, a significant increase in five-dimensional electron beam brightness. We present detailed studies of the beam dynamics associated with such a system, by examining an S-band photoinjector operated at $250\text{ }\text{ }\mathrm{MV}/\mathrm{m}$ peak electric field that reaches normalized emittances in the 40 nm-rad range at charges (100--200 pC) suitable for use in a hard x-ray free-electron laser (XFEL) scenario based on the LCLS. In this case, we show by start-to-end simulations that the properties of this source may give rise to high efficiency operation of an XFEL, and permit extension of the photon energy reach by an order of magnitude, to over 80 keV. The brightness needed for such XFELs is achieved through low source emittances in tandem with high current after compression. In the XFEL examples analyzed, the emittances during final compression are preserved using microbunching techniques. Extreme low emittance scenarios obtained at pC charge, appropriate for significantly extending temporal resolution limits of ultrafast electron diffraction and microscopy experiments, are also reviewed. While the increase in brightness in a cryogenic photoinjector is mainly due to the augmentation of the emission current density via field enhancement, further possible increases in performance arising from lowering the intrinsic cathode emittance in cryogenic operation are also analyzed. Issues in experimental implementation, including cavity optimization for lowering cryogenic thermal dissipation, external coupling, and cryocooler system, are discussed. We identify future directions in ultrahigh field cryogenic photoinjectors, including scaling to higher frequency, use of novel rf structures, and enabling of an extremely compact hard x-ray FEL.

We propose an approach to search for axion dark matter with a specially designed superconducting radio frequency cavity, targeting axions with masses $m_a \lesssim 10^{-6} \text{ eV}$. Our approach exploits axion-induced transitions between nearly degenerate resonant modes of frequency $\sim$ GHz. A scan over axion mass is achieved by varying the frequency splitting between the two modes. Compared to traditional approaches, this allows for parametrically enhanced signal power for axions lighter than a GHz. The projected sensitivity covers unexplored parameter space for QCD axion dark matter for $10^{-8} \text{ eV} \lesssim m_a \lesssim10^{-6} \text{ eV}$ and axion-like particle dark matter as light as $m_a \sim 10^{-14} \text{ eV}$., Comment: 30 pages, 7 figures

We present the design for a rapid proton energy modulator with radiofrequency accelerator cavities, which can deliver the proton radiation dose to varied depth in human tissues much faster than traditional mechanical beam energy degraders. The proton energy modulator is designed as a multi-cell 1-m long accelerator working at 2.856 GHz. Each individual accelerator cavity is powered by a 400 kW compact klystron to provide an accelerating/decelerating gradient of 30 MV/m. The high gradient is enabled by the individual power coupling regime, which provides a high shunt impedance. Beam dynamics simulations were performed, showing that the energy modulator can provide ±30 MeV of beam energy change for a 150 MeV, 7 mm long (full length) proton bunch, and the total energy spread of 3 MeV is satisfactory to clinical needs. A prototype experiment of a single cell has been built and tested, and the low-power microwave measurement results agree very well with simulations. The energy modulator is optimized for the 150 MeV cyclotron proton beam, while this approach can work with different beam energies.

هدفت هذه الدراسة إلى استخراج الخصائص السيكومترية لمقياس (نيف) للتعاطف الذاتي وتقنينه في البيئة الفلسطينية، ولذا فقد تم اختيار عينة عشوائية متوفرة قوامها 296 طالبا وطالبة من جامعات المحافظات الشمالية بفلسطين، وأمكن التحقق من دلالات صدق البناء وصدق الاتساق الداخلي، كما أمكن التحقق من دلالات الثبات بطريقة كرونباخ (ألفا)، وثبات الإعادة، وأسفر التحليل العاملي بعد تدوير المحاور بطريقة فاريماكس للاختبار عن ثلاثة عوامل تشبع بها الاختبار أطلق عليها على الترتيب: عامل الرأفة بالذات، وعامل اليقظة والوعي بالذات، وعامل الأحاسيس الإنسانية المشتركة، كما وأسفرت الدراسة عن وجود فروق في درجات التعاطف الذاتي تعزى لجنس الطالب لصالح الإناث، وإلى وجود فروق في التفاعل بين الجنس وموقع الجامعة لصالح فئة الإناث في كل من الشمال والوسط، فيما لم تكن هناك فروقا تعزى لموقع الجامعة. وقد أوصت الدراسة بإجراء مزيد من الدراسات التي تستخدم الاختبار في بيئات عربية أخرى وكذلك على فئات عمرية أخرى.

