Search

FELs based on SASE are believed to be powerful tools to explore the frontiers of basic sciences, from physics to chemistry to biology. Intense R&D programs have started in the USA and Europe in order to understand the SASE physics and to prove the feasibility of these sources. The allocation of considerable resources in the Italian National Research Plan (PNR) brought about the formation of a CNR‐ENEA‐INFN‐University of Roma “Tor Vergata” study group. A conceptual design study has been developed and possible schemes for linac sources have been investigated, bringing to the SPARX proposal. We report in this paper the results of a preliminary start to end simulation concerning one option we are considering based on an S‐band normal conducting linac with high brightness photoinjector integrated in a RF compressor.

The achievement of the highest luminosity in the 510 MeV electron-positron /spl Phi/-Factory DA/spl Phi/NE, in construction at Frascati Laboratories, requires a careful design of the RF accelerating cavity, being the main source of High Order parasitic Modes (HOM) which are responsible for multibunch instabilities. Intense R&D has been carried out to choose the cavity resonator which would better cope with those problems. Theoretical studies and simulations of the longitudinal beam dynamics with various cavity shapes have been performed and several HOM extraction and damping techniques have been studied and tested. This report presents the results of these investigations and the laboratory tests of the proposed accelerating RF cavity for DA/spl Phi/NE. >

An extension of the longitudinal thermal wave model, including both radiation damping and quantum excitation (stochastic effect) is presented here. We show that, in the presence of the RF potential well, the longitudinal dynamics is governed by a 1-D Schrodinger-like equation for a complex wave function whose squared modulus gives the longitudinal bunch profile. Remarkably, the appropriate emittance scaling is naturally recovered, and the asymptotic equilibrium condition for the bunch length is found. These results open the possibility to apply the thermal wave model, already tested for protons, in a more accurate way to electrons. >

An overview of the Frascati Phi -factory and the salient project features are presented. The engineering design of vacuum and magnetic components, diagnostics, power supplies of the accumulator ring and of the main rings is in progress. The main concern, at this time, is how to handle the multibunch instability that is the most harmful problem in the design of high current storage rings and the most serious limitation for the luminosity. The parasitic high-order modes of the RF cavities are responsible for such an instability. >

The lattice for the double ring e/sup +/e/sup -/ collider DA Phi NE of the Frascati Phi -factory project is presented. Electrons and positrons circulate in two horizontally separated storage rings and collide at a horizontal half angle of 10 mrad in one or two interaction points. This allows a very short bunch distance and therefore a very high collision frequency (

The recombination chamber in LHC (Large Hadron Collider) allows the separated proton beams to merge into a common vacuum chamber surrounding the interaction points. It has been subject of thorough studies concerning its interaction with the circulating beam. In this paper we present the numerical and experimental results of our investigation on an approximated geometry. We show that in the smooth transitions between pipes of different diameters a trapped mode may exist, both in the real and in the approximated geometry. In the real structure, the mode is weak and not harmful both for the beam stability and power loss

The problem of the wakefields generated by an ultrarelativistic particle traveling in a long beam tube with a periodic rough surface has been revisited by means of a standard theory based on the hybrid modes excited in a periodically corrugated rectangular waveguide. Slow surface waves synchronous with the particle can be excited in the structure, producing wakefields whose frequency and amplitude depend on the depth of the corrugation. We apply our results to the case of the CERN Large Hadron Collider beam screen and the Linac Coherent Light Source undulator. (19 refs).

After introducing the concepts of longitudinal wakefield and coupling impedance, we review the theory of longitudinal single-bunch collective effects in storage rings. From the Fokker-Planck equation we first derive the stationary solution describing the natural single-bunch regime, and then treat the problem of microwave instability, showing the different approaches used for estimating the threshold current. We end the lecture with the semi-empirical laws that allow us to obtain the single-bunch behavior above threshold, and with a description of the simulation codes that are now reliable tools for investigating all these effects.

The Green’s function method (GFM) is used to describe the effects of a statistical roughness on the propagation of electromagnetic fields in a circular waveguide. The GFM method, applied to a scalar Helmholtz equation with perturbed boundary conditions, allows us to treat multiple scattering of the field. Theoretical results for azimuthal and longitudinal roughness are reported, and the phase velocity of the field is discussed in both cases.

