LINAC 2004 - List of Keywords

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

resonance

Paper	Title	Other Keywords	Page
MOP20	Design of the R.T. CH-Cavity and Perspectives for a New GSI Proton Linac	impedance, simulation, linac, proton	81
	Z. Li IMP, Lanzhou W. Barth, K. Dermati, L. Groening GSI, Darmstadt G. Clemente, H. Podlech, U. Ratzinger, R. Tiede IAP, Frankfurt-am-Main
	The CH-Structure has been studied at the IAP Frankfurt and at GSI for several years. Compared with the IH structure (H110-mode), the CH structure (H210-mode) can work at higher frequency (700 MHz) and can accelerate ions to higher energy (up to 150 AMeV). Detailed Microwave Studio (MWS) simulations were performed for this structure. Since a multi-gap cavity can be approximated as a quasi-periodic structure, it is possible to analyze one βλ/2-cell at an energy corresponding to the cavity center. Additionally, a reduced copper conductivity of 85% was assumed. Geometry variations with respect to rf frequency and shunt impedance can be performed rapidly by that method in the first stage of optimization. Effective shunt impedances from 100 MΩ/m down to 25 MΩ/m were obtained for the energy range from 5 AMeV to 150 AMeV by this method. The rf frequency was 350 MHz up to 70 MeV and 700 MHz above. A systematic analysis of the influence of the cell number in long CH cavities on the effective shunt impedance is presented. The possibility to apply this structure to a 70 mA, 70 MeV, 352 MHz proton linac for GSI is discussed.

MOP64	Wire Measurement of Impedance of an X-Band Accelerating Structure	impedance, dipole, linear-collider, collider	165
	N. Baboi DESY, Hamburg G. Bowden, V.A. Dolgashev, R.M. Jones, J. Lewandowski, S.G. Tantawi, J. Wang SLAC/ARDA, Menlo Park, California
	Several tens of thousands of accelerator structures will be needed for the next generation of linear collders known as the GLC/NLC (Global Linear Collider/Next Linear Collider). To prevent the beam being driven into a disruptive BBU (Beam Break Up) mode or at the very least, the emittance being signifcantly diluted, it is important to damp down the wakefield left by driving bunches to a manageable level. Manufacturing errors and errors in design need to be measurable and compared with predictions. We develop a circuit model of wire-loaded X-band accelerator structures. This enables the wakefield (the inverse transform of the beam impedance) to be readily computed and compared with the wire measurement. We apply this circuit model to the latest series of accelerating for the GLC/NLC. This circuit model is based upon the single-cell model developed in [1] extended here to complete, multi-cell structures. [1] R.M. Jones et al, 2003, Proc. PAC2003 (also SLAC-PUB 9871)

MOP69	RF Control Modelling Issues for Future Superconducting Accelerators	feedback, diagnostics, linac, beam-loading	180
	A. Hofler, J. R. Delayen TJNAF, Newport News, Virginia V. Ayvazyan, A. Brandt, S. Simrock DESY, Hamburg T. Czarski WUT, Warsaw T. Matsumoto KEK, Ibaraki
	The development of superconducting accelerators has reached a high level of maturity following the successes of ATLAS at Argonne, CEBAF at Jefferson Lab, the TESLA Test Facility at DESY and many other operational accelerators. As a result many new accelerators under development (e.g. SNS) or proposed (e.g. RIA) will utilize this technology. Covering all aspects from cw to pulsed rf and/or beam, non-relativistic to relativistic particles, medium and high gradients, light to heavy beam loading, linacs, rings, and ERLs, the demands on the rf control system can be quite different for the various accelerators. For the rf control designer it is therefore essential to understand these issues and be able to predict rf system performance based on realistic rf control models. This paper will describe the features that should be included in such models and present an approach which will drive the development of a generic rf system model.