The next generation of accelerators, from the compact to the large infrastructure dedicated to high energy physics, is highly demanding in terms of accelerating gradients. To upgrade performances of X band linacs at 11.424 GHz many resources are devoted to achieve high accelerating gradients and at the same time to obtain a high reliability. In the framework of a three-year funded project by the Vth Committee of the INFN to the Laboratori Nazionali di Frascati (LNF) and to the Laboratori Nazionali di Legnaro (LNL). Within a broad international collaboration the LNF has been involved in the design, manufacture and test of compact high power standing wave (SW) sections operating at high frequency while LNL is actively involved in the development of new materials and multilayers using PVD (Physical Vapor Deposition) methods. We will report about the status of the accelerating device and of the different ongoing R&D activities and characterization procedures such as tests of different materials and metallic coatings.

Novel types of dual circular polarizer are developed to convert TE10 mode into two different polarized TE11 modes in a circular waveguide. These designs have MHz bandwidth and high power transmission capability.They can be used for broadcasting and receiving circular polarized signals.

We report the experimental demonstration of a mm-wave electron accelerating structure powered by a high-power rf source. We demonstrate reliable coupling of an unprecedented rf power—up to 575 kW into the mm-wave accelerator structure using a quasi-optical setup. This standing wave accelerating structure consists of a single-cell copper cavity and a Gaussian to TM01 mode converter. The accelerator structure is powered by 110 GHz, 10-ns long rf pulses. These pulses are chopped from 3 ms pulses from a gyrotron oscillator using a laser-driven silicon switch. We show an unprecedented high gradient up to 230 MV/m that corresponds to a peak surface electric field of more than 520 MV/m. We have achieved these results after conditioning the cavity with more than 105 pulses. We also report preliminary measurements of rf breakdown rates, which are important for understanding rf breakdown physics in the millimeter-wave regime. These results open up many frontiers for applications not only limited to the next generation particle accelerators but also x-ray generation, probing material dynamics, and nonlinear light-matter interactions at mm-wave frequency.

Experiments with high gradient traveling-wave mm-wave metallic accelerating structures were performed to research the physics of vacuum rf breakdowns. The accelerating structures are open, composed of two identical halves separated by an adjustable gap. The electromagnetic fields were induced by an ultrarelativistic electron beam at the Facility for Advanced Accelerator Experimental Tests (FACET) at SLAC National Accelerator Laboratory. These accelerating structures have a fundamental beam-synchronous mode with a frequency that varies from 95 to 140 GHz depending on the gap width. When the gap is opened by more than half of a freespace wavelength, the corresponding synchronous mode remains trapped demonstrating behavior consistent with the so called ``surface wave.'' This regime is of potential interest for femtosecond electron beam diagnostics and beam manipulation techniques. The behavior of the surface wave was characterized and the measured synchronous frequency, pulse length and beam deflection voltage are found to be in good agreement with simulations. The wave magnitude was changed by positioning the beam at different distances from the surface of a structure-half and the corresponding rf breakdown rate was recorded. The breakdown rate was $4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ per pulse at a peak surface electric field of $0.3\text{ }\text{ }\mathrm{GV}/\mathrm{m}$ and a pulse length of 60 ps.

We show high power test progress for 110 GHz high-gradient accelerating structures. The purpose of this work is to study the physics of particle accelerators in the mm-wave regime, as well as ultrahigh vacuum RF breakdown in such structures. The setup under investigation consists of a single-cell standing-wave accelerating cavity operated in the n-mode and fed via the TMm mode in a circular waveguide, which is in turn fed through a Gaussian horn. The cavities will be powered with nanosecond pulses from a MW gyrotron oscillator, allowing it to reach a peak accelerating gradient of 400 MeV/m.

