WPAT  —  Radio-Frequency Systems   (18-May-05   08:30—12:20)

Paper Title Page
WPAT001 HFSS Simulation of Vacuum Tube RF Power Amplifiers 767
  • V. Zviagintsev, I. Bylinskii
    TRIUMF, Vancouver
  Funding: TRIUMF receives funding via a contribution agreement through the National Research Council of Canada.

Development and upgrade of rf power amplifiers require comprehensive calculations to predict and optimize various parameters of the system before hardware modifications are applied. ANSOFT HFSS code provides a powerful tool for 3D EM simulation of the amplifier output resonator comprising a vacuum tube as a passive element. Two examples of this kind of simulation applied for upgrade of the TRIUMF Cyclotron rf system are presented in this paper.

WPAT002 High Power (35 kW and 190 kW) 352 Solid State Amplifiers for the SOLEIL Synchrotron 811
  • P. Marchand, M.D. Diop, R.L. Lopes, J. Polian, F. Ribeiro, T. Ruan
    SOLEIL, Gif-sur-Yvette
  In the SOLEIL Storage Ring, two cryomodules, each containing a pair of superconducting cavities will provide the maximum power of 600 kW, required at the nominal energy of 2.75 GeV with the full beam current of 500 mA and all the insertion devices. Each of the four cavities will be powered with a 190 kW solid state amplifier consisting in a combination of 315 W elementary modules (about 750 modules per amplifier). The amplifier modules, based on a technology developed in house, with MOSFET transistor, integrated circulator and individual power supply, are fabricated in the industry. In the booster, a 35 kW solid state amplifier (147 modules) will power a 5-cell copper cavity of the LEP type. The first operational results and the status of the RF power plants are reported in this paper. Although quite innovative for the required power range, the solid state technology proved to be very attractive with significant advantages as compared to vacuum tubes.  
WPAT003 Glycol-Substitute for High Power RF Water Loads 841
  • M. Ebert, F.-R. Ullrich
    DESY, Hamburg
  In water loads for high power rf applications, power is dissipated directly into the coolant. Loads for frequencies below approx. 1GHz are ordinarily using an ethylene glycol-water mixture as coolant. The rf systems at DESY utilize about 100 glycol water loads with powers ranging up to 600kW. Due to the increased ecological awareness, the use of glycol is now considered to be problematic. In EU it is forbidden to discharge glycol into the waste water system. In case of cooling system leakages one has to make sure that no glycol is lost. Since it is nearly impossible to avoid any glycol loss in large rf systems, a glycol-substitute was searched for and found. The found sodium-molybdate based substitute is actually a additive for corrosion protection in water systems. Sodium-molybdate is ecologically harmless; for instance, it is also used as fertilizer in agriculture. A homoeopathic dose of 0.4% mixed into deionised water gives better rf absorption characteristics than a 30% glycol mixture. The rf coolant features of this substitute were investigated and tested. The glycol coolant of all rf systems at DESY was substituted. The results of the investigations and tests are presented.  
WPAT004 Coupling Methods for Superconducting CH-Cavities 922
  • H. Liebermann, H. Podlech, U. Ratzinger, A.C. Sauer
    IAP, Frankfurt-am-Main
  Funding: GSI, BMBF contr. No. 06F134I, EU.

The cross-bar H-type (CH) cavity is a multi-gap drift tube structure based on the H-210 mode currently under development at IAP Frankfurt and in collaboration with GSI. Numerical simulations and rf model measurements showed that the CH-type cavity is an excellent candidate to realize Room Temperature and Superconducting multi-cell structures with a frequency range from about 150 MHz up to 800 MHz. For coupling into such a complex structure, we compare two coupling methods, one with capacitive and the other with inductive couplers. This paper will present detailed MicroWave Studio simulations and measurements for these different coupling methods for Room Temperature and Superconducting CH-Cavities. For coupling into a Superconducting CH-Cavity we prefer a capacitive coupler. We will also present an optimized Superconducting CH-Cavity for capacitive couplers.

WPAT005 A New Tuning Module for Resonant Coupling Structures 973
  • V.G. Vaccaro
    Naples University Federico II, Mathematical, Physical and Natural Sciences Faculty, Napoli
  • T. Clauser, A. Rainò, V. Variale
    INFN-Bari, Bari
  • A. D'Elia
    Naples University Federico II and INFN, Napoli
  • C. De Martinis, D. Giove
    INFN-Milano, Milano
  • M.R. Masullo
    INFN-Napoli, Napoli
  • M. Mauri
    INFN/LASA, Segrate (MI)
  In order to have efficient particle acceleration it is fundamental that the particles experience, in the accelerating gap, field amplitudes as uniform and as high as possible from gap to gap. Because of the unavoidable fabrication errors, an accelerating structure, when assembled, exhibits field values lower than the nominal ones and/or not uniform. All the usual procedures developed in order to adjust the parameter deviations responsible of the malfunction of these structures, are based on field amplitude measurements, by using the bead pull technique, which is a very invasive technique. In this paper the philosophy is reversed: it is assumed that all the information can be got by Sounding the Modes of the whole System (SMS) and correct the deviation of each frequency mode from its nominal value by means of an appropriate tuning of the cavities: resorting to a perturbative technique applied to a circuit model representing this kind of structures, it is possible to calculate the amount of tuning to give to the cavities. It will be shown that a very good equalization and maximization of the fields in the cavities can be achieved by using this technique.  
WPAT006 The SPARC RF Synchronization System 1024
  • A. Gallo, D. Alesini, M. Bellaveglia, R. Boni, G. Di Pirro, F. Tazzioli
    INFN/LNF, Frascati (Roma)
  The SPARC project consists in a 150 MeV Linac aimed at driving an ondulator for the production of 530 nm SASE FEL radiation. A bunch transverse emittance as low as 1mm mrad and a bunch peak current of about 100 A are required for this task. The RF voltages in the RF gun and in the 3 S-band accelerating sections have to be kept phase locked within 3 ps to the arrival time of the laser pulse on the photocathode to guarantee the required performances. This specification will be reduced to 0.5 ps in the phas·10-2 of the project when the rectilinear RF compression of the bunch will be tested. The general architecture of the SPARC RF control system together with some bench qualification measurements of the basic components is presented in this paper.  
WPAT007 Control Loops for the J-PARC RCS Digital Low-Level RF Control 1063
  • A. Schnase, M. Nomura, F. Tamura, M. Yamamoto
    JAERI/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
  • S. Anami, E. Ezura, K. Hara, C. Ohmori, A. Takagi, M. Yoshii
    KEK, Ibaraki
  The low-level radiofrequency control for the Rapic Cycling Syncrotron of J-PARC is based on digital signal processing. This system controls the acceleration voltages of 12 magnetic alloy loaded cavities. To achive a short overall delay, mandatory for stable loop operation, the data-processing is based on distributed arithmetics in FPGA. Due to the broadband characteristic of the acceleration cavities, no tuning loop is needed. To handle the large beam current, the RF system operates simultaneously with dual harmonics (h=2) and (h=4). The stability of the amplitude loops is limited by the delay of the FIR filters used after downconversion. The phase loop offers several operation modes to define the phase relation of (h=2) and (h=4) between the longitudinal beam signal and the vector-sum of the cavity voltages. Besides the FIR filters, we provide cascaded CIC filters with smoothly varying coefficients. Such a filter tracks the revolution frequency and has a substantially shorter delay, thereby increasing the stable operating region of the phase loops. The adaptive radial loop accumulates the orbit variation over several machine cycles to reduce the effects of measurement errors on the effective acceleration frequency program.  
WPAT008 Recent Status of RF Source in J-PARC Linac 1123
  • E. Chishiro, T. Hori, H. Suzuki, M. Yamazaki
    JAERI, Ibaraki-ken
  • S. Anami, S. Fukuda, Y. Fukui, M. Kawamura, S. Yamaguchi, M. Yoshida
    KEK, Ibaraki
  The construction of the J-PARC (Japan Proton Accelerator Research Complex) linac is under going. RF sources for the low beta linac section use 324-MHz klystrons and after the evaluation of seven prototype tubes, mass production of 20 tubes are conducted. These will be installed in the linac building from April 2005. Performances of the 324-MHz klystrons are described in this paper. The prototype klystron of 972-MHz klystron, which is planed to be installed in high beta linac section, oscillated strongly without any drive rf power, and it had been investigated to solve it. Though it was doubted to be a diode oscillation at first, recent experiment showed the drift-tube oscillation and we succeeded in stopping oscillation by deforming the integrated cavity and detuning. After this experiment, we built a new tube and started to test it. This experiment is written in this paper. Other status of construction related to the rf sources is also shown in this paper.  
WPAT009 Status of the RF System for the 6.5 GeV Synchrotron Light Source PF-AR 1168
  • S. Sakanaka, K. Ebihara, S. Isagawa, M. Izawa, T. Kageyama, T. Kasuga, H. Nakanishi, M. Ono, H. Sakai, T. Takahashi, K. Umemori, S.I. Yoshimoto
    KEK, Ibaraki
  The Photon Factory Advanced Ring (PF-AR) is a 6.5-GeV synchrotron light source at KEK. An rf system comprises two 1.2-MW klystrons, six alternating-periodic-structure (APS) cavities, and other components. It supplies an rf voltage of about 15 MV with a beam current of 60 mA. The system has been working well, except for a trouble (frequent trips with beams) in one of the cavities. We found that the trips were triggered by an irradiation of synchrotron radiation to the cavity wall. In the summer of 2004, we reorganized the rf system, which allows us to install two insertion devices in a part of the rf sections. We replaced the troubled cavity at a time. We report both the operation status and the modification of the rf system.  
WPAT010 RF Dielectric Properties of SiC Ceramics and their Application to Design of HOM Absorbers 1195
  • Y. Takeuchi, T. Abe, T. Kageyama, H. Sakai
    KEK, Ibaraki
  The KEKB ARES cavity is equipped with two types of HOM absorbers, which are made of different commercial products of the alpha-type SiC ceramics. Their dielectric responses to the RF frequency show the dielectric relaxation properties. Those properties can be clearly explained by the polycrystal structure model with electrically conductive grains and non-conductive grain boundaries. In this article, the RF dielectric properties of the SiC ceramics are discussed together with the application to HOM absorbers.  
WPAT011 Application of TRL Calibration in Longitudinal Coupling Impedance Measurement Platform for BEPCII 1225
  • G. Huang, W.-H. Huang, S. Zheng
    Tsinghua University, Beijing
  • D.M. Zhou
    IHEP Beijing, Beijing
  Funding: Supported by NSFC 10375035.

