A   B   C   D   E   F   G   H   I   K   L   M   N   O   P   Q   R   S   T   U   V   W  

coupling

Paper Title Other Keywords Page
MOP002 A High Phase Advance Damped and Detuned Structure for the Main Linacs of CLIC dipole, wakefield, beam-loading, HOM 49
 
  • R.M. Jones, A. D'Elia, V.F. Khan
    UMAN, Manchester
  • A. Grudiev, W. Wuensch, R. Zennaro
    CERN, Geneva
 
 

We report on the suppression of long-range wakefields in the main linacs of the CLIC collider. The wakefield is damped using a combination of detuning the frequencies of beam-excited higher order modes and by light damping, through slot-coupled manifolds. This unique accelerator, in the process of being fabricated, will be the first structure to demonstrate wakefield damping and the ability to sustain high accelerating gradients for CLIC. This serves as an alternative to the baseline CLIC design, which at present relies entirely on heavy damping. Detailed simulations are presented, on both the optimised surface fields resulting from the monopole mode, and from wakefield damping of the dipole modes. Preparations for the fabrication of a structure, suitable for high power testing, are also discussed. This design takes into account practical mechanical engineering issues and is the result of several optimisations since the original CLICDDS proposal[*].


*V.F. Khan and R.M. Jones, Presented at Particle Accelerator Conference (PAC 09), Vancouver, BC, Canada, 4-8 May 2009.

 
MOP021 Compensation of Transient Beam-Loading in the CLIC Main Linac linac, beam-loading, impedance, injection 94
 
  • A. Grudiev, A. Cappelletti, O. Kononenko
    CERN, Geneva
 
 

Compensating transient beam loading to maintain a 0.01% relative beam energy spread is a key issue for the CLIC two-beam acceleration technique. The combination of short pulses, narrow bandwidth rf components and the limited number of rf pulse shaping 'knobs' given by the drive beam generation scheme makes meeting this specification challenging. A dedicated model, which takes into account all stages of drive beam generation, including the delay loop and combiner rings, the single-bunch response of the power generation structure (PETS), the RF waveguide network transfer function and dispersive properties of the accelerating structure has been developed. The drive beam phase switching delays, resulting rf pulse shape, loaded and unloaded voltages and finally the energy spread are presented.

 
MOP022 Tuning of CLIC Accelerating Structure Prototypes at CERN cavity, monitoring, target 97
 
  • A. Grudiev, A. Olyunin, J. Shi, W. Wuensch
    CERN, Geneva
 
 

An RF measurement system has been set up at CERN for use in the X-band accelerating structure development program of the CLIC study. Using the system, S-parameters are measured and the field distribution is obtained automatically by using a bead-pull technique. The corrections for tuning the structure are calculated from the result. Integrated software guides cell-by-cell tuning to obtain the correct phase advance and minimum reflection at the operation frequency. The detailed configuration of the system, as well as the semi-automatic tuning procedure, is presented along with a few examples of measurement and tuning of CLIC accelerating structure prototypes.

 
MOP025 ACE3P Computations of Wakefield Coupling in the CLIC Two-beam Accelerator wakefield, simulation, damping, linear-collider 106
 
  • A.E. Candel, K. Ko, Z. Li, C.-K. Ng, V. Rawat, G.L. Schussman
    SLAC, Menlo Park, California
  • A. Grudiev, I. Syratchev, W. Wuensch
    CERN, Geneva
 
 

The Compact Linear Collider (CLIC) provides a path to a multi-TeV accelerator to explore the energy frontier of High Energy Physics. Its novel two-beam accelerator concept envisions rf power transfer to the accelerating structures from a separate high-current decelerator beam line consisting of power extraction and transfer structures (PETS). It is critical to numerically verify the fundamental and higher-order mode properties in and between the two beam lines with high accuracy and confidence. To solve these large-scale problems, SLAC's parallel finite element electromagnetic code suite ACE3P is employed. Using curvilinear conformal meshes and higher-order finite element vector basis functions, unprecedented accuracy and computational efficiency are achieved, enabling high-fidelity modeling of complex detuned structures such as the CLIC TD24 accelerating structure. In this paper, time-domain simulations of wakefield coupling effects in the combined system of PETS and the TD24 structures are presented. The results will help to identify potential issues and provide new insights on the design, leading to further improvements on the novel CLIC two-beam accelerator scheme.

