• R.P. Nunes
  UFPel, Pelotas
• L.C. Martins
  UDESC, Joinville
• F.B. Rizzato
  IF-UFRGS, Porto Alegre

Although undesired in many applications, the intrinsic spurious spatial inhomogeneity that permeates real systems is the forerunner instability which leads high-intensity charged particle beams to its equilibrium. In general, this equilibrium is reached in a particular way, by the development of a tenuous particle population around the original beam, conventionally known as the halo. In this way, the purpose of this work is to analyze the influence of the magnitude of initial inhomogeneity over the dynamics and over the equilibrium characteristics of initially quasi-homogeneous mismatched beams. For that, all beam constituent particles, which are initially disposed in an equidistant form, suffer a progressive perturbation through random noise with a variable amplitude. Dynamical and equilibrium quantities are quantified as functions of the noise amplitude, which indirectly is a consistent measure of the initial beam inhomogeneity. The results have been obtained by the means of full self-consistent N-particle beam numerical simulations and seem to be an important complement to the investigations already carried out in prior works.

• R.P. Nunes
  UFPel, Pelotas
• F.B. Rizzato
  IF-UFRGS, Porto Alegre

Beams of charged particles usually reach their stationary state by the development of a halo. Halo formation in charged beams is in fact a macroscopic transcription of microscopic instabilities acting inside the beam and upon its constituent particles. In previous works, investigations have been carried out to understand the role of the initial envelope mismatch and of magnitude of inhomogeneity in the beam route to the equilibrium. Although in that works the action of the mentioned instabilities has been studied individually, it is clear that in real implemented beams both act together. In this sense, the main purpose of this work is to generalize previous models, considering now concomitantly the effects of the envelope mismatch and of the inhomogeneity. As a final product of the investigation, a particle-core model for beam constituent particles is presented. The agreement with full self-consistent N-particle beam numerical simulations is satisfactory and the results provided by the model seem to be more compatible with that would be expected experimentally.

• H. Higaki, S. Fujimoto, K. Fukata
  Hiroshima University, Higashi-Hiroshima
• J. Aoki
  Osaka University, Graduate School of Science, Osaka
• K. Ito, M. Kuriki, H. Okamoto
  HU/AdSM, Higashi-Hiroshima

Space charge effects due to the strong Coulomb interactions expected in high intensity accelerator beams result in undesirable beam degradation and radio-activation of the vacuum tubes through halo formations. Various space charge effects have been studied intensively with particle simulations. This is partly because the analytical formulation of the nonlinear evolution in high intensity beams is not possible in general cases. And the systematic study of space charge effects with the real accelerators is not feasible. Although the development of computation environment is outstanding, some approximations are still necessary so far. Thus, it was proposed to use solenoid traps and linear Paul traps for investigating some properties of space charge dominated beams. The key idea is that the charged particles in these traps are physically equivalent with a beam in a FODO lattice. Some experimental results have been reported with the use of Paul traps. Here, a solenoid trap with a beam imaging system composed of a charge coupled device camera and a phosphor screen was employed to study the mismatch induced oscillations of a space charge dominated beams.

• H. Okamoto, K. Ito, H. Sugimoto
  HU/AdSM, Higashi-Hiroshima
• H. Higaki
  Hiroshima University, Higashi-Hiroshima
• S.M. Lund
  LLNL, Livermore, California

S-POD (Simulator for Particle Orbit Dynamics) is a tabletop, non-neutral plasma trap system developed at Hiroshima University for fundamental beam physics studies. The main components of S-POD include a compact radio-frequency quadrupole trap, various AC and DC power supplies, a vacuum system, a laser cooler, several diagnostics, and a comprehensive computer control system. A large number of ions, produced through the electron bombardment process, are captured and confined in the RFQ trap to emulate collective phenomena in space-charge-dominated beams traveling in periodic linear focusing lattices. This unique experiment is based on the isomorphism between a one-component plasma in the laboratory frame and a charged-particle beam in the center-of-mass frame. We here employ S-POD to explore the coherent betatron resonance instability which is an important issue in modern high-power accelerators. Ion loss behaviors and transverse plasma profiles are measured under various conditions to identify the parameter-dependence of resonance stopbands. Experimental observations are compared with PIC simulation results obtained with the WARP code.

• J. Yamazaki, A. Enomoto, Y. Kamiya
  KEK, Ibaraki

One of the most important issues for ERL injectors is to generate electron beams with ultra-low emittance and to accelerate the beams through the injector without emittance growth. For this purpose, we have developed an efficient simulation code to investigate the mechanism of emittance growth due to space charge effect and to exploit its suppression method. In this code, the longitudinal motion is treated by the one-dimensional difference equations for macro-particles, while the radial motion is solved by the envelope equations for the pieces of sliced bunch. We find that the total emittance takes a minimum when all ellipses of sliced envelope have the same direction on the a-a' plane, where a is the amplitude of sliced envelope and a' its derivative along the longitudinal direction. The parameters of a 5 MeV injector were optimized by this code, assuming that the voltage of the DC electron gun is 330 kV and the initial particle distribution at the exit of the gun has a uniform ellipse. Even for such a low voltage gun, we obtained a minimum value of the rms normalized emittance, 0.10 mm, and the rms bunch length, 0.83 mm, the values of which were calculated by using PARMELA.

• A.V. Voronkov, E.S. Masunov, S.M. Polozov
  MEPhI, Moscow

The undulator linear accelerator using electrostatic undulator (UNDULAC-E) is suggested as an initial part of high intensity ion linac*. In UNDULAC ion beam accelerating and focusing are realized by of the combined field of two non-synchronous harmonics. Indeed, the main factor limiting beam intensity in ion accelerator is a space charge force. There exist, at least, two ways to increase ion beam intensity: to enlarge the beam cross section and to use the space charge neutralization. The ribbon ion beam dynamics in UNDULAC-E was discussed in**. Accelerating force value in UNDULAC is proportional to squared particle charge and oppositely charged ions with the identical charge-to-mass ratio can be accelerated simultaneously within the same bunch and the beam space charge neutralization can be realized. These methods will be studied analytically and verified by numerical simulation for UNDULAC-RF in this paper.

*E.S. Masunov, Sov. Phys. ' Tech. Phys., 1990, v. 35 (8), pp. 962-965. **Masunov, S.M. Polozov. NIM A, 558 (2006), pp. 184-187.

• A.V. Voronkov, E.S. Masunov, S.M. Polozov, V.I. Rashchikov
  MEPhI, Moscow

The beam loading effect is one of main problems limiting the beam current. Usually this effect takes into account only in high energy electron linacs. Due to low energy electron and, especially, ion linacs nowadays current increasing the beam loading effect should be considered here. Self consistent beam dynamics simulation methods with Coulomb field and beam loading effect are discussed. The simulation results are in good agreement with experiment which have been carried out on NRNU MEPhI electron linac.

• D.A. Ovsyannikov, A.D. Ovsyannikov
  St. Petersburg State University, St. Petersburg

New approach to define geometry of the radial matching section in RFQ accelerator is suggested. Approach is based on the application methods of the control theory. In paper special functionals are introduced which allow optimize radial section parameters with taking into account space charge. This approach gives wider opportunities for the design of the radial matching section because it does not have certain prescribed laws of variation of focusing strength along the section.