TUP49	Simulations of the Ion-Hose Instability for DARHT-II Long-Pulse Experiments	simulation, induction, linac, electron	381
	K. C. D. Chan, C. Ekdahl LANL, Los Alamos, New Mexico C. Genoni, P. Hughes MRC, Albuquerque, NM
	Ion-hose effect has been described extensively in literatures. Computer simulations of the effect typically use particle-in-cell (PIC) computer codes or codes using the spread-mass formulation [1]. PIC simulations, though offering more reliable results, will require extended running time in large computers To support commissioning experiments in the DARHT-II induction linac in Los Alamos National Laboratory, we have modified a spread-mass code so that we can survey quickly the parameter space for the experiment. It can also be used to provide quick answers during experiment. The code was originally written by Genoni from Mission Research Corporation (MRC) for constant linac parameters. We have modified it so that parameters can have dependence along the length of the linac. In this paper, we will describe simulation results using this code for the DARHT-II commissioning experiment and also our benchmarking results comparing to LSP, a PIC code from MRC. [1] T. C. Genoni and T. P. Hughes, "Ion-hose instability in a long-pulselinear induction accelerator", PRST-AB, 6, 030401 (2003)

TUP77	Status of RF Control System for ISAC II Superconducting Cavities	feedback, controls, linac, alignment	450
	K. Fong, S. Fang, M.P. Laverty TRIUMF, Vancouver
	The rf control system for ISAC II superconducting cavities is a hybrid analogue/digital system using self-excited feedback loop. It has undergone more than a year of testing and improvements have been made to every aspect of the system, including power up sequencing, phase detection, loop regulation, data acquisition as well as communication with EPICS. With a loaded Q of 100,000, amplitude regulation bandwidth of 20 Hz, phase regulation bandwidth of 5 Hz have been achieved.

TUP89	Static Absolute Force Measurement for Preloaded Piezoelements Used for Active Lorentz Force Detuning System	impedance, linac, vacuum, linear-collider	486
	S. P. Sekalski, A. Napieralski, S. P. Sekalski TUL, Lodz A. Bosotti INFN/LASA, Segrate (MI) M. Fouaidy IPN, Orsay L. Lilje, S. Simrock DESY, Hamburg R. Paparella, P.F. Puricelli INFN Milano, Milano
	To reach high gradients in pulsed operation of superconducting (SC) cavities an active Lorentz force detuning compensation system is needed. For this system a piezoelement can be used as an actuator (other option is a magnetostrictive device). To guarantee the demanded lifetime of the active element, the proper preload force adjustment is necessary. To determine this parameter an absolute force sensor is needed which will be able to operate at cryogenic temperatures. Currently, there is no calibrated commercial available sensor, which will be able to measure the static force in such an environment. The authors propose to use a discovered phenomenon to estimate the preload force applied to the piezoelement. The principle of the proposed solution based on a shape of impedance curve, which changes with the value of applied force. Especially, the position of resonances are monitored. No need of specialized force sensor and measurement in-situ are additional advantages of proposed method.

TUP93	Results of a 3D-EM-Code Comparison on the TRISPAL Cavity Benchmark	coupling, simulation, rfq	495
	P. Balleyguier CEA/DAM, Bruyères-le-Châtel
	Several 3D electromagnetic codes (MAFIA, CST MicroWave-Studio, Vector-Fields Soprano, Ansoft HFSS, SLAC Omega3P) have been tested on a 2-cell cavity benchmark. Computed frequencies and Q-factors were compared to experimental values measured on a mock-up, putting the emphasis on the effect of coupling slots. It comes out that MAFIA limitations due to the staircase approximation is overcome by all other codes, but some differences still remain for losses calculations in re-entrant corners

WE103	State of the Art in RF Control	feedback, linac, diagnostics, laser	523
	S. Simrock DESY, Hamburg
	Nowadays the designer of a new rf control system has access to a wealth of powerful digital, analog, and rf circuitry. The requirements for the rf control system have changed from only controlling the amplitude and phase of the accelerating field to the required degree to stability. Additional tasks include exception handling and extensive build-in diagnostics while pursuing issues related to reliability, operability, and maintainability. Also operation close to the performance limit must be supported while maximizing the availability of the accelerator. With many accelerator projects in planning or under construction several state-of-the art rf control designs have evolved. This paper will present an overview of this new technology and discuss its performance.
	Transparencies

