LINAC 2006 - List of Keywords (linear-collider)

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

linear-collider

Paper	Title	Other Keywords	Page
TUP033	Performances of High-Purity Niobium Cavities with Different Grain Sizes	vacuum, pick-up, superconductivity, collider	318
	P. Kneisel, S. Chattopadhyay, G. Ciovati, G. Myneni Jefferson Lab, Newport News, Virginia
	Grain boundaries have for some time been suspected of influencing the performance of rf cavities made from high purity niobium by limiting the temperature dependent BCS surface resistance to a residual resistance because of impurity segregation and by causing field limitations due to flux penetration. We have carried out a comparative study of the rf behavior of 2.2 GHz TM010 cavities of identical shape, fabricated from single crystal niobium, niobium of grain sizes of the order of several cm² and standard poly-crystalline material. This contribution reports about the results of the measurements of the temperature dependence of the surface resistance Rs(T) and the Q0 vs Eacc behavior at 2 K. From the analysis of the Rs(T) data at low rf fields material parameters such as gap value, mean free path and residual resistance could be extracted. The dependence of the Q-value on rf field was analyzed with respect to the medium field Q-slope, “Q-drop” at high fields and the “quench” fields. The best performance resulted in a breakdown field of ~ 165 mT, corresponding to an accelerating gradient of Eacc ~ 45 MV/m.

TUP048	Beam-Loading Effect in the Normal-Conducting ILC Positron Source Pre-Accelerator	positron, beam-loading, focusing, linac	355
	V. V. Paramonov RAS/INR, Moscow K. Floettmann DESY, Hamburg
	Significant positron bunch charge (several nC) in the ILC Positron Source results in high pulse beam loading for normal-conducting accelerating structures in Positron Pre-Accelerator (PPA). Time interval between bunches (~ 300 ns) is not negligibly small in comparison with accelerating structure time constant (rise time for Standing Wave (SW) or filling time for Traveling Wave (TW) options). As the result, beam loading effect has particularities both from stored energy acceleration regime and continuous beam loading one. Taking into account particular PPA beam structure, beam loading effect is estimated for the present ILC base line parameters, both for SW and TW PPA options. Possible solutions for beam loading compensation are discussed.

TUP050	Microwave Helical Undulator-Based Production of Polarized Photons and Positrons	undulator, positron, radiation, polarization	361
	A. Smirnov, D. Yu DULY Research Inc., Rancho Palos Verdes, California
	Linac-driven undulator technology and capabilities are considered for production of polarized positrons and polarized high-brightness X-rays. Challenging requirements for polarized positron production reveal a number of benefits of a microwave undulator compared with a conventional magnetic undulator: larger gap, simpler construction, shorter length, reduced requirements on tolerances and alignment. Two novel approaches are introduced for open and closed structures: cross-polarized excitation of a circular waveguide and a twisted structure. For the CLIC project the microwave undulator becomes an integral part of the TBA, and as it is naturally powered by the same decelerator. Other applications include emittance dampers, synchrotron radiation sources, and FELs. Additionally the twisted undulator provides unique opportunity for studies of circular dichroism and multi-photon anomalous diffraction (MAD) in protein crystallography.

TH1002	Cryomodule Test Facilities and Multicell Cavity Performance for the ILC	linac, klystron, superconducting-RF, controls	516
	H. Hayano KEK, Ibaraki
	To address the ILC Main Linac gradient, which are greater than 35MV/m at vertical test and greater than 31.5MV/m in the operation of the cryomodule, ILC-GDE organized several task forces in the R&D board. They are S0 task force, S1 task force, and S2 task force. The charge of S0 is to achieve 35MV/m in the qualification with reasonable yield. S1 is to achieve 31.5MV/m operation of cryomodule. And S2 is to estimate how large test facility is required to test chain of cryomodules and to make industrialization of cryomodule production. The paper reports the task force activities status together with existing R&D of multicell cavity performance and cryomodule test facility status.