TRL calibration is one of the standard calibration methods for RF measurement. Applying the TRL calibration method into the longitudinal coupling impedance platform makes it possible to eliminate the error matrix of the matching section and the RF connector. By using TRL calibration in the platform, the reference pipe of each device under test no longer required. The formula of the calibration is discussed in this paper and the software based on it is introduced.

WPAT012 Status and Test Results of HPRF System for PEFP 1288
  • K.T. Seol, Y.-S. Cho, H.-S. Kim, H.-J. Kwon, M.-Y. Park, Y.G. Song
    KAERI, Daejon
  Funding: This work is supported by the 21C Frontier R&D program in the Ministry of Science and Technology of the Korean government.

The PEFP 20MeV proton accelerator is composed of 3MeV RFQ and 20MeV DTL and two sets of 1MW, 350MHz RF system are required for each accelerating structure. The high power RF system for 3MeV RFQ was already installed and operated to drive the RFQ. The klystron was tested up to 600kW itself and operated in pulse routinely. The HPRF system for 20MeV DTL which consists of 4 tanks was installed, and the RF test for 4 tanks has been carried out. The ridge-loaded power coupler was designed and installed to drive RFQ and DTL. In this paper, the status and test results of the RF system for 20MeV proton accelerator are discussed.

WPAT014 Sequence Control System of 1-MW CW Klystron for the PEFP 1401
  • B.R. Park, J. Choi, M.-H. Chun, Y.J. Han, M.H. Jeong, S.-C. Kim, J.S. Yang, I.H. Yu
    PAL, Pohang, Kyungbuk
  Funding: Work support by the PEFP(Proton Engineering Frontier Project), Korea.

Sequence control system of 1-MW CW klystron for the PEFP (Proton Engineering Frontier Project) has been developed in order to drive the 1-MW klystron amplifier. The system is able to control several power supplies and many environment conditions. The hardware of sequence control and the interlock system are based on the Allen-Bradley's SLC500 Program Logic Controller (PLC). Also the system can be controlled by a touch screen at local mode or Ethernet network with high level HMI at remote mode.

WPAT015 The Digital Feedback RF Control System of the RFQ and DTL1 for 100 MeV Proton Linac of PEFP 1443
  • I.H. Yu, Y.J. Han, H.-S. Kang, D.T. Kim, S.-C. Kim, I.-S. Park, J.C. Yoon
    PAL, Pohang, Kyungbuk
  • Y.-S. Cho, H.-J. Kwon, K.T. Seol
    KAERI, Daejon
  Funding: Work supported by the PEFP (Proton Engineering Frontier Project), Korea

The 100 MeV Proton linear accelerator (Linac) for the PEFP (Proton Engineering Frontier Project) will include 1 RFQ and 1 DTL1 at 350 MHz as well as 7 DTL2 cavities at 700 MHz. The low level RF system with the digital feedback RF control provides the field control to accelerate a 20mA proton beam from 50 keV to 20 MeV with a RFQ and a DTL1 at 350M Hz. The FPGA-based digital feedback RF control system has been built and is used to control cavity field amplitude within ± 1% and relative phase within ± 1°. The fast digital processing is networked to the EPICS-based control system with an embedded processor (Blackfin). In this paper, the detailed description of the digital feedback RF control system will be described with the performance test results.

WPAT016 Stable Low Noise RF Source for Main Ring 1494
  • G.Y. Kurkin
    BINP SB RAS, Novosibirsk
  • P. Wang
    DU/FEL, Durham, North Carolina
  The Duke Storage ring is a 1 Gev electron ring, which is designed for driving UV-VUV FEL. It also provides variable energy high intensive gamma rays by Compton back scattering. It requires an RF master oscillator with very low phase noise. We built a Surface Acoustic Wave (SAW) Oscillator. However, the long-term stability does not meet requirements for FEL ring. Previously we used a commercial signal generator HP 4400B as the master oscillator. It has excellent long-term stability, but the phase noise is not acceptable. A phase feedback loop has been added between the SAW oscillator and the HP source, which provides us an excellent RF source. The design details and the test results are presented in this paper.  
WPAT017 Commissioning of the New RF System with the HOM Damped RF Cavity 1555
  • G.Y. Kurkin, V.S. Arbuzov, A. Bushuev, N. Gavrilov, E.I. Gorniker, E. Kenjebulatov, M.A. Kholopov, A.A. Kondakov, Ya.G. Kruchkov, S.A. Krutikhin, I.V. Kuptsov, L.A. Mironenko, N. Mityanina, S.V. Motygin, V.N. Osipov, V. Petrov, A.M. Pilan, A.M. Popov, E. Rotov, I. Sedlyarov, A.G. Tribendis, V. Volkov
    BINP SB RAS, Novosibirsk
  • S. Mikhailov, P.W. Wallace, P. Wang
    DU/FEL, Durham, North Carolina
  A new 178 MHz RF system has been commissioned at Duke Storage Ring. It consists of a 140 kW tetrode transmitter, a high order modes (HOM) damped RF cavity and the necessary frequency and voltage control electronics. The cavity walls are made of copper-on-stainless steel bimetal (8 mm Cu, 7 mm SS). The cavity has a larger beam pipe opening (700 mm in diameter) in the down-stream side, which allows the HOM propagating out of the cavity and being absorbed by the ceramic loads. The design details and the commissioning results are presented in this paper.  
WPAT018 The LEIR RF System 1619
  • M.M. Paoluzzi, R. Garoby, M. Haase, P. Maesen, C. Rossi
    CERN, Geneva
  • C. Ohmori
    KEK, Ibaraki
  The lead-lead physics program of LHC relies on major changes of the CERN ion injector chain. In this framework, the conversion of LEAR (low energy antiproton ring) into the Low Energy Ion Ring (LEIR) is central and implies a new accelerating system covering a wide frequency range (0.35 - 5 MHz,) with a moderate voltage (4 kV). For this purpose two new wide-bandwidth cavities, loaded with Finemet® magnetic alloy cores, have been built in collaboration with KEK. Two 60 kW RF power amplifiers have also been built and the RF systems are now installed in the LEIR ring. They individually cover the whole frequency range without tuning and allow multi-harmonic operation. The design has been guided by need of safety margins, reliability and ease of maintenance. Some design aspects are presented as well as the performance achieved.  
WPAT019 Beam Tests of a New Digital Beam Control System for the CERN LEIR Accelerator 1649
  • M.-E. Angoletta, J. Bento, A. Blas, A. Findlay, P. Matuszkiewicz, F. Pedersen, A. Salom.Sarasqueta
    CERN, Geneva
  • J. DeLong
    BNL, Upton, Long Island, New York
  We are developing a digital beam control and cavity servo system for controlling the RF acceleration in CERN’s Low Energy Ion Ring (LEIR), a major component in the LHC lead ion injector chain. As the LEIR ring will only start during summer 2005, we have tested a simplified prototype of the system with low intensity beams on the CERN PS Booster (PSB). The hardware and software have been developed within the framework of a CERN-BNL collaboration. This fully digital beam control system is contained in VME mother boards which can accommodate several daughter boards. The fast signal processing is implemented in Field Programmable Gate Arrays (FPGAs), while the slower signal processing and communication with the software layer above is implemented in programmable Digital Signal Processors (DSPs). The objectives of the tests with beam in the PSB are to verify the multiple DSP and FPGA architecture, the sampling rates and data flows and the feedback loop dynamics. An additional goal is to integrate a number of highly complex intelligent VME modules with many sub-functions in the CERN controls environment to provide adequate signal acquisition, control and diagnostics to operate the system.  
WPAT022 Low Level RF System for the Energy Recovery Linac Prototype 1781
  • A.J. Moss
    CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire
  Funding: ASTeC Department, CCLRC Daresbury Laboratory.

The Low Level RF system is described for the Energy Recovery Linac Prototype (ERLP) being constructed at Daresbury Laboratory. An analogue based feedback system, built around low cost proprietary components, has been designed to control the 1.3GHz RF system for this project. The system is scaleable, has digital control and can be easily upgraded as greater understanding of the accelerator becomes known. The design of the system is based around the central core of a very low phase noise master oscillator, which can provide, multiple outputs and timing pulses at all the required frequencies for the RF, laser and accelerator sub-systems.

WPAT023 Combining Cavity for RF Power Sources: Higher Power Testing and Further Simulation 1823
  • E. Wooldridge, P.A. Corlett, J.H.P. Rogers
    CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire
  Funding: ASTeC, CCLRC Daresbury Laboratory.

A combining cavity for RF power sources has been investigated previously reported in EPAC’04 using computer simulations in CSTs’ Microwave Studio© and by building a low power model out of aluminium. The model has now been tested at higher power in a number different configurations and compared with earlier results. This paper discusses the results of the higher power test and options for a combiner that can be used at the high power required for particle accelerators. It discusses further design and future modelling.

WPAT024 First Results from the Use of Dual Harmonic Acceleration on the ISIS Synchrotron 1871
  • A. Seville, D. Bayley, R.G. Bendall, M.G. Glover, A. Morris, J.W.G. Thomason
    CCLRC/RAL/ISIS, Chilton, Didcot, Oxon
  • D.J. Adams, I.S.K. Gardner, C.M. Warsop
    CCLRC/RAL/ASTeC, Chilton, Didcot, Oxon
  The ISIS facility at the Rutherford Appleton Laboratory in the UK is currently the most intense pulsed, spallation, neutron source. The accelerator consists of a 70 MeV H- Linac and an 800 MeV, 50 Hz, rapid cycling, proton Synchrotron. The synchrotron beam intensity is 2.5x1013 protons per pulse, corresponding to a mean current of 200 μA. The synchrotron beam is accelerated using six, ferrite loaded, RF cavities with harmonic number 2. Four additional, harmonic number 4, cavities have been installed to increase the beam bunching factor with the potential of raising the operating current to 300 μA. This paper reports on the hardware commissioning and the first beam tests.  
WPAT025 First Results of the IOT Based 300 kW 500 MHz Amplifier for the Diamond Light Source 1883
  • M. Jensen, M. Maddock, S. Rains, A.V. Watkins
    Diamond, Oxfordshire
  • J. Alex, M. Mueller
    Thales Broadcast & Multimedia AG, Turgi
  We present the first RF measurements of the IOT based 300 kW 500 MHz amplifier for the Diamond Light Source. Four 80 kW IOTs are combined using a waveguide combiner to achieve the RF requirement of up to 300 kW for each of three superconducting cavities for the main storage ring. The IOTs are protected by a full power circulator and a 300 kW ferrite RF load. This is the first time IOTs will be used for a synchrotron light source. This paper gives an overview of the design of the Thales amplifiers and IOTs with commissioning results including measurements of key components and overall RF performance following factory tests and the installation of the first unit  
WPAT026 Status of 34 GHZ, 45 MW Pulsed Magnicon 1922
  • O.A. Nezhevenko, V.P. Yakovlev
    Omega-P, Inc., New Haven, Connecticut
  • J.L. Hirshfield, M.A. LaPointe
    Yale University, Physics Department, New Haven, CT
  • E.V. Kozyrev
    BINP SB RAS, Novosibirsk
  • S.V. Shchelkunov
    Columbia University, New York
  Funding: Research supported by the Department of Energy, Division of High Energy Physics.

