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impedance

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TUP004 Intense L-Band Electron Linac for Industrial Applications coupling, linac, electron, klystron 250
 
  • B. Park, M.-H. Cho, S. H. Kim, S.-I. Moon, W. Namkung
    POSTECH, Pohang, Kyungbuk
  • J.-S. Oh, S. J. Park
    PAL, Pohang, Kyungbuk
  An intense L-band travelling-wave electron linac is under development for irradiation applications. It is capable of producing 10 MeV electron beams of 30 kW average beam power. The operating energy is limited to prevent neutron production. On the other hand, the current is limited by the beam loading effect in the given structure. The accelerating structure operated with 2π/3 mode is constant-impedance and disk-loaded waveguides. We determined the optimum operating parameters by adjusting the duty factor, which is again governed by the available high-power pulsed klystron. The SUPERFISH code was used to design the bunching and accelerating cavities. The PARMELA code gives the result of beam dynamics. We present design details of the intense travelling-wave linac powered by a 1.3 GHz, 25 MW pulsed klystron with a duty factor of 0.21%. We also present cold test results for the prototype cavities.  
 
TUP044 Shunt Impedance Measurement of the APS BBC Gun cathode, gun, electron, photon 346
 
  • Y.-E. S. Sun, J. W. Lewellen
    ANL, Argonne, Illinois
  The Advanced Photon Source (APS) ballistic bunch compression (BBC) injector is presently in use as a beam source for a number of experiments, including THz generation, beam position monitor testing for the Linac Coherent Light Source (LCLS), novel cathode testing, and radiation therapy source development. The APS BBC gun uses three independently powered and phased rf cavities, one cathode cell and two full cells, to provide beam energies from 2 – 10 MeV with variable energy spread, energy chirp, and, to an extent, bunch duration. The shunt impedance of an rf accelerator determines how effectively the accelerator can convert supplied rf power to accelerating gradient. The calculation of the shunt impedance can be complicated if the beam energy changes substantially during its transit through a cavity, such as in a cathode cell. We present the results of direct measurements of the shunt impedance of the APS BBC gun on an individual cavity basis, including the cathode cell, as well as report on achieved gradients. We also present a comparison of the measured shunt impedance with theoretical values calculated from the rf models of the cavities.  
 
TUP071 Beam-Loading Effects on Phase Scan for the Superconducting Cavities linac, simulation, beam-loading, SNS 418
 
  • D.-O. Jeon, S. Henderson, S.-H. Kim, Y. Zhang
    ORNL, Oak Ridge, Tennessee
  When the beam is passing through superconducting cavities, it excites beam induced field in cavities. A systematic study was performed to study the beam loading effects by the nonrelativistic beam for β = 0.81 superconducting cavities of the SNS linac. The analysis indicates that the induced field level is quite close to the estimation and its effect on the phase scan is consistent with the model.  
 
TUP083 Development of High-Power RF Vector Modulator Employing TEM Ferrite Phase Shifters controls, SNS, linac, vacuum 451
 
  • Y. W. Kang, M. S. Champion, S.-H. Kim, M. P. McCarthy, A. V. Vassioutchenko, J. L. Wilson
    ORNL, Oak Ridge, Tennessee
  Construction and installation of cavity RF power distribution system in a high power superconducting RF accelerator can have cost savings if a fan-out configuration that feeds many cavities with a single high power klystron is realized. The configuration however requires independent control of RF amplitudes and phases to the cavities to perform properly. A prototype high power RF vector modulator for the control is built and tested. The vector modulator employs a quadrature hybrid and two fast ferrite phase shifters in square coaxial TEM transmission lines. The square coaxial format can provide the power handling capability and thermal stability. RF properties of the design and result of high power system testing of the design are presented.  
 
WE2005 HOM Damping and Power Extraction from Superconducting Cavities damping, linac, coupling, electron 506
 
  • J. S. Sekutowicz
    DESY, Hamburg
  Damping of Higher Order Modes plays an important role in achieving and preserving low emittance and low energy modulation of beams in accelerators based on the superconducting technology. In the overview, various damping schemes and damping devices and their advantages and disadvantages will be discussed.  
 
TH2001 High-Power Couplers for Linear Accelerators linac, vacuum, emittance, simulation 531
 
  • V. Variola
    LAL, Orsay
  High power input couplers are a fundamental component of the linear accelerating structures and in particular of the superconducting structures. In fact, in this case, the power couplers function is not only the power transfer and the vacuum separation but includes also the thermal transition and the integrity of the cavity cleanliness. A lot of activity has been recently worked out in the framework of different project on both CW (KEK and Cornell) and pulsed (SNS and TTF) power couplers. Particular attention has been devoted to the design phase to take care about the thermo mechanical and electromagnetic performances, the multipacting thresholds, the preparation procedures and, last but not least, the cost that in the case of high energy linacs is a fundamental parameter. In this framework not only the design phase but also the conditioning of the couplers has stimulated different studies. Partial reviews of the existing designs and of the couplers characteristics will be presented taking into account the different challenges.  
 
