Radio-Frequency Systems

Normal-Conducting Cavities

Paper Title Page
TPPT003 Development of a Normal Conducting CH-DTL 883
  • G. Clemente, H. Podlech, U. Ratzinger, R. Tiede
    IAP, Frankfurt-am-Main
  • L. Groening
    GSI, Darmstadt
  • S. Minaev
    ITEP, Moscow
  Funding: GSI, EU (CARE, contract number RII3-CT-2003-506395).

The normal conducting "Crossbar H-Type" (CH) accelerating structure is a good candidate for pulsed, high intensity linac application, covering the energy range from 3 to 100 MeV. H Mode cavities are outstanding in the low-beta range with respect to shunt impedance, high acceleration fields, and compact design, That's why we propose to base the 70 ma, 70 MeV, 352 MHz proton linan for GSI FAIR project on that structure. The actual design consists of 11 CH-DTL's for a total length of around 25 m. Latest results from beam dynamics optimisation will be discussed. Moreover, this paper describes the CH-DTL cavity design with enphasis on the optimisation with MacroWave Studio (single cell cross section, as well as multi cell cavity simulation), and on the achieved progress in the development of mechanical design concepts. A stainless steel multicell model cavity is presently fabricated by our institute in collaboration with GSI, in order to investigate manufacturing and assembly details. Based on this experience, the design of a CH prototipe power cavity will be optimised.