• C. Oliver, B. Brañas, A. Ibarra
  CIEMAT, Madrid
• A. Mosnier, P.A.P. Nghiem
  CEA, Gif-sur-Yvette

The design of the future IFMIF accelerators will be validated with the 9 MeV, 125 mA deuteron accelerator IFMIF-EVEDA. For this validation phase, a High Energy Beam Transport line (HEBT) is designed to drive the beam toward a beam dump with the required expansion, under the hands-on maintenance constraint. It consists of eight quadrupoles and one dipole. Given the very high space charge regime and the very high power (1.1 MW), any small deviation from the nominal conditions could seriously compromise the HEBT objective. That is why possible misalignments and rotations of those magnets as well as power supply errors have been thoroughly studied. The error budget is fairly distributed among the tolerances for the different components, and effects of those errors on loss distribution and beam profile at the beam dump entrance carefully analysed.

• N.Y. Huang, S.S. Yang
  NTHU, Hsinchu
• H. Hama
  Tohoku University, School of Scinece, Sendai
• W.K. Lau
  NSRRC, Hsinchu

Design of an intense but tightly focused ultrashort electron beam for production of sub-hundred femtosecond x-ray pulses that based on head-on inverse Compton scattering (ICS) has been studied. The three dimensional (3D) space charge dynamics has been tracked and optimized throughout the whole beamline. It is found that the focusing ultrashort electron pulses as short as 67 fs can be produced by compressing the energy-chirped beam from a thermionic cathode rf gun with an alpha magnet and linac operating at injection phase near zero crossing. This multi-bunch electron beam has an intensity of 30 pC per bunch and is accelerated to 27 MeV with an S-band linac structure. The compressed electron beam is focused to 64 μm for scattering with an 800 nm, 3.75 mJ laser in the laser-beam interaction chamber. With this method, total peak flux of back-scattered x-ray photons exceeds 10¹⁸ photons/sec is achievable with the shortest wavelength of 0.7 Å.

• A. Opanasenko, V.V. Mytrochenko, S.A. Perezhogin
  NSC/KIPT, Kharkov

The electron injector for a storage ring is one of numerous applications of the rf linacs of intensive short-pulsed beams with duration about 100 ns, current about 1 A and energy of particles in a few ten MeB. Since acceleration of intensive short-pulsed beams takes place in transient mode, then the energy spread is determined by both intro- and multi- bunch spread. Getting the energy spread less than 1% is the actual problem. In this work we simulate numerically unsteady self-consistent dynamics of charged particles in an rf linac that consist of a low-voltage (25 keV) thermionic gun, a compact evanescent wave buncher, a traveling wave accelerating structure. For transient beam loading compensation a method of delay of a beam relatively rf pulse are applied. The simulation takes into account influence on the beam dynamic of such factors as: initial energy and phase spread; sliding of particles in relation to a wave in the initial part of accelerating section; temporal dependence of phase and energy of bunches at the enter of section; space charge field.

• A. Opanasenko
  NSC/KIPT, Kharkov

Acceleration of intensive electron beams in transient mode with energy spread less than 1% is the actual problem for rf linacs. The transient beam loading phenomenon, consisting in coherent radiation of sequence of charged bunches, results in time dependence of electron energy loss within a beam pulse. In this work a method of delay of a beam relatively rf pulse for energy compensation at accelerating intense short-pulsed electron beams is discussed. An efficiency of the given method in depending on dispersion of group speed, phase advance per cell of an rf structure, an envelope profile of pulses both current and input rf field is studied. Contribution of non-resonant counter waves in the beam energy spread is estimated.

• A. Opanasenko, V.S. Kovalenko, K. Kramarenko, V.A. Kushnir, V.V. Mytrochenko, Z.V. Zhiglo, A. I. Zykov
  NSC/KIPT, Kharkov

At present work the results of numeral simulation of electron dynamics in an unhomogeneous disk-loaded waveguide which is used in the S-band linac are presented. Two approaches taking into account the self-fields of beam radiation are considered: the first method estimative based on the power diffusion equation; the second one based on of self-consistent equations of field excitation and particles motion. The self-consistent approach showed the presence of substantial phase slipping of particles in the homogeneous part of the rf structure, conditioned by the reactive beam loading.

• V.P. Yakovlev, T.N. Khabiboulline, N. Solyak, A. Vostrikov
  Fermilab, Batavia
• A. Saini
  University of Delhi, Delhi

Results of analysis are presented for the longitudinal and transverse effects of High-Order Mode (HOM) excitation in the acceleration RF system of the CW proton linac of the Project X facility. Necessity of HOM dampers in the SC cavities of the linac is discussed.

• E. Startsev, R.C. Davidson
  PPPL, Princeton, New Jersey

To achieve high focal spot intensities in ion-beam-driven high energy density physics and heavy ion fusion applications, the ion beam must be compressed longitudinally by factors of ten to one hundred before it is focused onto the target. The longitudinal compression is achieved by imposing an initial velocity profile tilt on the drifting beam, and allowing the beam to compress longitudinally until the space-charge force or the internal thermal pressure stops the longitudinal compression of the charge bunch. In this paper, the problem of longitudinal drift compression of intense charged particle beams is analyzed analytically and numerically for the two important cases corresponding to a cold beam, and a pressure-dominated beam, using a one-dimensional warm-fluid model describing the longitudinal beam dynamics. The hodograph transformation is used to transform the nonlinear fluid equations into a single, second-order, linear partial differential equation (PDE). The general solution of this equation describing the intense beam system with stagnation point is analyzed and illustrated with several examples.

• N.A. Tahir
  GSI, Darmstadt
• V.E. Fortov, I. Lomonosov, A. Shutov
  IPCP, Chernogolovka, Moscow region
• R. Piriz
  Universidad de Castilla-La Mancha, Ciudad Real
• R. Schmidt
  CERN, Geneva

Safety of the personnel and the equipment is an issue of great concern when operating with mighty particle beams like the ones generated by the LHC. Any uncontrolled release of even a very small fraction of the beam energy could cause considerable damage to the equipment. A worst case scenario is in which the entire beam is lost at a single point. Over the past years, we have carried out extensive numerical simulations to assess the consequences of an accident of this magnitude. We have simulated the thermodynamic and the hydrodynamic response of cylindrical targets made of solid copper and solid graphite, respectively, that are facially irradiated with one LHC beam. Our simulations show that the 7 TeV/c LHC protons will penetrate up to about 35 m in solid copper and about 10 m in solid graphite during the 89 μs beam duration time. In both cases, the target is severely damaged and a substantial part of the target is converted into High Energy Density Matter state.