A high efficiency, high power magnicon at 34.272 GHz has been designed and built as a microwave source to develop RF technology for a future multi-TeV electron-positron linear collider. To develop this technology, this new RF source is being perfected for necessary tests of accelerating structures, RF pulse compressors, RF components, and to determine limits of breakdown and metal fatigue. After preliminary RF conditioning the magnicon produced an output power of 10.5 MW in 0.25 microsecond pulses, with a gain of 54 dB. The new results of the experimental tests after the tube conditioning was resumed are presented in the paper.

WPAT027 Recent Results from the X-Band Pulsed Magnicon Amplifier 1979
  • O.A. Nezhevenko, V.P. Yakovlev
    Omega-P, Inc., New Haven, Connecticut
  • A.W. Fliflet, S.H. Gold
    NRL, Washington, DC
  • J.L. Hirshfield, M.A. LaPointe
    Yale University, Physics Department, New Haven, CT
  • A.K. Kinkead
  Funding: Research supported by the Department of Energy, Office of High Energy Physics, and the Office of Naval Research.

A frequency-doubling magnicon amplifier at 11.4 GHz has been designed and built as the prototype of an alternative microwave source for the Next Linear Collider project, and to test high power RF components and accelerating structures. The tube is designed to produce ~60 MW, ~1.2 microsecond pulses at 58% efficiency and 59 dB gain, using a 470 kV, 220 A, 2 mm-diameter beam. In the first tests the output power was limited to a level of 26 MW in a 200 nsec pulse. This limitation was caused by the oscillations in the tube collector. Experimental results of the magnicon tests with the new collector are presented in this paper

WPAT028 High Power Ferrolelectric Switches at Centimeter and Millimeter Wavelengths 2056
  • V.P. Yakovlev, O.A. Nezhevenko
    Omega-P, Inc., New Haven, Connecticut
  • J.L. Hirshfield
    Yale University, Physics Department, New Haven, CT
  Funding: Research supported by the Department of Energy, Division of High Energy Physics.

High-power ultra-fast, electrically-controlled switches based on ferroelectric elements for accelerator applications in the centimeter and millimeter wavelength ranges are discussed. Examples of fast switches and phase shifters for pulse compression and power distribution systems at X– and Ka- band are presented. It is shown that such proposed switch designs based on modern ferroelectric materials allow the generation of pulsed power of hundreds of MW’s in both the centimeter and millimeter wave ranges.

WPAT029 The RF Experimental Program in the Fermilab MUCOOL Test Area 2104
  • J. Norem
    ANL, Argonne, Illinois
  • A. Bross, A. Moretti, Z. Qian
    Fermilab, Batavia, Illinois
  • R.P. Johnson
    Muons, Inc, Batavia
  • D. Li, M.S. Zisman
    LBNL, Berkeley, California
  • R.A. Rimmer
    Jefferson Lab, Newport News, Virginia
  • R. Sandstrom
    CUI, Geneva
  • Y. Torun
    IIT, Chicago, Illinois
  Funding: DOE

The rf R&D program for high gradient, low frequency cavities to be used in muon cooling systems is underway in the Fermilab Muon Test Area. Cavities at 805 and 201 MHz are used for tests of conditioning techniques, surface modification and breakdown studies. This work has the Muon Ionization Cooling Experiment (MICE) as its immediate goal and efficient muon cooling systems for neutrino sources and muon colliders as the long term goal. We study breakdown, and dark current productions under a variety of conditions.

WPAT030 Upgrade of the ATLAS Positive Ion Injector Bunching System 2161
  • S.I. Sharamentov, M. Bogaty, E. Clifft, R.C. Pardo
    ANL, Argonne, Illinois
  Over the last few years, significant efforts were concentrated on improving the ATLAS Positive Ion Injector (PII) RF bunching system, consisting of a four-harmonic pre-buncher, Traveling Wave Chopper (TWC) and a single-frequency sinusoidal re-buncher. The primary goal was to improve RF field stability with a redesigned RF system and to improve buncher performance for higher current beams resulting in better bunch stability and time structure at the first PII superconducting resonator. The major parts of the system were redesigned and rebuilt, including the RF 12 – 48 MHz amplifiers for the harmonic pre-buncher and re-buncher, RF driver rack for the TWC, and the RF control chassis for both the pre-buncher and re-buncher. The four-harmonic resonant structure of the harmonic buncher itself was modified, too, mainly for better mechanical stability and better RF matching. These improvements will be described and the performance of the new system presented.  
WPAT031 Design and Operation of a High Power L-Band Multiple Beam Klystron 2170
  • A. Balkcum, H.P. Bohlen, M. Cattelino, L. Cox, M. Cusick, S. Forrest, F. Friedlander, A. Staprans, E.L. Wright, L. Zitelli
    CPI, Palo Alto, California
  • K. Eppley
    SAIC, Burlington, Massachusetts
  A 1.3 GHz, 10 MW, higher-order-mode multiple beam klystron (MBK) has been developed for the TESLA program. The relative advantages of such a device are many-fold. Multiple beams generate higher beam currents and thereby require much lower operating voltages which allows for the use of smaller, less expensive modulators. A lower perveance per cathode can also be used which leads to higher operating efficiencies. Higher-order-mode cavities allow for the use of much larger cathodes which leads to lower cathode current density loadings and subsequently longer cathode lifetimes. This requires that the cathodes be located far off the geometric axis of the device. The compromise is an increase in the complexity of the magnetic focusing circuit required to transport the off-axis electron beams. Such a device has been successfully built and tested. Excellent beam transmission has been achieved (99.5% DC and 98% at RF saturation). A peak power of 10 MW with 150 kW of average power and 60% efficiency, 49 dB gain have also been measured. The achieved low cathode loading of 2.1 A/cm2 corresponds to an expected cathode life of over 140,000 operational hours.  
WPAT032 Large Scale Production of 805-MHz Pulsed Klystrons for the Spallation Neutron Source Project 2230
  • S. Lenci, E.L. Eisen
    CPI, Palo Alto, California
  The Spallation Neutron Source (SNS) is an accelerator-based neutron source being built in Oak Ridge, Tennessee, by the U.S. Department of Energy. CPI is supporting the effort by providing 81 pulsed klystrons for the super-conducting portion of the accelerator. The primary output power requirements are 550 kW peak, 49.5 kW average at 805 MHz, with an electron beam-to-rf conversion efficiency of 65% and an rf gain of 50 dB. Through December 2004, 77 units have been factory-tested. Performance specifications, computer model predictions, operating results, and production statistics will be presented.  
WPAT034 The CEBAF Separator Cavity Resonance Control System 2339
  • M.J. Wissmann, AA. Guerra, C. Hovater, T. Plawski
    Jefferson Lab, Newport News, Virginia
  Funding: This work supported by the U.S. Department of Energy under contract DE-AC05-84ER40150.

The CEBAF energy upgrade from 6 GeV to 12GeV will increase the range of beam energies available to the experimental halls. RF deflection cavities (separators) are used to direct the electron beam to the three experimental halls. Consequently with the increase in RF separator cavity gradient needed for the higher energies, RF power will also increase requiring the cavities to have active resonance control. At the 6 GeV energy, the cavities are tuned mechanically and then stabilized with Low Conductivity Water (LCW), which is maintained at constant temperature of 95o Fahrenheit. This is no longer feasible and an active resonance control system, that controls both water temperature and flow has been built. The system uses a commercial PLC with embedded PID controls to control water temperature and flow to the cavities. The system allows the operator to remotely adjust temperature/flow and consequently cavity resonance for the full range of beam energies. Ultimately closed loop control will be maintained by monitoring the cavities reflected power. This paper describes this system.

WPAT035 The LANSCE 805 MHZ RF System History and Status 2402
  • M.T. Lynch, G. Bolme, P.J. Tallerico
    LANL, Los Alamos, New Mexico
  The Los Alamos Neutron Science Center (LANSCE) linear accelerator runs at 201.25 MHz for acceleration to 100 MeV. The remainder of the acceleration to 800 MeV is at 805 MHz. This is done with 44 accelerator cavity stages driven by 805 MHz klystrons. Each klystron has a peak power capability of 1.25 MeV. Originally, 97 klystrons were purchased, which was 70 from Varian/CPI and 27 from Litton. The 44 RF systems are laid out in sectors with either 6 or 7 klystrons per sector. The klystrons in each sector are powered from a common HV sytem. The current arrangement uses the Varian/CPI klystrons in 6 of the 7 sectors and Litton klystrons in the remaining sector. With that arrangement there are 38 CPI klystrons installed and 1 spare klystron per sector and 6 Litton klystrons installed in the final sector with 2 spares. The current average life of all of the operating and spare klystrons (52 total) is >112,000 filament hours and >93,000 HV hours. That is three times the typical klystron lifetime today for other similar klystrons. This paper summarizes the details of the LANSCE klystron history and status and a summary of the predicted failure rate.  
WPAT036 A 700 MHZ, 1 MW CW RF System for a FEL 100mA RF Photoinjector 2413
  • W. Roybal, D.C. Nguyen, W. Reass, D. Rees, P.J. Tallerico, P.A. Torrez
    LANL, Los Alamos, New Mexico
  Funding: U.S. Department of Energy.

This paper describes a 700 MHz, 1 Megawatt CW, high efficiency klystron RF system utilized for a Free Electron Laser (FEL) high-brightness electron photoinjector (PI). The E2V klystron is mod-anode tube that operates with a beam voltage of 95 kV. This tube, operating with a 65% efficiency, requires ~96 watts of input power to produce in excess of 1 MW of output power. This output drives the 3rd cell of a 2½-cell, p-mode PI cavity through a pair of planar waveguide windows. Coupling is via a ridge-loaded tapered waveguide section and "dog-bone" iris. This paper will present the design of the RF, RF transport, coupling, and monitoring/protection systems that are required to support CW operations of the 100 mA cesiated, semi-porous SiC photoinjector.