THP05	Superconducting beta=0.15 Quarter-Wave Cavity for RIA	linac, vacuum, superconductivity, ion	605
	M. Kelly ANL, Argonne, Illinois Z.A. Conway, J.D. Fuerst, M. Kedzie, K.W. Shepard ANL/Phys, Argonne, Illinois
	A production-design 115 MHz niobium quarter-wave cavity with a full stainless steel helium jacket has been built and tested as part of the R&D for the Rare Isotope Accelerator (RIA) driver linac. The two-gap cavity is designed to accelerate ions over the velocity range 0.14<β<0.24. Processing of the cavity RF surfaces, including high-pressure rinsing and assembly of the cavity with a moveable high-power RF coupler were all performed under clean room conditions. Cold test results including high-field cw operation, microphonics, and helium pressure sensitivity will be presented in this paper. Performance of a pneumatically actuated slow-tuner device suitable not only for this cavity but a number of other cavities required for RIA will also be discussed.

THP06	Cold Tests of a Superconducting Co-Axial Half-Wave Cavity for RIA	linac, vacuum, superconductivity, proton	608
	M. Kelly ANL, Argonne, Illinois J.D. Fuerst, M. Kedzie, K.W. Shepard ANL/Phys, Argonne, Illinois
	This paper reports cold tests of a superconducting niobium half-wave cavity with integral helium vessel, the design of which is suitable for production for the Rare Isotope Accelerator (RIA) driver linac. The cavity operates at 172 MHz and can provide more than 2 MV of accelerating voltage per cavity for ions with 0.24<β<0.37. Cavity RF surfaces were prepared using electropolishing, high-pressure rinsing and clean assembly. Measurements of Q₀ show a residual RF surface resistance RS = 5 nΩs in both 2 K and 4 K operations. The cavity can be operated at 4.5 K with E_Acc >10 MV/m (E_Peak >30 MV/m). Performance exceeds RIA specifications of an input power of 12 Watts at 4.5 K and E_Acc = 6.9 MV/m. RMS frequency jitter is only 1.6 Hz at E_Acc = 8 MV/m and T = 4.5 K as determined from microphonics measurements in a realistic accelerator environment connected to the ATLAS refrigerator.
	Transparencies

THP28	Multi-Mode SLED-II Pulse Compressors	coupling	660
	S. Kuzikov, Y.Y. Danilov, G. G. Denisov, V. G. Paveliev, D. Yu. Shegol'kov, A. A. Vikharev IAP, Nizhniy Novgorod I. Syratchev CERN, Geneva
	Compact SLED-II pulse compressors are considered. The primary idea of S. Kazakov to use a set of the cylindrical multi-mode cavities, to be free of high-Q resonances around the 11.4 GHz, is analyzed. This idea is developed, in order to provide more delaying time per miter of the line. Another idea to provide compactness is to avoid two-channel scheme with 3 dB coupler usually used for SLED-II pulse compressors. A reflectionless delay line is built in this case, using coupling in a form of the non-symmetrical mode converter. SLED-II pulse compressors of higher frequency bands also are considered. It is suggested to shape these compressors on a base of the multi-mirror transmission lines. The operating mode in this case is a Gaussian wavebeam traveling between mirrors. Various configurations of the mirrors are compared from the point of view of maximum of compactness at the given pulse duration. The results of the preliminary experiments at low power level are discussed.
	Transparencies

THP36	Vibration Stabilization of a Mechanical Model of a X-Band Linear Collider Final Focus Magnet	feedback, collider, linear-collider, site	684
	J. Frisch, A. Chang, V. Decker, L. Hendrickson, T. Markiewicz, R. Partridge, A. Seryi SLAC, Menlo Park, California E. Eric, L. Eriksson, T. Himel SLAC/NLC, Menlo Park, California
	The small beam sizes at the interaction point of a X-band linear collider require mechanical stabilization of the final focus magnets at the nanometer level. While passive systems provide adequate performance at many potential sites, active mechanical stabilization is useful if the natural or cultural ground vibration is higher than expected. A mechanical model of a room temperature linear collider final focus magnet has been constructed and actively stabilized with an accelerometer based system.

