07 Accelerator Technology

T07 Superconducting RF

 
Paper Title Page
MOPCH139 Results and Experience with Single Cavity Tests of Medium Beta Superconducting Quarter Wave Resonators at TRIUMF 375
 
  • V. Zviagintsev, K. Fong, M.P. Laverty, R.E. Laxdal, A.K. Mitra, T.C. Ries, I. Sekachev
    TRIUMF, Vancouver
 
  A heavy ion superconducting linac is being installed at ISAC/TRIUMF. A first stage of the ISAC-II upgrade will see the installation of 20 quarter wave bulk niobium cavities (Beta0=0.057,0.071). The cavities operate CW at 106MHz with design peak fields of Ep=30MV/m, Bp=60mT while delivering an accelerating voltage of 1.08MV at <7W power consumption. All cavities have been tested in a single cavity test stand with twenty of twenty-one meeting ISAC-II specifications. The cavity test results will be presented. In particular we will discuss our experience with BCP vs. EP surface treatments and with Q-disease. In addition the tuning plates of two of the cavities were modified to provide a unique compensation to the resonant frequency.  
MOPCH140 Compensation of Lorentz Force Detuning of a TTF 9-cell Cavity with a New Integrated Piezo Tuner 378
 
  • G. Devanz, P. Bosland, M. Desmons, E. Jacques, M. Luong, B. Visentin
    CEA, Gif-sur-Yvette
 
  The high gradient operation of superconducting elliptical multicells in pulsed mode is required for linear colliders or free-electron lasers based on the superconducting technology. Such an operation is limited by dynamic Lorentz force detuning if no compensation for this effect is attempted. The RF power headroom required for accelerating field amplitude and phase stabilisation by low-level RF control techniques solely would be too costly. A new active tuner with integrated piezo actuators has been developped in the framework of the european CARE/SRF program solve this issue. The design is based on the lever-arm concept of the Saclay tuner already installed on running TTF cavities. We have carried out integrated tests of the 9-cell cavity equipped with the piezo tuner and power coupler in the CryHoLab horizontal test cryostat. Characterisation of the electromechanical system consisting of the cavity and piezo-tuner assembly and full power pulsed tests will be presented.  
MOPCH141 Fast Argon-Baking Process for Mass Production of Niobium Superconducting RF Cavities 381
 
  • B. Visentin, J.-P. Charrier, Y. Gasser, S. Regnaud
    CEA, Gif-sur-Yvette
 
  Baking is a necessary stage to reach high gradients with niobium superconducting cavities. In the standard process, so called "in-situ UHV baking", Nb cavity is baked at 110°C, during 2 days. During this treatment the inner part of the cavity is pumped out under Ultra High Vacuum conditions. In order to save time, "fast UHV baking" at 145 °C during 3 hours, under UHV pumping, has been successfully demonstrated* with similar improvements for cavity performances compare to the standard treatment. With the same simplification concern, we report here about an alternative method to avoid restrictive UHV requirements. Experiments have been carried out to perform "fast baking" in oxygen-free atmosphere, because bad performances have been observed with "fast baking" in air. These degradations are closely connected with a strong oxygen penetration in bulk analysed by Secondary Ion Mass Spectroscopyon on Nb samples .

*Proceedings of SRF Workshop – Ithaca (July 2005) – TuP05.

 
MOPCH142 Commissioning of the SOLEIL RF Systems 384
 
  • P. Marchand, H.D. Dias, M.D. Diop, M.E. El Ajjouri, J.L. Labelle, R.L. Lopes, M. Louvet, C.M. Monnot, J. Polian, F. Ribeiro, T. Ruan, R.S. Sreedharan, K. Tavakoli, C. Thomas-Madec
    SOLEIL, Gif-sur-Yvette
  • P. Bosland, P. Bredy
    CEA, Gif-sur-Yvette
 
  The 352 MHz RF accelerating systems for the SOLEIL Booster (BO) and Storage Ring (SR) are being commissioned. In the BO a 5-cell copper cavity of the CERN-LEP type is powered with a 35kW solid state amplifier. In the SR the required RF accelerating voltage (up to 4.4MV) will be provided by two cryomodules, each containing a pair of superconducting cavities, specifically designed for SOLEIL. The parasitic impedances of the high order modes are strongly attenuated by means of four coaxial couplers, located on the tube connecting the two cavities. The first cryomodule is already installed in the SR tunnel, while the second one is being constructed by ACCEL (Germany). These cryomodules are supplied in liquid helium from a single 350W liquefier and each cavity is powered with a 190kW solid state amplifier. The RF system commissioning and first operation results are reported.  
MOPCH143 Electromechanical Characterization of Piezoelectric Actuators Subjected to a Variable Preloading Force at Cryogenic Temperature 387
 
  • M. Fouaidy, N. Hammoudi, M.S. Saki, H. Saugnac, L. Simonet
    IPN, Orsay
 
  Piezoelectric actuators are actually used in Fast Active Cold Tuning Systems (FACTS) for SRF cavities. The characteristics, performances and lifetime of these actuators depend on the preloading force applied by the cavity and the FACTS to the piezostacks. Experimental data are needed for reliable and optimum operation of piezostacks in superconducting protons or electrons linacs. In the frame of the CARE project supported by EU, we designed and constructed a dedicated apparatus for studying the electromechanical behavior of prototype piezoelectric actuators subjected to variable preloading force at cryogenic temperatures. This device was successfully used for testing piezoelectric actuators prototypes for T in the range 2K-300K. The dielectric properties as well as dynamic properties were measured including the actuator characteristics when used as force sensor. The corresponding data are reported and discussed.  
MOPCH144 Low Temperature Properties of Piezoelectric Actuators Used in SRF Cavities Cold Tuning Systems 390
 