WPAT037 LANSCE RF System Refurbishment 2476
  • D. Rees, G. Bolme, S.I. Kwon, J.T.M. Lyles, M.T. Lynch, M. Prokop, W. Reass, P.J. Tallerico
    LANL, Los Alamos, New Mexico
  The Los Alamos Neutron Science Center (LANSCE) is in the planning phase of a refurbishment project that will sustain reliable facility operations well into the next decade. The LANSCE accelerator was constructed in the late 1960s and early 1970s and is a national user facility that provides pulsed protons and spallation neutrons for defense and civilian research and applications. We will be replacing all the 201 MHz RF systems and a substantial fraction of the 805 MHz RF systems and high voltage systems. The current 44 LANSCE 805 MHz, 1.25 MW klystrons have an average in-service time in excess of 110,000 hours. All 44 must be in service to operate the accelerator. There are only 9 spares left. The klystrons receive their DC power from the power system originally installed in 1960. Although this power system has been extremely reliable, gas analysis of the insulating oil is indicating age related degradation that will need attention in the next few years. This paper will provide the design details of the new RF and high voltage systems.  
WPAT038 Instability of the RF Control Loop in the Presence of a High-Q Passive Superconducting Cavity 2553
  • S.A. Belomestnykh, R.P.K. Kaplan, J.J.R. Reilly, V. Veshcherevich
    Cornell University, Laboratory for Elementary-Particle Physics, Ithaca, New York
  Funding: Work is supported by the National Science Foundation.

An instability of the active RF cavity field control loop was observed during experiments with beam-driven (passive) superconducting cavities in CESR when the cavity external Q factor was raised to a value above 1x107. A computer model was developed and further experiments have been performed to study this instability and find a way to cure it. The results of simulations are presented alongside the experimental results.

WPAT039 Experience with the New Digital RF Control System at the CESR Storage Ring 2592
  • M. Liepe, S.A. Belomestnykh, J. Dobbins, R.P.K. Kaplan, C.R. Strohman, B.K. Stuhl
    Cornell University, Laboratory for Elementary-Particle Physics, Ithaca, New York
  Funding: This work is supported by NSF.

A new digital control system has been developed, providing great flexibility, high computational power and low latency for a wide range of control and data acquisition applications. This system is now installed in the CESR storage ring and stabilizes the vector sum field of two of the superconducting CESR 500 MHz cavities and the output power from the driving klystron. The installed control system includes in-house developed digital and RF hardware, very fast feedback and feedforward control, a state machine for automatic start-up and trip recovery, cw and pulsed mode operation, fast quench detection, and cavity frequency control. Several months of continuous operation have proven high reliability of the system. The achieved field stability surpasses requirements.

WPAT040 Pushing the Limits: RF Field Control at High Loaded Q 2642
  • M. Liepe, S.A. Belomestnykh, J. Dobbins, R.P.K. Kaplan, C.R. Strohman, B.K. Stuhl
    Cornell University, Laboratory for Elementary-Particle Physics, Ithaca, New York
  • C. Hovater, T. Plawski
    Jefferson Lab, Newport News, Virginia
  Funding: This work is supported by Cornell University.

The superconducting cavities in an Energy-Recovery-Linac will be operated with a high loaded Q of several 1E7, possible up to 1E8. Not only has no prior control system ever stabilized the RF field in a linac cavity with such high loaded Q, but also highest field stability in amplitude and phase is required at this high loaded Q. Because of a resulting bandwidth of the cavity of only a few Hz, this presents a significant challenge: the field in the cavity extremely sensitive to any perturbation of the cavity resonance frequency due to microphonics and Lorentz force detuning. To prove that the RF field in a high loaded Q cavity can be stabilized, and that Cornell's newly developed digital control system is able to achieve this, the system was connected to a high loaded Q cavity at the JLab IR-FEL. Excellent cw field stability – about 2·10-4 rms in relative amplitude and 0.03 deg rms in phase - was achieved at a loaded Q of 2.1·107 and 1.4E8, setting a new record in high loaded Q operation of a linac cavity. Piezo tuner based cavity frequency control proved to be very effective in keeping the cavity on resonance and allowed reliable to ramp up to high gradients in less than 1 second.

WPAT041 Klystron Linearizer for Use with 1.2 MW 476 MHz Klystrons in PEP-II RF Systems 2660
  • J.D. Fox, T. Mastorides, D. Teytelman, D. Van Winkle, Y.-B. Zhou
    SLAC, Menlo Park, California
  • A. Gallo
    INFN/LNF, Frascati (Roma)
  Funding: Work supported by U.S. Department of Energy contract DE-AC02-76SF00515.

The direct and comb loop feedback around the RF cavities in PEP-II is critical in reducing longitudinal instabilities driven by the cavity impedance, and the non-linear 1 MW klystron is in the signal path for these feedback loops. As a result, the effective small-signal gain of the klystron at 85% saturation reduces the impedance control by factors of 5 to 20 as compared to a linear power amplifier. A klystron linearizer circuit has been developed which operates in series with the power amplifier and acts to equalize the small and large signal gains through the combination. The technique must implement a 1 MHz linear control bandwidth over roughly 15 dB of RF signal level variation. The dynamics of this system is operating point dependent, and the channel must have dynamic gain compensation to keep the linearity compensation loop stable over changes in operating point. The design of this non-linear signal processing channel (incorporating RF and DSP techniques) and measured results from full-power klystron testing are presented.

WPAT043 Overview of the RF Systems for LCLS 2753
  • P.A. McIntosh, R. Akre, R.F. Boyce, P. Emma, S. Hill, E. Rago
    SLAC, Menlo Park, California
  Funding: Work supported by Department of Energy contract DE-AC03-76SF00515.

The Linac Coherent Light Source (LCLS) at SLAC, when it becomes operational in 2009, will provide its user community with an X-ray source many orders of magnitude brighter than anything available in the world at that time. The electron beam acceleration will be provided by existing and new RF systems capable of maintaining the amplitude and phase stability of each bunch to extremely tight tolerances. RF feedback control of the various RF systems will be fundamental in ensuring the beam arrives at the LCLS undulator at precisely the required energy and phase. This paper details the requirements for RF stability for the various LCLS RF systems and also highlights proposals for how these injector and Linac RF systems can meet these constraints.

WPAT044 Realization of an X-Band RF System for LCLS 2801
  • P.A. McIntosh, R. Akre, J. Brooks, P. Emma, E. Rago
    SLAC, Menlo Park, California
  Funding: Work supported by Department of Energy contract DE-AC03-76SF00515.

A single X-band (11.424 GHz) accelerating structure is to be incorporated in the LCLS Linac design to linearize the energy-time correlation (or gradient) across each bunch, features which originate in the preceding accelerating structures (L0 and L1). This harmonic RF system will operate near the negative RF crest to decelerate the beam, reducing these non-linear components of the correlation, providing a more efficient compression in the downstream bunch compressor chicanes (BC1 and BC2). These non-linear correlation components, if allowed to grow, would lead to Coherent Synchrotron Radiation (CSR) instabilities in the chicanes, effectively destroying the coherence of the photon radiation in the main LCLS undulator. The many years devoted at SLAC in the development of X-band RF components for the NLC/JLC linear collider project, has enabled the technical and financial realization of such an RF system for LCLS. This paper details the requirements for the X-band system and the proposed scheme planned for achieving those requirements.

WPAT045 A Non-Invasive Technique for Configuring Low Level RF Feedback Loops in PEP-II 2863
  • D. Teytelman
    SLAC, Menlo Park, California
  Funding: Work supported by U.S. Department of Energy contract DE-AC02-76SF00515.

The RF system of the PEP-II collider uses two fast feedback loops around each klystron and set of cavities. These loops reduce the impedance of the fundamental mode of the accelerating cavities seen by the beam, and are necessary to reduce the growth rates of longitudinal modes within the RF system bandwidth. Operation of the accelerator at high beam currents is very sensitive to the configuration of the low-level RF feedback loops. There are 7 loop control parameters that strongly influence the stability of the feedback loops and the achieved level of longitudinal impedance reduction. Diagnostic techniques for the analysis of the RF feedback via closed-loop system transfer function measurements will be presented. The model is fit to the measured closed-loop transfer function data and the extracted parameters are then used to calculate optimal tuning and corrections to the loop control elements in the physical channel. These techniques allow fine-tuning of RF feedback with stored beam as well as diagnosis of mis-configured or malfunctioning elements of the system. Results from PEP-II operation will be presented to illustrate the techniques and their applications.

WPAT047 Solid-State 2MW Klystron Power Control System 2950
  • M.A. Kempkes, J.A. Casey, M.P.J. Gaudreau, T.H. Hawkey, I. Roth
    Diversified Technologies, Inc., Bedford
  Under an SBIR effort for the DOE, Diversified Technologies, Inc. designed, built, and installed a solid state power control system for the Advanced Light Source klystrons at Argonne National Laboratory (ANL). This system consists of two major elements – a 100 kV, 20 A CW solid state series switch, and a solid state voltage regulator for the mod-anode of the klystron. The series switch replaces the existing mercury ignitron crowbar, eliminating these environmentally hazardous components while providing enhanced arc protection and faster return to transmit. The mod-anode voltage regulator uses series IGBTs, operating in the linear regime, to provide highly rapid and accurate control of the mod-anode voltage, and therefore the output power from the klystron. Results from the installation and testing of this system at ANL will be presented.  
WPAT048 Solid State Modulators for the International Linear Collider (ILC) 2998
  • M.A. Kempkes, N. Butler, J.A. Casey, M.P.J. Gaudreau, I. Roth
    Diversified Technologies, Inc., Bedford
  Diversified Technologies, Inc. is developing two solid state modulator designs for the ILC under SBIR funding from the DOE. The first design consists of a 150 kV hard switch. The key development in this design is the energy storage system, which must provide 25 kJ per pulse, at very tight voltage regulation over the 1.5 millisecond pulse. DTI’s design uses a quasi-resonant bouncer (with a small auxiliary power supply and switch) to maintain the voltage flattop, eliminating the need for massive capacitor banks. The second design uses a solid state Marx bank, with ~10 kV stages, to drive the ILC klystron. In this design, staggered turn-on of the Marx stages provides voltage regulation without the need for large capacitor banks. This paper will discuss design tradeoffs, power supply and control considerations, and energy storage requirements and alternatives for both designs.  
WPAT049 The Penetrability of a Thin Metallic Film Inside the RF Field 3073
  • Y. Zhao, I. Ben-Zvi, R.H. Beuttenmuller, X.Y. Chang, C. Chen, R. Di Nardo, T. Rao
    BNL, Upton, Long Island, New York
  Funding: Under contract with the U.S. Department of Energy, Contract Number DE-AC02-98CH10886.

Thin metallic film was widely applied in varies area. Especially, recently we are planning to apply it in a "Secondary emission enhanced photo-injector," of which a diamond cathode is coated with a golden film or so on its back to serve as a current path. The thickness of the film is originally considered to be in the order of 10 nm, which is much less than the skin depth, say 1/200. Since it is so thin, that intuitively the RF filed is penetrable. However, we found it is not true. The film will block most of the field. This paper addresses theoretic analysis as well as the experimental results. All demonstrated that the penetrability of a thin film is very poor. Consequently, most of the RF current will flow on the thin film causing a serous heating problem.