TH2003	Recent Developments in Pulsed High-Power Systems	pulsed-power, kicker, klystron, collider	541
	D. E. Anderson ORNL, Oak Ridge, Tennessee
	Pulsed power systems are inherent in any high power accelerator system. Applications include, among others, modulators for powering high power klystrons, pulsed power systems to drive linear induction accelerating cells, kicker magnet drivers for storage rings, and a wide variety of beam deflection and pulsed focusing systems. As with many enabling technologies, component limitations and materials properties dominate the engineering tradeoffs that must be made during the system design. An overview of the state-of-the-art in major components of pulsed power systems will be presented. An examination of how those components are being integrated into linac systems will also be performed and an overview of these systems shall be given. The relatively recent shift toward solid-state power electronics solutions to pulsed power engineering problems will be emphasized. Finally, some future trends in the field will be examined.

THP026	HIGH POWER TEST OF COUPLER WITH CAPACITIVE WINDOW	vacuum, coupling, linac, collider	625
	S. Kazakov, F. Furuta, T. Higo, J. H. Hong, H. Matsumoto, T. Saeki, K. Saito, M. Satoh KEK, Ibaraki R. S. Orr University of Toronto, Toronto, Ontario H. Urakata TETD, Otawara Y. Yano Toshiba, Yokohama O. Yushiro Toshiba Electron Tubes & Devices Co., Ltd, Tokyo
	New type of coupler with capacitive-coupling inner conductor is designed in KEK. This coupler has a module structure, which is convenient for mass-production, assembling and repairing. Four samples of couplers were made and two of them were tested at high power level. The main parameters of the couplers and test results are presented in this paper.

THP027	Study of PPM-Focused X-band Pulse Klystron	klystron, cathode, simulation, collider	628
	S. Matsumoto, M. Akemoto, S. Fukuda, T. Higo, H. Honma, S. Kazakov, N. K. Kudo, H. Nakajima, T. Shidara, M. Yoshida KEK, Ibaraki
	The R&D of PPM (Periodic Permanent Magnet)-focused X-band pulse klystrons has been conducted since 1999, originally for Global Linear Collider (GLC) project. So far six prototype tubes have been tested. Some of them successfully produce the power required in GLC (75MW, 1.6μsec pulse width). However their performance was not perfect as a GLC tube. The problems are the stability of RF output and the gun performance. Since GLC programs were terminated in 2004, some limited work on the improvement of the PPM tubes continues at X-Band Test Facility (XTF) in KEK. The work includes the test to evaluate the performance of revised (rebuilt) tubes as well as disassembling these tubes after the test for further inspection. Recent results are reported.

THP028	Master Oscillator for Fermilab ILC Test Accelerator	controls, simulation, power-supply, resonance	631
	J. Branlard, B. Chase, E. Cullerton Fermilab, Batavia, Illinois
	The low phase-noise master oscillator generates and distributes the various frequencies required for the LLRF system controlling ILCTA cavities. Two chassis have been developed for this design, generating the programmable frequencies and performing the distribution and amplification, respectively. It has been successfully used with the SNS and the DESY-SIMCON LLRF systems, driving two different superconducting cavities. The design approach and a full characterization of the master oscillator are presented in this paper. The measurement results include the frequency stability and the phase and amplitude noise spectrums of the multiple frequency outputs.

THP037	Wide-Range Frequency Compensation by Coaxial Ball-Screw Tuner	resonance, acceleration, booster, monitoring	658
	T. Higo, Y. Higashi, Y. Morozumi, K. Saito, K. Ueno, H. Yamaoka KEK, Ibaraki
	Low-loss 9-cell 1.3GHz cavities are studied at KEK aiming at a high-gradient operation for the International Linear Collider. One of the most important issues to realize such a high gradient in a pulsed operation of super-conducting cavities is the issue of how to compensate the Lorentz detuning. The Lorentz detuning of the cavity amounts to 3kHz at 45MV/m acceleration field. None of the tuners to date have achieved this range. A coaxial ball-screw tuner was designed and proved to reach this level in the room temperature operation. The performance at liquid Nitrogen temperature is also studied. From these results, we try to evaluate the feasibility of the operation at 2K.