  • G. Martinet, S. Blivet, F. Chatelet, M. Fouaidy, N. Hammoudi, A. Olivier, H. Saugnac
    IPN, Orsay
 
  High accelerating gradients (10 MV/m for SNS, 33 MV/m for ILC) at which SRF cavities will be operated in pulsed machines induce frequency shift much higher than the resonator bandwidth. This so-called Lorentz detuning should be compensated dynamically by means of an active piezo-tuning system. In the frame of the CARE project activities supported by EU, IPN Orsay participates to the development of a fast cold tuning system based and piezoelectric technology for SRF cavities operating at temperature T=2K. The aim of this study is the full characterization of piezoelectric actuators at low temperature including dielectric properties (capacitance, impedance, dielectric losses), radiation hardness tests (fast neutron tolerance), mechanical measurements (maximum displacement, maximum stroke) and thermal properties (heating, heat capacity). Results obtained in the temperature range from 2K up to 300K will be presented and discussed.  
MOPCH145 Tests Results of the Beta 0.07 and Beta 0.12 Quarter Wave Resonators for the SPIRAL2 Superconducting Linac 393
 
  • G. Olry, J.-L. Biarrotte, S. Bousson, C. Joly, T. Junquera, J. Lesrel, G. Martinet, D. Moura, H. Saugnac, P. Szott
    IPN, Orsay
  • P.-E. Bernaudin, P. Bosland, G. Devanz
    CEA, Gif-sur-Yvette
 
  New developments and tests have been carried out on low beta (0.07) and high beta (0.12) 88 MHz superconducting Quarter Wave Resonators. These resonators will be installed in the LINAC driver, respectively in the low beta section, composed of cryomodules A (developed at CEA-Saclay) and the high beta section composed of cryomodules B (developed at IPN-Orsay). Both resonators' types will be equipped with the same power coupler (developed at LPSC-Grenoble) and designed for a maximum power of 20 kW. RF tests results of the prototype cavities and power couplers are reported. The fabrication of the two cryomodules prototypes, fully equipped, is in progress in order to be ready for high power RF tests at 4.2 K at the beginning of 2007.  
MOPCH146 Status of the Beta 0.12 Superconducting Cryomodule Development for the Spiral2 Project 396
 
  • H. Saugnac, J.-L. Biarrotte, S. Blivet, S. Bousson, C. Commeaux, C. Joly, T. Junquera, J. Lesrel, fl. Lutton, G. Martinet, G. Olry, P. Szott
    IPN, Orsay
 
  SPIRAL2 is a radioactive beams facility, composed of a superconducting linac driver, delivering deuterons with an energy up to 40 MeV (5 mA) and heavy ions with an energy of 14.5 MeV/u (1 mA). This facility is now fully approved by the French government. IPN Orsay is in charge of the study and manufacture of the beta 0.12 cryomodule of the superconducting LINAC. These cryomodule, designed for an overall cryogenic power of 30 W at 4.2 K, is composed of two quarter wave type 88 MHz rf resonator providing a minimum of 6.5 MV/m with a quality factor of 1 10 9, two tuning mechanisms controlling the resonator frequency and an alignment system allowing to adjust the cavity position with a ± 1 mm accuracy. Several tests performed on a first resonator prototype fabricated by the "Ettore Zanon SpA" Company, have validated the cavity and its auxiliary components design. A first cryomodule fully equipped (cavities, cryostat, tuning and alignment systems), planned to be tested at the beginning of 2007, is under manufacturing. The details of the cryomodule design and the resonator tests results are discussed in the paper.  
MOPCH147 Developments in Conditioning Procedures for the TTF-III Power Couplers 399
 
  • H. Jenhani, T. Garvey, P. Lepercq, M. Omeich, C.P. Prevost, V. Variola
    LAL, Orsay
 
  Despite extensive experience in many laboratories on power conditioning of couplers for RF superconducting accelerators, it is still not a well understood procedure and can produce many unpredictable phenomena. There remains considerable interest in reducing the power coupler conditioning time necessary for superconducting linear accelerators. This paper presents studies of optimisation of the conditioning procedure for the couplers intended for use on the European XFEL project.  
MOPCH148 First RF Tests in the HoBiCaT Superconducting Test Facility at BESSY 402
 
  • O. Kugeler, W. Anders, J. Borninkhof, H.G. Hoberg, S. Klauke, J. Knobloch, M. Martin, G. Mielczarek, A. Neumann, D. Pflückhahn, S. Rotterdam, M. Schuster, T. Westphal
    BESSY GmbH, Berlin
 