WPAT050 High Power Phase Shifter 3123
  • I. Terechkine, G.W. Foster, I.G. Gonin, T.K. Khabiboulline, A. Makarov, N. Solyak, D. Wildman
    Fermilab, Batavia, Illinois
  One of the approaches to power distribution system of a superconducting proton linac that is under discussion at Fermilab requires development of a fast-action, megawatt-range phase shifter. Using two phase shifters with a waveguide hybrid junction can allow independent control of phase and amplitude of RF power at the input of each superconducting cavity of the linac. This promises significant saving in number of klystrons and modulators required for the accelerator. A prototype of a waveguide version of a phase shifter that uses Yttrium-Iron Garnet (YIG) blocks was developed and tested. This report presents design concept of the device and main results of simulation and proof-of-principle tests.  
WPAT051 Development of Toshiba L-Band Multi-Beam Klystron for European XFEL Project 3153
  • Y.H. Chin
    KEK, Ibaraki
  • S. Choroba
    DESY, Hamburg
  • M. Y. Miyake, Y. Yano
    Toshiba, Yokohama
  A 10MW L-band multi-beam klystron (MBK)is under develpment at Toshiba, Japan for DESY X-FEL and a future linear collider projects. The design goals are to have 10MW peak power with 65% efficiency at 1.5 ms pulse length at 10Hz repetition rates. The Toshiba MBK has six low-perveance beams operated at low voltage of 115kV (for 10MW) to enable a higher efficiency than a single-beam klystron for a similar power. The prototyp·10-0 has been built and is now under testing. At the first step, it was tested without RF and operates stably at the cathode voltage of 115KV at 1.7ms pulse length at 10Hz repetition rate with beam transmission of better than 99%. No spurious oscillation was observed. The testing is now progressed with RF on. Up to date of November 10, 2004, The output power of 10.3MW has been demonstrated at the beam voltage of 115kV with efficinecy of 68.4% at the RF pulse length of 1ms at 10Hz. The testing is under way to increase the RF pulse length to the goal value of 1.5ms. This paper summarizes the design and the testing results.  
WPAT052 Present Status of RF System for Medical Proton Synchrotron 3185
  • Z. Fang, K. Egawa, K. Endo, S. Yamanaka
    KEK, Ibaraki
  • Y. Cho, T. Fusato, T. Hirashima
    DKK, Kanagawa
  The 200MeV proton synchrotron of circumference of 9.54m is being developed for medical radiotherapy. The rf system has been carried out with a wide bandwidth of frequency sweeping from 2.0MHz to 17.8MHz. The rf cavity is designed of a compact dimension and a high acceleration gradient. The high power test of the rf system has been successfully performed and maximal acceleration gradient of 60kV/m has been achieved. The experiments with feedback control system are being studied by using a dummy beam signal. In this paper, the recent progress of the rf system and test results will be presented in detail.  
WPAT053 Results of a High-Power Klystron Dip Test in the KEK Linac 3235
  • K. Nakao, S. Fukuda, H. Katagiri, T. Matsumoto, S. Michizono, T. Takenaka, Y. Yano, M. Yoshida
    KEK, Ibaraki
  Dip test, which is the measurement of a klystron heater activity, is recently adopted as the standard measurement to maintain the klystron operation in the KEK electron-positron linac. In 2003, we began to use a dip test as the quick way to measure the emission characteristics from the klystron cathode. After the successful results, we made the dedicated measuring systems and measured the dips of the cathode emission of 60 operating klystrons in KEK electron-positron linac. These data are important to estimate the klystron cathode life and used to select the candidate klystrons of replacement in the summer maintenance period.  
WPAT054 5 MW 805 MHz SNS RF System Experience 3280
  • K.A. Young, J.T. Bradley, T.W. Hardek, M.T. Lynch, D. Rees, W. Roybal, P.J. Tallerico, P.A. Torrez
    LANL, Los Alamos, New Mexico
  Funding: Work supported by the U.S. DOE.

The RF system for the 805 MHz normal conducting linac of the Spallation Nuetron Source (SNS) accelerator was designed, procured and tested at Los Alamos National Laboratory(LANL) and then installed and commissioned at Oak Ridge National Laboratory (ORNL). The RF power for this room temperature coupled cavity linac (CCL) of SNS accelerator is generated by four pulsed 5 MW peak power klystrons operating with a pulse width of 1.25 mSec and a 60 Hz repetition frequency. The RF power from each klystron is divided and delivered to the CCL through two separate RF windows. The 5 MW RF system advanced the state of the art for simultaneous peak and average power. This paper summarizes the problems encountered, lessons learned and results of the high power testing at LANL of the 5 MW klystrons, 5 MW circulators, 5 MW loads, and 2.5 MW windows.*

*Tom Hardek is now at ORNL.

WPAT055 Enhancements for the 1 MW High Voltage Converter Modulator Systems at the SNS 3313
  • D.E. Anderson, J. Hicks, D. E. Hurst, E.R. Tapp, M. Wezensky
    ORNL, Oak Ridge, Tennessee
  • D. Baca, W. Reass
    LANL, Los Alamos, New Mexico
  • V.V. Peplov
    RAS/INR, Moscow
  Funding: SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy.

The first-generation high frequency switching megawatt-class high voltage converter modulators (HVCM) developed by Los Alamos National Laboratory for the Spallation Neutron Source at Oak Ridge National Laboratory have been installed and are now operational. Each unit is capable of delivering pulses up to 11 MW peak, 1 MW average power at voltages up to 140 kV to drive klystron(s) rated up to 5 MW. To date, three variations of the basic design have been installed, each optimized to deliver power to a specific klystron load configuration. Design improvements, with the primary intention of improving system reliability and availability, have been under development since the initial installation of the HVCM units. This paper will examine HVCM reliability studies, reliability operational data, and modifications and improvements performed to increase the overall system availability. We will also discuss system enhancements aimed at improving the ease of operation and providing for additional equipment protection features.

WPAT057 Overview of the Spallation Neutron Source Linac Low-Level RF Control System 3396
  • M. Champion, M.T. Crofford, K.-U. Kasemir, H. Ma, M.F. Piller
    ORNL, Oak Ridge, Tennessee
  • L.R. Doolittle, A. Ratti
    LBNL, Berkeley, California
  Funding: SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy.

The design and production of the Spallation Neutron Source Linac Low-Level RF control system is complete, and installation will be finished in Spring 2005. The warm linac beam commissioning run in Fall 2004 was the most extensive test to date of the LLRF control system, with fourteen (of an eventual 96) systems operating simultaneously. In this paper we present an overview of the LLRF control system, the experience in designing, building and installing the system, and operational results.

WPAT058 Operational Experience with the Spallation Neutron Source High Power Protection Module 3411
  • M.T. Crofford, M. Champion, K.-U. Kasemir, H. Ma, M.F. Piller
    ORNL, Oak Ridge, Tennessee
  The Spallation Neutron Source (SNS) High Power Protection Module provides protection for the High Power RF Klystron and Distribution System and interfaces with the Low-Level Radio-Frequency (LLRF) Field Control Module (FCM). The fault detection logic is implemented in a single FPGA allowing modifications and upgrades to the logic as we gain operational experience with the LINAC RF systems. This paper describes the integration and upgrade issues we have encountered during the initial operations of the SNS systems.  
WPAT059 High Power RF Test Facility at the SNS 3450
  • Y.W. Kang, D.E. Anderson, I.E. Campisi, M. Champion, M.T. Crofford, R.E. Fuja, P.A. Gurd, S. Hasan, K.-U. Kasemir, M.P. McCarthy, D. Stout, J.Y. Tang, A.V. Vassioutchenko, M. Wezensky
    ORNL, Oak Ridge, Tennessee
  • G.K. Davis, M. A. Drury, T. Powers, M. Stirbet
    Jefferson Lab, Newport News, Virginia
  RF Test Facility has been completed in the SNS project at ORNL to support test and conditioning operation of RF subsystems and components. The system consists of two transmitters for two klystrons powered by a common high voltage pulsed converter modulator that can provide power to two independent RF systems. The waveguides are configured with WR2100 and WR1150 sizes for presently used frequencies: 402.5 MHz and 805 MHz. Both 402.5 MHz and 805 MHz systems have circulator protected klystrons that can be powered by the modulator capable of delivering 11 MW peak and 1 MW average power. The facility has been equipped with computer control for various RF processing and complete dual frequency operation. More than forty 805 MHz fundamental power couplers for the SNS superconducting linac (SCL) cavitites have been RF conditioned in this facility. The facility provides more than 1000 ft2 floor area for various test setups. The facility also has a shielded cave area that can support high power tests of normal conducting and superconducting accelerating cavities and components.

SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy. SNS is a partnership of six national laboratories: Argonne, Brookhaven, Jefferson, Lawrence Berkeley, Los Alamos, and Oak Ridge.

WPAT060 SNS Low-Level RF Control System: Design and Performance 3479
  • H. Ma, M. Champion, M.T. Crofford, K.-U. Kasemir, M.F. Piller
    ORNL, Oak Ridge, Tennessee
  • L.R. Doolittle, A. Ratti
    LBNL, Berkeley, California
  Funding: ORNL managed by UT-Battelle for US DOE.

A full digital Low-Level RF controller has been developed for SNS LINAC. Its design is a good example of a modern digital implementation of the classic control theory. The digital hardware for all the control and DSP functionalities, including the final vector modulation, is implemented on a single high-density FPGA. Two models for the digital hardware have been written in VHDL and Verilog respectively, based on a very low latency control algorithm, and both have been being used for supporting the testing and commissioning the LINAC to the date. During the commissioning, the flexibility and ability for precise controls that only digital design on a larger FPGA can offer has proved to be a necessity for meeting the great challenge of a high-power pulsed SCL.

WPAT061 Spallation Neutron Source High Power RF Installation and Commissioning Progress 3520
  • M.P. McCarthy, D.E. Anderson, R.E. Fuja, P.A. Gurd, T.W. Hardek, Y.W. Kang
    ORNL, Oak Ridge, Tennessee
  • J.T. Bradley, D. Rees, W. Roybal, K.A. Young
    LANL, Los Alamos, New Mexico
  Funding: SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy.