 
MOP026 A Novel Alignment Procedure for the Final Focus of Future Linear Colliders alignment, multipole, linear-collider, collider 109
 
  • A. Latina
    Fermilab, Batavia
  • P. Raimondi
    INFN/LNF, Frascati (Roma)
 
 

An algorithm for the simultaneous optimization of orbit, dispersion, coupling and beta-beating in the final focus of future linear colliders is presented. Based on orbit and dispersion measurements the algorithm determines the optimal corrector settings in order to simultaneously minimize the r.m.s orbit, the r.m.s dispersion, the r.m.s coupling, the r.m.s. beta-beating and the r.m.s strength of the dipoles correctors. A number of different options for error handling of beam position monitors, weighting, and correction have been introduced to ensure the stability of the algorithm. A sextupole tuning procedure is also applied to further optimize the beam parameters at the interaction point. Preliminary results for the beam delivery systems of CLIC are presented.

 
MOP032 Application of X-band Linac for Material Recognition with Two Fold Scintillator Detector linac, target, site, simulation 124
 
  • K. Lee, S. Hirai, M. Uesaka
    The University of Tokyo, Nuclear Professional School, Ibaraki-ken
  • E. Hashimoto
    JAEA, Ibaraki-ken
  • T. Natsui
    UTNL, Ibaraki
 
 

950 keV X-band Linac has the merits of compact system, and it does not need the radiation safety manager on-site in the public space. Therefore the system we have developed is suitable for the more safe circumstance in airport. Dual energy X-ray concept is introduced for material recognition with Linac these days, because it produce high energy X-ray which is available in case the target is thick and high atomic number material. We suggest two fold scintillator detector concept to induce dual energy X-ray effect. The design of two fold scintillator is decided by MCNP simulation with two scintillator code, CsI and CdWO4. The material recognition is confirmed using aluminium, iron and lead metal in conditions such as various thicknesses and containers.

 
MOP033 Low Energy RF Accelerator for Various Applications cavity, linac, gun, focusing 127
 
  • P.K. Ambattu, G. Burt, M.I. Tahir
    Cockcroft Institute, Lancaster University, Lancaster
  • P.A. Corlett, P.A. McIntosh, A.J. Moss
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire
 
 

Compact X-ray sources are integral parts of systems used in medical, industrial and security applications. The X-ray dose rate for a particular application mainly depends on the energy and current of the beam used to hit the target, usually made of tungsten. In applications that need higher penetration (100s of mm in steel), the beam energy needed is in the range of 1-5 MeV which can only be obtained using an RF linear accelerator. In order to reduce the size of the linac, higher RF frequencies (X-band) should be used while in order to reduce the overall bulk, RF focusing is employed instead of solenoidal focusing. Thus the main attraction of an X-band linac compared to a lower frequency version is the amount of lead required for shielding the system, and hence its weight. For capturing and bunching the low energy dc beam, a bunching section is needed in front of the main linac. The bunching cavity can either be a part of the main linac cavity or an independently powered section which can be used for certain specific applications as a shorter 1 MeV linac. In this paper, the design and simulations of an X-band buncher to be suitable for compact X-ray sources is presented.