  In preparation for the construction of the BESSY-FEL User Facility, BESSY recently completed the installation of the HoBiCaT cryogenic test facility for superconducting RF (SRF) TESLA cavity units, including all ancillary devices (helium tank, input coupler, tuner, magnetic shielding). It is designed to house two such units in a configuration similar to that envisaged for the superconducting CW linac of the BESSY FEL. Commissioning of the facility is now complete and the first TTF-III RF coupler and cavity unit have been tested. In particular, the complete production, cleaning and assembly of the cavity unit was carried out by industry. These tests thus serve as a first step at qualifying industrial partners for series production of such systems, which will be essential for the future construction of SRF based light sources. Results will be presented.  
MOPCH149 Microphonics Measurements in a CW-driven TESLA-type Cavity 405
 
  • O. Kugeler, W. Anders, J. Knobloch, A. Neumann
    BESSY GmbH, Berlin
 
  Superconducting cavities with a high quality factor exhibit a very low bandwidth in their resonant frequency, which makes their operation very sensitive to mechanical oscillations. In CW mode of operation, as is intended for the BESSY-FEL Linac, microphonics are therefore the dominant error source for field stability. In order to compensate the detuning, it is necessary to properly characterize amplitude and frequency with respect to all involved mechanical and electrical components. Such measurements have been performed at the HoBiCaT test facility at BESSY and will be described in detail.  
MOPCH150 Characterization of a Piezo-based Microphonics Compensation System at HoBiCaT 408
 
  • A. Neumann, W. Anders, S. Klauke, J. Knobloch, O. Kugeler, M. Schuster
    BESSY GmbH, Berlin
 
  In the superconducting driver linac for the BESSY FEL, piezo actuators will be utilized to rapidly counteract the detuning of the cavity resonance caused by nm mechanical oscillations (microphonics). This is of importance to guarantee field stability and lower the power consumption of the RF system for the superconducting cavities. To design a suitable compensator, mechanical and electro-mechanical transfer functions, as well as the tuning range of the system under operating conditions have been measured and will be presented.  
MOPCH151 Pulsed RF System for the ELBE Superconducting Accelerator 411
 
  • A. Buechner, F.G. Gabriel
    FZR/FWFE, Dresden
  • H. Buettig, U. Lehnert, P. Michel, Ch. Schneider, R. Schurig
    FZR, Dresden
 
  The RF system for the ELBE accelerator was originally designed for CW mode. Although this works problem-free tests have shown that it is possible to reach higher gradients in the TESLA cavities with a pulsed RF system. The new RF system will be presented together with measurements of the achievable gradients. Roughly 30% higher gradients could now be used in pulsed mode. As positive side effects the radiation by field emission is reduced by the duty cycle and an easy in situ RF conditioning of cavities and coupler windows is possible.  
MOPCH152 A Pulsed-RF High-power Processing Effect of Superconducting Niobium Cavities observed at the ELBE Linear Accelerator 413
 
  • U. Lehnert, H. Buettig, P. Michel, Ch. Schneider, R. Schurig
    FZR, Dresden
  • A. Buechner, F.G. Gabriel
    FZR/FWFE, Dresden
 
  The driver LINAC of the ELBE radiation source is built for cw operation. However, in some cases a pulsed-mode operation was desired to extend the otherwise stringent gradient limits. The main restriction results from field emission that decreases the Q of the cavities which was evaluated from measurements of the liquid helium consumption. After pulsed-mode operation with gradients exceeding the maximum cw accelerating gradients by 30–40\% a significant reduction in the field emission was observed. This in turn allows higher accelerating gradients to be used in cw as well. We attribute this behaviour to an rf-processing of the cavity surface which burns off field emitters.  
MOPCH153 Peak Field Optimization for the Superconducting CH Structure 415
 
  • H. Liebermann, H. Podlech, U. Ratzinger
    IAP, Frankfurt-am-Main
 
  The Cross-Bar H-type (CH) cavity is a multi-gap drift tube structure operated in the H-210 mode which has been developed at the IAP Frankfurt and in collaboration with GSI. Based on detailed numerical simulations a 19 cell prototype cavity from massive Nb was realised. For optimization of the magnetic and electric peak fields, detailed numerical simulations with CST MicroWave Studio have been performed. After successful experiments on the superconducting prototype cavity calculations about improved drift tube geometries with respect to field emission took place. Additionally, the stem geometry was further improved by simulations.  
MOPCH154 Dry-ice Cleaning on SRF Cavities 418
 
  • A. Brinkmann, J.I. Iversen, D. Reschke, J. Ziegler
    DESY, Hamburg
 
  High pressure rinsing with ultra-pure water is the well-proven standard cleaning step after chemical or electrochemical surface treatment of SRF cavities. Dry-ice cleaning (DIC) is a powerful additional cleaning option which depends on the sublimation-impulse method. Particles and film contaminations, especially hydro-carbons, are removed without residues. Furthermore DIC offers the possibility of a final horizontal cleaning of a fully equipped cavity because water is not present in the cleaning process. Horizontal cleaning tests on single-cell cavities showed promising high gradient, high Q-value performances, but field emission is still the limiting effect. On the basis of these tests a new IR-heater module is installed to keep a high temperature gradient between the CO2 jet and the cavity surface. New test results for this optimized cleaning set-up will be presented.  
MOPCH155 Performance Limitations of Tesla Cavities in the Flash Accelerator and their Relation to the Assembly Process 421
 
  • L. Lilje
    DESY, Hamburg
 
  Several accelerator modules with superconducting cavities have been assembled for TTF. The paper reviews the performance of these structures and will try to correlate their performance to information about the assembly process. In some cases a performace degradation could be attributed to problems in this process. The introduction of additional quality control steps improved accelerator module performance. For example, the more recently assembled modules have shown the expected acceleration gradients and no vacuum leaks.  
MOPCH157 Structural Analysis for a Half-reentrant Superconducting Cavity 424
 