The Spallation Neutron Source (SNS) linac will provide a 1 GeV proton beam for injection into the accumulator ring. In the normal conducting (NC) section of this linac, the Radio Frequency Quadupole (RFQ) and six drift tube linac (DTL) tanks are powered by seven 2.5 MW, 402.5 MHz klystrons and the four coupled cavity linac (CCL) cavities are powered by four 5.0 MW, 805 MHz klystrons. Eighty-one 550 kW, 805 MHz klystrons each drive a single cavity in the superconducting (SC) section of the linac. The high power radio frequency (HPRF) equipment was specified and procured by LANL and tested before delivery to ensure a smooth transition from installation to commissioning. Installation of RF equipment to support klystron operation in the 350-meter long klystron gallery started in June 2002. The final klystron was set in place in September 2004. Presently, all RF stations have been installed and high power testing has been completed. This paper reviews the progression of the installation and testing of the HPRF Systems.

WPAT062 The Spallation Neutron Source RF Reference System 3573
  • M.F. Piller, M. Champion, M.T. Crofford, H. Ma
    ORNL, Oak Ridge, Tennessee
  • L.R. Doolittle
    LBNL, Berkeley, California
  The Spallation Neutron Source (SNS) RF Reference System includes the master oscillator (MO), local oscillator(LO) distribution, and Reference RF distribution systems. Coherent low noise Reference RF signals provide the ability to control the phase relationships between the fields in the front-end and linear accelerator (linac) RF cavity structures. The SNS RF Reference System requirements, implementation details, and performance are discussed.  
WPAT063 Design and Status of the BPM RF Reference Distribution in the SNS 3615
  • A. Webster, C. Deibele, J. Pogge
    ORNL, Oak Ridge, Tennessee
  • J.F. Power
    LANL, Los Alamos, New Mexico
  Funding: SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy. SNS is a partnership of six national laboratories: Argonne, Brookhaven, Jefferson, Lawrence Berkeley, Los Alamos, and Oak Ridge.

The Spallation Neutron Source (SNS) is an accelerator-based neutron source being built at Oak Ridge National Laboratory. The BPMs (Beam Position Monitors) requires RF reference signals to measure the phase of the beam with respect to the RF. In the MEBT (Medium Energy Beam Transport) Line and in the DTLs (Drift Tube Linac Cavities) are cavities that accelerate and bunch the beam at 402.5 MHz. In the CCLs (Coupled Cavity Linac) and SCLs (Superconducting Linac) accelerate the beam at 805 MHz. To mitigate effects of RF leakage into the BPM electrodes it is required to measure the phase in the MEBT and DTLs at 805 MHz and in the CCL and SCL at 402.5 MHz. We are directly connected to the RF group MO (master oscillator) and send these signals along the entire linac using fiber optic technology. Schematics, measurements, and installation update are discussed.

WPAT064 Low Level RF Control System of J-PARC Synchrotrons 3624
  • F. Tamura
    JAERI/LINAC, Ibaraki-ken
  • S. Anami, E. Ezura, K. Hara, C. Ohmori, A. Takagi, M. Yoshii
    KEK, Ibaraki
  • M. Nomura, A. Schnase, M. Yamamoto
    JAERI, Ibaraki-ken
  We present the concept and the design of the low level RF (LLRF) control system of the J-PARC synchrotrons. The J-PARC synchrotrons are the rapid cycling 3-GeV synchrotron (RCS) and the 50-GeV main ring (MR) which require very precise and stable LLRF control systems to accelerate the ultra-high proton beam current. The LLRF system of the synchrotron is a full-digital system based on the direct digital synthesis (DDS). The functions of the system are (1) the multi-harmonic RF generation for the acceleration and the longitudinal bunch shaping, (2) the feedbacks for stabilizing the beam, (3) the feedforward for compensating the heavy beam loading, and (4) other miscellaneous functions such as the synchronization and chopper timing. The LLRF system of the RCS is now under construction. We present the details of the system. Also, we show preliminary results of performance tests of the control modules.  
WPAT065 HLS RF System Improvement in NSRL Phase II Project 3653
  • K. Jin, Y. An, L. Feng, G. Huang, G. Liu, G. Wang, X. Zeng
    USTC/NSRL, Hefei, Anhui
  Hefei Light Source (HLS) is mainly composed of an 800 MeV electron storage ring and a 200 MeV Linac functioning as its injector. The RF system has been improved successfully for HLS storage-ring in NSRL Phase II Project. In this paper, the improvement of generator and power transmission system, the development of a new RF cavity and the perfection of RF controls are described in detail. The results and some analyses are presented.  
WPAT066 ALS Booster Ring RF System Upgrade for Top-Off Mode of Operation 3709
  • S. Kwiatkowski, K.M. Baptiste
    LBNL, Berkeley, California
  Funding: Supported by the U.S. Department of Energy under Contract No.DE-AC03-76SF00098.

ALS is one of the first third generation synchrotron light sources which has been operating since 1993 at Berkeley Lab. In the present ALS operation scenario 1.5GeV electron beam is injected from the booster into the storage ring every 8 hours where is accelerated to the final energy of 1.9GeV. The beam decays between fills from 400mA to 200mA with the time average current of 250mA. In order to increase the beam brighthess ALS team plans to increase the beam current to 500mA and maintain it constant during machine operation ("Top-Off" mode of operation). This operation scenario will require full energy injection from the booster ring into the storage ring and constant operation of the injector (10 bunches with the total charge of 1nC every 30 to 35 seconds). In this paper we will present the results of the ALS injector RF system analysis fo Top-Off mode of operation and describe the way we intent to implement the necessary modifications to the booster RF system.

WPAT067 High Power Disk Loaded Guide Load 3715
  • Z.D. Farkas
    SLAC, Menlo Park, California
  Funding: Department of Energy, contract DE-AC03-76SF00515.

A method to design a matching section from a smooth guide to a disk loaded guide, using a variation of broadband matching* is described. Using this method, we show how to design high power loads, filters and attenuators. The load consists of a disk loaded coaxial guide, operating in the T·1001 mode. This mode has no electric field terminating on a conductor, has no axial currents. Therefore, it is expected that it will carry the 600 MW peak output power of the pulse compression network. We use coaxial geometry and stainless steel material to increase the attenuation per cell.

*S. B. Cohn, Optimum Design of Stepped Transmission Line Transformers. IRE Trans., Vol. MTT-3 pp16-21, April, 1995.

WPAT068 Development of Low Level RF Control Systems for Superconducting Heavy Ion Linear Accelerators, Electron Synchrotrons and Storage Rings
  • B. A. Aminov, A. Borisov, S. K. Kolesov, H. Piel
    CRE, Wuppertal
  • M. Pekeler, C. Piel
    ACCEL, Bergisch Gladbach
  Since 2001 ACCEL Instruments is supplying low level RF control systems together with turn key cavity systems. The early LLRF systems used the well established technology based on discrete analogue amplitude and phase detectors and modulators. Today analogue LLRF systems can make use of advanced vector demodulators and modulators combined with a fast computer controlled analogue feed back loop. Feed forward control is implemented to operate the RF cavity in an open loop mode or to compensate for predictable perturbations. The paper will introduce the general design philosophy and show how it can be adapted to different tasks as controlling a synchrotron booster nc RF system at 500 MHz, or superconducting storage ring RF cavities, as well as a linear accelerator at 176 MHz formed by a chain of individually driven and controlled superconducting λ/2 cavities.  
WPAT069 Development of a Solid State RF Amplifier in the kW Regime for Application with Low Beta Superconducting RF Cavities
  • C. Piel
    ACCEL, Bergisch Gladbach
  • B. A. Aminov, A. Borisov, S. K. Kolesov, H. Piel
    CRE, Wuppertal
  Projects based on the use of low beta superconducting cavities for ions are under operation or development at several labs worldwide. Often these cavities are individually driven by RF power sources in the kW regime. For an ongoing project a modular 2 kW, 176 MHz unconditionally stable RF amplifier for CW and pulsed operation was designed, built, and tested. Extended thermal analysis was used to develop a water cooling system in order to optimize the performance of the power transistors and other thermally loaded components. The paper will outline the design concept of the amplifier and present first results on the test of the amplifier with a superconducting cavity.  
WPAT070 500 MHz Coaxial Transition Between the ELETTRA Input Coupler and the Transmission Waveguide 3810
  • C. Pasotti, A. Fabris, M. Svandrlik
    ELETTRA, Basovizza, Trieste
  The investigations have shown that the 500 MHz ELETTRA input power coupler can safely sustain more than 150 KW. The critical component limiting the increase of the trasmitted RF power is the connection element between the input power coupler and the transmission line. An optimized design has been studied to overcome this limit. During the optimization process, the entire RF chain (input power coupler, connection element and transition to the standard waveguide WR1800) has been verified. The analysis has been carried out to check the performances of the whole lay-out in terms of efficiency of transmitted power and sensitivity to any signal coming from the cavity ( HOMs included). A prototype with an improved cooling system has been realized and tested.  
WPAT071 R&D Status of the 700 MHz, 1MW Klystron for PEFP 3850
  • S.-H. Kim, B.H. Chung, K.-H. Chung, J.-S. Hong, J.-H. Jeon, sk. Ko, K. Lee, sj. Noh
    KAPRA, Cheorwon
  Funding: This study is supported by Proton Engineering Frontier Project at Korea Atomic Energy Research Institute.

KAPRA (Korea Accelerator and Plasma Research Association) are undertaking the first phase R&D for the 1 MW, CW 700 MHz klystron, which is targeting the future stage of the PEFP (Proton Engineering Frontier Project) accelerator at KAERI (Korea Atomic Energy Research Institute). The objectives of the first phase R&D are 1) setting up all infra structures/procedures for the design and fabrication, 2) developing a prototype klystron for proofs of principles, and 3) making a performance test of the prototype at a reduced duty. The second phase R&D is supposed to cover full power, CW operation and reliability issues. In this paper, a summary of R&D Status during the first phase for PEFP 1 MW, 700 MHz klystron is reported.

WPAT072 A 1.3GHz Inductive Output Tube for Particle Accelerators 3883
  • E. Sobieradzki, A.E. Wheelhouse
    e2v technologies, Chelmsford, Essex
  There is an increasing requirement for RF power sources in the L-band frequency range for operation in particle accelerators. The paper describes the development and presents test results of a new inductive output tube (IOT) for use at 1.3GHz. A target specificationof 16kW cw output power at an efficiency of 60% was set. The paper discusses progress to date having used an electron gun geometry that minimizes transit time effects in the cathode to grid gap.  
WPAT074 In Depth Diagnostics for RF System Operation in the PEP-II B Factory 3931
  • D. Van Winkle, J.D. Fox, D. Teytelman
    SLAC, Menlo Park, California
  Funding: Work supported by U.S. Department of Energy contract DE-AC02-76SF00515.