THP50	The CEBAF RF Separator System Upgrade	power-supply, controls, cathode, ion	721
	C. Hovater, M. Augustine, A. Guerra, R. Nelson, R.A. Terrel, M. Wissmann TJNAF, Newport News, Virginia
	The CEBAF accelerator uses RF deflecting cavities operating at the third sub-harmonic (499 MHz) of the accelerating frequency (1497 MHz) to “kick” the electron beam to the experimental halls. The cavities operate in a TEM dipole mode incorporating mode enhancing rods to increase the cavity’s transverse shunt impedance. As the accelerators energy has increased from 4 GeV to 6 GeV the RF system, specifically the 1 kW solid state amplifiers, have become problematic, operating in saturation because of the increased beam energy demands. Two years ago we began a study to look into replacement for the RF amplifiers and decided to use a commercial broadcast Inductive Output Tube (IOT) capable of 30 kW. The new RF system uses one IOT amplifier on multiple cavities as opposed to one amplifier per cavity originally. In addition the new RF system supports the proposed 12 GeV energy upgrade to CEBAF. Currently we are halfway through the upgrade with two IOTs in operation and two more to be installed. This paper reports on the new RF system and the IOT performance.

THP51	Tuning of External Q And Phase for The Cavities of A Superconducting Linear Accelerator	impedance, scattering, linac, coupling	724
	V.V. Katalev, S. Choroba DESY, Hamburg
	The RF power required for a certain gradient of a superconducting cavity depends on the beam current and coupling between the cavity and waveguide. The coupling with the cavity may be changed by variation of Qext. Different devices can be used to adjust Qext or phase. In this paper three stub and E-H tuners are compared and their usability for the RF power distribution system for the superconducting accelerator of the European Xray laser and the TESLA linear collider is considered. The tuners were analyzed by using the scattering matrix. Advantages and limitations of the devices are presented.

THP58	Development of C-band High-Power Mix-Mode RF Window	vacuum, klystron, acceleration, electron	745
	S. Michizono, S. Fukuda, T. Matsumoto, K. Nakao, T. Takenaka KEK, Ibaraki K. Yoshida MELCO, Hyogo
	High power c-band (5712 MHz) rf system (40 MW, 2 μs, 50 Hz) is under consideration for the electron-linac upgrade aimed for the super KEKB project. An rf window, which isolates the vacuum and pass the rf power, is one of the most important components for the rf system. The window consists of a ceramic disk and a pill-box housing. The mix-mode rf window is designed so as to decrease the electric field on the periphery of the ceramic disk. A resonant ring is assembled in order to examine the high-power transmission test. The window was tested up to the transmission power of 160 MW. The rf losses are also measured during the rf operation.

THP60	High-Power RF Distribution System for the 8-Pack Project	linear-collider, collider, diagnostics, vacuum	751
	C.D. Nantista SLAC/ARDB, Menlo Park, California D.P. Atkinson LLNL, Livermore J.Q. Chan SLAC/NLC, Menlo Park, California S.Y. Kazakov KEK, Ibaraki D.C. Schultz SLAC, Menlo Park, California S.G. Tantawi SLAC/ARDA, Menlo Park, California
	The 8-Pack Project at SLAC is a prototype rf system whose goal is to demonstrate the high-power X-band technology developed in the NLC/GLC program. In its first phase, it has reliably produced a 400 ns rf pulse of over 500 MW using a solid-state modulator, four 11.424 GHz klystrons and a dual-moded SLED-II pulse compressor [1]. In Phase 2, the output power of our system has been delivered into the bunker of the NLCTA (Next Linear Collider Test Accelerator) and divided between several accelerating structures, first four and finally eight, for beam acceleration. We describe here the design, cold-test measurements, and processing of this power distribution system. Due to the high power levels and the need for efficiency, overmoded waveguide and components are used. For power transport, the TE 01 mode is used in 7.44 cm and 4.064 cm diameter circular waveguide. Only near the structures is standard WR90 rectangular waveguide employed. Components used to manipulate the rf power include transitional tapers, mode converters, overmoded bends, fractional directional couplers, and hybrids. [1] S. Tantawi, et al., “Status of High-Power Tests of the Dual-Mode SLED-II System for an X-Band Linear Collider,” FR202, these proceedings.