 
MOP036 Beam Commissioning of C-band Standing-wave Accelerator for X-ray Source linac, cavity, gun, electron 136
 
  • H.R. Yang, M.-H. Cho, S.D. Jang, S.H. Kim, W. Namkung, S.J. Park
    POSTECH, Pohang, Kyungbuk
  • K.H. Chung, K. Lee
    KAPRA, Cheorwon
  • J.-S. Oh
    NFRI, Daejon
 
 

A C-band standing-wave electron linac for a compact X-ray source is now being commissioned at ACEP (Advanced Center for Electron-beam Processing in Cheorwon, Korea). It is designed to produce 4-MeV electron beam with pulsed 50-mA, using a 5-GHz RF power generated by a magnetron with pulsed 1.5 MW and average 1.2 kW. The accelerating structure is a bi-periodic and on-axis-coupled one operated with π/2-mode standing-waves. It is consisted of 3 bunching cells, 6 accelerating cells and a coupling cell. As a result of measurements, the beam energy is almost 4 MeV. In this paper, we present the design details and the commissioning status.

 
MOP051 RF Power Tests and Results of the First Rebuncher for the SPIRAL 2 Driver cavity, impedance, resonance, simulation 172
 
  • M. Lechartier, D. Besnier, R. Beunard, J.F. Leyge, M. Michel, P. Robillard, P. Toussaint
    GANIL, Caen
 
 

Three normal conducting rebunchers are located in the MEBT line of the SPIIRAL2 driver.  The cavity are designed for a beta of 0.04, work at 88 MHz and have to supply beam voltages up to 120 kV in continuous mode or up to 190 kV in  pulsed mode with 50%dutycycle. The  paper describes the  RF measurements and first results

 
MOP065 C-Band Magnetic Coupled Accelerating Structure Optimization impedance, HOM, simulation, insertion 202
 
  • S.V. Kutsaev, R.O. Bolgov, M. Gusarova, D.S. Kamenshikov, K.I. Nikolskiy, A.Yu. Smirnov, N.P. Sobenin, S.E. Toporkov
    MEPhI, Moscow
 
 

This paper presents the results of a research that analyzed the possibility of using a magnetic coupled disk-loaded structure (DLS-M) as an accelerating structure. DLS-M seems to have decent advantages comparing to the classical electrical coupled structure (DLS). The electrodynamics parameters of such a structure at various modes in C-band for a wide range of phase velocities as a function of aperture radii and coupling slot sizes are presented. Both forward and backward travelling wave regimes are considered. The essential parameters are compared to those of classical DLS. The design of an input coupler to the accelerator consisting of this type structure cells is also presented.

 
MOP071 The Hot Prototype of the PI-Mode Structure for Linac4 cavity, linac, proton, vacuum 220
 
  • F. Gerigk, P. Bourquin, A. Dallocchio, G. Favre, J.-M. Geisser, L. Gentini, J.-M. Giguet, S.J. Mathot, M. Polini, D. Pugnat, B. Riffaud, S. Sgobba, T. Tardy, P. Ugena Tirado, M. Vretenar, R. Wegner
    CERN, Geneva
 
 

The PIMS cavities for Linac4 are made of 7 coupled cells operating in pi-mode at 352 MHz frequency. The mechanical concept is derived from the 5-cell cavities used in the LEP machine, whereas cell length and coupling are adapted for proton acceleration in the range from 50 to 160 MeV. Linac4 will be the first machine to employ this type of cavities for low-beta protons. During the first years of operation the PIMS will be used at low duty cycle as part of the consolidated LHC proton injector complex. It is designed, however, to operate eventually in a high duty cycle (10%) proton injector, which could be used as proton front-end for neutrino or RIB applications. To prepare for the series construction of the 12 PIMS units the first cavity (102 MeV beam energy) has been designed and constructed at CERN, to be used as a hot prototype for RF tests and as a pre-series mechanical unit. In this paper we report on some of the design features, the construction experience, and first measurements.