• T. Mimashi, N. Iida, M. Kikuchi
  KEK, Ibaraki
• K. Abe, S. Abe
  Hitachi Haramachi Electronics Co. Ltd., Hitachishi, Ibaraki
• K. Iwamoto
  KFG, NEUSS
• Y. Makino, T. Ozawa
  Kikusui Chemical Industries Co. Ltd, Kagamihara Shiga
• A. Sasagawa
  KYOCERA Corporation, Higashiomi-city, Shiga
• A. Tokuchi
  Pulsed Power Japan Laboratory Ltd., Kusatsu-shi Shiga

New beam abort system designed for KEKB upgrade, consists of horizontal and vertical kicker magnets, pulsed quadrupole magnets, a Lambertoson septum magnet and a beam dump. Water-cooling ceramic chambers are used for the kicker and pulsed quadrupole magnets. At the KEKB upgrade project, the beam abort gap is required to be less than 200 nsec. The beam currents are increased and their emittance is supposed to be much smaller than KEKB. In order to avoid melting the extraction Ti window, the pulsed quadrupole magnets will be installed. They enlarge the beam cross section at the extract window. The components for the SuperKEKB abort system are developed. The compact water-cooling ceramic chambers are developed to reduce the gap of kicker magnets and bore radius of the pulsed quadrupole magnets. The power supply for the kicker magnet is also developed to satisfy the 200 nsec rise time requirement.

• M. Kwiatkowski, A. Castañeda, B. Todd
  CERN, Geneva

Mission critical systems at the European Organisation for Nuclear Research (CERN) make extensive use of Programmable Logic Devices (PLDs) such as Field Programmable Gate Arrays (FPGAs) to implement their safety critical functions. The dependability of these safety critical functions is difficult to determine using traditional techniques. A robust approach is needed if PLD technology is to be accepted in mission critical systems. This paper discusses techniques which are being developed and employed by CERN to give confidence in the use of PLDs in mission critical systems, the Safe Machine Parameter system development is used as an example.

• Y. Polsky, P.J. Geoghegan, L.L. Jacobs, S.M. McTeer, M.A. Plum
  ORNL, Oak Ridge, Tennessee
• W. Lu
  ORNL RAD, Oak Ridge, Tennessee

The use of a beam stop to absorb full or partial beam at various points along a particle accelerator is commonplace. The design of accelerator components such as magnets, linacs and beam instruments tends to be a fairly focused and collective effort within the particle accelerator community with well established performance and reliability criteria. Beam stop design by contrast has been relatively isolated and unconstrained historically with much more general goals. This combination of conditions has lead to a variety of facility implementations with virtually no standardization and minimal concensus on approach to development within the particle accelerator community. At the Spallation Neutron Source (SNS), for example, there are four high power beam stops in use, three of which have significantly different design solutions. This paper describes the design of a new off-momentum beam stop for the SNS. Content will be balanced between hardware description, analyses performed and the methodology used during the development effort. Particular attention will be paid to the approach of the design process with respect to future efforts to meet beam stop performance metrics.

• M. Kanazawa, Y. Iwata
  NIRS, Chiba-shi
• T. Fujimoto
  AEC, Chiba
• K. Watanabe
  Toshiba Medical Systems Corporation, Tochigi

In the routine operation of HIMAC synchrotron, a pulse system of field change with 0.2 Gauss in the monitor dipole magnet (B-clock) is used to generate pattern data in the acceleration system. To eliminate error pulse due to noise in analogue field signal, a clock system locked to a 1.2kHz clock for a power supplies was developed, which can be used to generate pattern data of an acceleration system with maximum frequency of 192kHz. This 1.2kHz clock is synchronized to a power line frequency of 50Hz that will fluctuate about 0.1%, so the clock of 192kHz must also follow this frequency fluctuation. To demonstrate the performance of new clock system, we have tested beam acceleration, and compared with the conventional B-clock system. Acceleration efficiencies were checked with changing these clock rates in the both systems. With these tests, we have found that the relatively low clock rate in the newly developed system is enough to get good acceleration performance. In this paper the clock system, and their beam tests will be presented.

• T. Ohshima, N. Hosoda, H. Maesaka, S. Matsubara, Y. Otake
  RIKEN/SPring-8, Hyogo

The pulse width of an X-ray laser at XFEL/SPring-8 is several tens femto-seconds, which requires reference rf signals to have the same time-stability. The reference signals with a low phase-noise oscillator are sent to instruments in 19" racks developed along an accelerator by an optical fiber system. The temperature drift of the fiber makes phase shifts of the reference signals. Therefore, the fiber is put in a thermal-insulated duct. By feeding temperature-controlled water (26.1 ± 0.1 deg. C) in a pipe attached to the duct, the fiber temperature was kept to be 26.2 ± 0.08 deg. C at the ambient temperature change of 29.1 ± 1.7 deg. C. From this temperature controllability, the phase shifts of the signals through a 400 m fiber of a thermal coefficient of 5 ps/km/K are 160 fs. Further reduction of the shifts is required and will be achieved by a fiber-length feedback control in a future plan. Vibration of the fiber also degrades the quality of the signals. The fiber is embedded on a vibration buffer material. A test to evaluate the effect of the vibration to the transmitted signal phase was carried out. The test result will be also shown in this paper.

• D. Qiang, Y.-C. Du, W.-H. Huang, C.-X. Tang, L.X. Yan
  TUB, Beijing

The Tsinghua Thomson scattering X-ray source (TTX) has a strict laser-electron synchronization requirement and a comprehensive system structure including dual high-power laser system, RF system and beam diagnostic instruments, etc. Recently, a synchronization and control system is developed to meet these requirements, which includes a laser-RF synchronizer with 100fs time jitter, a FPGA based event generator for laser and RF systems with 250ps time resolution, and an EPICS based control system for system integration and remote monitor and control. The electron bunch arrival time jitter is carefully measured and analyzed with the help of a RF deflecting cavity. This paper reports the development status, technical implementation, and measurement results of the synchronization and control system.

• M. Liu, D.K. Liu, C.X. Yin, L.Y. Zhao
  SINAP, Shanghai

Currently, the real-time data transfer system is widely implemented in the accelerator control system. If timing system and real-time data transfer system could be combined into one uniform system, it would be convenient to build distributed feedback system, fast interlock system and so on. So, a new timing system, the real-time synchronized data bus is developed to realize this idea. The architecture of the system and the hardware prototype design are introduced in the paper. The data exchange mechanism and system specification, including timing trigger synchronization accuracy, timing jitter relative to RF clock, data transfer rate and latency are described in detail. Redundant topology structure and fiber length compensation are specially considered. In the end, the results of testing in lab are presented.

• J.M. Byrd, L.R. Doolittle, G. Huang, J.W. Staples, R.B. Wilcox
  LBNL, Berkeley, California

Stabilized optical fiber links have been under development for several years for high precision transmission of timing signals for remote synchronization of accelerator and laser systems. In our approach, a master clock signal is modulated on an optical carrier over a fiber link. The optical carrier is also used as the reference in a heterodyne interferometer which is used to precisely measure variations, mainly thermal, in the fiber length. The measured variations are used to correct the phase of the transmitted clock signal. We present experimental results showing sub-10 fsec relative stability of a 200 m link a sub-20 fsec stability of a 2.2 km link.