TPPT004 A 175 MHz RFQ Design for IFMIF Project 904
  • S. Maebara, S. Moriyama, M.S. Sugimoto
    JAERI, Ibaraki-ken
  • M.S. Saigusa, Y. Saitou
    Ibaraki University, Electrical and Electronic Eng., Ibaraki
  International Fusion Materials Irradiation Facility (IFMIF) is an accelerator-based neutron irradiation facility employing the D-Li stripping reaction, to produce the neutron field similar to the D-T Fusion reactor (2MW/m2,20 dpa/year for Fe). The required beam current of 250 mA is realized by two beam lines of 125mA, and the output energies at injector,RFQ and DTL were designed to be 0.1, 5 and 40 MeV,respectively. The operation frequency of 175MHz was selected to accelerate the large current of 125mA. After an intensive beam simulation, the RFQ with a total length of 12m was designed to keep the minimum emittance growth with the RF injection power of 2.3MW CW. For such a 175MHz RFQ, a design for RF input coupler with loop antenna and co-axial window, supplying RF power shared by 3 x 4 ports, was conducted by using the 3-D electromagnetic code of MW-Studio. In order to withstand the voltage exceeding 200kW CW per one loop antenna, the co-axial line of 4 1/16” diameter is necessary, and it is found that the electric field distortion factor less than 1% can be achieved in beam bore only by employing the 4-loop antenna configuration providing the same power for each quadrants.  
TPPT005 Dual Harmonic Operation with Broadband MA Cavities in J-PARC RCS 931
  • M. Yamamoto, M. Nomura, A. Schnase, F. Tamura
    JAERI/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
  • S. Anami, E. Ezura, K. Hara, Y. Hashimoto, C. Ohmori, A. Takagi, M. Yoshii
    KEK, Ibaraki
  In the J-PARC RCS RF system, the fundamental rf acceleration voltage and the 2nd higher harmonic one are applied to each cavity. This is possible, because the magnetic alloy loaded cavities have a broadband characteristic and require no resonant frequency tuning. The tube amplifier provides both rf components. We calculate the operation of the tube under the condition of the dual harmonic, the non-pure resistive load and the class AB push-pull mode.  
TPPT006 Development of RF Input Coupler with a Coaxial Line TiN-Coated Against Multipactoring 1006
  • T. Abe, T. Kageyama, H. Sakai, Y. Takeuchi
    KEK, Ibaraki
  In one of the normal-conducting RF cavities used in the KEKB operation, we observed an unexpected rise of the vacuum pressure at certain input-power levels with and without a beam current. From the simulation study, we identify the pressure rises as an effect of the multipactoring discharge in the coaxial line of the input coupler. According to the simulation results, we have decided to make TiN coating on the inner surface of the outer conductor to suppress the multipactoring. In this paper, the status of the development of the TiN-coated input coupler is reported including the recent results of the high-power tests.  
TPPT008 New Design of Crab Cavity for SuperKEKB 1129
  • K. Akai, Y. Morita
    KEK, Ibaraki
  Crab-crossing scheme has been adopted as a baseline design for SuperKEKB, which is planned as an upgrade of KEKB. For the design of crab cavities for SuperKEKB, a very high beam current of 10A with a short bunch length of 3mm must be taken into account. Much heavier damping of any parasitic mode as well as smaller loss factor are required, compared with those of KEKB crab cavities. We propose new design of crab cavities for SuperKEKB. It has a high kick voltage, sufficiently low coupling impedance to any parasitic modes including the fundamental mode, and a considerably low loss factor. The new crab cavity meets the requirements for SuperKEKB.  
TPPT009 High Gradient Study at KEK on X-Band Accelerator Structure for Linear Collider 1162
  • T. Higo, M. Akemoto, A. Enomoto, S. Fukuda, H. Hayano, N.K. Kudo, S.M. Matsumoto, T. Saeki, N. Terunuma, N. Toge, K.W. Watanabe
    KEK, Ibaraki
  • T.S. Suehara
    University of Tokyo, Tokyo
  We have fabricated accelerator structures for linear collider of the warm X-band design. These were composed of high-precision-machined parts for reliable wake-field suppression and possible cheap mass production. The structure design is mostly based on GLC/NLC design in collaboration with SLAC but the fabrication and the high-power test are being performed at KEK to conclude the feasibility, though the application to the present linear collider project was terminated. In this paper are presented the high gradient performance of these structures, such as the initial conditioning characteristics, the stability under high-field operation and various characteristics at high-gradient operation. We conclude that the stability requirement for the linear collider of the warm X-band design is barely satisfied but the preservation of the stability over very long period of more than several years is to be further studied.  
TPPT010 HOM Damping of ARES Cavity System for SuperKEKB 1186
  • T. Kageyama, T. Abe, H. Sakai, Y. Takeuchi
    KEK, Ibaraki
  The ARES cavity scheme is a decisive edge for KEKB to stably accelerate high-current electron and positron beams. The RF structure is a coupled-cavity system where a HOM-damped accelerating cavity is coupled with a large cylindrical energy storage cavity via a coupling cavity between. The HOM-damped structure is designed to be smoothly embedded into the whole coupled-cavity scheme without any structural or electromagnetic incompatibility. Currently, the total HOM power dissipated in the RF absorbers per cavity is about 5 kW according to calorimetric measurements in the KEKB LER with a beam current of 1.6 A. On the other hand, for SuperKEKB aiming at luminosity frontiers over 1035 cm-2 s-1, the total HOM power per cavity is estimated about 100 kW for the LER with the design beam current of 9.4 A. In this article, a new HOM-damped structure of the ARES cavity system designed for the SuperKEKB LER is reported together with the recent activities and future plans for upgrading the HOM absorbers.  
TPPT011 R&D Status of C-Band Accelerating Section for SuperKEKB 1233
  • T. Kamitani, N. Delerue, M. Ikeda, K. Kakihara, S. Ohsawa, T. Oogoe, T. Sugimura, T. T. Takatomi, S. Yamaguchi, K. Yokoyama
    KEK, Ibaraki
  • Y. Hozumi
    GUAS/AS, Ibaraki
  For future energy upgrade of the KEKB injector linac, C-band accelerating section has been developed. First prototype 1-m long section has been installed in the linac and has achieved the accelerating field gradient of 42 MV/m. Developments of second prototype which has thicker coupler iris and third prototype which has smooth surface of the iris are in progress for less frequent breakdown. This paper reports on the recent R and D status of these C-band accelerating sections.  
TPPT012 High Power Testing of Input Couplers for SuperKEKB 1294
  • H. Sakai, T. Abe, T. Kageyama, Y. Takeuchi
    KEK, Ibaraki
  In KEKB, 32 ARES cavities have been successfully operated to stably accelerate high-current electron and positron beams. Currently, each ARES cavity is fed with RF power (frequency = 509 MHz) of about 300 kW through an input coupler, which has a ceramic disk window at the coaxial line section following the doorknob transformer section with a capacitive iris at the rectangular waveguide entrance. For SuperKEKB, which is a challenging project to boost the luminosity frontier beyond 1035 cm-2 s-1, the power capability of the input coupler needs to be upgraded to more than 900 kW, while the design power capability for KEKB is 400 kW. Recently, we have constructed a new test stand in order to simulate the actual operating condition for the input coupler to drive the ARES cavity with the maximum beam loading of 9.4 A expected for the SuperKEKB LER. In this article, the key features of the new test stand are described together with the recent results of high-power tests.  
TPPT013 Effect of HOM Couplers on the Accelerating Mode in the Damped Cavity at the Photon Factory Storage Ring 1339
  • T. Takahashi, M. Izawa, S. Sakanaka, K. Umemori
    KEK, Ibaraki
  • T. Koseki
    RIKEN/RARF/CC, Saitama
  Four damped cavities have been working very stably in the Photon Factory storage ring since 1997. The damped cavity has several trapped higher order modes (HOMs) with high Q values. Each frequency of these HOMs is detuned so as not to induce coupled-bunch instabilities. However, the frequency detuning method becomes less effective for a ring with a lower revolution frequency. Therefore, we have developed a HOM coupler that can reduce Q values of these trapped HOMs. The HOM coupler is a rod antenna type and located in the cylindrical wall of the cavity. Two or Three HOM couplers will be used for the cavity. The affect of these HOM couplers on the accelerating mode is investigated using MAFIA and the result is presented in this paper.  
TPPT014 Induction System for a Proton Bunch Acceleration in Synchrotron 1398
  • K. Torikai, Y.A. Arakida, J. Kishiro, T. Kono, E. Nakamura, Y. Shimosaki, K. Takayama, T. Toyama, M. Wake
    KEK, Ibaraki
  Funding: The project is officially supported by Grant-In-Aid for Creative Scientific Research (KAKENHI 15GS0217, 5 years term).