THP61	SKIP - A Pulse Compressor for SuperKEKB	coupling, linac, acceleration, positron	754
	T. Sugimura, M. Ikeda, K. Kakihara, T. Kamitani, S. Ohsawa, K. Yokoyama KEK, Ibaraki
	An upgrade of KEKB injector linac is planned. A main purpose of this upgrade is to increase injection energy of positrons from 3.5 GeV to 8.0 GeV for the SuperKEKB project. By a limitation of land area, our choice is to double an acceleration field utilizing a C-band accelerator structures instead of present S-band structures. Last year we developed C-band components such as accelerator structure, dummy load, 3 dB hybrid coupler, RF window, sub booster, modulator system, and so on. These components were assembled at a test stand and processed. This accelerator unit was installed in the beam line of injector linac and has been under operation. This summer we will install an RF pulse compressor system to the C-band accelerator unit. This paper reports the status of development of the RF pulse compressor system.

THP64	Waveguide Stub Tuner Analysis for CEBAF Application	klystron, coupling, simulation, insertion	757
	H. Wang Jefferson Lab, Newport News, Virginia M. Tiefenback TJNAF, Newport News, Virginia
	Three-stub WR650 waveguide tuners have been used on the CEBAF superconducting cavities for two changes on the external Qs: increasing the Q from 6·10⁶ to 8·10⁶ on 5-cell cavities to reduce the klystron power at operation gradients and decreasing the Q from 2·10⁷ to 8·10⁶ on 7-cell cavities to ease the control system handling the Lorenz Force detuning. To understand the reactive tuning effects in the machine operations with beam current and mechanical tuning, a network analysis model was developed. The S parameters of the stub tuner were simulated by MAFIA and measured on the bench. We used this stub tuner model to study tuning range, sensitivity, frequency pulling as well as cold waveguide and window heating problems. Detailed experimental results will be compared against this model. Pros and cons of this stub tuner application will be summarized.

THP70	Experimental Study of an 805 MHz Cryomodule for the Rare Isotope Accelerator	linac, vacuum, alignment, coupling	773
	T.L. Grimm, S. Bricker, C. Compton, W. Hartung, M. Johnson, F. Marti, J. Popielarski, R.C. York NSCL, East Lansing, Michigan G. Ciovati, P. Kneisel Jefferson Lab, Newport News, Virginia L. Turlington TJNAF, Newport News, Virginia
	The Rare Isotope Accelerator (RIA) driver linac will use superconducting, 805 MHz, 6-cell elliptical cavities with geometric β values of 0.47, 0.61 and 0.81. Each elliptical cavity cryomodule will have four cavities [1]. Room temperature sections between each cryomodule will consist of quadrupole doublets, beam instrumentation, and vacuum systems. Michigan State University (MSU) has designed a compact cryostat that reduces the tunnel cross-section and improves the linac real estate gradient. The cold mass alignment is accomplished with a titanium rail system supported by adjustable nitronic links from the top vacuum plate, and is similar to that used for existing MSU magnet designs. The same concept has also been designed to accommodate the quarter-wave and half-wave resonators with superconducting solenoids used at lower velocity in RIA. Construction of a prototype β=0.47 cryomodule was completed in February 2004 and is presently under test in realistic operating conditions. Experimental results will be presented including: alignment, electromagnetic performance, frequency tuning, cryogenic performance, low-level rf control, and control of microphonics. [1] “Cryomodule Design for the Rare Isotope Accelerator”, T.L. Grimm, M. Johnson and R.C. York, PAC2003, Portland OR (2003)