• I. Yamane
  KEK, Ibaraki
• M. Nakamura, H. Okuno
  RIKEN Nishina Center, Wako

An asymmetrical con-focal cavity is composed of tow concave mirrors with different focal length, placed face to face, and their axes and focal points coincide. When a laser beam is injected in parallel with the mirror axis, from backward of and just outside of the mirror with the smaller focal length, the laser beam is trapped in the cavity and repeats reflection by mirrors. Then, the beam reflected by the mirror with the larger focal length passes every time the focal point and the period by which pulses return to the focal point is constant. Therefore, if the repetition period of the injected laser pulse is equal to the repetition period in the cavity, all laser pulses comes to the focal point at the same time and the beam intensity is stacked up. Calculation on the performance of an asymmetrical con-focal cavity shows that a laser pulse can be recycled more than a few tens turns and the beam intensity can be stacked to more than a few tens times of the original beam intensity when the laser beam is a Gaussian beam and the reflectance of the mirrors is 100%. Results of calculation is examined using a He-Ne laser and a pair of high reflection mirrors.

• Z.G. He, Q.K. Jia, X.E. Wang
  USTC/NSRL, Hefei, Anhui

A Photo-Cathode RF Gun is under development at NSRL. In this paper, the drive laser system is introduced and performance parameters are presented. We adopt a BNL type gun with laser illuminating the cathode at oblique incidence. To orrect 'time slew' and 'elliptical spot' problems arisen on the cathode, an adjustable optical transport line is designed.

• I. Jovanovic, Y. Yin
  Purdue University, West Lafayette, Indiana
• S. Boucher, R. Tikhoplav
  RadiaBeam, Marina del Rey
• G. Travish
  UCLA, Los Angeles, California

One approach for detecting special nuclear material (SNM) at a distance is to use highly penetrating gamma-rays (>6 MeV) to produce photofission. We are investigating inverse gamma-ray sources (IGS), based on inverse Compton scattering (ICS) of a laser pulse on a relativistic electron bunch. Nearly monochromatic gamma rays with high brightness, very small source size and divergence can be produced in IGS. For the interaction drive laser recirculation it is necessary to meet the repetition rate requirements. Three implementations of laser recirculation are proposed for the interaction drive laser, which can significantly reduce the requirements on the interaction drive laser average power. It is found that the recently demonstrated recirculation injection by nonlinear gating (RING) technique offers unique advantages for beam recirculation in IGS.

• K.-P. Ningel, P. Hülsmann, H. Klingbeil, U. Laier, C. Thielmann, B. Zipfel
  GSI, Darmstadt

The heavy ion synchrotron SIS18 at the GSI facility will be upgraded by a dual harmonic RF acceleration system in the process of using SIS18 as booster for the future FAIR SIS100 accelerator. The dual harmonic mode will extend the SIS18 operating towards higher beam currents. As a part of a large LLRF upgrade at the synchrotron RF systems at GSI, new FPGA and DSP based electronics have been designed, built and commissioned. To prove the functionality of the LLRF equipment as well as the general dual harmonic topology, machine development experiments using the existing cavities have been performed. During these experiments, the main parameters of the control loop were determined. Additionally, the impact of RF gap voltage amplitude and phase variations onto the ion beam have been investigated, like e.g. creation of a dual harmonic bucket or fast changes in harmonic number. The experiments showed a high sensitivity of the ion beam to small deviations in the phase between both harmonics and thereby confirmed the requirements on the high precision regarding phase accuracy of the electronic setup especially for the closed loop phase control systems.

• R. Eichhorn, A. Araz, U. Bonnes, F. Hug, M. Konrad, P. Nonn
  TU Darmstadt, Darmstadt
• G. Schreiber, W. Vinzenz
  GSI, Darmstadt
• R. Stassen
  FZJ, Jülich

During the redesign of the low level RF system for the S-DALINAC, a baseband approach was chosen. The RF signals from/ to the cavity are converted into the baseband via I/Q Modulators/ Demodulators. The advantage of this design was realized lateron, as adaption of other frequencies becomes rather easy. The system, originally designed for 3 GHz superconducting cavity in cw operation is currently modified to control a 324 MHz room temperature CH cavity in pulsed operation. We will report on the rf control system principle, the required modifications and first results.

• V. Ayvazyan, S. Choroba, Z. Geng, G. Petrosyan, S. Simrock, V. Vogel
  DESY, Hamburg

The Free Electron Laser in Hamburg (FLASH) is a user facility providing high brilliant laser light for experiments. It is also a unique facility for testing the superconducting accelerator technologies. FLASH cavities are operating at pulsed mode. There is a filling stage to build the RF voltage in the cavities and then follow a flattop for beam operation. By the limitation of the klystron pulse length the filling time of the cavities is limited to several hundred microseconds. In order to fill the cavities to the dedicated voltage usually large RF power is required for the filling stage. For European XFEL during RF operation the klystrons will be working quite near the saturation point for better efficiency. So lowering the unnecessary klystron peak power under closed loop operation is very important for close-limitation operation. The paper will present the method which allows decreasing the required klystron peak power as well as the reflected power by filling the cavity in resonance. Simulation results will be presented as well as experimental demonstrations at FLASH.

• F. Ludwig, C. Gerth, K.E. Hacker, M. Hoffmann, G. Moeller, P. Morozov, Ch. Schmidt
  DESY, Hamburg
• W. Jalmuzna
  TUL-DMCS, Łódź

Future FELs (Free-Electron-Lasers) requires a precise detection of the cavity field in the injector section with a resolution of much less than 0.01 deg in phase and 0.01% in amplitude for a cavity operation frequency at 1.3GHz. Long-term stable SASE (Self Amplified Spontaneous Emission) operation mainly suffers from injector accelerator components and the stability of the reference distribution. Especially thermal instabilities of the distributed cavity field detectors, probe pickup cables and their mechanical vibrations influence the energy stability dramatically on a scale of 0.1%, a scale which is 10 times worse than required. To eliminate the long-term amplitude and phase changes, we injected a reference signal prior to the arrival of the cavity field signal. This enabled pulse-to-pulse calibration which compensated for the drifts of the field detectors. We demonstrated a dramatic phase and amplitude stability improvement from the ps-range to the 0.008 deg (peak-to-peak) range in phase and 0.02% (peak-to-peak) in amplitude; this represents an improvement in drifts by a factor of about 100. The injected calibration was successfully employed during FLASH operation.

• M.G. Hoffmann, M. Hoffmann, F. Ludwig, P. Morozov, Ch. Schmidt
  DESY, Hamburg

For future FELs (Free-Electron-Lasers) a 3rd harmonic system was proposed to increase the SASE intensity by linearization of the beam phase space after the first bunch compression section. At DESYs FLASH facility, a 3rd harmonic cavity system, consisting of four single cavities operating at 3.9GHz has been successfully tested at the module test stand. In this paper we present field regulation measurements using a step wised down converted field detector system and a model based designed LLRF field controller. First measurements showed a promising in loop vectorsum amplitude stability of about 2·10^-5 for pulse-to-pulse operation.

