• H. Chen, Q.X. Jin, R.K. Li, Y. Z. Lin
  TUB, Beijing
• J. Gao
  Tsinghua University, Beijing

The method of intensity-modulated radiotherapy (IMRT) is increasingly concerned by the medical world in recent years. Based on the performance characteristic of IMRT accelerator, a 6MeV S-band on axis-coupled SW, Suitable for IMRT, electron linear accelerating tube has been developed in Accelerator Lab of Tsinghua University. This paper provides the design performance characteristics of the tube and the results of the high-power tests,analyzes the performance and problems in the operation.

• D. Egger
  EPFL, Lausanne
• A.E. Dabrowski, S. Döbert, D. Egger, T. Lefèvre, O. Mete
  CERN, Geneva

To improve the quality of the CLIC Test Facility 3 drive beam, it has been proposed that a photo injector replaces the actual thermionic gun. This would produce a lower emittance beam and minimize beam losses in the injector since the RF bunching and sub‐harmonic bunching systems would not be needed anymore. Such a photo injector, named PHIN, is currently being developed at CERN. One of the difficulties is to provide a high intensity beam (3.5A) with a stable (0.1%) beam energy over 1.5us as well as a relative energy spread less than 1%. A 90° spectrometer line featuring a segmented dump and an Optical Transition Radiation screen has been constructed and commissioned in order to study the time evolution of the beam energy along the pulse duration. In the following paper, we present the design as well as the results from the previous two PHIN runs.

• 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.

• 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.

• 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.

• Y. Morita, K. Akai, T. Furuya, A. Kabe, S. Mitsunobu, M. Nishiwaki, S. Takano
  KEK, Ibaraki

Eight superconducting accelerating cavities have been stably operated in the KEKB with sufficiently low trip rates. Two superconducting crab cavities were installed in 2007 and soon the crab crossing operation started. Recently the KEKB luminosity reached the world record of 2.1 x 10³⁴ cm^-1s^-1. Stable operations of the accelerating cavities contributed for the luminosity increase. For the future Super-KEKB, we are developing a high power coupler for an input power of 600 kW and a HOM damper for RF power absorption more than 30 kW. The Super-KEKB requires RF operations with the high beam loading and the low RF voltage than the present KEKB operation. To suppress klystron output powers the external Q value has to be reduced. A new operation was proposed for superconducting cavities. In order to keep high RF voltages in each cavity, some cavities reverse its synchronous beam phase while the total RF voltage is kept as low as the required one. Beam studies were successfully carried out with one cavity reversed its synchronous beam phase.

• H. Zen
  UVSOR, Okazaki
• M. A. Bakr, K. Higashimura, T. Kii, R. Kinjo, K. Masuda, K. Nagasaki, H. Ohgaki
  Kyoto IAE, Kyoto
• H. Zen
  Sokendai - Okazaki, Okazaki, Aichi

Thermionic RF guns are compact, economical and high brightness electron sources. However, when the guns are used for a driver linac of oscillator-type Free Electron Lasers (FELs), which requires moderate bunch charge (several tens pico-coulomb) and long macro-pulse duration (several micro-seconds), the guns have been suffered from the back-bombardment effect*. The effect induces beam current increment in a macro-pulse. And consequently the current increment leads to decrement of beam energy during a macro-pulse and significantly limits the beam macro-pulse duration after some bending magnets. Our group found a new energy compensation scheme called as cavity detuning** and the method was introduced to compensate the beam energy decrement in the thermionic RF gun used for KU-FEL***. In this presentation, we will introduce the principle of the method and experimental results. Detailed analysis of the method will be also presented.

* C.B. McKee et al., NIM, A296, pp. 716-719, 1990.
** H. Zen et al., IEEE Trans. of Nucl. Sci., vol. 56, No. 3, pp. 1487-1491
*** T. Yamazaki et al., Proc. of 23rd FEL Conf., pp. II-13-14, 2002.

• S.V. Kutsaev
  MEPhI, Moscow

This paper introduces "Hellweg 2D" code, a special tool for electron dynamics simulation in waveguide accelerating structure. The underlying theory of this software is based on the numerical solutions of differential equations of particle motion. The effects considered in this code include beam loading, space charge forces, external focusing magnetic field. "Hellweg 2D" is capable to deal with multisectional accelerators. Along with a manual input of electrodynamical parameters of the cells, for disk-loaded structures they can be calculated automatically with a help of experimental data tables. In order to obtain the maximum capture in the buncher section, the optimizer of phase velocity and electric field strength functions is developed. The comparison of U-1-M buncher beam dynamics simulations via "Hellweg 2D" and experimental data is provided.