The development of high brightness electron sources can enable an increase in performance and reduction in size of extreme X-ray sources such as free electron lasers (FELs). A promising path to high brightness is through larger electric fields in radio-frequency (rf) photoinjectors. Recent experiments with 11.4 GHz copper accelerating cavities at cryogenic temperatures have demonstrated $500\text{ }\text{ }\mathrm{MV}/\mathrm{m}$ surface electric fields with low rf breakdown rates. However, when the surface electric fields are larger than $300\text{ }\text{ }\mathrm{MV}/\mathrm{m}$, the measured cavity quality factor, ${Q}_{0}$, decreases during the input rf pulse by up to 30%, recovering before the next rf pulse. In this paper, we present an experimental study of the rf losses, manifested as degradation of ${Q}_{0}$, in a copper cavity operated at cryogenic temperatures and high gradients. The experimental conditions range from temperatures of 10--77 K and rf pulse lengths of 100--800 ns, using surface electric fields up to $400\text{ }\text{ }\mathrm{MV}/\mathrm{m}$. We developed a model for the change in ${Q}_{0}$ using measured field emission currents and rf signals. We find that the ${Q}_{0}$ degradation is consistent with the rf power being absorbed by strong field emission currents accelerated inside the cavity.

A new compact low-loss fast phase-shift high-power microwave (HPM) phase shifter (PS) is proposed, designed, and cold and high-power tested. Firstly, based on solving the scattering matrix and eigenvectors, we design a novel HPM dual circular polarizer, and then a dumbbell-like metal plug driven by a high-speed servomotor is used to slide a short circuit along the dual circular polarized port to adjust the output RF phase, which varies 180 $^{\circ}$ by moving the plug with a quarter of the guided wavelength. The X-band PS has a total length of 9.5 cm and a power capacity achieved 300 MW at 30-ns HPM pulse. A fast phase shift of 310 $^{\circ}$ was achieved within 0.1 s in test, a high precision of phase shift 1 $^{\circ}$ can be realized, and the tested insertion loss was $ 0.15 dB.

We have successfully designed, fabricated, installed, and tested a super compact $X$-band SLAC Energy Doubler system at SLAC. It is composed of an elegant 3 dB coupler--mode converter--polarizer coupled to a single spherical energy storage cavity with high ${Q}_{0}$ of 94000 and a diameter less than 12 cm. The available rf peak power of 50 MW can be compressed to a peak average power of more than 200 MW in order to double the kick for the electron bunches in a rf transverse deflector system and greatly improve the measurement resolution of both the electron bunches and the x-ray free-electron laser pulses. The design physics and fabrication as well as the measurement results will be presented in detail. High-power operation has demonstrated the excellent performance of this rf compression system without rf breakdown, sign of pulse heating, and rf radiation.

Traditional linear interaction RF sources (klystrons and traveling wave tubes) provide limited amounts of power at the mm-wave and terahertz part of the spectrum because their critical dimensions have to be small compared to the wavelength they operate. Due to these small dimensions, the amount of current that can go through the beam apertures is limited. We designed, built and hot-tested a new gyrocon-like mm-wave source, with an output interaction circuit based on a spherical sector cavity. This spherical sector cavity provides a large beam aperture, allowing for a significant amount of current to go through. This source operates as a 5th harmonic frequency multiplier, with an output frequency of 57.12 GHz. The measured peak output power was 54.26 W at the 5th harmonic, while power at the other harmonics was at least 33.28 dB lower than the 5th harmonic.

We are exploring the physics of vacuum rf breakdowns in high gradient metallic accelerating structures at sub-THz frequencies. We present the experimental results of rf tests performed in beam-driven travelling-wave accelerating structures. We measured the breakdown rates, the frequency of the emitted radiation, and the gradients. As the next step in this study, we are developing accelerating structures powered by an rf source. We report on the status of this project.

The use of infrared lasers to power optical-scale lithographically fabricated particle accelerators is a developing area of research that has garnered increasing interest in recent years. The physics and technology of this approach is reviewed, which is referred to as dielectric laser acceleration (DLA). In the DLA scheme operating at typical laser pulse lengths of 0.1 to 1 ps, the laser damage fluences for robust dielectric materials correspond to peak surface electric fields in the $\mathrm{GV}/\mathrm{m}$ regime. The corresponding accelerating field enhancement represents a potential reduction in active length of the accelerator between 1 and 2 orders of magnitude. Power sources for DLA-based accelerators (lasers) are less costly than microwave sources (klystrons) for equivalent average power levels due to wider availability and private sector investment. Because of the high laser-to-particle coupling efficiency, required pulse energies are consistent with tabletop microJoule class lasers. Combined with the very high (MHz) repetition rates these lasers can provide, the DLA approach appears promising for a variety of applications, including future high-energy physics colliders, compact light sources, and portable medical scanners and radiative therapy machines.