• H. Shaker
  IPM, Tehran
• R. Corsini, H. Shaker, P.K. Skowronski, I. Syratchev, F. Tecker
  CERN, Geneva

The pulse compressor is located after the klystron to increase the power peak by storing the energy at the beginning and releasing it near the end of klystron output pulse. In the CTF3 [1] pulse compressors a doubling of the peak power is achieved according to our needs and the machine parameters. The magnitude of peak power, pulse length and flatness can be controlled by using a phase modulator for the input signal of klystrons. A C++ code is written to simulate the pulse compressor behaviour according to the klystron output pulse power. By manually changing the related parameters in the code for the best match, the quality factor and the filling time of pulse compressor cavities can be determined. This code also calculates and sends the suitable phase to the phase modulator according to the klystron output pulse power and the desired pulse length and peak power.

• A. Gennai, F. Bedeschi, S. Galeotti, C. Magazzu, F. Paoletti, E. Pedreschi, F. Spinella
  INFN-Pisa, Pisa
• D. Passuello
  University of Pisa and INFN, Pisa

Superconductive cavities for future linear accelerators, such as ILC, have extremely large quality factors requiring an effective stabilization with both slow and fast tuners. Piezoelectric actuators are the most common choice for fast tuners, but one drawback for a large scale application is the limited bandwidth and the large cost of commercially available drivers. In this paper we present a low cost driver which is ideally suited for fast tuner application, large system packaging and has an excellent flexibility in its implementation. Driving piezoelectric actuators having capacitive loads up to a few microfarads in the kHz range requires amplifiers with good current output capabilities at a few hundred volts. The Piezo Control Unit we developed for the ILC Test Area at Fermilab is composed by a 6U Eurocard crate hosting 5 Piezo Driver modules capable of driving up to 10 piezoelectric actuators. Main specifications include large voltage rails (-175 V to +175V), wide signal bandwidth (DC to10 kHz) and low output noise ( <10 mVrms). The driver is equipped with both output voltage and output current monitor.

• F. Spinella, F. Bedeschi, S. Galeotti, A. Gennai, E. Pedreschi
  INFN-Pisa, Pisa
• A. Basti, D. Passuello
  University of Pisa and INFN, Pisa

Active devices based on piezoelectric actuators are widely used to dump unwanted vibrations in a variety of applications; for instance fast tuners for superconducting RF cavities. In another poster, we describe a low cost modular system of drivers for piezoelectric actuators developed at INFN-Pisa; we show here that the same system can easily be extended, with the inclusion of a simple plug-in board, to include sufficient I/O and computing capability to allow control of the device up to frequencies in the kHz range. This implementation is extremely cost effective and can be used in all situations where a high granularity distributed control system is desirable. We also show our first test results obtained using this system to control a warm single cell 1.3 GHz cavity. The cavity is perturbed using a piezoelectric actuator to generate random noise, while another piezo is used in the control loop to stabilize the resonance frequency. We use the phase of the RF pickup from the cavity as a measure of the deviation from the resonance caused by the perturbation. This simple setup allows to easily test various control algorithms without the need to work at large complex facilities.

• Z. Fang, S. Anami, Y. Fukui, M. Kawamura, C. Kubota, S. Michizono, F. Naito, K. Nanmo, S. Yamaguchi
  KEK, Ibaraki
• H. Asano, K. Hasegawa, T. Itou, T. Kobayashi, S. Shinozaki, N. Tsubota
  JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
• E. Chishiro, H. Suzuki
  JAEA, Ibaraki-ken

The output energy of the J-PARC LINAC will be upgraded from 181 to 400 MeV in the next two years by adding high-beta acceleration sections. The upgrade of the FPGA-based digital LLRF controller for the 400 MeV LINAC will be presented in this paper. The new LLRF control system works for both the 324 MHz low-beta and 972 MHz high-beta sections. Many functions are added into the LLRF controller, such as 1) working for different RF frequencies, 2) gradually increasing the feedback gains in the feedback loop instead of fixed ones, 3) automatic chopped-beam compensation, 4) automatically switching the beam loading compensation in accordance with the different beam operation mode, 5) input rf-frequency tuning carried out by a FPGA to match the rf cavities during the rf start-up, 6) auto-tuning of the rf cavity tuner by detecting the phase curve of the rf cavity during the field decay instead of the phase difference between the cavity input and output signals.

• S. Michizono, D.A. Arakawa, S. Fukuda, H. Katagiri, T. Matsumoto, T. Miura, Y. Yano
  KEK, Ibaraki

S1 global will be operated at STF in KEK, where total 8 cavities will be installed. The digital llrf system to control the vector sum of the field gradients to be flat has been developed. All the digital llrf system including rf monitoring, piezo-control system will be shown. The new llrf system suitable for the DRFS scheme, which is also studied during S1 grobal, is also under development.

• T. Miura, A. Akiyama, D.A. Arakawa, S. Fukuda, H. Katagiri, T. Matsumoto, S. Michizono, J.-I. Odagiri, Y. Yano
  KEK, Ibaraki

The compact ERL(cERL) is the energy recovery linac(ERL) test facility that is under construction at KEK. The stability of accelerating electric field of 0.1% rms in amplitude and 0.1deg. in phase is required for LLRF system. The status of LLRF system for cERL will be reported.

• F. Tamura, M. Nomura, A. Schnase, T. Shimada, H. Suzuki, M. Yamamoto
  JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
• K. Hara, C. Ohmori, M. Tada, M. Yoshii
  KEK/JAEA, Ibaraki-Ken
• K. Hasegawa
  KEK, Ibaraki

The wide-band RF cavities in the J-PARC RCS are operated in the dual-harmonic operation, in which each single cavity is driven by a superposition of the fundamental and the second harmonic RF signals. By the dual-harmonic operation large amplitude second harmonic signals for the bunch shape manipulation are generated without extra cavities. The phase control of the second harmonic RF is a key for the bunch shape manipulation. The fundamental RF signal is controlled by the phase feedback loop to damp the dipole oscillation. The second harmonic is locked to the phase of the vector-sum phase of the fundamental RF signals. We present the system detail and the performance in the beam operation of the RCS.

• A. Schnase, K. Hasegawa, M. Nomura, T. Shimada, H. Suzuki, F. Tamura, M. Yamamoto
  JAEA/J-PARC, Tokai-mura
• K. Hara, C. Ohmori, M. Tada, M. Yoshii
  KEK/JAEA, Ibaraki-Ken
• T. Koseki, T. Toyama
  J-PARC, KEK & JAEA, Ibaraki-ken
• M. Tomizawa
  KEK, Ibaraki

Applying narrow band longitudinal noise to the beam in J-PARC Main Ring in flattop, while the acceleration voltage is off might help to counteract the effect of ripple on the slow extraction. For this purpose, a complex noise sequence output by DSP modulates a custom made DDS synthesizer to create single side spectra without carrier. The noise is calculated starting from a description in frequency domain. Then an algorithm creates narrow band spectra with optimized behavior in time domain. Frequency domain data is transformed to time domain, and the amplitude is smoothed. The smoothed data is transformed back to frequency domain, and the spectral shape is restored. This process repeats until the amplitude in time domain has converged, while the desired spectrum shape is preserved. Noise generated in this way can be tailored for different requirements. We show the signal properties, the hardware, and preliminary beam test results, when the noise is applied to the MR RF system.