 
MOP077 Design of RF Feed System for Standing-wave Accelerator Structures cavity, wakefield, vacuum, acceleration 235
 
  • J. Neilson, V.A. Dolgashev, S.G. Tantawi
    SLAC, Menlo Park, California
 
 

Typical surface damage in travelling wave accelerator structures occurs on the high field region of the iris. As the damage accumulates the coupling between cavities is affected resulting in changes in the phase shift between cells. This issue can be reduced by use of SW cells that are fed in parallel. RF breakdown is contained to the cell where it originates and the available electromagnetic energy for a given gradient is minimized by the parallel feed. Several schemes[1] have been proposed for parallel fed SW structures. Some of the proposed designs fed several cells from each arm, which reduces the advantage of localizing a RF breakdown to an individual cavity. In addition they use a standing wave in the feed arms which allows coupling between cells. We are proposing a somewhat more complex approach using a directional coupler on each cell and serpentine waveguide connection between couplers. This design approach isolates the cells and gives an individual rf feed to each cell resulting in the maximum increase in the operational robustness of the accelerator structure.


1. O. N. Brezhnev, P. V. Logatchev, V. M. Pavlov, O. V. Pirogov, S. V. Shiyankov,' Parallel-Coupled Accelerating Structures', Proceedings of LINAC 2002, Gyeongju, Korea, pg 215-217

 
MOP081 The PITZ CDS Booster Cavity RF Tuning and Start of Conditioning cavity, booster, vacuum, electron 241
 
  • V.V. Paramonov, A. Naboka
    RAS/INR, Moscow
  • A. Donat, L. Jachmann, W. Köhler, M. Krasilnikov, J. Meissner, D. Melkumyan, M. Otevrel, B. Petrosyan, J. Schultze, F. Stephan, G. Trowitzsch, R.W. Wenndorff
    DESY Zeuthen, Zeuthen
  • K. Flöttmann
    DESY, Hamburg
  • D. Richter
    HZB, Berlin
 
 

The DESY PITZ booster cavity, based on the Cut Disk Structure (CDS), is completed in construction. The L-band normal conducting cavity is intended to operate with accelerating rate up to 12.5 MV/m and RF pulse length up to 800 mks to increase the electron bunch energy in the PITZ facility at 20 MeV. The cavity was vacuum conditioned to reduce the out-gassing rate for operation in the facility with photo cathodes. The cavity is mounted in the PITZ tunnel and RF conditioning is started. The results of RF tuning before and after cavity brazing, together with first results of conditioning, are presented.

 
MOP099 Status of the Design of 650 MHz Elliptical Cavities for Project X cavity, linac, proton, beam-losses 289
 
  • S. Barbanotti, M.H. Foley, I.G. Gonin, J. Grimm, T.N. Khabiboulline, L. Ristori, N. Solyak, V.P. Yakovlev
    Fermilab, Batavia
 
 

Project X is a proposed high-intensity proton accelerator complex that could provide beam to create a high-intensity neutrino beam, feed protons to kaon- and muon-based precision experiments, and for other applications still under investigation. The present configuration of the proton accelerator foresees a section with 650 MHz beta = 0.6 and beta = 0.9 elliptical cavities. Prototypes of single-cell 650 MHz cavities and five-cell beta = 0.9 650 MHz cavities are being designed and fabricated at Fermilab in the R&D process for Project X. This paper summarizes the design status of the beta = 0.6 and beta = 0.9 single-cell prototype cavities, and also addresses the design effort focused on the five-cell beta = 0.9 cavities.

 
MOP105 Preparation of Adjustable Permanent Magnet Quadrupole Lens for Beam Test at ATF2 multipole, quadrupole, permanent-magnet, vacuum 307
 
  • S. Ushijima, H. Fujisawa, Y. Iwashita, H. Tongu
    Kyoto ICR, Uji, Kyoto
  • M. Masuzawa, T. Tauchi
    KEK, Ibaraki
 
 

A permanent magnet quadrupole lens with continuously adjustable strength originally designed by Gluckstern was fabricated for a final focus. It consists of five PMQ discs that rotate on their axis, where odd and even numbered discs rotate oppositely but with the same absolute angle. By setting their lengths appropriately, the coupling between x and y components can be minimized. In order to reduce multipole components higher than quadrupole, we adjust positions of magnet wedge pairs. At the same time we improve differences between the magnetic center and the mechanical center of the PMQ discs by measuring harmonics of fields in magnets. In order to carry out the beam test, a high precision movable table for the lens system is also fabricated. This table can evacuate the lens system from the beam line completely without vacuum breaking, which should ease the evaluation of the system at decreased strength region.