In the framework of the modified Bethe's diffraction theory, we study the energy lost by a relativistic particle beam traveling in a coaxial liner with many holes, including the effect of attenuation in the coaxial region. The interference among the holes is the main source of losses and is affected by the attenuation in the coaxial only over sufficiently long distances. We derive analytical formulas for all the interesting quantities and particular attention is given to clarifying the physical meaning of the results; numerical examples are considered using LHC-like parameters. (17 refs).

Assuming the validity of the Boussard criterion for the determination of the microwave instability threshold, we derive two coupled non linear differential equations which describe the time evolution of the energy spread and of the instability growth rate under different conditions. The equations reproduce the characteristic features of the saw tooth instability and are in agreement with the results of a time domain simulation code.

The saw-tooth instability in storage rings is studied by means of a time-domain simulation code which takes into account the self-induced wake fields. The results are compared with those from a dynamical heuristic model exploiting two coupled non-linear differential equations, accounting for the time behavior of the instability growth rate and for the anomalous growth of the energy spread. This model is shown to reproduce the characteristic features of the instability in a fairly satisfactory way.

This working group was charged with reviewing the general area of plasma phenomena in beams. The group reviewed our present understanding and discussed critical issues for a wide variety of topics, including longitudinal and transverse wakefield instabilities in high intensity rings, numerical computation of wakes at short scale length, ion instabilities, wakefields and emittance growth from coherent synchrotron radiation, the nature of self-amplified spontaneous emission (SASE), soliton theory and its role in beam physics, the control of transverse instabilities by feedback or by temporal variation of ring parameters, and the use of plasma concepts in beam dynamics, particularly applications of beam echo measurements.

The problem of many holes in a coaxial beam pipe is studied by means of the modified Bethe theory. The electromagnetic fields propagating in the coaxial region couple the equivalent dipole moments of the holes. The effect of the coupling on the longitudinal impedance and on the loss factor is investigated, showing that the interference phenomena are significant for such geometries.

Experimental observations on FEL Storage Rings (Aco, Super-Aco, VEPP3, TERAS) have shown that in a storage ring with an operating FEL there is a mutual effect between the FEL operational mode and the beam longitudinal distribution. The main effects are the birth of a macro-temporal structure of the FEL radiation and a suppression of the synchrotron sidebands, evidence of beam stabilisation against the microwave instabilities. In this paper we discuss the main features of the beam dynamics analysed with a simulation code recently developed, which includes the FEL-beam interaction. Furtherly, we propose an heuristic model which enable to describe in a simple way the overall system.

In this paper we illustrate the tuning procedure we implemented to tune the traveling wave structures designed and constructed for the SPARC photo-injector energy upgrade. The procedure has been derived from that proposed and adopted for the CLIC structures at CERN (J. Shi et al., Tuning of clic accelerating structure prototypes at Cern, Proc. of LINAC 2010, Tsukuba, Japan, 2010). In the first part of the paper we go through the analytical formulas also illustrating and discussing an algorithm to tune the input and output couplers. A detailed description of the measurements we have done before and after the tuning of the SPARC C-band structure prototype is then illustrated.

n this paper we derive the impedance of a circular hole in the inner tube of a coaxial beam pipe. The method used differs from the classic Bethe's diffraction theory, since, in the calculation of the magnetic and electric dipole moments, we take into account also the scattered fields in the aperture to match the power conservation law. The low-frequency impedance shows a real contribution accounting for the TEM waves propagating within the coaxial waveguide.

The DAΦNE Φ-Factory is an e+e− high luminosity collider under construction at the INFN-LNF. At present its accumulator ring is being commissioned, and the first beam has been successfully stored. The preliminary estimates of the beam impedance have shown that the nominal current is above the microwave instability threshold. In this paper we investigate the single bunch behavior in the microwave regime for the DAΦNE accumulator machine using both a time domain tracking code and an analytical study based on the Vlasov equation and mode coupling theory.

The design of a synchrotron radiation source dedicated to X-ray lithography is presented. The parameter optimization carried out is based on the lithography requirements, on the radiation spectrum and beam source sizes, and on the machine performances, such as long lifetime, absence of beam instabilities and reliable operation at design current. High-field conventional magnets are proposed for the radiation production.