• X. Zheng, H.T. Hou, J.F. Liu, C. Luo, Zh.G. Zhang, S.J. Zhao
  SINAP, Shanghai
• Z.Q. Feng, Z. Li, D.Q. Mao, Y.B. Zhao, X. Zheng
  Shanghai KEY Laboratory of Cryogenics & Superconducting RF Technology, Shanghai

The digital low level radio frequency (DLLRF) system and the beam trip diagnostic system in the storage ring of Shanghai Synchrotron Radiation Facility (SSRF) have been operational for more than one year. The DLLRF has successfully maintained the amplitude and phase stability of the cavity field in the superconducting cavity even when the beam current in the storage ring reached 300mA at 3.5GeV, and the beam trip diagnostic system has been realized and is helpful for improving the reliability of the RF system.

• K.P. Przygoda, A. Napieralski, T. Pozniak
  TUL-DMCS, Łódź
• M.K. Grecki
  DESY, Hamburg

DESY FLASH accelerator is composed of 6 accelerating modules. The single accelerating module contains 8 superconducting resonant cavities. Since FLASH operation is dedicated for various energy physics experiments such as high current beam acceleration or SASE tuning, the sc cavities are Lorentz force detuned when operated with high gradient accelerating fields*. The ACC 3, 5 and 6 cryomodules are equipped with piezo tuners allow compensating of dynamic detuning during the RF pulse. In order to assure the simultaneous control of all available piezo tuners a distributed, multichannel digital and analogue piezo control system was applied. The paper describes the main parts of the system as well as its efficiency measurements obtained during high current beam acceleration (9 mA tests) performed in DESY. The piezo tuners were operable for 23 cavities for several hours. Moreover, the first piezo sensor measurements using double stack piezos installed in ACC 6 cryomodule are briefly demonstrated.

*M. Grecki, A. Andryszczak, T. Poźniak, K. Przygoda, S. Sękalski,
"Compensation of Lorentz Force Detuning For SC Linacs (With Piezo
Tuners)", Proceedings of EPAC 2008, pp. 862-864.

• G. Jug, A. Kosicek
  I-Tech, Solkan

In this article we are presenting tests and development of digital low level RF control system Libera LLRF. Libera LLRF is a digital system small in size but powerful in terms of performance as tests revealed. Size of unit matches industrial standards and is in 19" 2U sustainable metal box that fits into racks. Development of the Libera LLRF reflects needs of accelerator's and their operators. With its capabilities it is a system that is able to control RF at 4th generation light sources. Concept of the Libera LLRF system also enables implementation of operator's own solutions in controlling RF. During preparations for testing Libera LLRF's features proved to be useful since little time was needed to install and operate the system. In some cases its features and capability enabled operators to identify and quickly resolve problems that were accelerator's components related.

• H. Hassanzadegan, N. Garmendia
  ESS Bilbao, Bilbao
• F.J. Bermejo
  Bilbao, Faculty of Science and Technology, Bilbao
• M. Eguiraun
  ESS-Bilbao, Zamudio
• V. Etxebarria
  University of the Basque Country, Faculty of Science and Technology, Bilbao
• D.J.S. Findlay, A.P. Letchford
  STFC/RAL/ISIS, Chilton, Didcot, Oxon

Design, implementation and some practical results of the pulsed digital LLRF system (amplitude, phase and tuning loops) of the RFQ for the ISIS front end test stand are presented. The design is based on a fast analog front-end for RF-baseband conversion and a model-based Virtex-4 FPGA unit for signal processing and PI regulation. Complexity of the LLRF timing is significantly reduced and the LLRF requirements are fulfilled by utilizing the RF-baseband conversion method compared to the conventional RF-IF approach. Validity of the control loops is ensured practically by hardware-in-the-loop co-simulation of the system in MATLAB-Simulink using an aluminium mock-up cavity. It was shown through extensive tests that the LLRF system meets all the requirements including amplitude and phase stability, dynamic range, noise level and additionally provides a full amplitude and phase control range and a phase margin larger than 90 degrees for loop stability.

• M. E. Angoletta, A. Blas, A.C. Butterworth, A. Findlay, P.M. Leinonen, J.C. Molendijk, F. Pedersen, J. Sanchez-Quesada, M. Schokker
  CERN, Geneva

In 2008 a project was started to renovate the CERN's PS Booster (PSB) low-level RF (LLRF). Its aim is to equip all four PSB rings with modern LLRF systems by 2013 at the latest. Required capabilities for the new LLRF include frequency program, beam phase, radial and synchronization loops. The new LLRF will control the signals feeding the three RF cavities present in each ring; it will also shape the beam in a dual harmonic mode, operate a bunch splitting and create a longitudinal blow-up. The main benefits of this new LLRF are its full remote and cycle-to-cycle controllability, built-in observation capability and flexibility. The overall aim is to improve the robustness, maintainability and reliability of the PSB operation and to make it compatible with the injection from the future LINAC4. The chosen technology is an evolution of that successfully deployed in CERN's ion accumulator ring LEIR and it is based upon modular VME 64X hardware and extensive digital signal processing. This paper outlines the main characteristics of the software and hardware building blocks. Promising initial beam tests are shown and hints are included on the main milestones and future work.

• M. E. Angoletta, J. Bento, A. Blas, E. Bracke, A.C. Butterworth, F. Dubouchet, A. Findlay, F. Pedersen, J. Sanchez-Quesada
  CERN, Geneva

The Low Energy Ion Ring (LEIR) is an accumulation ring in the Large Hadron Collider ion injector chain. After its successful start in 2005, it has been running in three operational campaigns. The LEIR LLRF system is the first all-digital low-level RF (LLRF) system to be made operational in a CERN circular machine. Composed of modular VME 64X hardware, it carries out extensive digital signal processing via Field Programmable Gate Arrays and Digital Signal Processors. System capabilities include beam control tasks, such as frequency program, beam phase, radial and synchronization loops, as well as cavity voltage/phase loops. All the system's control parameters are fully configurable, remotely and in-between cycles; extensive built-in diagnostics and signal observation features are available. The system has proven to be not only flexible and powerful but also extremely reliable. This is very important as the LEIR LLRF system is the pilot project for the LLRF renovation of other CERN's machines. This paper gives an overview of the main system building blocks and outlines their capabilities and operational features, along with results obtained during the first years of beam operation.

• A.J. Moss, S.P. Jamison, P.A. McIntosh, A.E. Wheelhouse
  STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
• B.B. Baricevic
  I-Tech, Solkan

The Low Level RF (LLRF) control system on EMMA (Electron Model for Many Applications), the world's first Non-Scaling Fixed Field Alternating Gradient (NS-FFAG) accelerator is presently being installed and commissioned at Daresbury Laboratory. The LLRF is required to synchronize with ALICE (Accelerators and Lasers in Combined Experiments) its injector, which operates at 1.3GHz, and to produce an offset frequency as required (+1.5Mhz to -4MHz) to then maintain the phase and amplitude of the 19 copper RF cavities of the EMMA machine. The design and commissioning of the LLRF system is presented.