 
MOP113 Multipacting Simulation of the Demountable Damped Cavity cavity, simulation, electron, HOM 328
 
  • T. Konomi
    Sokendai, Ibaraki
  • F. Furuta, K. Saito
    KEK, Ibaraki
 
 

We have designed Demountable Damped Cavity (DDC) as an ILC R&D. DDC has an axial symmetric structure, the coaxial waveguide HOM coupler and absorber at the end of beam pipe of SRF cavity. It is also demountable structure. These structures are expected to bring better cavity performance. However, DDC have many parallel faced surfaces and the multipacting might be a concerned issue. We have simulated MP on the DDC with CST-Studio and found MP could be not serious issue. In this paper we will report the simulation result in detail.

 
TU201 Status of J-PARC Linac Energy Upgrade linac, klystron, cavity, injection 357
 
  • H. Ao
    JAEA/LINAC, Ibaraki-ken
 
 

The J-PARC (Japan Proton Accelerator Research Complex) accelerator comprises the 400-MeV injector linac (at present 181 MeV), the 3-GeV Rapid-Cycling Synchrotron (RCS) and the 50-GeV Main Ring (MR). The 3-MeV RFQ, the 50-MeV DTL and the 181-MeV Separated-type DTL have been operated in the linac for experimental users. The 400-MeV energy upgrade of the linac started from March 2009. The ACS (Annular Coupled Structure) cavities, the RF sources, the beam monitors and the utilities are in production. Although some components are prepared in the annual summer shutdown separately, the all cavities will be installed and commissioned for 6 months from July 2012. In this paper, we present the current status and the preliminary results of the energy upgrade.

 
TU302 Applications of Spoke Cavities cavity, linac, ion, superconducting-cavity 377
 
  • J.R. Delayen
    ODU, Norfolk, Virginia
 
 

Review of the theory, design and applications of Spoke cavities, with particular emphasis on SRF spoked cavities. Aspects of low level RF control for spoke cavities will also be presented.

 

slides icon

Slides

 
TUP001 Conceptual Design of the C-Band Module for SwissFEL klystron, cavity, wakefield, linac 392
 
  • R. Zennaro, J. Alex, M. Bopp, H.-H. Braun, A. Citterio, H. Fitze, M. Pedrozzi, J.-Y. Raguin
    PSI, Villigen
 
 

The Swiss FEL linac consists of a 450 MeV S-band injector and of a main linac at the C-band frequency (5.712 GHz) aiming at a final energy of 5.8 GeV. The main linac is composed of 26 RF modules. Each module consists of a single 50 MW klystron and its solid-state modulator feeding a pulse compressor and four accelerating structures. The two-meter long C-band accelerating structures have 110 cells, including the two coupler cells, and operate with a 2π/3 phase advance. We report here on RF studies performed on the accelerating structures with different cell topologies and on the pulse compressor where a Barrel-Open Cavity (BOC) design is adopted. The power requirements for the different accelerating structures with the single and two-bunch operation are also presented.

 
TUP017 The Resonant Method of Stabilization for Plane of Deflection in the Disk Loaded Deflecting Structures cavity, polarization, controls, linac 434
 
  • V.V. Paramonov, L.V. Kravchuk
    RAS/INR, Moscow
 
 

The hybrid HE11 mode in the cylindrical disk loaded deflectors is twice degenerated. To ensure operational performance and stabilize the position for the plane of deflection, the dispersion curve for modes with perpendicular field polarization must be shifted in frequency with respect to the curve for modes with operating polarization. A lot of decisions, based on the deterioration of the axial symmetry of the structure, are known for this purpose. The resonant method of stabilization is proposed. Resonant elements ' slots, coupled only with modes of perpendicular polarization, are placed in the disks. Two created branches of dispersion curve for composed slot - structure modes are generated and placed symmetrically with respect to the non perturbed dispersion curve for operating modes. In the plane stabilization it provides qualitative advantage with respect a simple frequency shift, because cancels, in the first order, the influence of modes with perpendicular field polarization on the plane of deflection. The criteria for the slots definition are presented. The example of application for the traveling wave S-band deflector is described as well.