The PEP-II RF systems incorporate numerous feedback loops in the low-level processing for impedance control and operating point regulation. The interaction of the multiple loops with the beam is complicated, and the systems incorporate online diagnostic tools to configure the feedback loops as well as to record fault files in the case of an RF abort. Rapid and consistent analysis of the RF-related beam aborts and other failures is critical to the reliable operation of the B-Factory, especially at the recently achieved high beam currents. Procedures and algorithms used to extract diagnostic information from time domain fault files are presented and illustrated via example interpretations of PEP-II fault file data. Example faults presented will highlight the subtle interpretation required to determine to root cause. Some such examples are: abort kicker firing asynchronously, klystron and cavity arcs, beam loss leading to longitudinal instability, tuner read back jumps and poorly configured low-level RF feedback loop.

WPAT075 Design and Calibration of a Phase and Amplitude Detector
  • Z. Geng, P. Gu, H.Mi. Hou, G. Pei
    IHEP Beijing, Beijing
  The phase and amplitude detector (PAD) is a key unit of the phasing system for BEPCII linac. One of the main functions of the PAD is to measure the phase of each klystron accurately from such large noises. To meet the need of the phasing system, a new PAD is constructed based on I/Q demodulator and industrial computer. But the I/Q demodulator suffers form phase and amplitude mismatch, which can draw big error on phase measurement. In order to compensate the mismatch of the I/Q demodulator, we develop a calibration program using an adaptive method, LMS method. Almost all the mismatches of the I/Q demodulator are compensated after calibration.  
WPAT076 Resonant High Power Combiners 3970
  • M.L. Langlois, J.P. Buge, G. Peillex-Delphe
    TED, Vélizy Cedex
  Particle accelerators need radio frequency sources. Above 300 MHz, the amplifiers mostly used high power klystrons developed for this sole purpose. As for military equipment, users are drawn to buy "off the shelf" components rather than dedicated devices. IOTs have replaced most klystrons in TV transmitters and find their way in particle accelerators. They are less bulky, easier to replace, more efficient at reduced power. They are also far less powerful. What is the benefit of very compact sources if huge 3 dB couplers are needed to combine the power? To alleviate this drawback, we investigated a resonant combiner, operating in TM010 mode, able to combine 3 to 5 IOTs. Our IOTs being able to deliver 80 kW C.W. apiece, combined power would reach 400 kW minus the minor insertion loss. Values for matching and insertion loss are given. The behavior of the system in case of IOT failure is analyzed.  
WPAT077 Finite-Element 2D & 3D PIC Modeling of RF Devices with Applications to Multipacting
  • J.F. DeFord
    LLNL, Livermore, California
  • E.M. Nelson
    LANL, Los Alamos, New Mexico
  • J.J. Petillo
    SAIC, Burlington, Massachusetts
  Multipacting currently limits the performance of many high power radio-frequency (RF) devices, particularly couplers and windows. Models have helped researchers understand and mitigate this problem in 2D structures, but useful multipacting models for complicated 3D structures are still a challenge. A combination of three recent technologies that have been developed in the Analyst and MICHELLE codes begin to address this challenge: high-order adaptive finite-element RF field calculations, advanced particle tracking on unstructured grids, and comprehensive secondary emission models. Analyst employs high-order adaptive finite-element methods to accurately compute driven RF fields and eigenmodes in complex geometries, particularly near edges, corners, and curved surfaces. To perform a multipacting analysis, we use the mesh and fields from Analyst in a modified version of the self-consistent, finite-element gun code MICHELLE. MICHELLE has both a fast, accurate, and reliable particle tracker for unstructured grids and a comprehensive secondary emission model. We will demonstrate this capability on an RF coupler.  
WPAT078 A High Power RF Power Supply for High Energy Physics Applications 4018
  • M.J. Bland, J. Clare, P. W. Wheeler
    University of Nottingham, Nottingham
  • J.S. Przybyla
    EEV, Chelmsford, Essex
  Funding: Particle Physics and Astronomy Research Council (PPARC).

Accelerators used for experiments in high-energy physics require very high power radio frequency sources to provide the energy needed to accelerate the particles. The RF power needs to be stable and predictable such that any variation in the supplied RF power has a limited and acceptable impact on the accelerated beam quality. The output load specifications for high voltage DC power systems are becoming increasingly more demanding. In addition, the impact of such systems on the electricity source is becoming more tightly regulated through power quality directives. These regulations set limits, for example, on the allowable individual harmonic current amplitudes and on "flicker" caused by transient load demands - the latter is particularly important for "long-pulse" modulators. The requirements above have to be met while still providing higher reliability to a higher specification at lower cost. A situation has now been reached where modulators based on existing approaches cannot meet these specifications and stay within acceptable cost and size limits. This demands that new approaches be taken to provide the power supplies needed for such applications. The research proposed here addresses this need.

WPAT079 Design of a Direct Converter for High Power, RF Applications 4033
  • D. Cook, M. Catucci, J. Clare, P. W. Wheeler
    University of Nottingham, Nottingham
  • J.S. Przybyla
    EEV, Chelmsford, Essex
  Funding: Particle Physics and Astronomy Research Council.

This paper is concerned with a new type of power supply for high power RF applications for CW operation. The converter is a direct topology operating with a high frequency (resonant) link. Switching losses are minimised by switching at zero current. High operating frequency allows for minimised transformer and filter size. Advantages of this topology over conventional approaches are discussed, along with the potential problems and proposed solutions. Recently, considerable interest has been shown in direct converter topologies as an alternative topology in motor drive applications. This approach offers advantages such as reduced energy storage and higher energy density compared to conventional topologies. The work presented in this paper capitalises on these advantages in other fields, namely power conversion for RF supplies. The RF power needs to be stable and predictable such that any variation has a limited impact on the accelerated beam quality. In order to meet the required output voltage specification such designs require output filters with consequent energy storage. Management of this energy in the event of a fault is necessary if destruction of the tube is to be avoided.

WPAT080 Calculation of Beam-Loaded Q in High-Power Klystrons 4060
  • J.F. DeFord, B. H. Held
    STAR, Inc., Mequon, Wisconsin
  • V. Ivanov, K. Ko
    SLAC, Menlo Park, California
  Funding: Work supported by DOE SBIR Grant DE-FG02-03ER83776.

Instabilities in the gun region of a high-power klystron can occur when there is positive feedback between a mode and an induced current on the quasi-steady state beam emitted by the gun cathode.* This instability is dependent on the gun voltage, is predicted on the basis of a negative beam-loaded Q. The established method for computing the beam-loaded Q of a cavity involves using a time-dependent electromagnetic particle-in-cell (PIC) code to track beam particles through the quasi-static gun fields perturbed by the electromagnetic fields of a cavity eigenmode.** The energy imparted to the beam by the mode is obtained by integrating the Lorentz force along the particle tracks, and this quantity is simply related to the beam-loaded Q. We have developed an alternative approach that yields comparable accuracy but is computationally much simpler. The new method is based on a much simpler time-independent electrostatic PIC calculation, resulting in much faster solutions without loss of accuracy. We will present the theory and implementation of the new method, as well as benchmarks and results from analysis of the XP-4 klystron that show a potential instability near 3 GHz.

*B. Krietenstein, et al., "Spurious oscillations in high-power klystrons," PAC95, 1995. **U. Becker, et al., "Simulation of oscillations in high-power klystrons," EPAC, 1996.

WPAT081 Ceramic Power Extractor Design at 15.6 GHz 4078
  • A. Smirnov, Y. Luo, R. Yi, D. Yu
    DULY Research Inc., Rancho Palos Verdes, California
  Funding: Work supported by DOE SBIR Grant No. DE-FG03-01ER83232.

Power extractor and coupler designs developed for an experiment planned at the 12th beam harmonic of the upgraded Advanced Wakefield Accelerator (AWA) facility is described. New features are an upstream HOM dielectric damper with additional tapering, and a single-port coupler considered in two variants. Performance analysis includes coupler geometric tolerances, overvoltage, dipole mode wake and BBU; and wakefield losses induced in the damper.

WPAT082 An Improved Pneumatic Frequency Control for Superconducting Cavities 4090
  • G. Zinkann, E. Clifft, S.I. Sharamentov
    ANL, Argonne, Illinois
  Funding: U.S. Department of Energy.

The ATLAS (Argonne Tandem Linear Accelerator System) superconducting cavities use a pneumatic system to maintain the cavity eigenfrequency at the master oscillator frequency. The present pneumatic slow tuner control has a limitation in the tuning slew rates. In some cases, the frequency slew rate is as low as 30 Hz/sec. The total tuning range for ATLAS cavities varies from 60 KHz to as high as 450 KHz depending on the cavity type. With the present system, if a cavity is at the extreme end of its tuning range, it may take an unacceptable length of time to reach the master oscillator frequency. We have designed a new slow tuner control system that increases the frequency slew rates by at least a factor of ten to a factor of three hundred in the more extreme cases. This improved system is directly applicable for use on the RIA (Rare Isotope Accelerator) cavities. This paper discusses the design of the system and the results of a prototype test.

WPAT083 Steering and Focusing Effects in TESLA Cavity Due to High Order Mode and Input Couplers 4135
  • P. Piot
    Fermilab, Batavia, Illinois
  • M. Dohlus, K. Floettmann, M. Marx, S.G. Wipf
    DESY, Hamburg
  Funding: This work was supported by Universities Research Association Inc. under contract DE-AC02-76CH00300 with the U.S. Department of Energy, and by NICADD.

Many state-of-art electron accelerator proposals incorporate TESLA-type superconducting standing wave cavities. These cavities include input coupler (to feed the RF power into the cavity) and a pairs of high order mode couplers (HOM) to absorb the energy associated to HOM field excited as the bunch passes through the cavity. In the present paper we investigate, using numerical simulations, the impact of the input and HOM couplers on the beam dynamics. We show the overall effects are: a dipole kick (zeroth order) and normal and skew quadrupole-type focusing (first order). We present parametric studies of the strength of these effect for various operating gradients and incoming beam energies. We finally study the impact of this non-asymmetric field on the beam dynamics, taking as an example the low energy section of the European X-FEL injector.

  • H. Matsumoto, S. Kazakov, K. Saito
    KEK, Ibaraki
  Funding: Toshiba Electron Tube & Devices Co. Ltd., Tochigi, Otawa, Japan.

An attractive structure using capacitive coupling has been found for the input coupler for the 45 MV/m versions of the International Linear Collider (ILC) project. The coupler supports an electrical field gradient of ~1 kV/m around the rf window ceramic with 500 kW through power, a VSWR of 1.1 and a frequency bandwidth of 460 MHz. No unwanted resonances were found in the rf window near the first and second harmonics of the operation frequency.