An induction cavity capable of operating at a repetition rate of 1MHz with a 50% duty has been built and employed for the first induction acceleration of a proton bunch from 500MeV to 8GeV in the KEK-PS.* In this experiment, an acceleration voltage of 4.7kV and an repetition frequency of 667kHz-882kHz were required. The installed induction device consists of three induction cells, each of which can generate a bipolar induction voltage of a maximum output voltage of 2 kV with a flat-top of 300ns and a 25ns rising/falling time. Electrical characteristics of the cavity itself, such as inductance, capacitance, and resistance, have been evaluated in three independent ways: (1) excitation due to a small signal from a network analyzer, (2) excitation by a proton beam as a primary driver, (3) excitation with a actual pulse modulator in an entire system. This paper will compare these results as well as theoretical design values. A general design procedure for an induction acceleration cavity will be given.

*K.Takayama et al., submitted to Phys. Rev. Lett.

TPPT015 Coupler Matching Techniques for C-Band Accelerating Section 1431
  • K. Yokoyama, M. Ikeda, K. Kakihara, T. Kamitani, S. Ohsawa, T. Sugimura, T. T. Takatomi
    KEK, Ibaraki
  Research and development of the c-band accelerating section has proceeded since 2002. This paper reports the development of the second prototype accelerating section. The coupler iris with a 4 mm thick is thicker than the first prototype because of preventing the rf breakdown at the iris edge. The coupler has a single port and the coupler cell is the same length as the waveguide(WR-187). The coupler cavity diameter and the coupling iris were optimized by using the iteration of the rf measurement which is the nordal shift method.  
TPPT016 Development of Co-Based Amorphous Core for Untuned Broadband RF Cavity 1511
  • T. Misu, M. Kanazawa, A. Sugiura, S. Yamada
    NIRS, Chiba-shi
  • K. Katsuki, K. S. Sato
    Toshiba, Yokohama
  We have developed a co-based amorphous core as a new magnetic-alloy (MA) core for the loaded RF cavity. Because of its permeability found to be approximately twice as high as that of FINEMET, this MA core is an excellent candidate for constructing a compact broadband RF cavity with less power consumption. In this report, we present our recent studies of the co-based amorphous core’s physical properties, performance, and development.  
TPPT017 Fabrication and Test of the Drift Tubes for PEFP 20 MeV DTL 1552
  • Y.-H. Kim, Y.-S. Cho, H.-J. Kwon, M.-Y. Park
    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.

Drift tubes of PEFP (Proton Engineering Frontier Project) 20MeV DTL contain electro-quadrupole magnet composed of commercial enamel wire cooled with water coolant. Those were fabricated through the process of brazing, assembling, electron-beam welding, and post-machining. During the e-beam welding, temperature increase was kept under 50 degree to protect the EQM wire from thermal damage. We performed several tests such as vacuum leak test, hydraulic test, and electrical test. EQM properties such as effective length, magnetic saturation, and offset between magnetic center and geometric center of DT were measured and recorded also.

TPPT018 Tuning of 20MeV PEFP DTL 1598
  • M.-Y. Park, Y.-S. Cho, H.-S. Kim, H.-J. Kwon, K.T. Seol, 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 (Proton Engineering Frontier Project) 20 MeV DTL have been constructing in KAERI site. The tuning goals for PEFP DTL are achieving the tank frequency as ± 5 kHz of designed resonant frequency and 1% of field profile through a tank. To tune the tank frequency 8 low power slug tuners per tank are fabricated and the tuning range is ±125 kHz per a tuner. Post couplers with tap to stabilize the field against the perturbation also are fabricated and will be installed every 3rd (1st tank) and 2nd (2,3,4th tank) drift tubes. We set up the bead perturbation measurement equipment as measuring the phase shift of a tank using network analyzer and LabView program. We are finalizing the tuning procedures and also the data calculation program. In this presentation we will show the overall features of the PEFP DTL tuning and discuss the measurement results.

TPPT019 Numerical Study of Coupling Slot Effects on Beam Dynamics in Industrial Accelerator Prototype 1622
  • V.V. Tarnetsky, V. Auslender, I. Makarov, M.A. Tiunov
    BINP SB RAS, Novosibirsk
  Funding: The work is supported by ISTC grant #2550.