The cure of multibunch instabilities is of utmost importance for the next generation of very high current storage rings. The parasitic modes of the rf cavities are chiefly responsible of these instabilities. A perturbation method is proposed to decouple the cavity parasitic modes from the bunch relative oscillation sidebands, without affecting the fundamental mode. Signal level measurements on a test pillbox cavity give encouraging results.

The injection of laser-generated protons through conventional drift tube linear accelerators (linacs) has been studied numerically. For this, we used the parameters of the proton source produced by ultraintense lasers, i.e., with an intrinsic high beam quality. The numerical particle tracing code PARMELA [L. M. Young and J. H. Billen, LANL Report No. LA-UR-96-1835, 2004] is then used to inject experimentally measured laser-generated protons with energies of 7±0.1 MeV and rms un-normalized emittance of 0.180 mm mrad into one drift tube linac tank that accelerated them to more than 14 MeV. The simulations exhibit un-normalized emittance growths of 8 in x direction and 22.6 in y direction, with final emittances lower than those produced using conventional sources, allowing a potential luminosity gain for the final beam. However, the simulations also exhibit a limitation in the allowed injected proton charge as, over 0.112 mA, space charge effect worsens significantly the beam emittance.

The coupling impedance between a particle beam and a surrounding lossy vacuum chamber with elliptic cross-section is usually evaluated using expressions derived for circular geometry, considering an equivalent radius equal to the minor radius of the ellipse. The approximation may lead to unrealistic results expecially when considering transverse oscillations of the beam parallel to the ellipse major axis. In this paper we present a method for the exact evaluation of both longitudinal and transverse impedances without any restrictions on the beam position and oscillation directions.

The increase in energy spread and beam size and the decay rate due to intra-beam scattering in a storage ring are evaluated in the case of a ring designed for the generation of high intensity coherent radiation in the VUV region.

Background Transforming growth factor beta 1 (TGF-β1) gene play an important role in the acute myocardial infarction (AMI), however no investigation has been conducted so far in young AMI patients. In this study, we evaluated the influence of TGF-β1 polymorphisms/haplotypes on the onset and progression of AMI in young Italian population. Methods 201 cases and 201 controls were genotyped for three TGF-β1 polymorphisms (G-800A, C-509T and Leu10Pro). The main follow-up end-points (mean follow-up, 107 ± 49 months) were death, myocardial infarction or revascularization procedures. Results Significant risk factors were smoking (p < 10-4), family history for coronary artery disease (p < 10-4), hypercholesterolemia (p = 0.001) and hypertension (p = 0.002). The C-509T and Leu10Pro polymorphisms showed significant differences (p = 0.026 and p = 0.004) between cases and controls. The most common haplotypes revealed a possible protective effect (GCT, OR 0.75, 95% CI 0.57–0.99, p = 0.042) and an increased risk of AMI (GTC, OR 1.51, 95% CI 1.13–2.02, p = 0.005), respectively. No statistical differences were observed in genotype distribution in the follow-up study between the two groups: 61 patients with subsequent events (13 deaths) and 108 without events. Conclusion Even though our results need to be further confirmed in larger studies, this is the first study reporting on a possible role of TGFβ1 common haplotypes in the onset of AMI in young patients.

The paper presents the design of an X-band accelerating section for linearizing the longitudinal phase space in the Frascati Linac Coherent Light Source (SPARC). The structure, operating on the π standing wave mode, is a 9 cells structure fed by a central coupler and it has been designed to obtain a 42 MV/m accelerating gradient. The 2D profile has been determined using the electromagnetic codes Superfish and Oscar-2D while the coupler has been designed using HFSS. Beadpull measurements made on a copper prototype have been done and the results are illustrated and compared with the numerical ones. Mechanical details of the realized prototype and RF properties of the structure as a function of the assembly characteristics are also discussed.

In particle accelerators, the beam quality can be strongly affected by the interaction with self-induced electromagnetic fields excited by the beam in the passage through the elements of the accelerator. The beam coupling impedance quantifies this interaction and allows predicting the stability of the dynamics of high intensity, high brilliance beams. The coupling impedance can be evaluated with finite element methods or using analytical approaches, such as field matching or mode matching. In this paper we present an application of the mode matching technique for an azimuthally uniform structure of finite length: a cylindrical cavity loaded with a toroidal slab of lossy dielectric, connected with cylindrical beam pipes. In order to take into account the finite length of the structure, with respect to the infinite length approximation, we decompose the fields in the cavity into a set of orthonormal modes. We obtain a complete set of equations using the magnetic field matching and the nonuniform convergence of the electric field on the cavity boundaries. We present benchmarks done with CST Particle Studio simulations and existing analytical formulas and codes, pointing out the effect of different material conductivities, finite length, and nonultrarelativistic particle beam velocity.