 
TUP047 Investigation on Mode Separation Methods and Accuracy of Field Measurement in RFQ Structures with 3-D Electromagnetic Simulation rfq, dipole, quadrupole, simulation 512
 
  • K.R. Shin, Y.W. Kang, S.-H. Kim, A.V. Vassioutchenko
    ORNL, Oak Ridge, Tennessee
  • A.E. Fathy
    University of Tennessee, Knoxville, Tennessee
 
 

In radio frequency quadrupole (RFQ) structures, the fundamental quadrupole mode is used for focusing and acceleration of ion particles. The fields are maintained to have negligible interference with other unwanted modes of the structure using mode suppressors of different types especially in vane type RFQs that require dipole mode separation. The field distribution on the beam axis is usually measured and referenced using multiple loop-type magnetic probe antennas on the wall along the structure. Since the structures are equipped with many slug tuners on the outer wall for correction of fields, the tuner-probe interference can be a concern. In order to investigate the mode separation properties of the commonly used mode suppressors and the accuracies in field distribution with respect to localized perturbation due to the tuners, a systematic 3D simulation was carried out using a full-scale model of the SNS RFQ.

 
TUP060 Possibility of Thermal Instability for 4-vane RFQ Operation with High Heat Loading cavity, rfq, linac, controls 545
 
  • V.V. Paramonov
    RAS/INR, Moscow
 
 

Due to dispersion properties 4-vane RFQ cavity without resonant coupling is a thermally unstable structure. With deterioration of balance for local detuning there is a possibility for runaway in the field distribution and related thermal effects. It can results, in principle, in irreversible plastic deformations and cavity frequency shift. Both the increment and the threshold of instability are proportional to the average dissipated RF power. This possibility is more probable for long RFQ cavities. Also particularities for the cavity ends design are important. Some general features of this effect are discussed qualitatively and illustrated with simulations.

 
TUP072 An Equivalent Circuit for Post Coupler Stabilization in a Drift Tube Linac DTL, linac, cavity, simulation 578
 
  • F. Grespan
    INFN/LNL, Legnaro (PD)
  • G. De Michele, S. Ramberger, M. Vretenar
    CERN, Geneva
 
 

Post Couplers (PC's) are devices used in order to reduce the effect of perturbations on the operating mode of a DTL, using the resonant coupling stabilization method. In this paper an equivalent circuit for a DTL equipped with PC's is presented, together with a 3D simulation analysis, which can explain the post coupler stabilization principle and define a new tuning strategy for DTL cavities. The PC tuning procedure based on the equivalent circuit and on frequency measurements has been tested and validated with measurements on the Linac4 DTL aluminum model.

 
TUP082 Cryomodule Tests of Tesla-like Cavities in S1-Global for ILC cavity, cryomodule, linac, vacuum 602
 
  • E. Kako, H. Hayano, Y. Kojima, T. Matsumoto, H. Nakai, S. Noguchi, N. Ohuchi, M. Satoh, T. Shishido, K. Watanabe, Y. Yamamoto
    KEK, Ibaraki
 
 

Cryomodule tests of four Tesla-like superconducting cavities is under preparation in the S1-Global project at KEK. Assembly of the cryomodule was started in January 2010, and the installtion in the STF tunnel was completed in April. First cool-down tests are scheduled in June. The low rf power tests of the Tesla-like cavities will be carried out in July. The high rf power tests are scheduled between September and December, 2010.