At Budker INP, the work is in progress on development of high-efficiency, high-power electron accelerator named ILU-12. The accelerator has a modular structure and consists of a chain of accelerating cavities connected by on-axis coupling cavities with coupling slots in the common walls (the coupling constant is about 0.08). Main parameters of the accelerator are: operating frequency of 176 MHz, electron energy of up to 5 MeV, average beam power of 300 kW. The paper presents results of 3D electromagnetic field numerical simulations for ILU-12 accelerating structure with recovery of quadrupole filed disturbance because of large coupling holes. The results show that accelerating cell geometry chosen eliminates coupling slot influence on the beam dynamics.

TPPT020 30 GHz Power Production in CTF3 1695
  • W. Wuensch, C. Achard, H.-H. Braun, G. Carron, R. Corsini, A. Grudiev, S.T. Heikkinen, D. Schulte, J.P.H. Sladen, I. Syratchev, F. Tecker, I. Wilson
    CERN, Geneva
  One of the major objectives of CTF3 (CLIC Test Facility) is the production of 30 GHz power for the high-gradient testing of CLIC accelerating structures. To this end a dedicated beam line, power generating structure and power transfer line have been designed, installed and commissioned. 52 MW of 30 GHz power with a pulse length of 74 ns and a repetition rate of 16 Hz were delivered to the high-gradient test area. This will allow operation of test accelerating structures in the coming run of CTF3 up to the nominal CLIC accelerating gradient of 150 MV/m and beyond the nominal pulse length. The system is described and the performances of the CTF3 linac, beam line and the rf components are reviewed.  
TPPT021 Characterization and Tuning of a Microwave Gun Cavity 1748
  • W.K. Lau, J. Chan, L.-H. Chang, C.W. Chen, H.Y. Chen, K.-T. Hsu, S.Y. Hsu, J.-Y. Hwang, Y.C. Wang, T.-T. Yang
    NSRRC, Hsinchu
  The SSRL rf gun cavity is electromagnetic structure with a half-cell at the cathode end and a full cell at the other end. Instead of coupling through beam pipe to produce the desired pi-mode for beam acceleration, these two cells are coupled through a frequency tunable side-coupled cell. Therefore, the strucuture is actually 3-cell cavity and the pi/2-mode will be used. This paper reports the characterization of these resonant modes at various side-coupled cell tuning conditions. And the behavior of this cavity will also be analytically examined.  
TPPT022 The Structure of the High Frequency Focusing Cells in Linear Ion Accelerators 1796
  • V.A. Bomko, O.F. Dyachenko, A.P. Kobets, E.D. Marynina, Z.O. Ptukhina, S.S. Tishkin, B.V. Zajtsev
    NSC/KIPT, Kharkov
  The versions of the high frequency quadrupole doublets (RFQD) for proton and heavy ion linear accelerators are discussed. Advantages of focusing of this type over magnetic quadrupoles lie in the simplicity of the structure and high efficiency and reliability of focusing. In the multi-gap structures, focusing periods contain a sequence of focusing and accelerating cells. The elaborated technique of the local cell adjustment provides the high acceleration rate. Various RFQD versions for the specific peculiarities of accelerating structures are discussed. Application of the RF-quadrupole doublets in the spoke cavity, CCDTL and Crossbar structures will allow the application of superconductive cavities for proton acceleration in the range of intermediate energies of 5-100 MeV. In the interdigital H-structures, the application of RFQDs will allow to increase the efficiency of ion beam focusing and to expand the energy range of the ions being accelerated over 10 MeV/u.  
TPPT025 Breakdown in RF Cavities 1886
  • J. Norem, A. Hassanein, Z. Insepov, I. Konkashbaev
    ANL, Argonne, Illinois
  Funding: DOE

We present a simple model of breakdown in rf cavities. For most events this involves tensile stress and tensile strength, however other effects can also contribute. We discuss the effects of different materials, fatigue, high pressure gas, primary and secondary emission sites, local field enhancements, dark currents, secondary emission, work functions, magnetic fields, macro and microscopic fracture mechanisms high current densities, surface and subsurface defects, and astronomical power densities. While primarily devoted to normal conductors, this work also has consequences for superconducting rf surfaces.

TPPT027 53 MHz Beam Loading Compensation for Slip Stacking in the Fermilab Main Injector 1958
  • J.E. Dey, I. Kourbanis
    Fermilab, Batavia, Illinois
  Funding: Operated by Universities Research Association, Inc. for the U.S. Department of Energy under contract DE-AC02-76CH03000.

Recently In-Phase and Quadrature (I&Q) was added to both the 53 MHz Feedback and Feedforward Beam Loading Compensation for Slip Stacking in the Fermilab Main Injector. With 53 MHz Feedback, we can now turn the 18 Radio Frequency (RF) Stations off down to below 100 V. In using I&Q on Feedforward, beam loading compensation to the beam on both the upper and lower frequencies of Slip Stacking can be applied as we slip the beam. I&Q theory will be discussed.

TPPT028 Design of a New Main Injector Cavity for the Fermilab Proton Driver Era 2015
  • V. Wu, A.Z. Chen, Z. Qian, D. Wildman
    Fermilab, Batavia, Illinois
  Funding: Operated by Universities Research Association, Inc. for the U.S. Department of Energy under contract DE-AC02-76CH03000.