  • E. Zaplatin
    FZJ, Jülich
  • T.L. Grimm, W. Hartung, M. J. Johnson, M.S. Meidlinger, J. Popielarski
    NSCL, East Lansing, Michigan
 
  A half-reentrant cavity (1300 MHz, beta=1.0) is being developed at Michigan State University for use in a superconducting linear collider and other applications. The electromagnetic performance of a half-reentrant cell shape is similar to that of a fully reentrant cavity, but a multi-cell half-reentrant cavity can be cleaned using traditional techniques. We present the results of structural analyses of the half-reentrant cavity for the mid-cell, single-cell, and multi-cell cases. The analysis includes the static and dynamic response of the cavity. Stiffening options to minimize the resonant RF frequency shift due to pressure and the Lorentz force are explored.  
MOPCH158 HIPPI Triple-spoke Cavity Design 427
 
  • E. Zaplatin, M. Pap, R. Tölle
    FZJ, Jülich
 
  In the frames of the European project of High Intensity Pulsed Proton Injector (HIPPI) the 352 MHz, beta=0.48 triple-spoke cavity is under development and will be built at the research center FZJ in Juelich. The criteria and results of the cavity RF and structural analyses are presented.  
MOPCH159 Coupler Design Considerations for the ILC Crab Cavity 430
 
  • P. Goudket, C.D. Beard
    CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire
  • G. Burt
    Microwave Research Group, Lancaster University, Lancaster
 
  Transverse deflecting cavities, such as the ILC crab cavity, commonly operate in the TM110 dipole mode. This means that in addition to the higher order modes (HOMs), that need to be controlled for every cavity, the fundamental TM010 mode and the other polarisation of the dipole mode also need to be damped. As the resonant frequency of the fundamental mode is much lower than the cut-off frequency of the beampipe, this mode becomes trapped in the cavity and difficult to extract using conventional HOM couplers, hence a dedicated coupler is likely to be required. The ILC crab cavities will require excellent damping of all undesirable modes in order to maintain maximum luminosity at the IP.  
MOPCH160 A Beam-based High Resolution Phase Imbalance Measurement Method for the ILC Crab Cavities 433
 
  • A. Kalinin, L. Ma, R.J. Smith
    CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire
 
  A high resolution method of RF phase adjustment and test is proposed for the Crab Cavity system of the ILC. The method is based on beam as ultimate test instrument. To measure phase imbalance in the pair of crab cavities (<0.02deg at 1.3GHz is required), a low energy (~1GeV) beam is used. A bunch center-of-mass trajectory through the cavities spaced (n+1/2) RF wavelengths and excited as in the case of the ILC, is a straight line for phase-balanced cavities and gets a kick when unbalanced. The kick is measured by two spaced BPMs with reference to the initial trajectory angle measured by two other BPMs. The method is insensitive to a bunch arrival time jitter and RF phase Common Mode jitter. A prototype of the test bench based on the method, is proposed. Using a 10MeV beam, two simple dipole cavities and low RF power, the prototype can be utilized for mastering high resolution measurements, for adjustment and tests of low level electronics of the Crab Cavity system and RF systems of XFEL ERLs as well. The phase resolution of the prototype is estimated as 0.01deg and the amplitude resolution as 0.01%.  
MOPCH161 Development of a Prototype Superconducting CW Cavity and Cryomodule for Energy Recovery 436
 
  • P.A. McIntosh, C.D. Beard, D.M. Dykes, B. Todd
    CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire
  • S.A. Belomestnykh
    Cornell University, Laboratory for Elementary-Particle Physics, Ithaca, New York
  • A. Buechner, P. Michel, J. Teichert
    FZR, Dresden
  • J.M. Byrd, J.N. Corlett, D. Li
    LBNL, Berkeley, California
  • T. Kimura, T.I. Smith
    Stanford University, Stanford, Califormia
  • M. Liepe, V. Medjidzade, H. Padamsee, J. Sears, V.D. Shemelin
    Cornell University, Ithaca, New York
  • D. Proch
    DESY, Hamburg
 
  Energy Recovery LINAC (ERL) and LINAC-driven FEL proposals and developments are now widespread around the world. Superconducting RF (SRF) cavity advances made over the last 10 years for TESLA/TTF at 1.3 GHz, in reliably achieving accelerating gradients >20 MV/m, suggest their suitability for these ERL and FEL accelerators. Typically however, photon fluxes are maximised from the associated insertion devices when the electron bunch repetition rate is as high as possible, making CW-mode operation at high average current a fundamental requirement for these light sources. Challenges arise in controlling the substantial HOM power and in minimizing the power dissipated at cryogenic temperatures during acceleration and energy recovery, requiring novel techniques to be employed. This paper details a collaborative development for an advanced high-Qo cavity and cryomodule system, based on a modified TESLA cavity, housed in a Stanford/Rossendorf cryomodule. The cavity incorporates a Cornell developed resistive-wall HOM damping scheme, capable of providing the improved level of HOM damping and reduced thermal load required.  
MOPCH162 RF Requirements for the 4GLS Linac Systems 439
 