• S. Pei, C. Adolphsen
  SLAC, Menlo Park, California
• J. Carwardine
  ANL, Argonne
• N.J. Walker
  DESY, Hamburg

The FLASH L-band (1.3 GHz) superconducting accelerator facility at DESY has a Low Level RF (LLRF) system that is similar to that envisioned for ILC. This system has extensive monitoring capability and was used to gather performance data relevant to ILC. Recently, waveform data were recorded with both beam on and off for three, 8-cavity cryomodules to evaluate the input RF and cavity gradient stability and study the RF overhead required to achieve constant gradient during the 800μs pulses. In this paper, we present the recent experimental results and discuss the pulse-to-pulse input RF and cavity gradient stability for both beams on and off cases. In addition, a model of the gradient variation observed in the beam off case will be described.

• B. Hong, R. Akre, V. Pacak
  SLAC, Menlo Park, California

The Linac Coherent Light Source (LCLS) at SLAC is in full user operation and has met the stability goals for stable lasing. The 250pC bunch can be compressed to below 100fS before passing through an undulator. In a new mode of operation a 20pC bunch is compressed to what is believed to be about 10fS. Experimenters are regularly using this shorter X-ray pulse and getting pristine data. The 10fS bunch has timing jitter on the order of 100fS. Physicists are requesting that the RF system achieve better stability to reduce timing jitter. Drifts in the RF system require longitudinal feedbacks to work over large ranges and errors result in reduced performance of the LCLS. This paper describes the new RF system being designed to help diagnose and reduce jitter and drift in the SLAC linac.

• T. Mastorides, J.D. Fox, C.H. Rivetta, D. Van Winkle
  SLAC, Menlo Park, California
• P. Baudrenghien, A.C. Butterworth, J.C. Molendijk
  CERN, Geneva

Radio Frequency (RF) accelerating system noise and non-idealities can have detrimental impact on the LHC performance through longitudinal motion and longitudinal emittance growth. A theoretical formalism has been developed to relate the beam and RF loop dynamics with the bunch length growth [1]. Measurements were conducted at LHC to validate the formalism, determine the performance limiting RF components, and provide the foundation for beam diffusion estimates for higher energies and intensities. A brief summary of these results is presented in this work.

[1] T. Mastorides et. al., "RF system models for the LHC with Application to
Longitudinal Dynamics", prepared for submission to Physical Review ST-AB.

• D. Van Winkle, J.D. Fox, T. Mastorides, C.H. Rivetta
  SLAC, Menlo Park, California
• P. Baudrenghien, A.C. Butterworth, J.C. Molendijk
  CERN, Geneva

The LHC Low Level RF system (LLRF) is a complex multi-loop system used to regulate the superconductive cavity gap voltage as well as to reduce the impedance presented by RF stations to the beam. The RF system can have a profound impact on the stability of the beam; a mis-configured RF system has the potential of causing longitudinal instabilities, beam diffusion and beam loss. To configure the RF station for operation, a set of parameters in the LLRF multi-loop system have to be defined. Initial system commissioning as well as ongoing operation requires a consistent method of computer based remote measurement and model-based design of each RF station feedback system. This paper describes the suite of Matlab tools used for configuring the LHC RF system during the start up in Nov2009-Feb2010. We present a brief overview of the tool, examples of commissioning results, and basics of the model-based design algorithms. This work complements our previous presentation [1], where the algorithms and methodology followed in the tools were described.

[1] D. Van Winkle et. al. 'Feedback Configuration Tools for LHC Low Level RF System,' PAC'09, Vancouver, Canada, May 2009, THZCH03, p. 249 (2009); http://www. JACoW.org.

• B. Bolzon, L. Brunetti, A. Jeremie
  IN2P3-LAPP, Annecy-le-Vieux
• M. Esposito, U. Rotundo, S. Tomassini
  INFN/LNF, Frascati (Roma)

Following previous measurements, more detailed preliminary ground motion measurements have been performed at the LNF site for the Super B project site characterization. First, results of vertical ground motion measurements done during 18 hours are shown in order to get an idea of the evolution of the ground motion amplitude with time. Secondly, measurements of ground motion (in the 3 directions of space) were performed at different locations on surface in order to evaluate and to compare the influence of various vibration sources. Then, results of ground motion coherence measured for different distances at two locations close to each other but with soft and rigid floor are compared. These measurements are also compared to the ones done in the ATF2 beam line where a special floor was built for stability. By this way, the results reveal that the LNF is a good site to use ground motion coherence properties for stability like it has been done for ATF2.

• E. Bagli
  INFN-Ferrara, Ferrara
• V. Guidi
  UNIFE, Ferrara
• V.A. Maisheev
  IHEP Protvino, Protvino, Moscow Region

We present an analytical model to calculate the physical quantities of interest experienced by relativistic particles in their motion aligned with periodic complex atomic structures. Classical physics equations and the expansion of periodic functions as a Fourier series have been used for the calculation. This method allows calculating the contribution from all the planes and axes inside the crystal, in contrast to other simulation codes for which the motion is evaluated only on nearest neighbors atomic strings. Based on the calculation technique we have developed the "ECHARM" program, which allows calculating one- and two- dimensional averaged physical quantities of interest. The calculation holds for the main axes of any orthorhombic and tetragonal structures and for any orientation in the cubic structure. To underline the capability of the program, complex structures such as zeolites have been worked out. Based on the "ECHARM" code, simulation of the relativistic particle motion within complex structures has been developed. With this code it is possible to simulate the motion in bent crystal to study planar and axial channeling volume reflection.

• T. Hasegawa, T. Inagaki, Y. Otake, T. Sakurai
  RIKEN/SPring-8, Hyogo
• S. Takahashi
  JASRI/SPring-8, Hyogo-ken

This paper describes the present status of a precise temperature-regulation system for the C-band accelerator at XFEL (X-ray Free Electron Laser)/SPring-8. It is essential to maintain a constant temperature of an rf cavity for stable lasing. We therefore installed a heater-assembly unit into a cooling water circuit of each rf cavity. By controlling the heater power, the temperature of the cavity can be stabilized. We constructed a prototype of this system at the SCSS (SPring-8 Compact SASE Source) test accelerator to check its feasibility for the XFEL. The prototype significantly contributes to a stable supply of SASE to users. For the XFEL, we simplified this system in consideration of cost and controllability. For example, to make one regulation system simultaneously controlling two C-band accelerating structures was tried. Keeping a temperature variation as tight as ±0.02 K at any operational mode could be achieved by this system. The preliminary test results of the system are also reported in this paper.