In the design report of the Fermilab Proton Driver [1],* the Main Injector (MI) needs to be upgraded to a 2 MW machine. For the Main Injector radiofrequency (rf) upgrade, R&D efforts are launched to design and build a new rf system. This paper presents the new cavity design study for the rf system. The cavity is simulated with the design code Mafia [2].**

**Proton Driver Study II, FERMILAB-TM-2169, May 2002, edited by G.W. Foster, W. Chou and E. Malamud. **Computer Simulation Technology, MAFIA 4, December 1996.

TPPT029 Fabrication of the Prototype 201.25 MHz Cavity for a Muon Ionization Cooling Experiment 2080
  • R.A. Rimmer, S. Manning, R. Manus, H.L. Phillips, M. Stirbet, K. Worland, G. Wu
    Jefferson Lab, Newport News, Virginia
  • R.A. Hafley, R.E. Martin, K.M. Taminger
    NASA Langley, Hampton, Virginia
  • D. Li, R.A. MacGill, J.W.  Staples, S.P. Virostek, M.S. Zisman
    LBNL, Berkeley, California
  • M. Reep, D.J. Summers
    UMiss, University, Mississippi
  Funding: This manuscript has been authored by SURA, Inc. under DoE Contract No. DE-AC05-84ER-40150, LBNL contract No. DE-AC03-76SF00098 and NASA contract IA1-533 subagreement #2

We describe the fabrication and assembly of the first prototype 201.25 MHz copper cavity for the muon ionization cooling experiment (MICE). This cavity was developed by the US MUCOOL collaboration and will be tested in the new Muon Test Area at Fermilab. We outline the component and subassembly fabrication steps and the various metal forming and joining methods used to produce the final cavity shape. These include spinning, brazing, TIG welding, electron beam welding, electron beam annealing and deep drawing. Assembly of the loop power coupler will also be described. Final acceptance test results are included. Some of the methods developed for this cavity are novel and offer significant cost savings compared to conventional construction methods.

TPPT030 RF, Thermal and Structural Analysis of the 201.25 MHz Muon Ionization Cooling Cavity 2119
  • S.P. Virostek, D. Li
    LBNL, Berkeley, California
  Funding: This work was supported by the Office of Science, U.S. Department of Energy under DOE contract number DE-AC03-76SF00098.

A finite element analysis has been carried out to characterize the RF, thermal and structural behavior of the prototype 201.25 MHz cavity for a muon ionization cooling channel. A single ANSYS model has been developed to perform all of the calculations in a multi-step process. The high-gradient closed-cell cavity is being designed and fabricated for the MUCOOL and MICE (international Muon Ionization Cooling Experiment) experiments. The 1200 mm diameter cavity is constructed of 6 mm thick copper sheet and incorporates a rounded pillbox-like profile with an open beam iris terminated by 420 mm diameter, 0.38 mm thick curved beryllium foils. Tuning is accomplished through elastic deformation of the cavity, and cooling is provided by external water passages. Details of the analysis methodology will be presented including a description of the ANSYS macro that computes the heat loads from the RF solution and applies them directly to the thermal model. The process and results of a calculation to determine the resulting frequency shift due to thermal and structural distortion of the cavity will be presented as well.

TPPT031 Coupler Design for the LCLS Injector S-Band Structures 2176
  • Z. Li, L.D. Bentson, J. Chan, D. Dowell, C. Limborg-Deprey, J.F. Schmerge, D.C. Schultz, L. Xiao
    SLAC, Menlo Park, California
  Funding: Work supported by the U.S. DOE Contract No. DE-AC03-76SF00515.

The LCLS injector is required to provide a 1-nC, 10-ps bunch with a normalized rms transverse projected emittance of less than 1.0-μm. The LCLS beam is generated and accelerated in a 1.6-cell S-band RF gun to 6-MeV followed by two SLAC 3-m S-band accelerator structures to further accelerate the beam to 135 MeV to move it out of the space-charge dominated regime. In the SLAC S-band structures, the RF power feed is through a single coupling-hole (single-feed coupler) which results in a field asymmetry. The time dependent multipole fields in the coupler induce a transverse kick along the bunch and cause the emittance to increase above the LCLS specification. To meet the stringent emittance requirements for the injector, the single-feed couplers will be replaced by a dual-feed racetrack design to minimize the multipole field effects. We will present detailed studies of the multipole fields in the S-band coupler and the improvements with the dual-feed racktrack design using the parallel finite element eigenmode solver Omega3P.

TPPT032 Modifications on RF Components in the LCLS Injector 2233
  • C. Limborg-Deprey, D. Dowell, Z. Li, J.F. Schmerge, L. Xiao
    SLAC, Menlo Park, California
  Funding: This work was supported by U.S. Department of Energy, contract No. DE-AC03-76SF00515A06.