THP038	Normal Conducting High-Gradient Studies at KEK	collider, acceleration, extraction, vacuum	661
	T. Higo, M. Akemoto, S. Fukuda, Y. Higashi, N. K. Kudo, S. Matsumoto, K. Takata, T. T. Takatomi, K. Ueno, K. Yokoyama KEK, Ibaraki
	Normal-conducting high field studies have been pursued at XTF, a high power X-band RF facility of KEK developed for linear collider. Three traveling-wave structures developed for X-band linear collider were studied in high field of more than 70MV/m level. High-field characteristic such as field emission properties and trip rate, etc. are studied carefully as the processing proceeds. Operation at 50MV/m level was found very stable while breakdowns happened once an hour or so at more than 70MV/m, indicating the approach to some critical point. This characteristics is discussed in conjunction with various author’s trials to make a scaling law of severe breakdowns among power, pulse width and so on. Further basic studies on field/power limitation or robustness against breakdowns in various materials are planned using narrowed waveguide configuration. Unique features related to this study is also described.

THP066	Lorentz-Force Detuning Analysis for Low-Loss, Re-entrant and Half-Reentrant Superconducting RF Cavities	simulation, coupling, collider, superconducting-RF	734
	E. Zaplatin FZJ, Jülich T. L. Grimm, W. Hartung, M. J. Johnson, M. S. Meidlinger, J. Popielarski, R. C. York NSCL, East Lansing, Michigan
	The RF design of a superconducting elliptical cavity requires a trade-off in the optimization of the cell shape between the region of high electric field and the region of high magnetic field. In practice, the cavity performance may be limited not by the RF characteristics, but by detuning due to the Lorentz force, bath pressure fluctuations, or microphonics; Lorentz force detuning is of concern primarily for pulsed accelerators such as the proposed International Linear Collider. Hence the structural properties must also be taken into account in the cavity design. Several new cavity shapes are being developed in which the surface magnetic field is decreased relative to the TeSLA cavity shape, with the goal of reaching a higher accelerating gradient. This study will compare the Lorentz force detuning characteristics of the TeSLA, "low-loss", "reentrant", and "half-reentrant" cavity middle cells, and explore possible methods for stiffening the structures.

THP078	High-Gradient Test of a Tungsten-Iris X-Band Accelerator Structure at NLCTA	vacuum, collider, RF-structure, impedance	764
	S. Doebert, A. Grudiev, S. T. Heikkinen, J. A. Rodriguez, I. Syratchev, M. Taborelli, W. Wuensch CERN, Geneva C. Adolphsen, L. Laurent SLAC, Menlo Park, California
	The CLIC study group at CERN has built two X-band accelerating structures to be tested at SLAC in NLCTA. The structures consist of copper cells with insert irises made out of Molybdenum and Tungsten, clamped together and installed in a vacuum tank. These structures are exactly scaled versions from structures tested previously at 30 GHz and with short pulses (16 ns) in the CLIC Test Facility at CERN. At 30 GHz these structures reached gradients of 150 MV/m for Tungsten and 195 MV/m for Molybdenum. These experiments were designed to provide data on the dependence of rf breakdown on pulse length and frequency. This paper reports in particular on the high-gradient test of the tungsten-iris structure. At a pulse length of 16 ns a gradient of 125 MV/m was reached at X-band, 20 % lower than the 150 MV/m measured at 30 GHz in the CLIC Test Facility. The pulse length dependence and the dependence of the break down rate as a function of gradient were measured in detail. The results are compared to data obtained from the Molybdenum-Iris experiment at X-band which took place earlier as well as to 30 GHz data.

FR1004	Recent Developments in SRF Cavity Science and Performance	superconductivity, collider, controls, cathode	818
	G. Ciovati Jefferson Lab, Newport News, Virginia
	The performances of SRF cavities made of high purity bulk niobium have been improving in the last few years and surface magnetic fields (Bp) close to the thermodynamic critical field of niobium have been achieved in a few cases. The recommendation made in 2004 in favor of SRF as the technology of choice for the International Linear Collider (ILC), requires to improve the reliability of multi-cell cavities operating at accelerating gradients (Eacc) of the order of 35 MV/m . Additionally, a better understanding of the present limitations to cavity performance, such as the high-field Q-drop is needed. This contribution presents some recent developments in SRF cavity science and performance. Among the most significant advances of the last few years, new cavity shapes with lower ratio Bp/Eacc were designed and tested. Cavities made of large-grain niobium became available, promising lower cost at comparable performance to standard fine-grain ones and several tests on single-cell cavities were done to gain a better understanding of high-field losses. In addition, studies to improve the reliability of electropolishing are being carried out by several research groups.