 
TUP089 Transverse Emittance Measurements in MEBT at SNS emittance, electron, linac, ion 614
 
  • A.P. Zhukov, A.V. Aleksandrov, A.P. Shishlo
    ORNL, Oak Ridge, Tennessee
 
 

The latest modifications of the MEBT emittance scanner and the test results are presented. The scanner consists of a slit and harp placed in the MEBT section of SNS Linac with H- energy of 2.5 MeV. It was initially commissioned during the early days of SNS. The initial design allowed to get information about beam core but was incapable of getting precise data about halo. Several improvements in hardware and software were performed recently. They significantly increased signal to noise ratio, reduced harp wires electron coupling and increased scan speed. The latest measurements with the new system show a good agreement with the simulation results from simple models.

 
TUP110 Mass Production Report of C-Band Choke Mode Accelerating Structure and RF Pulse Compressor resonance, cavity, acceleration, linac 668
 
  • K. Okihira
    MHI, Kobe
 
 

C-band RF pulse compressor is a device that generates high peak RF-power by saving, and compressing the RF-power output from the klystron. XFEL project is scheduled to be installed 64 pulse compressor units, 2009 of December we have completed the fabrication and RF measurement of all units. A high-power examination was conducted in the test stand at RIKEN. The RF output of the pulse compressor is 260 MW in peak value, and the acceleration gradient of the accelerating structure is achieved to be 40 MV/m.It reports on the mass production passage of these 64 C-Band RF pulse compressors and on the installation result of injector section.

 
THP021 Higher Order Mode Heating Analysis for the ILC Superconducting Linacs* cavity, linac, HOM, scattering 803
 
  • K.L.F. Bane, C. Adolphsen, C.D. Nantista
    SLAC, Menlo Park, California
 
 

The superconducting cavities and interconnects in the 12 km long linacs of the International Linear Collider (ILC) are designed to operate at 2K where cooling costs are very expensive. Thus it is important to ensure that any additional cryogenic heat loads are small in comparison to those from static losses and the fundamental 1.3 GHz accelerator mode. One potential heat source is the higher order modes (HOM) excited by the beam. Such modes will be damped by specially designed HOM couplers that are attached to the cavities (for trapped modes), and by 70K ceramic dampers that are located in each of the eight or nine cavity cryomodules (for propagating modes). Brute force calculations of the higher frequency, non-trapped modes excited in a string of cryomodules is limited by computing capacity. We present, instead, an approach that combines scattering matrix and wakefield calculations to study the effectiveness of the dampers in limiting the heat deposited in the 2K cryogenic system.

 
THP038 Ultimate-Gradient Srf Test Cavity and Low Loss Tangent Measurements in Ultra Pure Sapphire cavity, vacuum, niobium, collider 842
 
  • P.M. McIntyre, N. Pogue
    Texas A&M University, College Station, Texas
  • C.E. Reece
    JLAB, Newport News, Virginia
 
 

A 1.3 GHz superconducting test cavity is being developed to test wafer samples of advanced SRF materials with surface fields at or beyond the Nb BCS limit. The mushroom-shaped Nb cavity is dielectric-loaded, with a hemisphere of high-purity sapphire located just above a detachable end flange. Wafer samples are mounted on the end flange. The cavity is operated in the TE011 mode, so no currents flow from the end flange to the side walls. Fields are concentrated on the wafer sample so that the peak surface field there is 4 times greater than anywhere else on the cavity walls. The loss tangent of ultrapure sapphire is critical to the performance of the test cavity. A separate first experiment has been conducted in a special 1.8 GHz cavity to measure this loss tangent in L band as a function of temperature for the first time. Results of the measurement and the final design of the ultimate-gradient test cavity will be presented.

