LINAC 2006 - List of Keywords (superconductivity)

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

superconductivity

Paper	Title	Other Keywords	Page
MOP067	Higher Order Mode Wakefield Simulations and Beam Dynamics Simulations in the ILC Main Linacs	emittance, linac, simulation, electron	199
	R. M. Jones, C. J. Glasman UMAN, Manchester
	The progress of approximately 3000 electron (and positron) bunches down the main linacs of the ILC (International Linear Collider) can readily give rise to dipole modes which distrupt the progress of the beam. We investigate the transverse modes which are excited and monitor the resulting emittance dilution which occurs down the linac. At present there are two design configurations for the ILC: the BCD (Baseline Configuration Design) and the ACD (Alternate Configuration Design). We investigate the wake fields and beam dynamics for both configurations. In particular, the influence of trapped modes on the emittance of the beam is studied.

TUP025	Optimization of Surface Treatment of High-Gradient Single-Cell Superconducting Cavities at KEK	vacuum, pick-up, cryogenics, electron	299
	F. Furuta, Y. Higashi, T. Higo, I. H. Inoue, S. Kazakov, H. Matsumoto, Y. Morozumi, R. S. Orr, T. Saeki, K. Saito, M. Satoh, K. Ueno, H. Yamaoka KEK, Ibaraki
	We have continued the study of a series of single cell superconducting cavities at KEK. These tests are aimed at establishing a prescription for a surface treatment that would reliably allow cavities to reach gradients in excess of 45 MV/m in vertical tests. The cavity profiles were all of the KEK Low Loss design, and were fabricated from deep drawn Niobium half shells using electron beam welding. The cavity initial surface preparation followed an established KEK procedure of centrifugal barrel polishing, high temperature annealing, light chemical polishing, electropolishing. and final a high pressure water rinse. Early results from this series test demonstrated that reaching gradients as high as 50 MV/m is feasible. However, the initial yield was of order 50%. In this paper we will discuss our studies of further improvement of the surface treatment aimed at increasing the yield.

TUP026	Status of the XFEL Testcavity Program	vacuum, electron, gun, superconducting-RF	302
	D. Reschke, A. Brinkmann, J. Iversen, W. Singer DESY, Hamburg
	In preparation of the European XFEL-project a testcavity program of about 25 1.3GHz niobium single-cell cavities was launched at DESY beginning of 2005 in parallel to the accelerator nine-cell structure activities. After successful start-up of the DESY in-house fabrication main topics of the program are the optimisation of cavity electron beam welding preparation, the performance of large grain niobium and the qualification of further niobium vendors for cavity production. So far reproducibly all cavities (TESLA cell shape) exceed gradients of 30 MV/m at high Q-values. An electropolished mono-cell fabricated of large grain material reached 41 MV/m at Qo = 1.4·10¹⁰. The present status and results of the program are presented.

TUP033	Performances of High-Purity Niobium Cavities with Different Grain Sizes	vacuum, pick-up, linear-collider, 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.

TUP036	Large Grain Superconducting RF Cavities at DESY	superconducting-RF, scattering, free-electron-laser, RF-structure	327
	W. Singer, A. Brinkmann, J. Iversen, G. Kreps, A. Matheisen, D. Reschke, X. Singer DESY, Hamburg
	The DESY R&D program on cavities fabricated from large grain niobium explores the potential of this material for the production of approx. 1000 nine-cell cavities for the European XFEL. The program investigates both, the basic material properties comparing large grain material to standard sheet niobium and the material availability, fabrication and preparation aspects. Several single-cell cavities of TESLA shape have been fabricated from large grain niobium. A gradient up to 41 MV/m at Q₀ = 1.4·10¹⁰ (TB = 2K) was measured after electropolishing. Recently the first large grain nine-cell cavities worldwide have been produced under contract of DESY with ACCEL Instruments Co. The first cavity is already tested with an accelerating gradient of 29 MV/m after BCP (Buffered Chemical Polishing) treatment.

THP047	Prototyping of a Single-Cell Half-Reentrant Superconducting Cavity	simulation, vacuum, resonance, coupling	685
	M. S. Meidlinger, J. Bierwagen, S. Bricker, C. Compton, T. L. Grimm, W. Hartung, M. J. Johnson, J. Popielarski, L. Saxton, R. C. York NSCL, East Lansing, Michigan E. Zaplatin FZJ, Jülich
	As superconducting niobium cavities achieve higher gradients, it is anticipated they will reach a performance limit as the peak surface magnetic field approaches the critical magnetic field. "Low loss" and "reentrant" cavity designs are being studied at CEBAF, Cornell, DESY, and KEK, with the goal of reaching higher gradients via lower surface magnetic field, at the expense of higher surface electric field. At present, cavities must undergo chemical etching and high-pressure water rinsing to achieve good performance. It is not clear whether this can be done effectively and reliably for multi-cell low loss or reentrant cavities using traditional techniques. A "half-reentrant" cavity shape has been developed with RF parameters similar to the low loss and reentrant cavities, but with the advantage that the surface preparation can be done easily with existing methods. Two prototype single-cell half-reentrant cavities are being fabricated at 1.3 GHz; the non-reentrant wall angle is 8 degrees, the beam tube radius is 29 mm, and the cell-to-cell coupling is 1.47%. The half-reentrant cavity design and the results and status of the prototyping effort will be presented.

THP075	RF Performance of a Superconducting S-Band Cavity Filled with Liquid Helium	vacuum, pick-up, radiation, controls	755
	W. Hartung, J. Bierwagen, S. Bricker, C. Compton, T. L. Grimm, M. J. Johnson, D. Meidlinger, D. Pendell, J. Popielarski, L. Saxton, R. C. York NSCL, East Lansing, Michigan
	Copper RF cavities filled with hydrogen gas at high pressure have been studied recently by Muons, Inc. and IIT for simultaneous acceleration and ionisation cooling of a muon beam. A further step in this direction would be a superconducting RF cavity filled with liquid helium. One might imagine that this would make the cavity less vulnerable to thermal breakdown, field emission, and multipacting. A disadvantage is that magnetostatic focussing of the beam could not be done simultaneously. Preliminary RF testing has been done on a 2.45 GHz single-cell elliptical cavity filled with liquid helium. Low-field results indicate little or no increase in the power dissipation, consistent with predictions and measurements in the literature. The frequency shift with pressure for a cavity filled with saturated liquid is about 100 times greater than for a cavity under vacuum, consistent with published values of liquid helium permittivity as a function of temperature. Investigation of the high-field performance of a liquid-filled cavity is in progress.

THP090	Initial Studies of 9-Cell High-Gradient Superconducting Cavities at KEK	pick-up, insertion, coupling, higher-order-mode	794
	T. Saeki, F. Furuta, H. Hayano, Y. Higashi, T. Higo, I. H. Inoue, S. Kazakov, H. Matsumoto, Y. Morozumi, R. S. Orr, K. Saito, M. Satoh, N. Toge, K. Ueno, H. Yamaoka, K. Yokoya KEK, Ibaraki
	Vertical tests of single cell cavities of the KEK Low Loss "Ichiro" design have established that gradients as high as 51 MV/m are feasible in principle. We have also performed vertical tests of 9-cell cavities. The internal surface was prepared according to the prescription developed in the single cell series test. In this paper we report results on the accelerating gradients achieved so far, an investigation of the possible presence of hydrogen "Q Disease," and other high-field related studies. We also present the measurement of the higher modes of the cavities.

FR1004	Recent Developments in SRF Cavity Science and Performance	linear-collider, 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.