  • P.A. McIntosh, C.D. Beard, D.M. Dykes, A.J. Moss
    CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire
 
  The 4GLS facility at Daresbury will combine energy recovery linac (ERL) and free electron laser (FEL) technologies to deliver a suite of naturally synchronised state-of-the-art sources of synchrotron radiation and FEL radiation covering the terahertz (THz) to soft X-ray regimes. CW-mode operation at high acceleration gradients are needed for the various 4GLS accelerator systems and here is where Superconducting Radio Frequency (SRF) cavities excel. Since resistive losses in the cavity walls increase as the square of the accelerating voltage, conventional copper cavities become uneconomical when the demand for high CW voltage grows with particle energy requirements. After accounting for the refrigeration power needed to provide the liquid helium operating temperature, a net power gain of several hundred remains for SRF over conventional copper cavities. This paper details the RF requirements for each of the SRF accelerating stages of the 4GLS facility, outlining techniques necessary to cope with CW-mode operation and HOM power generation.  
MOPCH163 Analysis of Wakefields in the ILC Crab Cavity 442
 
  • G. Burt, A.C. Dexter
    Microwave Research Group, Lancaster University, Lancaster
  • C.D. Beard, P. Goudket
    CCLRC/DL/ASTeC, Daresbury, Warrington, Cheshire
  • L. Bellantoni
    Fermilab, Batavia, Illinois
  • R.M. Jones
    UMAN, Manchester
 
  The large crossing angle schemes of the ILC need a correction of bunch orientation at the IP in order to recover a luminosity loss of up to 80%. The orientation of bunches can be changed using a transverse deflecting cavity. The location of the crab cavity would be close to the final focus, and small deflections caused by wakefields in the cavities could cause misalignments of the bunches at the IP. Wakefields in the FNAL CKM cavities have been analysed and their effects studied in view of use as the ILC crab cavity. Numerical simulations have been performed to analyse the transverse wakepotentials of up to quadrupole order modes in this cavity and the effect upon bunches passing through this cavity. Trapped modes within the CKM cavity have been investigated. Perturbation tests of normal conducting models of this cavity have been launched to verify these results. The effect of the final focus quadrupole magnets on the deflection given to the bunch have also been calculated and used to calculate luminosity loss due to wakefields.  
MOPCH164 Status of the Diamond Storage Ring Radio Frequency System 445
 
  • M. Jensen, M. Maddock, S.A. Pande, S. Rains, A. F. Rankin, D. Spink, A.V. Watkins
    Diamond, Oxfordshire
  • J. Alex, M. Mueller
    Thomson Broadcast & Multimedia AG, Turgi
  • B. A. Aminov
    CRE, Wuppertal
  • M. Pekeler
    ACCEL, Bergisch Gladbach
 
  The installation and commissioning of the Diamond Storage Ring RF system is nearing completion. Diamond will initially operate with two RF high power amplifiers and two cavities. The key components in each RF system are a 300 kW amplifier implemented through the combination of four 80 kW IOTs, a 500 MHz superconducting cavity providing up to 2 MV of accelerating voltage and an advanced analogue IQ Low Level RF (LLRF) system to control the cavity frequency, voltage and phase. We present here an update on the recent installation and early commissioning results of the RF systems.  
MOPCH165 Low- and Intermediate-beta, 352 MHz Superconducting Half-wave Resonators for High Power Hadron Acceleration 448
 
  • A. Facco, F. Scarpa, D. Zenere
    INFN/LNL, Legnaro, Padova
  • R. Losito
    CERN, Geneva
  • V. Zviagintsev
    TRIUMF, Vancouver
 
  A beta=0.17, 352 MHz superconducting Half-Wave resonator was designed and constructed at INFN-LNL in the framework of the SPES and EURISOL projects. This cavity, together with the beta=0.31 HWR of similar design that was previously built in the framework of the SPES project, allows acceleration of high power hadron beams in the 5?100 MeV/u energy range, as required in the SPES primary linac and in the first part of the EURISOL proton driver. Main features of this structure, compared to other ones developed elsewhere with different geometries for similar applications, are compactness and mechanical stability. Characteristics and test results will be presented.  
MOPCH166 Construction, Tuning and Assembly of the Beta=0.12 SC Ladder Resonator at LNL 451
 
  • G. Bisoffi, E. Bissiato, A. Palmieri
    INFN/LNL, Legnaro, Padova
 
  The Ladder resonator is a 4-gap full Nb cavity suitable for the 0.1< beta <0.2 range of high current proton linacs. A beta=0.12 Nb prototype of this cavity has been built by ZANON (Schio, Italy) on the basis of LNL design. In this paper we describe the construction procedure of such cavity, as well as the tuning steps, aimed at the achievement of the target frequency of 352.2 MHz and the desired field uniformity along the four gaps. Related results of RF simulations and room temperature tests are presented. The preparation of the SC test at LNL is at an advanced stage.  
MOPCH167 PBG Superconducting Resonant Structures 454
 
  • M.R. Masullo
    INFN-Napoli, Napoli
  • A. Andreone, E. Di Gennaro, F. Francomacaro, G. Lamura
    Naples University Federico II, Napoli
  • V. Palmieri, D. Tonini
    INFN/LNL, Legnaro, Padova
  • M. Panniello, V.G. Vaccaro
    Naples University Federico II and INFN, Napoli
 