A novel type of dual circular polarizer for simultaneously receiving and transmitting right-hand and left-hand circularly polarized waves is developed and tested. It consists of a H-plane T junction of rectangular waveguide, one circular waveguide as an E- plane arm located on top of the junction, and two metallic pins used for matching. The theoretical analysis and design of the three-physical- port and four-mode polarizer were researched by solving Scattering- Matrix of the network and using a full-wave electromagnetic simulation tool. The optimized polarizer has the advantages of a very compact size with a volume smaller than 0:6‚ 3 , low complexity and manufacturing cost. A couple of the polarizer has been manufactured and tested, and the experimental results are basically consistent with the theories.

We present a novel method of reducing the footprint and increasing the efficiency of the modern multi-MW rf pulse compressor. This system utilizes a high power rf polarizer to couple two circular waveguide modes in quadrature to a single resonant cavity in order to replicate the response of a traditional two cavity configuration using a 4-port hybrid. The 11.424 GHz, high-Q, spherical cavity has a 5.875 cm radius and is fed by the circularly polarized signal to simultaneously excite the degenerate $T{E}_{114}$ modes. The overcoupled spherical cavity has a ${Q}_{0}$ of $9.4\ifmmode\times\else\texttimes\fi{}{10}^{4}$ and coupling factor ($\ensuremath{\beta}$) of 7.69 thus providing a loaded quality factor ${Q}_{L}$ of $1.06\ifmmode\times\else\texttimes\fi{}{10}^{4}$ with a fill time of 150 ns. Cold tests of the polarizer demonstrated good agreement with the numerical design, showing transmission of $\ensuremath{-}0.05\text{ }\text{ }\mathrm{dB}$ and reflection back to the input rectangular WR 90 waveguide less than $\ensuremath{-}40\text{ }\text{ }\mathrm{dB}$ over a 100 MHz bandwidth. This novel rf pulse compressor was tested at SLAC using XL-4 Klystron that provided rf power up to 32 MW and generated peak output power of 205 MW and an average of 135 MW over the discharged signal. A general network analysis of the polarizer is discussed as well as the design and high power test of the rf pulse compressor.

Vacuum electronic devices, such as rf sources for accelerator applications, must provide high rf power with high efficiency. To achieve these requirements, multi-beam klystron and sheet-beam klystron devices have been developed. Multi-beam klystrons, at high frequency employ separate output cavities; hence they have the disadvantage that combining externally all the rf pulses is challenging. Sheet-beam klystrons have problems with instabilities and with space charge forces that makes the beam not naturally confined. We are proposing an alternative approach that reduces space charge problems, by adopting geometries in which the space charge forces are naturally balanced. In this paper we will present the design and challenges of a radial klystron, composed by concentric pancake resonant cavities. In this case, space charge forces are naturally balanced in the azimuthal direction.

This report is a survey of technical options for generating a MeV-class accelerator for space based science applications. The survey was performed focusing on the primary technical requirements of the accelerator in the context of a satellite environment with its unique challenges of limited electrical power (PE), thermal isolation, dimensions, payload requirement and electrical isolation.

This paper explores a hybrid mode rf structure that served as a superconducting radio-frequency coupler. This application achieves a reflection ${\mathrm{S}}_{(1,1)}$ varying from 0 to $\ensuremath{-}30\text{ }\text{ }\mathrm{db}$ and delivers cw power at 7 KW. The coupler has good thermal isolation between the 2 and 300 K sections due to vacuum separation. Only one single hybrid mode can propagate through each section, and no higher order mode is coupled. The analytical and numerical analysis for this coupler is given and the design is optimized. The coupling mechanism to the cavity is also discussed.

We present the applications of advanced RF acceleration to X-ray sources. We give an overview of high-gradient research activities and its applications to extremely high brightness electron guns and short period rf undulators. Article not available.

We report on the development of W-band (75–110 GHz) heterodyne receiver technology for large-format astronomical arrays. The receiver system is designed to be both mass producible, so that the designs could be scaled to thousands of receiver elements, and modular. Most of the receiver functionality is integrated into compact monolithic microwave integrated circuit (MMIC) amplifier-based multichip modules. The MMIC modules include a chain of InP MMIC low-noise amplifiers, coupled-line bandpass filters, and sub-harmonic Schottky diode mixers. The receiver signals will be routed to and from the MMIC modules on a multilayer high-frequency laminate, which includes splitters, amplifiers, and frequency triplers. A prototype MMIC module has exhibited a band-averaged noise temperature of 41 K from 82 to 100 GHz and a gain of 29 dB at 15 K, which is the state-of-the-art for heterodyne multichip modules.