Design of the first generation LCLS injector has now been completed. Components are currently under fabrication and their installation is planned for 2006. We discuss the last modifications made on both the 1.6 cell S-Band RF gun and the SLAC S-Band accelerating structures to minimize the beam emittance. We present results from PARMELA computations which justify those modifications, in particular the suppression of the time dependent dipole and quadrupole kicks. Geometry changes to increase the mode separation between the 0 and PI modes are also presented. For the initial geometry with a mode separation of 3.5MHz, the emittance can increase if the appropriate injection time along the klystron pulse is not chosen. For a mode separation of 15MHz, this problem is minimized and the beam dynamics are improved leading to a substantial reduction of total projected emittance.

TPPT033 Simulations Using the VORPAL Code of Electron Impact Ionization Effects in Waveguide Breakdown Processes 2298
  • P. Stoltz, J.R. Cary, P. Messmer, C. Nieter
    Tech-X, Boulder, Colorado
  Funding: Supported by Department of Energy SBIR Grant No. DE-FG03-02ER83554.

We present results of three-dimensional simulations using the VORPAL code of power absorbtion by stray electrons in X-band waveguides. These simulations include field emission from the waveguide surfaces, impact ionization of background gas, and secondary emission from the walls. We discuss the algorithms used for each of these electron effects. We show the power abosrbed as a function of background gas density. Finally, we present scaling results for running these simulations on Linux Clusters.

TPPT035 High-Power RF Testing of a 352-MHz Fast-Ferrite RF Cavity Tuner at the Advanced Photon Source 2407
  • D. Horan, E.E. Cherbak
    ANL, Argonne, Illinois
  Funding: Work supported by U.S. Department of Energy, Office of Basic Energy Sciences, under contract No. W-31-109-ENG-38.

A 352-MHz fast-ferrite rf cavity tuner, manufactured by Advanced Ferrite Technology, was high-power tested on a single-cell copper rf cavity at the Advanced Photon Source. These tests measured the fast-ferrite tuner performance in terms of power handling capability, tuning bandwidth, tuning speed, stability, and rf losses. The test system comprises a single-cell copper rf cavity fitted with two identical coupling loops, one for input rf power and the other for coupling the fast-ferrite tuner to the cavity fields. The fast-ferrite tuner rf circuit consists of a cavity coupling loop, a 6-1/8” EIA coaxial line system with directional couplers, and an adjustable 360° mechanical phase shifter in series with the fast-ferrite tuner. A bipolar DC bias supply, controlled by a low-level rf cavity tuning loop consisting of an rf phase detector and a PID amplifier, is used to provide a variable bias current to the tuner ferrite material to maintain the test cavity at resonance. Losses in the fast-ferrite tuner are calculated from cooling water calorimetry. Test data will be presented.

TPPT036 Higher-Order-Mode Damper Testing and Installation in the Advanced Photon Source 352-MHz Single-Cell RF Cavities 2443
  • G.J. Waldschmidt, N.P. Di Monte, D. Horan, L.H. Morrison, G. Pile
    ANL, Argonne, Illinois
  Funding: Work supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. W-31-109-ENG-38.

Higher-order-mode dampers were recently installed in the storage ring rf cavities at the Advanced Photon Source to eliminate longitudinal coupled-bunch instability. It was discovered that the 540-MHz cavity dipole mode created beam instability at beam currents in excess of 85 mA causing horizontal emittance blowup. Methods of compensating for the instability by detuning the cavities and adjusting the cavity water temperature were becoming more difficult at higher beam currents as tests were performed to prepare for eventual 300-mA beam current operation. Electric field passive dampers located on the median plane of each cavity were determined to be the most promising solution. Simulation models were created and verified with low-power testing of the dampers. High-power testing of the dampers as well as conditioning of the damper ceramic load were also performed at the APS 352-MHz rf test stand and compared with simulation results. Preliminary test results will be discussed.

TPPT037 A Coaxial Subharmonic Cavity Design for Direct Injection at the Advanced Photon Source 2497
  • G.J. Waldschmidt, A. Nassiri
    ANL, Argonne, Illinois
  Funding: Work supported by U.S. Department of Energy, Office of Basic Energy Sciences, under Contract No. W-31-109-ENG-38.

Coaxial subharmonic cavity designs are being investigated at the Advanced Photon Source to improve injector reliability by injecting beam directly from the linac to the booster in storage ring top-up mode. The subharmonic system must operate jointly with the present 352-MHz booster to accelerate the beam to 7 GeV with minimal beam degradation. Design considerations must be made to ensure that bunch purity is maintained and that a large percentage of the linac macropulse is captured. An analysis of rf cavity designs using electromagnetic simulation software has been conducted at 58 MHz and 117 MHz. The final design evaluates the total power loss, field uniformity, and peak surface fields to achieve the required gap voltage.

