FIR

Paper	Title	Other Keywords	Page
TUOAFI03	Production of MeV Photons by the Laser Compton Scattering Using a Far Infrared Laser at SPring-8	laser, photon, electron, storage-ring	961
	H. Ohkuma, M. Shoji, S. Suzuki, K. Tamura, T. Yorita JASRI/SPring-8, Hyogo-ken Y. Arimoto Osaka University, Osaka M. Fujiwara, K. Kawase RCNP, Osaka K. Nakayama, S. Okajima Chubu University, Kasugai, Aichi
	In order to produce MeV gamma-ray by the Laser Compton scattering (LCS), a high power optically pumped Far Infrared (FIR) laser has been developed at SPring-8. In the case of the SPring-8 storage ring, the momentum acceptance is so large (± 200 MeV) that the scattered electron is re-accelerated, then the stored beam is not lost by the LCS process. The beam diagnostics beamline is used to inject a FIR laser beam against 8-GeV stored electron beam and to extract MeV gamma-ray produced by LCS. The FIR laser system, gamma-ray production system, and measured gamma-ray spectrum will be presented. Future plans will also be introduced. In order to produce higher intense gamma-ray, we are constructing new gamma-ray production system at another beamline.
	Transparencies
TUPCH130	Development of the Feed-forward System for Beam Loading Compensation in the J-PARC RCS	beam-loading, FFC, CIC, controls	1319
	F. Tamura, M. Nomura, A. Schnase, M. Yamamoto JAEA/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken S. Anami, E. Ezura, K. Hara, C. Ohmori, A. Takagi, M. Yoshii KEK, Ibaraki
	In the J-PARC Rapid Cycling Synchrotron (RCS), the heavy beam loading effects due to the high intensity proton beam must be compensated for stable acceleration. The beam feedforward technique is used to compensate the beam loading in the RCS. We present the development of the feedforward system. We designed and built the full-digital system with modern FPGAs to realize high accuracy, stability and predictability of the compensation. Because of the low Q value of each accelerating cavity, the wake voltage consists of not only the accelerating harmonic component but also higher harmonics. Thus, the system is designed to compensate the beam loading at several harmonics. The system has two parts. In the first part, vector components of the selected harmonic are detected from the beam signal picked up by a wall current monitor. The compensation RF signal is generated from the vector components with proper gain and phase in the latter part. The gain and phase are set individually for each harmonic and each cavity of the twelve cavities. We also present the preliminary test results of the newly developed modules.
TUPCH189	FPGA-based RF Field Control at the Photocathode RF Gun of the DESY VUV-FEL	controls, gun, electron, DESY	1456
	E. Vogel, W. Koprek, P. Pucyk DESY, Hamburg
	At the DESY Vacuum Ultraviolet Free Electron Laser (VUV-FEL) bunch peak current and the SASE effect are (amongst other parameters) sensitive to beam energy and beam phase variations. The electron bunches are created in an rf gun, which does not have field probes. Variations of the gun rf field cause beam energy and phase variations. They have a significant influence on the overall performance of the facility. DSP based rf field control used previously was only able to stabilize the rf output of the klystron. This was due to the lack of processing power and the over-all loop delay. The controller was not able to provide satisfactory rf field stability in the gun. Replacing the DSP hardware by the new FPGA-based hardware Simulation Controller (SimCon), we are able to reduce the latency within the digital part significantly allowing for higher loop gain. Furthermore SimCon provides sufficient processing power for calculating a probe signal from the forward and reflected power as input for PI and adaptive feed forward (AFF) control. In this paper we describe the algorithms implemented and the gun rf field stability obtained.
TUPCH197	Low level RF System Development for the Superconducting Cavity in NSRRC	controls, feedback, klystron, linac	1477
	M.-S. Yeh, L.-H. Chang, F.-T. Chung, K.-T. Hsu, Y.-H. Lin, C. Wang NSRRC, Hsinchu
	The present low level system in NSRRC is based on analogy feedback control scheme. It provides feedback regulation on EM field, phase, and resonant frequency of the superconducting RF cavity. In order to address the required flexibility and improve diagnostic of the RF control system, a new digital low-level RF system based on Field Programmable Gate Array (FPGA) is proposed to be develop in house. The status of current analogy low level RF system and the specification of new digital FPGA based low level RF system are reposted herein.