THP018 Design Progress of the Re-bunching RF Cavities and Hybrid Quadrupoles for the RAL Front-End Test Stand (FETS) quadrupole, linac, simulation, proton 604
 
  • D. C. Plostinar
    CCLRC/RAL/ASTeC, Chilton, Didcot, Oxon
  • M. A. Clarke-Gayther, C. M. Thomas
    CCLRC/RAL/ISIS, Chilton, Didcot, Oxon
  The proposed FETS project at RAL will test a fast beam chopper in a 3.0 MeV H- Medium Energy Beam Transport (MEBT) line. Space restrictions in the MEBT line place constraints on component length and drive the requirement to identify compact component configurations. Two candidate re-bunching RF cavity designs are considered: the space efficient Drift Tube Linac type (DTL) with integrated quadrupoles, and the high shunt impedance Coupled Cavity Linac type (CCL) with external quadrupoles. Preliminary RF simulations in 2D and 3D are presented, and a comparison, emphasising the advantages and disadvantages of each design is made. The compact hybrid quadrupole configurations considered are the 'tandem' combination of permanent magnet (PMQ) and electro-magnetic (EMQ) types, and the concentric combination of PMQ and laminar conductor (Lambertson) EMQ types. The suitability of the compact hybrid quadrupole for implementation in the low energy Drift Tube Linac (DTL) is suggested and discussed.  
 
THP030 Investigation of Ferroelectrics for High-Power RF Phase Shifters in Accelerator Systems simulation, vacuum, SNS, klystron 637
 
  • Y. W. Kang, J. L. Wilson
    ORNL, Oak Ridge, Tennessee
  • A. E. Fathy
    University of Tennessee, Knoxville, Tennessee
  High power vector modulators enable independent control of RF power to each accelerating cavity, allowing a fan-out configuration to be used to power many cavities from a single high-power klystron. Previously, ferrite materials have been used in high-power phase shifters and vector modulators. It is shown that ferroelectric materials such as barium-strontium titanate (BST) can also be used in such tunable structures. Since ferroelectrics are controlled by an electric, rather than magnetic field, tuning can be faster than tuning a ferrite-loaded device. A BST-loaded coaxial structure is investigated theoretically and experimentally. Good high voltage performance is critical since DC biasing voltages of up to 80 kV can be impressed on the BST sections for tuning. It can also be seen that matching structures around the BST can improve performance over a wider range of amplitudes and phases.  
 
THP031 Pulse Cables For XFEL Modulators klystron, simulation, pulsed-power, radiation 640
 
  • H.-J. Eckoldt
    DESY, Hamburg
  For the XFEL, housed in a single tunnel, most of the modulators will be placed in a central modulator building outside of the tunnel. The pulse transformers and the klystrons will be positioned inside the tunnel near the superconducting linac. Therefore the energy has to be transported via pulse cables. These cables have lengths between 350m and 1.7 km. The power is up to 16.8 MW per pulse with a repetition rate of 10 Hz. In order to keep the rise time short and match the klystron impedance four 25Ohm cables will be put in parallel. A tri-axial design was chosen to prevent magnetic field outside of the cables in order not to disturb electronics or electron beam. A prototype of the cable was produced in industry and delivered to DESY. A set of four 1.5km long parallel cables is in test at present at one of the modulators of the TTF/VUV-FEL at DESY. The cable design criteria and test results are presented in this paper.  
 
THP034 Effective Standing-Wave RF Structure for Charged-Particle Beam Deflector RF-structure, linac, coupling, simulation 649
 
  • V. V. Paramonov, L. V. Kravchuk
    RAS/INR, Moscow
  • S. A. Korepanov
    DESY Zeuthen, Zeuthen
  In this report we describe new standing wave pi-mode rf structure for charged particles deflection. For L-band frequency range parameters of the proposed structure are compared with classical TM110 mode deflecting cavity ones. With originating TE11n mode, our proposal has several times higher rf efficiency, one order wider pass-band and smaller (in times) transverse dimensions. The cavity design idea and typical are parameters are presented. Some particularities of the beam dynamics in the proposed structure are pointed out. Preferable field of structure application is discussed.  
 
THP053 Simulations and Optimizations of a New Power Coupler for 3.9-GHz Superconducting Cavities at Fermilab simulation, electron, coupling, cryogenics 701
 
  • J. Li, I. G. Gonin, T. K. Khabiboulline, D. O. Olis, N. Solyak
    Fermilab, Batavia, Illinois
  • T. Wong
    Illinois Institute of Technology, Chicago, Illinois
  3.9 GHz third harmonic superconducting cavities have been used to increase the peak bunch current and to compensate for non-linear distortions in the longitudinal phase space due to sinusoidal 1.3 GHz accelerating cavity voltage. The power coupler is one of the important and complicated components of the third harmonic system for the TTF3 project. From electromagnetic, multipacting, and thermal simulations of the power coupler, optimized designs have been achieved, enabling one to minimize or eliminate potential problems in advance. This paper presents our recent work on simulation and optimization of the power coupler.  
 