 
THP054 A Diplexer to Operate Two Cavity Eigenmodes in Parallel cavity, gun, SRF, HOM 875
 
  • A. Arnold
    FZD, Dresden
 
 

To fulfil the demand of future high power and high luminosity FEL and Storage Ring sources, an intensive electron beam with short bunch length, small emittance and large bunch charge is required. Laser driven superconducting radio frequency (SRF) photocathode guns in combination with SRF LINACs appear to be the best solution. First long term operation was demonstrated at the FZD*. In difference to the normal conducting guns, the application of static magnetic fields is not possible. Instead, the use of a transverse electric (TE) mode in parallel to the accelerating mode was proposed. Numerical simulations have shown that such RF focusing can be applied to compensate emittance growth**. This contribution will introduce a possibility to use the existing coaxial RF coupler of TESLA like cavities, as RF power input for TE modes in parallel. An additional coupler component outside the module satisfies the job of combining two frequencies from different sources to one load. Thus, it corresponds to the working principle of a high power RF diplexer. Based on the 3 1/2 cell FZD SRF gun, a concrete technical implementation and results of its operation at the cold cavity will be presented.


* J. Teichert et al., AIP Conf. Proc. 1149, 1119 - 1124 (2009).
** K. Flöttmann, D. Janssen, V. Volkov, Phys. Rev. ST Accel. Beams 7, 090702 (2004).

 
THP060 X-band Pulse Compression System using One Channel Circular Polarized Traveling Wave Delay Line simulation, cavity, linac, klystron 890
 
  • M. Yoshida, S. Fukuda, Y. Higashi, T. Higo, N.K. Kudo, S. Matsumoto, H. Matsushita
    KEK, Ibaraki
  • S. Kazakov
    Fermilab, Batavia
 
 

The X-band pulse compression system has been developed for the high gradient experiment of the accelerating structure in the new X-band test facility (Nextef). The one channel circular polarized traveling wave delay line was selected to obtain the higher RF compression efficiency under limited delay line length and the easier operation than the cavity chain type. This delay line of the circular waveguide is also frequently used for the C-band feed line from the modulator floor to the accelerator test floor. Thus the delay line is tilted and has the limited length of around 20m. It is designed to obtain the three times compressed power which has the pulse duration of 150 ns. Further we also proceed the upgrade plan using the TE21 mode to double the pulse duration. In this paper, the design overview of this pulse compression system and the RF components including the mode launcher and the TE11-TE21 reflector will be presented.

 
THP081 The Stretched Wire Method: A Comparative Analysis Performed by Means of the Mode Matching Technique cavity, impedance, vacuum, scattering 932
 
  • M. Panniello, V.G. Vaccaro
    Naples University Federico II and INFN, Napoli
  • M.R. Masullo
    INFN-Napoli, Napoli
 
 

The Wire Method for Coupling Impedance evaluations is quite appealing for the possibility to make bench measurements on the Device Under Test (DUT). However, it is not entirely reliable because the stretched wire perturbs the boundary conditions, introducing a TEM wave that has a zero cut off frequency. We expect that, for frequencies smaller than the cutoff one, this behaviour produces an additional power loss which drastically lowers the high Q resonances of DUT. Above cutoff frequency, the impact of the stretched wire is not as dramatic as below cutoff. The Mode Matching Technique will be used to simulate the measurement with the Wire Method. In this way one may get a result which is not affected by the errors intrinsic of experimental measurements. The same method will be used to get, according to its standard definition, the Coupling Impedance of the real structure. The two results will be compared in order to define the frequency ranges in which they agree or disagree. As expected large discrepancies appear below cutoff frequency, while above cutoff, for certain ranges of parameters, an agreement is found.

 
THP104 S-Band Photocathode Gun with a 1 kHz Repetition Rate gun, vacuum, cathode, simulation 974
 
  • J.H. Han, D. Brice, M.P. Cox, H.C. Huang, S.A. Pande
    Diamond, Oxfordshire
 
 

Photocathode RF guns are widely used as injectors for accelerators requiring very high quality beams such as free electron lasers and linear colliders and recently used as ultrafast electron diffraction sources. Even with the limited repetition rate, normal conducting photocathode RF guns generate very low emittance and short pulse electron beams thanks to their high accelerating field and the efficient positioning of focusing solenoids. We report our activity of the design and production of an S-band normal conducting photocathode gun. The RF characteristics, thermal heating and vacuum analyses are discussed.