THPCH039	Beam Studies with Coherent Synchrotron Radiation from Short Bunches in the ANKA Storage Ring	synchrotron, radiation, storage-ring, synchrotron-radiation	2868
	A.-S. Müller, I. Birkel, S. Casalbuoni, B. Gasharova, E. Huttel, Y.-L. Mathis, D.A. Moss, P. Wesolowski FZK, Karlsruhe C. J. Hirschmugl UWM, Milwaukee, Wisconsin
	In the ANKA storage ring it is possible to store bunches with RMS lengths of the order of 1 ps using a dedicated optics with reduced momentum compaction factor. For short bunch operation a beam energy of 1.3 GeV is chosen as a trade-off between low energy longitudinal instabilities and the increase in natural bunch length with energy. At this medium energy (the energy range of the ANKA storage ring is 0.5 to 2.5 GeV) steady state emission of coherent synchrotron radiation is observed by the ANKA-IR beamline below the threshold current defined by the micro-bunching instability. At lower beam energies where the natural bunch length is significantly shorter, bursts of coherent synchrotron radiation are detected in spite of the longitudinal oscillation. The far infrared spectrum is sensitive to the dynamics of the charge distribution generating the radiation. Measurements of the frequency spectrum of the infrared detector signal add information on bunch dynamics. This paper gives an overview of the studies performed at the ANKA storage ring.
THPCH082	Broadband Bunch by Bunch Feedback for the ESRF using a Single High Resolution and Fast Sampling FPGA DSP	feedback, kicker, damping, pick-up	2976
	E. Plouviez, P. Arnoux, F. Epaud, J. Jacob, J.M. Koch, N. Michel, G.A. Naylor, J.-L. Revol, V. Serriere, D. Vial ESRF, Grenoble
	In order to increase the current in the ESRF storage ring we have developed a set of multibunch feedback systems aimed at fighting longitudinal and transverse coupled bunch instabilities. The longitudinal feedback (LFB) has been the first system installed and tested. It was designed using the scheme developed at SLAC, ALS and INFN Frascati: bunch by bunch processing of a beam phase error signal and correction using a low Q kicker driven by a QPSK modulator. However, we took advantage for this development of the latest available technology for the signal processing electronics with high resolution, high sampling rate ADC and DAC, and FPGA DSP, as well as for the FPGA programming environment. It allowed us to substantially reduce the complexity: the algorithm runs on a single processor, the kicker requires only 200W of RF power to control a 6GeV beam, and the implementation took only about one year. We will describe the main features of our LFB and present the results already achieved in the damping of instabilities driven by our RF cavity HOM. We will also report on the status of the transverse feedback, which is being built up using the same FPGA system as the longitudinal one.
THPCH084	Control Path of Longitudinal Multibunch-feedback System at HERA-p	controls, kicker, proton, feedback	2982
	F.E. Eints, S. Choroba, M.G. Hoffmann, U. Hurdelbrink, P.M. Morozov, J. Randhahn, S. Ruzin, S. Simrock DESY, Hamburg
	A longitudinal broadband damper system to control coupled bunch instabilities has been developed and installed in the proton accelerator HERA-p at the DESY. The control system consists of a control path and a Fast Diagnostic System (FDS) for oscillation diagnostic. The control path consists of FPGA-based digital controller, vector modulator, 1kW power amplifier, kicker-cavity and beam. In the FDS, the bunch phase signals are sampled by a digital FPGA board with 14Bit ADC (controller) with a sampling frequency of 10.4MHz. Phase calculation for all bunches and offset correction will be done by FPGA software which includes a digital filter. The filter has to be able to deal with a slowly changing synchrotron frequency. Here we consider a filter design which treats each of maximum 220 bunches as an independent oscillator which has to be damped. More sophisticated mode filter algorithms may be required to get better noise performance. The FPGA-board output signal modulates a 104 MHz sine-wave. The resulting logitudinal correction kick signal is provided by the kicker-cavity. Beside the technical details we present first operational experience and the actual system performance.