THP82	Experiences in Fabrication and Testing the Prototype of the 4.90 GHz Accelerating Sections for MAMI C	coupling, vacuum, microtron, linac	788
	A. Jankowiak, H. Euteneuer, S. Schumann, O. Tchoubarov IKP, Mainz
	The fourth stage of the Mainz Microtron (MAMI) is under construction as a 855 to 1500 MeV Harmonic Double Sided Microtron[1], with one of its two linacs operating at the MAMI-frequency of 2.45 GHz, the other at 4.90 GHz. The bi-periodic on axis coupled accelerating structure in operation at MAMI has been optimised for 4.90 GHz[2], such a high frequency till now not having been used for high power cw-acceleration. To ensure a smooth and efficient industrial production of the ten 35 AC-sections needed, a prototype was built and high power tested fully in-house at IKPH. After a short recapitulation of the design of the cavity profile, the configuration of the section with its tuners and diagnostic probes is discussed. Details of the procedures of machining, tuning and brazing the resonator discs, and the rf-parameters achieved for the section are given. Finally, the experiences and measurements during its high power test up to 22 kW are reported: the conditioning behaviour and the irreversible permanent as well as the reversible dynamic changes of passband gap and resonance frequency as a function of maximal applied rf-power. [1] A. Jankowiak et al., "Design and Status of the 1.5 GeV-Harmonic Double Sided Microtron for MAMI", Proceedings EPAC2002, [2] H. Euteneuer et al., "The 4.90GHz Accelerating structure for MAMI C", Proceedings EPAC2000
	Transparencies

THP92	Effect of the Tuner on the Field Flatness of SNS Superconducting RF Cavities	simulation, coupling, superconducting-RF, pick-up	815
	A. Sun ORNL/SNS, Oak Ridge, Tennessee H. Wang, G. Wu Jefferson Lab, Newport News, Virginia
	Field flatness in a multi-cell superconducting cavity affects not only the net accelerating voltage, but also the peak surface field and the Lorenz Force detuning coefficient. Our measurement indicates that the field flatness changes both external Q of the Fundamental Power Coupler (FPC) and external Q of the Field Probe (FP). The field amplitude tilts linearly to the distance between the cell center and the cavity’s geometry center (pivot point). The tilt rate has been measured in a cryomodule cold (2 K) test, being about 2%/100 kHz, relative the field flatness at the cavity’s center frequency of 805 MHz. Bead-pull measurements confirmed that the field flatness change is 2.0%/100 kHz for a medium β cavity with helium vessel, and 1.72%/100 kHz without helium vessel. These results matched the predictions of simulations using ANSYS and SUPERFISH. A detailed analysis reveals that longitudinal capacitive gap deformation is the main cause of the frequency change. Field flatness change was not only due to the uneven stored energy change within the cell, but also due to cell-to-cell coupling.

THP94	Cold Tests of a 160 MHz Half-Wave Resonator	linac, coupling, simulation, vacuum	821
	R. Stassen, R. Maier FZJ/IKP, Jülich R. Eichhorn, F. M. Esser, B. Laatsch, G. Schug, H. Singer FZJ, Jülich
	The number of polarized particle in the cooler synchrotron COSY is limited by the present injector system. A new linac was projected based on superconductive half-wave resonators to fill COSY up to the space charge limit. The first prototype of a 160 MHz Half-Wave Resonator (HWR) has been built and tested. RF-measurements in CW as well as in a pulsed operation will be presented. A second prototype with a slightly different way of fabrication will be completed soon. All measurements have been done using the new 4 kW loop-coupler. The use of a cold window allows to change the coupling from 1· 10⁶ to 1· 10¹⁰ without any risk of contamination. The mechanical tuner consisting of a stepper motor driven coarse tuner and a fast piezo system to compensate the Lorentz-Force detuning has successfully integrated into the vertical test-cryostat.