• Y. Sun, L.G. Shen, Z. Shu, X.C. Wang
  USTC/PMPI, Hefei, Anhui
• Y.J. Pei
  USTC/NSRL, Hefei, Anhui

Collinear load is a substitute for waveguide load to miniaturize irradiation accelerators and make the system compact. The key technology is to design coaxial cavities coated inside with attenuating materials which will terminate the remnant power, meanwhile the operation frequency of 2856 MHz retains. For lossy materials such as Kanthal (25%Cr-5%Al-Fe) alloy, CST is used to simulate the effect of the coating on the load cavity properties like the operation frequency and attenuation. The frequency shifts caused by the coatings would be compensated by the strategy of cavity dimensions adjustment. Simulations revealed the compensation rules of the cavity inner radius b. Meanwhile the relationship between the attenuation and the coating area was also resolved. Based on a specified power allocation, a 15 kW collinear load consisting of six cavities at 2π/3 mode was designed with one-way attenuation of -18.8 dB. Two sets of prototype cavities have been manufactured and the experiment results are presented, compared with the CST simulations.

• X.C. Wang, L.G. Shen, Z. Shu, Y. Sun
  USTC/PMPI, Hefei, Anhui
• K. Jin, Y.J. Pei
  USTC/NSRL, Hefei, Anhui

Microwave-absorbing material is an essential part of LINAC collinear load. It is coated on the inner walls of several trailing accelerating cavities to transform the remnant microwave power into heat. Fe-85%Si-9.6%Al-5.4% alloy, which reveals low outgassing rate and high attenuation, is selected for collinear load R&D. To measure the permittivity and permeability of FeSiAl at 2856 MHz, the coaxial transmission-reflection method is adopted. The system is firstly examined by testing the hollow coaxial fixture and comparing the results with the electromagnetic parameters of the air. Measurements of two PTFE rings show that the air gaps between the fixture and samples influence the test results seriously. CST is utilized to simulate the effects on the FeSiAl measure-ments. Eventually a scheme of molding the samples of FeSiAl powder mixed with paraffin to form a wax mold is proposed and the permittivity and permeability of FeSiAl are derived from the electromagnetic parameters equivalent formulas of mixed medium.

• F. Caspers, S. Federmann, E. Mahner, P.C. Pinto, D. Seebacher, M. Taborelli
  CERN, Geneva
• B. Salvant
  EPFL, Lausanne
• C. Yin Vallgren
  Chalmers University of Technology, Chalmers Tekniska Högskola, Gothenburg

Electron cloud is a limitation to increasing the beam current in the CERN SPS in the frame of an intensity upgrade of the LHC complex. Coating the vacuum chamber with a thin amorphous carbon layer is expected to reduce the electron cloud build-up. Three SPS straight sections have been coated to study the performance of this carbon coating. The microwave transmission method is one possible way to monitor electron cloud and hence to test the effect of the coating. In this paper the evolution of the experimental setup for measurements of the electron cloud using LHC type beams with different bunch spacing will be described. Due to the low revolution frequency of about 43 kHz serious electromagnetic compatibility problems and intermodulation have been found. These effects and their mitigation are described. Finally we present the measurement results illustrating the possible reduction due to the carbon coating.

• I. Montero, L.S. Aguilera
  CSIC, Madrid
• F. Caspers, E. Montesinos
  CERN, Geneva
• L. Galan
  UAM, Madrid
• D. Raboso
  ESA-ESTEC, NOORDWIJK

We are presenting first results of direct measurements of the secondary electron emission yield (SEY) for several magnetic materials like ferrites at energies of primary electrons from 5 to 10⁰⁰ eV. In order to minimize the impact of surface charging, the primary electron beam had a short pulse modulation of 400ns with a very low repetition rate. This paper discusses a method of developing a secondary-electron-suppressing highly textured ferrite surface with low SEY by depositing a layer of very fine ferrite particles onto a substrate. The experimental results indicate that the SEY of the particulate ferrite surfaces is much lower than that of flat ferrites. In comparison we have confirmed that ordinary carbon coating with rather large grain size returns SEY value close to unity. However, a surface with very finely powdered carbon has a much smaller secondary emission yield of about 0.5, but the adhesion of these carbon powders to the surface is often not reliable enough for many applications. As a remarkable fact it has been found that gold- and also carbon-coated ferrites have SEY peak values lower than unity up to 1000eV.

• Ya.V. Getmanov, O.A. Shevchenko
  BINP SB RAS, Novosibirsk
• N. Vinokurov
  NSU, Novosibirsk

We consider a technique for electron injection into a cyclic accelerator using the laser wakefield acceleration (LWFA) technique. Accelerators with this type of injector can be used for different purposes due to lower size, cost and low radiation hazard. To use the LWFA technique it is necessary to create a small gas cloud inside the accelerator vacuum chamber. But it leads to the increase of particle losses due to scattering on residual gas atoms. Therefore we propose to use magnesium as evaporated gas because of its high absorbability ' its atoms stick to walls at the first contact. We presented estimations of the LWFA-based injection system parameters, including maximum stored current. The proposed technique looks very prospective for compact accelerators and storage rings.

• I.C. Sheng, J.-R. Chen, Y.T. Cheng, G.-Y. Hsiung, C.K. Kuan, C.Y. Yang
  NSRRC, Hsinchu

The Taiwan Photon Source (TPS) is a third generation synchrotron accelerator which the designed energy will be 3 GeV whereas the current is 500mA. The role of crotch absorber is designed to protect downstream UHV vacuum chamber. It is is the only mask component to absorb large amount of synchrotron radiation (bending magnet) in the storage ring. Crotch absorber is installed from transverse direction of the bending chamber to intercept the power. Two bent OFHC copper tubes are vacuum brazed on the copper mask. A 30 degree groove is machined to face bending magnet fan. The reason is not only to dissipate the heat but also to limit back scattering to the rest of chambers. Top and bottom of the absorber are bolted with beryllium copper springs; they will provide extra support for the absorber after it is installed in the Aluminum chamber. Three thermocouples will be embedded inside of the mask to monitor the temperature gradient. Final prototype of the crotch absorber with thermal analysis, design and machined parts are also presented in this paper.

• A. Hershcovitch, M. Blaskiewicz, J.M. Brennan, W. Fischer, C.J. Liaw, W. Meng
  BNL, Upton, Long Island, New York
• A.X. Custer, M.Y. Erickson, N.Z. Jamshidi, H.J. Poole
  PVI, Oxnard
• N. Sochugov
  Institute of High Current Electronics, Tomsk

Electron clouds, which can limit machine performance, have been observed in many accelerators including RHIC at BNL. They can be suppressed by low secondary electron yield beam pipe surfaces. Additional concern for the RHIC machine, whose vacuum chamber is made from relatively high resistivity 316LN stainless steel, is high wall resistivity that can result in unacceptably high ohmic heating for superconducting magnets. The high resistivity can be addressed with a copper (Cu) coating; a reduction in the secondary electron yield can be achieved with a TiN or amorphous carbon (a-C) coating. Applying such coatings in an already constructed machine is rather challenging. We started developing a robotic plasma deposition technique for in-situ coating of long, small diameter tubes. The technique entails fabricating a device comprising of staged magnetrons mounted on a mobile mole for deposition of about 5 μm (a few skin depths) of Cu followed by about 0.1 μm of a-C. As a first step, a 15-cm Cu cathode magnetron is being designed and fabricated, after which, 30-cm long sample of the RHIC pipe are to be Cu coated. Deposition rates and affects on RF resistivity are to be measured.