THP057 Design of Normal Conducting 325-MHz Crossbar H-Type Resonators at Femirlab linac, lattice, focusing, vacuum 710
 
  • L. Ristori, I. G. Gonin, T. K. Khabiboulline, G. Romanov
    Fermilab, Batavia, Illinois
  The warm section of the proposed High Intensity Neutrino Source at Fermilab is designed to accelerate H- ions and protons from 2.5 MeV to 10 MeV (β=0.0744 to β=0.1422). After the ion source, the beam will travel through a radio frequency quadrupole, a medium energy beam transport (two buncher cavities and a chopper) and finally 16 normal-conducting resonators, all separated by superconducting solenoids in individual cryostats. Over 10 MeV the design uses superconducting resonators and solenoids in common cryomodules. In this paper the electromagnetic design and optimization of all the 325 MHz Crossbar H-type normal-conducting resonators is presented. The mechanical design, performance and fabrication of the first prototype (β=0.0744) is presented in detail. The design of the prototype for the input coupler that will be used in the resonators is included.  
 
THP078 High-Gradient Test of a Tungsten-Iris X-Band Accelerator Structure at NLCTA vacuum, linear-collider, collider, RF-structure 764
 
  • S. Doebert, A. Grudiev, S. T. Heikkinen, J. A. Rodriguez, I. Syratchev, M. Taborelli, W. Wuensch
    CERN, Geneva
  • C. Adolphsen, L. Laurent
    SLAC, Menlo Park, California
  The CLIC study group at CERN has built two X-band accelerating structures to be tested at SLAC in NLCTA. The structures consist of copper cells with insert irises made out of Molybdenum and Tungsten, clamped together and installed in a vacuum tank. These structures are exactly scaled versions from structures tested previously at 30 GHz and with short pulses (16 ns) in the CLIC Test Facility at CERN. At 30 GHz these structures reached gradients of 150 MV/m for Tungsten and 195 MV/m for Molybdenum. These experiments were designed to provide data on the dependence of rf breakdown on pulse length and frequency. This paper reports in particular on the high-gradient test of the tungsten-iris structure. At a pulse length of 16 ns a gradient of 125 MV/m was reached at X-band, 20 % lower than the 150 MV/m measured at 30 GHz in the CLIC Test Facility. The pulse length dependence and the dependence of the break down rate as a function of gradient were measured in detail. The results are compared to data obtained from the Molybdenum-Iris experiment at X-band which took place earlier as well as to 30 GHz data.  
 
THP087 Status of C-band Accelerating Section Development at the KEKB Injector Linac linac, klystron, positron, acceleration 788
 
  • T. Kamitani, T. Higo, M. Ikeda, K. Kakihara, N. K. Kudo, S. Ohsawa, T. Sugimura, T. T. Takatomi, K. Yokoyama
    KEK, Ibaraki
  This paper reports on C-band accelerating section development for future energy upgrade of the KEKB injector linac. Target field gradient is 42 MV/m, that is twice of the present S-band sections in the linac. Until now, we have developed four 1m-long sections based on a half-scale design of the S-band section with improvements in coupler cavity shape and in fabrication method. And the fifth accelerating section is in fabrication now. The four sections have already installed in the beam line of the linac. Together with a unit of C-band rf source (50 MW klystron, pulse modulator, rf-pulse compressor) installed in the linac, we will perform an operation test of a model C-band accelerator module that has almost same configuration as a design module in the upgrade. Results of the long-term operation test and beam acceleration study will be described. And present status of development of the fifth accelerating section will also be given.  
 
FR2003 New Materials and Designs for High-Power, Fast-Phase Shifters klystron, linac, resonance, rfq 829
 
  • R. L. Madrak, D. Sun, D. Wildman
    Fermilab, Batavia, Illinois
  • E. E. Cherbak, D. Horan
    ANL, Argonne, Illinois
  In the 100 MeV H- Linac to be constructed at Fermilab, the use of fast ferrite high power phase shifters will allow all accelerating RF cavities to be driven by a single 2.5 MW, 325 MHz klystron. This results in substantial cost savings. The tuners are coaxial with aluminum doped Yttrium Iron Garnet (YIG) ferrite. In combination with a branch line couplers, they will provide independent phase and amplitude control for each cavity. This is achieved by adjusting the solenoidal magnetic field applied to the ferrite. We report on our results in both low power (timing) and high power tests, for both 3'' and 1-5/8'' OD phase shifters. The low power measurements demonstrate that the rate of phase shift is well within the spec of 1 degree/us. The high power tests were performed at the Advanced Photon Source at Argonne National Lab. We measured phase shifts and the failure point (applied power) for tuners in various configurations. In addition, we performed phase and amplitude measurements for a setup consisting of a 1-5/8'' OD phase shifter along with a prototype branch line coupler.