  We have realized normal conducting and superconducting “open resonators” based on the Photonic Band Gap (PBG) concept. We present the study, the optimisation and the measurements (from room temperature to 1.5 K) of Copper and Niobium PBG accelerating cavities operating at two different frequencies, 6 GHz and 16 GHz. All the structures are realised by extruding a single bulk piece of material, using a new machining method that minimizes the surface losses caused by the contact between different conducting parts. Measurements on the compact (54 mm external diameter) 16 GHz Nb structure are very good, showing in the superconducting state a quality factor Q =1.2x105 at the lowest temperature (1.5 K), limited by radiation losses only. The shunt impedance measured for the 16 GHz prototype is 70 MOhm/m, underlining the applicability of such resonant structures as accelerating cavities.  
MOPCH168 Novel Development on Superconducting Niobium Film Deposition for RF Applications 457
 
  • A. Cianchi, L. Catani, D. D. Di Giovenale, J. Lorkiewicz
    INFN-Roma II, Roma
  • J. Langner, M. S. Sadowski, P. Strzyzewski
    The Andrzej Soltan Institute for Nuclear Studies, Centre Swierk, Swierk/Otwock
  • V. M. Merlo, M. Salvato, S. Tazzari
    Università di Roma II Tor Vergata, Roma
  • B.R. Ruggiero, R. Russo
    ICIB, Pozzuoli (NA)
 
  A new deposition technology has been developed, based on a cathodic arc system working under UHV conditions, to produce metallic thin films. The technique presents several advantages compared to standard sputtering, mainly: ionized state of the evaporated material, absence of gases to sustain the discharge, higher energy of atoms reaching the substrate surface, possibility to apply bias to the substrate and to guide the arc plasma using magnetic fields. Recent results on superconducting Niobium films deposited under several conditions and on sapphire substrate are reported. A cavity deposition system has been developed and the plasma transport to the cavity cell studied  
MOPCH169 High Pressure Rinsing Water Jet Characterization 460
 
  • D. Sertore, E. Cavaliere, M. Fusetti, P. Michelato, C. Pagani, P. Pierini
    INFN/LASA, Segrate (MI)
 
  High pressure rinsing is widely used as the final wet step in the high field superconducting cavities production. The interaction of an high speed ultra pure water jet with the niobium surface depends on various parameters such as water pressure, water throughput, treatment duration, cavity rotation speed, etc. In this paper we illustrate a simple technique for the characterization of water jet parameters based on the momentum transfer between the water jet and a load cell. The jet profile and its dependence on water pressure as well as the force exerted by the jet on the surface are easily measured. Moreover a portable apparatus has been set up and the information gathered in different laboratories will be used for a quantitative comparison of the different HPR systems. These measurements allow to study the correlation of the jet parameters with the effects (surface status, oxide formation, corrosion, etc) of the water interaction with the niobium surface. Furthermore a new analysis, based on the luminescence induced on transparent dielectric samples, is used for confirmation of the water jet structure.  
MOPCH170 Experimental and Theoretical Analysis of the Tesla-like SRF Cavity Flanges 463
 
  • L. Monaco, P. Michelato, C. Pagani, N. Panzeri
    INFN/LASA, Segrate (MI)
 
  In view of the future large SC accelerator, an improvement of the reliability and a cost reduction of the SRF cavities cold flanges is required. In this paper, a critical analysis of the TESLA-like cold connection flanges at room and at cryogenic temperature is presented. This analysis is based on experimental characterization of the mechanical properties of the joint and of the leak rates during the sealing process. A FEM model, that agrees with the experimental data, is also presented. This model is being used for the optimization of the present SRF flanges and the development of new cold connections.  
MOPCH171 ILC Coaxial Blade Tuner 466
 
  • C. Pagani, A. Bosotti, P. Michelato, N. Panzeri, R. Paparella, P. Pierini
    INFN/LASA, Segrate (MI)
 
  A coaxial (blade) tuner solution has been developed for the compensation of the Lorentz force detuning of the superconducting cavities under the high gradient pulsed operation foreseen for ILC operation. The device is based on prototypes successfully tested at DESY in 2002 both on CHECHIA and on the superstructures inserted in the TTF string. During both tests the blade tuner performed as expected in terms of stiffness, frequency sensitivity and tuning capabilities. An improvement of the tuner characteristics has been designed by the integration of fast tuning capabilities by means of piezo-ceramic element. Two prototipes of the new INFN coaxial piezo blade tuner have just been manufactured and they will be tested at DESY and BESSY after the cavity integration. In this paper the blade tuner design and main characteristics are presented, together with the early interpretation of the cold test results.  
MOPCH174 Optimization of the BCP Processing of Elliptical Nb SRF Cavities 469
 
  • C. Boffo, C. A. Cooper, A.M. Rowe
    Fermilab, Batavia, Illinois
  • G. Galasso
    University of Udine, Udine
 
  Bulk niobium (Nb) electropolished SRF cavities performing at or above 35 MV/m is an aggressive goal recently put forth by the International Linear Collider (ILC) collaboration. Buffered chemical polishing (BCP) is still the most cost effective and least complex processing technique known today to optimize the surface properties of high gradient single crystal and relatively low gradient polycrystalline SRF cavities. BCP will be the preferred chemical process in the production of the nine-cell third harmonic 3.9 GHz cavities at Fermilab. The internal shape of these cavities will result in uneven material removal rates between iris and equator of the cells. We will describe a thermal-fluid finite element model adopted to simulate the etching process, and thus revealing the issues at hand. Experimental work, such as flow visualization tests performed to verify the simulation, will also be discussed. Finally we are presenting results obtained with a novel device, which allows to homogenize the flow pattern and to resolve the problem.  
MOPCH175 High Power Testing RF System Components for the Cornell ERL Injector 472
 