The longitudinal impedance and loss factor for a long narrow slot in a coaxial pipe are calculated by means of the modified Bethe's diffraction theory. The effects of the interference between the fields scattered by dipoles along the slot are taken into account, obtaining a final expression valid even for slots longer than the wavelength.

The last generation of storage rings is designed to operate with low emittances (longitudinal and transverse) and rather high currents. Performances of these machines are limited by the collective effects. The interaction of a beam with the surrounding walls produces parasitic fields which, acting back on the beam, can lead to instability phenomena. Other instability effects are known, where the beam interacts with foreign (ions, electrons, dust,etc.). Recently, new types of instabilities have drown the attention of accelerator physicists.

The first phase of the SPARX project now funded by MIUR (Research Department of Italian Government) is an R&D activity focused on developing techniques and critical components for future X-ray FEL facilities. The aim is the generation of electron beams with the ultra-high peak brightness required to drive FEL experiments. A FEL source realization is foreseen within this program, which comprises two lines of activity: a) the use of the SPARC high brightness photoinjector to test RF compression techniques and the emittance degradation in magnetic compressors due to CSR, b) the production of radiation in the range of 3-5 nm, both in SASE and SEEDED FEL configurations, in the so called SPARXINO test facility, based on the upgrade of existing Frascati 800 MeV LINAC. In this paper we present and discuss the preliminary start to end simulations results for SPARXINO.

In this paper we study the electromagnetic fields propagating in a coaxial waveguide with periodic slots in the inner conductor. We have performed a theoretical analysis by using the moment method, and have obtained a dispersion curve and an expression of the field components as a function of the geometrical parameters. The calculations show a slowing down of the phase velocity due to the slot array. We have then compared the predictions with the results of MAFIA simulation code and with measurements on a copper prototype.

The time evolution of the energy spread above the microwave instability threshold in a storage ring is described by means of two coupled nonlinear differential equations. The results are in agreement with a time domain simulation code. The model equations are combined to those accounting for the storage ring free electron laser dynamics, in order to study the interplay between the FEL and the storage ring instability dynamics.

The paper presents the design of an X-band accelerating section for linearizing the longitudinal phase space in the Frascati Linac Coherent Light Source (SPARC). The nine cells structure, operating on the π standing wave mode, is fed by a central coupler and has been designed to obtain a 42 MV/m accelerating gradient. The 2D profile has been obtained using the electromagnetic codes Superfish and Oscar2D while the coupler has been designed using HFSS. Bead-pull measurements made on a copper prototype have been performed and the results are illustrated and compared with the numerical predictions.

It is shown that the evolution of the saw-tooth instability can be reproduced by two coupled nonlinear differential equations, accounting for the time behavior of the instability growth rate and for the anomalous growth of the energy spread. These model equations, which under appropriate conditions reduce to the ordinary Volterra equations, are shown to describe the characteristic features of the instability.

New high-gradient accelerating RF cavities are nowadays developed in several national laboratories for high-energy physics applications. Ultra high gradients, up to the order of GV/m, can be achieved by using ultra compact accelerating structures in the sub-THz regime. Nevertheless, the experimental setup for measuring the main RF parameters for such compact structures is not trivial and can easily produce errors due to lack of accuracy. Moreover, Radio-Frequency (RF) simulations for these types of cavities can require a large amount of computational time. In particular, one of the main RF parameters that needs to be evaluated and measured for the accelerating structures is the reflection coefficient. In order to obtain a fast and accurate analytical estimation, we have developed the electromagnetic theory for the calculation of the coupling of a resonant cavity with an RF waveguide. This theory is based on the Bethe's small aperture polarization approach, also developed by Collin's. In this paper, we give an exact analytical expression of the reflection coefficient as function of the physics parameters of the cavity-waveguide system, which can be applied to any geometry, material and frequency.