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

The Longitudinal emittance in J-PARC RCS should be controlled to accelerate a high intensity proton beam with minimal beam loss. In order to study and minimize the beam loss during acceleration, the optimized way to add the 2nd higher harmonic rf has been calculated by a particle tracking code. Furthermore, the bunch shape at RCS extraction should be controlled and optimized for the MR injection. For this purpose, the optimum RCS acceleration pattern has been calculated. We describe the simulation results and the comparison with the beam test.

• I. Syratchev, A. Cappelletti
  CERN, Geneva

One crucial development for CLIC is an adjustable high-power rf device which controls the output power level of individual Power Extraction and Transfer Structures (PETS) even while fed with a constant drive beam current. The CLIC two-beam rf system is designed to have a low, approximately 10^-7, breakdown rate during normal operation and breakdowns will occur in both accelerating structures and the PETS themselves. In order to recover from the breakdowns and reestablish stable operation, it is necessary to have the capability to switch off a single PETS/accelerating structure unit and then gradually ramp generated power up again. The baseline strategy and implementation of such a variable high-power mechanism is described.

• J.K. Pozimski, M. Aslaninejad, C. Bontoiu
  Imperial College of Science and Technology, Department of Physics, London
• J.S. Berg
  BNL, Upton, Long Island, New York
• S.A. Bogacz
  JLAB, Newport News, Virginia
• S. Machida
  STFC/RAL/ASTeC, Chilton, Didcot, Oxon

The IDS study showed that a Neutrino Factory seems to be the most promising candidate for the next phase of high precision neutrino oscillation experiments. A part of the increased precision is due to the fact that in a Neutrino Factory the decay of muons produces a neutrino beam with narrow energy distribution and divergence. The effect of beam loading on the energy distribution of the muon beam in the Neutrino Factory has been investigated numerically. The simulations have been performed using the baseline accelerator design including cavities for different number of bunch trains and bunch train timing. A detailed analysis of the beam energy distribution expected is given together with a discussion of the energy spread produced by the gutter acceleration in the FFAG and the implications for the neutrino oscillation experiments will be presented.

• J.G. Power, M.E. Conde, W. Gai
  ANL, Argonne
• Z. Li
  SLAC, Menlo Park, California
• D. Mihalcea
  Northern Illinois University, DeKalb, Illinois

We report on the design of a 7 cell, standing wave, 1.3 GHz LINAC cavity and the associated beam dynamics studies for the upgrade of the drive beamline for the Argonne Wakefield Accelerator (AWA) facility. The LINAC design is a compromise between single bunch operation (100 nC @ 75 MeV) and minimizing the energy droop due to beam loadning along the bunch train during bunch train operation. The 1.3 GHz drive bunch train target parameters are: 75 MeV, 10-20 ns macropulse duration, 16x60nC microbunches; this is equivalent to a macropulse current and beam power of 80 Amps and 6 GW, respectively. Each LINAC structure accelerates approximately 1000 nC in 10 ns by a voltage of 11 MV at an RF power of 10 MW. Due to the short bunch train duration desired (~10 ns) and the existing frequency (1.3 GHz), compensation of the energy droop along the bunch train is difficult to accomplish with the two standard techniques: time-domain or frequency-domain beam loading compensation. Therefore, to minimize the energy droop, our design is based on a large stored energy LINACs. In this paper, we present our LINAC optimization method, detailed LINAC design, and beam dynamics studies of the drive beamline.

• D. Alesini, C. Biscari, A. Ghigo
  INFN/LNF, Frascati (Roma)

After a short description of the Frequency Multiplication Scheme of the CLIC drive beam we present the impact of beam loading in the RF deflectors. First order scaling laws for the beam loading have been obtained to compare the effects in CLIC with those in the Test Facility CTF3. A dedicated tracking code has been written to study the multi-bunch multi-turn beam dynamics and the results are presented. Possible solutions to mitigate the beam loading effects such as the use of multiple RF deflectors are shown.