  • S.A. Belomestnykh, R.P.K. Kaplan, M. Liepe, P. Quigley, J.J.R. Reilly, C.K. Sinclair, V. Veshcherevich
    Cornell University, Laboratory for Elementary-Particle Physics, Ithaca, New York
 
  There are two high power 1300 MHz RF systms under development for the Cornell University ERL Injector. The first system, based on a 16 kWCW IOT transmitter, will provide RF power to a buncher cavity. The second system employs five 120 kWCW klystrons to feed 2-cell superconducting cavities of the injector cryomodule. All components of these systems were ordered and some have already been delivered, including the IOT transmitter (manufactured by Thales-BM), 20 kWCW AFT circulator, 170 kWCW circulators (Ferrite Co.) and two prototype input couplers for superconducting cavities. A special LN2 cryostat has been designed and built for testing/processing the input couplers. The results of the first high-power tests are presented.  
MOPCH176 A Comparison of Large Grain and Fine Grain Cavities Using Thermometry 475
 
  • G.V. Eremeev, H. Padamsee
    Cornell University, Laboratory for Elementary-Particle Physics, Ithaca, New York
 
  An important limitation for SRF niobium cavities is the ”high field Q-slope.” To investigate this phenomenon we compare the behavior of large grain and fine grain cavities using thermometry. Thermometry allows us to distinguish between different problems which occur in cavities, and to distinguish between different areas showing high field Q-slope. We looked for the difference in heating between grain boundaries and inside grains. We have found interesting differences between the heating of high field slope regions and the heating of point-like defects.  
MOPCH177 Status of HOM Load for the Cornell ERL Injector 478
 
  • V.D. Shemelin, B. Gillett
    Cornell University, Ithaca, New York
  • P. Barnes, M. Liepe, V. Medjidzade, H. Padamsee, G.R. Roy, J. Sears
    Cornell University, Laboratory for Elementary-Particle Physics, Ithaca, New York
 
  The HOM load for the injector of the Energy Recovery Linac at Cornell University is proposed to work at a temperature of 80 K. The anticipated absorbed power of the load is up to 200 W. Versions with inner diameter of 78 and 106 mm are under development. Two different kinds of ferrites and a lossy ceramic are chosen as RF absorbers for the load to cover a wide frequency range. Measurements of electromagnetic properties of absorbing materials have been performed in a frequency range from 1 to 40 GHz. The engineering design of the load is ready and technological issues of brazing the absorbing tiles and cooling have been solved. Brazing quality is controlled by IR thermograms. First warm measurements of a prototype load are expected this summer.  
MOPCH178 Tests on MgB2 for Application to SRF Cavities 481
 
  • T. Tajima
    LANL, Los Alamos, New Mexico
  • I.E. Campisi
    ORNL, Oak Ridge, Tennessee
  • A. Canabal-Rey
    NMSU, Las Cruces, New Mexico
  • Y. Iwashita
    Kyoto ICR, Uji, Kyoto
  • B. Moeckly
    STI, Santa Barbara, California
  • C.D. Nantista, S.G. Tantawi
    SLAC, Menlo Park, California
  • H.L. Phillips
    Jefferson Lab, Newport News, Virginia
  • A.S. Romanenko
    Cornell University, Laboratory for Elementary-Particle Physics, Ithaca, New York
  • Y. Zhao
    University of Wollongong, Institute of Superconducting and Electronic Materials, Wollongong
 
  Magnesium diboride (MgB2) has a transition temperature (Tc) of ~40 K, i.e., about four times higher than niobium (Nb). The studies in the last three years have shown that it could have about one order of magnitude less RF surface resistance (Rs) than Nb and seems much less power dependent compared to high-Tc materials such as YBCO. In this paper we will present results on the dependence of Rs on surface magnetic fields and possibly the critical RF surface magnetic field.  
MOPCH179 Design of a New Electropolishing System for SRF Cavities 484
 
  • T. Tajima
    LANL, Los Alamos, New Mexico
  • C. Boffo
    Fermilab, Batavia, Illinois
  • M.P. Kelly
    ANL, Argonne, Illinois
  • J. Mammosser
    Jefferson Lab, Newport News, Virginia
 
  Electropolishing (EP) is considered the baseline surface treatment for Superconducting RF (SRF) cavities to achieve >35 MV/m accelerating gradient for the International Linear Collider (ILC). Based on the lessons learned at the forerunners such as KEK/Nomura, DESY and JLAB and on the recent studies, we have started a new design of the next EP system that will be installed in the US. This paper presents requirements, specifications, and the detail of the system design as well as the path forward towards the future industrialization.  
MOPCH181 1.3 GHz Electrically-controlled Fast Ferroelectric Tuner 487
 
  • V.P. Yakovlev
    Omega-P, Inc., New Haven, Connecticut
  • J.L. Hirshfield
    Yale University, Physics Department, New Haven, CT
  • S. Kazakov
    KEK, Ibaraki
 