TPPT038 Development of C-Band Accelerator Structure with Smooth Shape Couplers 2530
  • T. Sugimura, M. Ikeda, K. Kakihara, T. Kamitani, S. Ohsawa, T. T. Takatomi, K. Yokoyama
    KEK, Ibaraki
  The first C-band accelerator structure for the SuperKEKB injector linac has been operated in the beam line of e+/e- injector linac for KEKB/PF/PF-AR since September, 2003. A new accelerator structure will locate upstream of the first structure. The upstream structure is exposed to higher RF field than that of downstream structure. For the case of first structure, most of an RF breakdown occurs in an input coupler. In order to reduce a frequency of the breakdown, improvement of a coupler is required. In order to suppress a thermionic emission around the coupler iris, thick and smooth iris is adopted for the upstream structure. The development status of this type of upstream structure is described.  
TPPT039 Installation and Testing for Commissioning of Normal Conducting RF Linac Segment in the SNS 2571
  • Y.W. Kang, A.V. Aleksandrov, D.E. Anderson, M.M. Champion, M. Champion, M.T. Crofford, C. Deibele, G.W. Dodson, R.E. Fuja, P.E. Gibson, P.A. Gurd, T.W. Hardek, G.A. Johnson, P. Ladd, H. Ma, M.P. McCarthy, M.F. Piller, J.Y. Tang, A.V. Vassioutchenko, D.C. Williams
    ORNL, Oak Ridge, Tennessee
  • J.A. Billen, J.T. Bradley, D. Rees, W. Roybal, J. Stovall, K.A. Young, L.M. Young
    LANL, Los Alamos, New Mexico
  The Spallation Neutron Source (SNS) linac employs both normal conducting and superconducting linac cavities that will inject a 1.0 GeV proton beam into its accumulator ring. The normal conducting segment of this linac accelerates the beam to 185 MeV and employs one RFQ and six DTL cavities powered by seven 2.5 MW, 402.5 MHz klystrons and four CCL modules powered by four 5.0 MW, 805 MHz klystrons. Installation and RF conditioning of the RF equipment for normal conducting linac segment have been completed at ORNL with the support of LANL experts. After conditioning the accelerating structures, the linac has been successfully commissioned with beam. This paper reviews the experience in installation, RF conditioning, and commissioning of the normal conducting linac accelerating structures and RF subsystems. Checkout and operation of the RF systems and structures including conditioning procedure establishment and test results compared to the RF design specifications will be discussed.

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.

TPPT040 X-Band Dipole Mode Deflecting Cavity for the UCLA Neptune Beamline 2627
  • R.J. England, B. O'Shea, J.B. Rosenzweig, G. Travish
    UCLA, Los Angeles, California
  • D. Alesini
    INFN/LNF, Frascati (Roma)
  Funding: This work was funded by the Department of Energy under Grant No. DE-FG03-92ER40693.

We report progress on the design and construction of a nine-cell dipole (TM 110 mode) cavity for use as a temporal diagnostic of the 14 MeV 300 pC electron bunches generated at the UCLA Neptune Laboratory linear accelerator, with an anticipated temporal resolution of 150 fs at a peak input power of 50 kW. The cavity is a center-fed standing-wave pi-mode structure, operating at 9.6 GHz, and incorporating a knife-edge and gasket assembly which minimizes the need for brazing or welding. Results of initial RF tests are discussed and compared with simulation results obtained using the commercial code HFSS.

TPPT041 RF Tuning and Fabrication Status of the First Module for J-PARC ACS 2684
  • H. Ao, T. Morishita, A. Ueno
    JAERI/LINAC, Ibaraki-ken
  • K. Hasegawa
    JAERI, Ibaraki-ken
  • M. Ikegami
    KEK, Ibaraki
  • V.V. Paramonov
    RAS/INR, Moscow
  • Y. Yamazaki
    JAERI/J-PARC, Tokai-Mura, Naka-Gun, Ibaraki-Ken
  J-PARC Linac starts with 180-MeV SDTL temporary, and it is upgraded to 400-MeV with 21 ACS (Annular Coupled Structure) modules and two ACS bunchers and two debunchers. First buncher module is under fabrication, and second buncher and a few accelerating modules are also planed until FY2006. The first ACS module consists of two 5-cells ACS tanks and a 5-cells bridge cavity for the buncher module. Three RF tuners are installed to the bridge cavity for fine RF tuning. An operating frequency should be tuned to 972 MHz within the fine-tuning range before a brazing process in a factory. The tuning procedure has been studied with RF simulation analysis and cold-model measurements for ACS and bridge cells. This paper describes RF tuning results, fabrication status and related development items.  
TPPT042 The Simulation Calculations and Dielectric Characteristics Investigation of an X-Band Hybrid Dielectric-Iris-Loaded Traveling Accelerating Structure 2720
  • C.-F. Wu, S. Dong, S. Hongbing, D. Jia, H. Lin, L. Wang
    USTC/NSRL, Hefei, Anhui
  Funding: This work is supported by the National Natural Science Foundation of China(No.10375060,10205014)and the Project of Knowledge Innovation Program of the Chinese Academy of Sciences.