WPAT085 4.2 K Operation of the SNS Cryomodules 4173
  • I.E. Campisi, S. Assadi, F. Casagrande, M. Champion, C. Chu, S.M. Cousineau, M.T. Crofford, C. Deibele, J. Galambos, P.A. Gurd, D.R. Hatfield, M.P. Howell, D.-O. Jeon, Y.W. Kang, K.-U. Kasemir, Z. Kursun, H. Ma, M.F. Piller, D. Stout, W.H. Strong, A.V. Vassioutchenko, Y. Zhang
    ORNL, Oak Ridge, Tennessee
  Funding: SNS is managed by UT-Battelle, LLC, under contract DE-AC05-00OR22725 for the U.S. Department of Energy. SNS is a partnership of six national laboratories: Argonne, Brookhaven, Jefferson, Lawrence Berkeley, Los Alamos and Oak Ridge.

The Spallation Neutron Source being built at the Oak Ridge National Laboratory employs eighty one 805 MHz superconducting cavities operated at 2.1 K for the H- beam to gain energy in the main linac from 187 MeV to about 1 GeV. The superconducting cavities and cryomodules with two different values of beta .61 and .81 have been designed and constructed at Jefferson Lab for operation at 2.1 K with unloaded Q’s in excess of 5x109. To gain experience in testing cryomodules in the SNS tunnel before the final commissioning of the 2.1 K Central Helium Liquefier, integration tests were conducted on a medium beta (.61) cryomodule at 4.2 K. This is the first time that a superconducting cavity system specifically designed for 2.1 K operation has been extensively tested at 4.2 K without superfluid helium. Even at 4.2 K it was possible to test all of the functional properties of the cryomodule and of the cavities. In particular, at a nominal BCS Qo˜7x108, simultaneous pulse operation of all three cavities in the cryomodule was achieved at accelerating gradients in excess of 12 MV/m. These conditions were maintained for several hours at a repetition rate of 30 pps. Details of the tests will be presented and discussed.

WPAT086 Superconducting RF Cavity Frequency and Field Distribution Sensitivity Simulation 4194
  • S. An
    ORNL, Oak Ridge, Tennessee
  Funding: Under contract DE-AC05-00OR22725 for the U.S. Department of Energy.

Frequency and electromagnetic field distribution sensitivity of a superconducting RF (SRF) cavity due to cavity’s small deformation are the fundamental phyical paramethers in cavity and tuner design. At low temperature, the frequency sensitivity can be obtained by measuring prototype cavity, but it is not easy to test the filed distribution sensitivity. This paper presents and describes a simulation method combining ANSYS and SUPERFISH to calculate the cavity frequency and field distribution variation due to cavity’s small deformation caused by mechanical force, radiation force, thermal expansion etc.. As an example, the simulation results of the frequency and field flatness sensitivity on the SNS cavities were confirmed by their test results.


WPAT088 Performance of TESLA Cavities After Fabrication and Preparation in Industry 4221
  • M. Pekeler, S. Bauer, P. vom Stein
    ACCEL, Bergisch Gladbach
  • W. Anders, J. Knobloch
    BESSY GmbH, Berlin
  • W.-D. Müller
    DESY, Hamburg
  In order to demonstrate cw operation of TESLA cavities in linear accelerators driving FEL applications, two TESLA cavities were manufactured and prepared by ACCEL for BESSY. After production, both cavities were prepared for vertical test at ACCEL's premises using state of the art chemical polishing and high pressure water rinsing techniques. The cavities were tested in DESY's vertical RF test installation. Accelerating gradients close to 25 MV/m were reached. One cavity was completed with a helium vessel modified for cw operation and prepared with chemical polishing, high pressure water rinsing, and assembled with the required High Power Coupler at ACCEL. The fully dressed cavity was then shipped under vacuum to BESSY and tested in the horizontal cryostat HoBiCaT. Horizontal RF test results will be presented and compared with the vertical test results.  
WPAT089 Test Bed for Superconducting Materials 4227
  • C.D. Nantista, V.A. Dolgashev, R. Siemann, S.G. Tantawi, J. Weisend
    SLAC, Menlo Park, California
  • I.E. Campisi
    ORNL, Oak Ridge, Tennessee
  Funding: Work supported by the U.S. Department of Energy under contract DE-AC03-76SF00515.

Superconducting rf cavities are increasingly used in accelerators. Gradient is a parameter of particular importance for the ILC. Much progress in gradient has been made over the past decade, overcoming problems of multipacting, field emission, and breakdown triggered by surface impurities. However, the quenching limit of the surface magnetic field for niobium remains a hard limitation on cavity fields sustainable with this technology. Further exploration of materials and preparation may offer a path to surpassing the current limit. For this purpose, we have designed a resonant test cavity. One wall of the cavity is formed by a flat sample of superconducting material; the rest of the cavity is copper or niobium. The H field on the sample wall is 74% higher than on any other surface. Multipacting is avoided by use of a mode with no surface electric field. The cavity will be resonated through a coupling iris with high-power rf at superconducting temperature until the sample wall quenches, as detected by a change in the quality factor. This experiment will allow us to measure critical magnetic fields up to well above that of niobium with minimal cost and effort.

WPAT091 Fabrication and Final Field Tuning of Copper Cavity Models for a High-Current SRF ERL at 703.75 MHz 4257
  • M.D. Cole, A. Burger, M. Falletta, D. Holmes, E. Peterson, R. Wong
    AES, Medford, NY
  • I. Ben-Zvi
    BNL, Upton, Long Island, New York
  Advanced Energy Systems is currently under contract to BNL to fabricate a five cell superconducting cavity and cryomodule for the RHIC eCooler SRF Energy Recovery Linac (ERL) program.* The cavity is designed and optimized for ampere class SRF ERL service. As part of this program, we have fabricated two low power copper models of the RF cavities. During the fabrication process a series of frequency measurements were made and compared to the frequency expected at that point in the fabrication process. Where possible, the cavity was modified either before or during, the next fabrication step to tune the cavity frequency toward the target frequency. Following completion of the cavities they were tuned for field flatness and frequency. This paper will review the measurements made, frequency tuning performed, and discuss discrepancies between the expected and measured results. We will also review the as fabricated field profiles and the results of the tuning steps. Further, the cost and benefits of extensive in process tuning will be discussed from an industrial perspective.

*Electron cooling of RHIC, Ilan Ben-Zvi, these proceedings.

WPAT092 Fabrication Tuning of Four 748.5 MHz Single Cell SRF Booster Cavities for a 100 mA SRF FEL Injector 4272
  • M.D. Cole, E. Peterson, J. Rathke, T. Schultheiss
    AES, Medford, NY
  Funding: This work is supported by NAVSEA, NSWC Crane, the Office of Naval Research, and the DOD Joint Technology Office.

Advanced Energy Systems has recently completed the fabrication of four 748.5 MHz single cell superconducting cavities which are to be used in the JLAB FEL SRF Injector Test Stand. During the fabrication process a series of frequency measurements were made and compared to the frequency expected at that point in the fabrication process. Where possible, the cavity was modified either before or during, the next fabrication step to tune the cavity frequency toward the target frequency. The target frequency is calculated making a series of assumptions about the frequency effects of subsequent fabrication and processing steps.

WPAT093 A Three-Cell Superconducting Deflecting Cavity Design for the ALS at LBNL 4287
  • J. Shi, H. Chen, S. Zheng
    TUB, Beijing
  • J.M. Byrd, D. Li
    LBNL, Berkeley, California
  Deflecting RF cavities can be used to generate sub-pico-second x-rays by creating correlations between longitudinal and transverse phase space of electron bunches in radiation devices. Up to 2-MV defecting voltage at 1.5-GHz is required for 1.9-GeV electron beam at the Advanced Light Source (ALS) at LBNL. We present a conceptual design for a 1.5-GHz three-cell superconducting RF cavity and its coupler. The cavity geometry and deflecting shunt impedance are optimized using MAFIA code. The cavity impedance from lower and higher order modes (LOM and HOM) are computed. Possible schemes for damping most harmful LOM and HOM modes are discussed and simulated.  
WPAT094 Traveling Wave Accelerating Structure for a Superconducting Accelerator 4296
  • A. Kanareykin
    Euclid TechLabs, LLC, Solon, Ohio
  • P.A. Avrakhov
    LPI, Moscow
  • N. Solyak
    Fermilab, Batavia, Illinois
  We are presenting a superconducting traveling wave accelerating structure (STWA) concept, which may prove to be of crucial importance to the International Linear Collider. Compared to the existing design of a TESLA cavity, the traveling wave structure can provide ~20-40% higher accelerating gradient for the same aperture and the same peak surface magnetic RF field. The recently achieved SC structure gradient of 35 MV/m can be increased up to ~50 MV/m with the new STWA structure design. The STWA structure is supposed to be installed into the superconducting resonance ring and is fed by the two couplers with appropriate phase advance to excite a traveling wave inside the structure. The system requires two independent tuners to be able to adjust the cavity and feedback waveguide frequencies and hence to reduce the unwanted backward wave. In this presentation we discuss the structure design, optimization of the parameters, tuning requirements and plans for further development.  
WPAT095 Low-Loss Ferroelectric for Accelerator Application 4305
  • A. Kanareykin
    Euclid TechLabs, LLC, Solon, Ohio
  • A. Dedyk, S.F. Karmanenko
    Eltech University, St. Petersburg
  • E. Nenasheva
    Ceramics Ltd., St. Petersburg
  • V.P. Yakovlev
    Omega-P, Inc., New Haven, Connecticut
  Funding: U.S. Department of Energy.

Ferroelectric ceramics have an electric field-dependent dielectric permittivity that can be altered by applying a bias voltage. Ferroelectrics have unique intrinsic properties that makes them attractive for high-energy accelerator applications: very small response time of ~ 10-11 sec, considerably high breakdown limit of more than 100 kV/cm, good vacuum properties. Because of these features, bulk ferroelectrics may be used as active elements of tunable accelerator structures,* or in fast, electrically - controlled switches and phase shifters in pulse compressors or power distribution circuits of future linear colliders.** One of the most critical requirements for ferroelectric ceramic in these applications is the dielectric loss factor. In this paper, the new bulk ferroelectric ceramic is presented. The new composition shows a loss tangent of 4× 10-3 at 35 GHz. The ceramics have high tunability factor: the bias voltage of 50 kV/cm was enough to reduce the permittivity from 500 to 400. The material chemical compound, features of the technology process, and mechanical and electrical properties are discussed. The ways of BST ferrolectric parameters further improvement are discussed as well.

*A. Kanareykin, W. Gai, J. Power, E. Sheinman, and A. Altmark, AIP Conf. Proc. 647, Melville, N.Y., 2002, p. 565. **V.P. Yakovlev, O.A. Nezhevenko, J.L. Hirshfield, and A.D. Kanareykin, AIP Conf. Proc. 691, Melville, N.Y., 2003, p.187.