  A fast, electrically-controlled tuner is described with parameters suitable for operation with the 9-cell SC accelerator structure of ILC. The tuner is based on a magic tee and two phase shifters that contain ferroelectric rings. The dielectric constant of the ferroelectric ring is altered by applying a 4.2 kV DC pulse that provides an RF phase shift from 0 deg to 180 deg. This, in turn allows a change of the input signal amplitude from zero to its maximum value, or a change in phase from 0 deg to 360 deg during the RF pulse. It is shown that the possibility of changing the cavity coupling to the input line during the RF pulse allows significant RF power savings, up to 12.5 MW for the 800 GeV ILC option. In addition, fast electrically-tuned amplitude and phase control with a feed-back system should be useful to compensate for possible phase deviations of the input RF fields in each cavity of ILC to match the cavity with the feeding transmission line as the beam load varies.  
MOPCH182 The JLAB Ampere-class Cryomodule Conceptual Design 490
 
  • R.A. Rimmer, G. Ciovati, E. Daly, T. Elliott, J. Henry, W.R. Hicks, P. Kneisel, S. Manning, R. Manus, J.P. Preble, K. Smith, M. Stirbet, L. Turlington, L. Vogel, H. Wang, K. Wilson, G. Wu
    Jefferson Lab, Newport News, Virginia
 
  For the next generation of compact high-power FELs a new cryomodule is required that is capable of accelerating up to Ampere levels of beam current. Challenges include strong HOM damping, high HOM power and high fundamental-mode power (in operating scenarios without full energy recovery). For efficient use of space a high real-estate gradient is desirable and for economic operation good fundamental-mode efficiency is important. The technology must also be robust and should be based on well-proven and reliable technologies. For Ampere-class levels of beam current both halo interception and beam break-up (BBU) are important considerations. These factors tend to drive the designs to lower frequencies where the apertures are larger and the transverse impedances are lower. To achieve these goals we propose to use a compact waveguide-damped multi-cell cavity packaged in an SNS-style cryomodule.  
MOPCH184 Plasma Treatment of Bulk Niobium Surfaces for SRF Cavities 493
 
  • L. Vuskovic, S. Popovic, M. Raskovic
    ODU, Norfolk, Virginia
  • L. Godet, S.B. Radovanov
    VSEA, Gloucester, Maryland
  • H.L. Phillips, A-M. Valente-Feliciano
    Jefferson Lab, Newport News, Virginia
 
  Cavity surface preparation has been one of the major problems in superconducting radio-frequency (SRF) accelerator technology. Accelerator performance depends directly on the physical and chemical characteristics at the SRF cavity surface. The primary objective of our work is to explore the effects of various types of electric discharge plasmas to minimize surface roughness and eliminate or minimize deterioration of cavity properties by oxygen, hydrogen and other chemical contaminants. To optimize the plasma etching process, samples of bulk Nb are being exposed to three types of electrical discharge in various experimental set-ups. The surface quality obtained by the three methods was compared with samples treated with buffer chemical polishing techniques. Surface comparisons are made using digital imaging (optical) microscopy, scanning electron microscopy, and atomic force microscopy. In preliminary tests, samples compared with those treated conventionally have shown comparable or superior properties. Tests have also shown that surface quality varies with plasma conditions and their optimization to obtain the best SRF cavity surface is a major goal of the ongoing work.  
WEXPA01 Latest Developments in Superconducting RF Structures for Beta=1 Particle Acceleration 1837
 
  • P. Kneisel
    Jefferson Lab, Newport News, Virginia
 
  Superconducting RF technology is since nearly a decade routinely applied to different kinds of accelerating devices: linear accelerators, storage rings, synchrotron light sources and FEL's. With the technology recommendation for the International Linear Collider (ILC) a year ago, new emphasis has been placed on improving the performance of accelerating cavities both in Q-value and in accelerating gradients with the goal to achieve performance levels close to the fundamental limits given by the material parameters of the choice material, niobium. This paper will summarize the challenges to SRF technology and will review the latest developments in superconducting structure design. Additionally, it will give an overview of the newest results and will report on the developments in alternative materials and technologies.  
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THPCH176 Deposition of Lead Thin Films Used as Photo-cathodes by Means of Cathodic Arc under UHV Conditions 3209
 
  • P. Strzyzewski, J. Langner, M. S. Sadowski, J. Witkowski
    The Andrzej Soltan Institute for Nuclear Studies, Centre Swierk, Swierk/Otwock
  • T. Rao, J. Smedley
    BNL, Upton, Long Island, New York
  • R. Russo, S. Tazzari
    Università di Roma II Tor Vergata, Roma
  • J.S. Sekutowicz
    DESY, Hamburg
 
  The cathodic arc technology has been used for various technical purposes for many years. Recently, it has been demonstrated that the cathodic arc can be operated under ultra-high vacuum (UHV) conditions and it might solve the problem of the oxygen contamination coming from water remnants. It opens a new road to many applications where very pure metallic and/or superconducting films are needed. The paper reports on recent experimental studies aimed on the deposition of superconducting films of pure lead (Pb) by means of the UHV cathodic arc. Such layers can be used as photo-cathodes needed for modern accelerator injectors. The system configuration, used for thin film deposition inside the RF Gun designed at DESY, is also described and the main results and characteristics of thin superconducting Pb-films are presented.