We propose to couple two coaxial waveguides by 2D periodic perforation in the common wall in order to ensure selective coupling between two waves propagating in these waveguides. In the experiment at a frequency of 10 GHz, the H 01 mode of the internal waveguide was converted to the rotating H 51 mode of the external waveguide with a power loss of several percent.

We report cryogenic noise temperature and gain measurements of a prototype heterodyne receiver module designed to operate in the atmospheric window centered on 150 GHz. The module utilizes monolithic microwave integrated circuit (MMIC) InP high electron mobility transistor (HEMT) amplifiers, a second harmonic mixer, and bandpass filters. Swept local oscillator (LO) measurements show an average gain of 22 dB and an average noise temperature of 87 K over a 40 GHz band from 140 to 180 GHz when the module is cooled to 22 K. A spot noise temperature of 58 K was measured at 166 GHz and is a record for cryogenic noise from HEMT amplifiers at this frequency. Intermediate frequency (IF) sweep measurements show a 20 GHz IF band with less than 94 K receiver noise temperature for a fixed LO of 83 GHz. The compact housing features a split-block design that facilitates quick assembly and a condensed arrangement of the MMIC components and bias circuitry. DC feedthroughs and nano-miniature connectors also contribute to the compact design, so that the dimensions of the moduleare approximately 2.5 cm per side.

A new compact and wide-band waveguide dual circular polarizer at Ka-band is presented and tested in this paper. This compact structure is composed of a three-port polarizing diplexer and a circular polarizer realized by a simple pair of large grooves. The polarizing diplexer includes two rectangular waveguides with a perpendicular H-plane junction, one circular waveguide coupled in E- plane. A cylindrical step and two pins are used to match this structure. For a LHCP or RHCP wave in the circular port, only one speciflc rectangular port outputs power and the other one is isolated. The accurate analysis and design of the circular polarizer are conducted by using full-wave electromagnetic simulation tools. The optimized dual circular polarizer has the advantage of compact size with a volume smaller than 1.5‚ 3 , broad bandwidth, uncomplicated structure, and is especially suitable for use at high frequencies such as Ka-band and above. The prototype of the polarizer has been manufactured and test, the experimental results are basically consistent with the theories.

A fundamental element of the CLIC concept is two-beam acceleration, where RF power is extracted from a high current, low energy drive beam in order to accelerate the low current main beam to high energy. The CLIC Power Extraction and Transfer Structure (PETS) is a passive microwave device in which bunches of the drive beam interact with the constant impedance of the periodically loaded waveguide and excite preferentially the synchronous mode. The RF power produced is collected downstream of the structure by means of the RF power extractor; it is delivered to the main linac using the waveguide network connecting the PETS to the main CLIC accelerating structures. The PETS should produce 135 MW at 240 ns RF pulses at a very low breakdown rate: BDR < 10{sup -7}/pulse/m. Over 2010, a thorough high RF power testing program was conducted in order to investigate the ultimate performance and the limiting factors for the PETS operation. The testing program is described and the results are presented.

Fabrication technologies for X-band high gradient accelerating structures have been studied at KEK with SLAC, INFN and CERN. A scanning field emission microscope has been developed at KEK for the observation of the microscopic surface defects which may be related to the rf breakdown trigger. We present the progress on the experimental results of studying field emission characteristics by scanning an arbitrary area of 0.5 mm×0.5 mm on OFHC copper surface using a newly developed scanning field emission microscope.

We summarize recent progress in a program to develop externally powered dielectric-loaded accelerating (DLA) structures that can sustain high accelerating gradients. High-power RF tests of earlier structures showed strong multipactor loading. In addition, arcing at dielectric joints between the uniform DLA structure and matching sections at either end limited the achievable gradient. In this paper, we study the onset of multipactor in a DLA structure. We also study the effect of thin-film TiN coatings applied by atomic layer deposition and the effect of a reduction in the inner diameter of the structure. Test results of these structures show significant decreases in multipactor loading. We also test new structure designs that eliminate separate dielectric matching sections and, thus, the requirement for dielectric joints, including a DLA structure using a coaxial coupler and a clamped DLA structure. The clamped structure demonstrated a significantly improved gradient without breakdown.