THPCH092	Single-loop Two-dimensional Transverse Feedback for Photon Factory	feedback, damping, kicker, factory	3006
	T. Nakamura, K. Kobayashi JASRI/SPring-8, Hyogo-ken W.X. Cheng, T. Honda, M. Izawa, T. Obina, M. Tadano KEK, Ibaraki
	We installed a 500MS/s single-loop two-dimensional transverse bunch-by-bunch feedback system in the Photon Factory ring at KEK and the system is in operation at its user mode. The system composed of a single feedback loop; one skewed pair of BPM electrodes and one kicker stripline at skewed position to detect position and kick horizontally and vertically with a single signal line, and a SPring-8 feedback processor. Consequently, this system is easy to tune and cost effective. SPring-8 feedback processor employs FPGA that has enough computing power for processing more than 20-tap FIR filter required for newly developed two-dimensional feedback signal processing. We report the principle of the system, the result of test and the experience.
THPCH097	Commissioning of the Digital Transverse Bunch-by-bunch Feedback System for the TLS	feedback, kicker, damping, controls	3020
	K.H. Hu, J. Chen, P.J. Chou, K.-T. Hsu, S.Y. Hsu, C.H. Kuo, D. Lee, C.-J. Wang NSRRC, Hsinchu A. Chao SLAC, Menlo Park, California K. Kobayashi, T. Nakamura JASRI/SPring-8, Hyogo-ken W.-T. Weng BNL, Upton, Long Island, New York
	Multi-bunch instabilities degrade the beam quality leading to increased beam emittance, energy spread or even to beam loss. The feedback system is used to suppress multi-bunch instabilities due to resistive wall of the beam ducts, cavity-like structures and trapped ions. A new digital transverse bunch-by-bunch feedback system was commissioned at the Taiwan Light Source recently, and has replaced the previous analog system. The new system has the advantages that it enlarges the tune acceptance compared with the old system, enhances damping for transverse instability at high current, and as a result, top-up operation was achieved. In this new system, a single feedback loop simultaneously suppresses both the horizontal and vertical multi-bunch instabilities. The feedback system employs the latest generation FPGA feedback processor to process bunch signals. Memory installed to capture up to 250 msec bunch oscillation signal has included the considerations for system diagnostic and should be able to support various beam physics study.
THPCH098	FPGA-based Longitudinal Bunch-by-bunch Feedback System for TLS	feedback, kicker, impedance, synchrotron	3023
	C.H. Kuo, J. Chen, P.J. Chou, K.-T. Hsu, S.Y. Hsu, K.H. Hu, W.K. Lau, D. Lee, C.-J. Wang, M.-H. Wang, M.-S. Yeh NSRRC, Hsinchu M. Dehler PSI, Villigen K. Kobayashi, T. Nakamura JASRI/SPring-8, Hyogo-ken
	A FPGA Based Longitudinal Bunch-by-Bunch Feedback System for TLS is commissioning recently to suppress strong longitudinal oscillation. The system consists of pickup, Bunch oscillation detector, FPGA based feedback processor borrow form the design of Spring8. Modulator converts the correction signal to the carrier frequency and longitudinal kicker which was re-designed form SLS' and working at 1374 MHz. The feedback processor is based upon latest generation FPGA feedback processor to process bunch signals. The memory capture is up to 250 msec bunch oscillation signal. The software and hardware design are also included for system diagnostic and support various beam physics study. Preliminary commission result will be summaried in this report.
THPLS133	Simulations of Electromagnetic Undulator for Far Infrared Coherent Source of TTF at DESY	undulator, electron, radiation, simulation	3595
	E. Syresin, V.V. Borisov, E.A. Matushevsky, N.A. Morozov JINR, Dubna, Moscow Region O. Grimm, M.V. Yurkov DESY, Hamburg J. Rossbach Uni HH, Hamburg
	A perspective extension of the VUV FEL user facility at DESY is infrared coherent source on the base of electromagnetic undulator. The undulator consists of 9 periods, period length is 40 cm long, and peak magnetic field is up to 1.2 T. With the energy of electron beam of 500 MeV maximum radiation wavelength is about 200 mkm. An important feature of the beam formation system of the VUV FEL is the possibility to produce ultra-short, down to 50 mkm rms electron bunches. Such short bunches produce powerful coherent radiation with multi-megawatt power level. FIR coherent source operates in a parasitic mode utilizing electron beam passed VUV undulator. Generation of two-colors by a single electron bunch reveals unique possibility to perform pump-probe experiments with VUV and FIR radiation pulses. In this report we present simulations of the undulator magnetic system and beam dynamics.