Mafia code has been used to calculate the RF properties versus the geometric parameters and dielectric permittivity for the X-band (f=9.37GHz) hybrid dielectric-iris-loaded traveling accelerating structure. The simulation results show that when the range of the permittivity is about 5-9, the new structure may have lower ratio (about 1) of peak surface electric field at the iris to axial accelerating electric field by optimizing the geometric parameters, while r, Q, r/Q of the new structure being comparable to iris-loaded accelerating structure. The experimental investigations of the permittivity of the ceramics have been made at the X-band by using the cavity perturbation technique. The measured results are in good agreement with the simulation results of Microwave Studio. Furthermore, the stability of the ceramics is examined. A number of experimental results show that the certain ceramic with permittivity of 5.78 is applied to the design of the new accelerating structure.

TPPT043 The Studies of Hybrid Dielectric-Iris-Loaded Accelerating Structure 2747
  • C.-F. Wu, S. Dong, H. Lin
    USTC/NSRL, Hefei, Anhui
  Funding: This work is supported by the National Natural Science Foundation of China(No.10375060,10205014) and the Project of Knowledge Innovation Program of the Chinese Academy of Sciences.

The dispersion property and the propagation characteristics of the accelerating mode (TM01 mode) and higher-order-modes about a new hybrid dielectric-iris-loaded accelerating structure have been analysed and discussed by the field matching method. Mafia code has been used to calculate the RF properties versus the geometric parameters and dielectric permittivity for the X-band (f=9.37GHz) hybrid dielectric-iris-loaded traveling accelerating structure. Some model cavities have been developed, and experimental investigations have been carried on. The above results will provided some beneficial datum for the design and manufacture of X-band hybrid dielectric-iris-loaded traveling-wave accelerating structure.

TPPT044 Beam Position Monitoring Using the HOM-Signals from a Damped and Detuned Accelerating Structure 2804
  • S. Doebert, C. Adolphsen, R.M. Jones, J.R. Lewandowski, Z. Li, M.T.F. Pivi, J.W. Wang
    SLAC, Menlo Park, California
  • T. Higo
    KEK, Ibaraki
  Funding: Work Supported by DOE Contract DE-AC02-76F00515.

The Next Linear Collider (NLC) and Global Linear Collider (GLC) designs require precision beam-to-accelerator-structure alignment to reduce the effect of short range wakefields. For this purpose, the HOM signals from the structure dipole mode damping ports would be used to determine the beam position in the structure, and then the structures would be moved remotely to center them about the beam (a 5 micron rms alignment is required). In 2000, a test of a 1.8 m prototype structure in the ASSET facility at SLAC achieved 11 micron rms centering accuracy, which was limited by systematic effects caused by beam jitter. This year, such measurements were repeated for a pair of shorter structures (60 cm) that were developed to improve high gradient performance. In addition, the beam position resolution was determined by measuring simultaneously three signal frequencies (14.3, 15, 15.7 GHz) corresponding to modes localized at the beginning, the middle and the end of the structures. In this paper, we present results from the beam centering and position resolution measurements.

TPPT049 Design and Cold Model Test of 500MHz Damped Cavity for ASP Storage Ring RF System 3076
  • J. Watanabe, K. Nakayama, K. S. Sato, H. Suzuki
    Toshiba, Yokohama
  • M. Izawa
    KEK, Ibaraki
  • A. Jackson, G. LeBlanc, K. Zingre
    ASP, Clayton, Victoria
  • T. Koseki
    RIKEN/RARF/CC, Saitama
  • N. Nakamura, H. Sakai, H. Takaki
    ISSP/SRL, Chiba
  TOSHIBA is constructing the storage ring RF system for the Australian Synchrotron Project(ASP). Two pairs of the 500MHz Higher Order Mode(HOM) damped cavities will be applied for this system. The cavities are modified KEK-PF type with silicon-carbide(SiC) microwave absorber and added three HOM anttenas for damping the longitudinal HOM impedance less than 20kOhm/GHz to meet requirement of ASP specification. The shunt impedance has been improved more than 5% in comparison with the original design by reducing the beam bore diameter without degrading HOM damping capability. The design of the cavity and the test results of an Al cold model are described.  
TPPT050 Rod-Loaded and PBG Multi-Beam Klystron Cavities 3094
  • A. Smirnov, D. Yu
    DULY Research Inc., Rancho Palos Verdes, California
  Funding: Work supported by DOE SBIR Grant No. DE-FG02-03ER83845.

Performance of PBG-like structures was studied for multi-defect and single-defect metal cavities. Conceptual designs of a 6-beam, X-band, multi-beam klystron (MBK) demonstrate feasibility of high power generation with efficiency ~63% in a compact structure. Sheet-beam and annular-beam rod-loaded configurations were also investigated.