Kneisel P.

Paper	Title	Page
TUP01	A Coaxial TE011 Cavity and a System to Measure DC and RF Properties of Superconductors	98
	G. Ciovati, P. Kneisel, G. R. Myneni, M. Morrone, R. Bundy, B. Clemens, T. Elliott, G. Slack, L. Turlington JLab J. Mondal BARC
	A coaxial niobium cavity has been designed and built where the center conductor consists of a removable sample. In addition, a system to measure properties such as magnetization, penetration depth, critical temperature and thermal conductivity on the same cylindrical sample has been designed and built. The purpose of this effort is to investigate possible correlations between DC and RF properties of superconductors. In this contribution, the design of the various components is discussed and the test results on a niobium sample obtained so far are presented.
TUP14	Measurement of the High-Field Q-Drop in a Large-Grain Niobium Cavity for Different Oxidation Processes	137
	G. Ciovati, P. Kneisel JLab A. Gurevich NHMFL, FSU
	In this contribution, we present the results from a series of RF tests at 1.7 K and 2.0 K on a single-cell cavity made of high-purity large (with area of the order of few cm2) grain niobium which underwent various oxidation processes. After initial buffered chemical polishing, anodization, baking in pure oxygen atmosphere and baking in air up to 180 degree C was applied with the objective of clearly identifying the role of oxygen and the oxide layer on the Q-drop. During each rf test a temperature mapping system was used allowing to measure the local temperature rise of the cavity outer surface due to RF losses, which gives information about the losses location, their field dependence and space distribution on the RF surface. The results confirmed that the depth affected by baking is about 20-30 nm from the surface and showed that the Q-drop did not re-appear in a previously baked cavity by further baking at 120 degree C in pure oxygen atmosphere or in air up to 180 degree C. A statistic of the position of the "hot-spots" on the cavity surface showed that grain-boundaries are not the preferred location. An interesting correlation was found between the Q-drop onset, the quench field and the low-field energy gap, which supports the hypothesis of thermo-magnetic instability governing the Q-drop and the baking effect.
TUP55	Fine Grain and Large Grain Niobium Cavity Prototyping for a Proton Linac	255
	W. Hartung, J. Bierwagen, S. Bricker, C. Compton, T. Grimm, M. Johnson, D. Meidlinger, J. Popielarski, L. Saxton, R. C. York Michigan State University G. W. Foster, I. Gonin, T. Khabiboulline, N. Solyak, R. Wagner, V. Yarba Fermilab P. Kneisel JLab
	A superconducting cavity has been designed and prototyped for acceleration of particles travelling at 81% the speed of light (beta = 0.81). The application of interest is an 8 GeV proton linac proposed as an upgrade to the Fermilab accelerator complex, although the cavity would also be suitable for other ion accelerators. The cell shape is similar to that of the 805 MHz high-beta cavity developed for the Spallation Neutron Source Linac, but the resonant frequency is 1.3 GHz and the beam tube diameter matches that of the 1.3 GHz cavity for the TeSLA Test Facility. Four single-cell prototypes have been fabricated and tested before and after post-purification. Two of the cavities were formed from standard high purity fine grain niobium sheet; the other two were fabricated from large grain niobium, following up on the work at Jefferson Lab to investigate the potential of large grain material for cost savings and/or improved RF performance. Two 7-cell cavity prototypes (one fine grain, one large grain) have also been fabricated. The single-cell results are presented in this paper, and the status of the prototyping effort is reported.
TUP65	JLAB CW Cryomodules for 4th Generation Light Sources	288
	R. A. Rimmer, R. Bundy, G. Cheng, G. Ciovati, W. Clemens, E. F. Daly, J. Henry, W. R. Hicks, P. Kneisel, S. Manning, R. Manus, F. Marhauser, J. Preble, C. Reece, K. Smith, M. Stirbet, L. Turlington, H. Wang, K. M. Wilson JLab
	Fourth generation light sources hold the prospect of unprecedented brightness and optical beam quality for a wide range of scientific applications. Many of the proposed new facilities will rely on large superconducting radio frequency (SRF) based linacs to provide high energy, low emittance CW electron beams. For high average power applications there is a growing acceptance of energy recovery linac (ERL) technology as the way to support large recirculating currents with modest RF power requirements. CW SRF and high current ERLs are two core competencies at Jefferson Lab. JLab has designed and built a number of CW cryomodules of several different types starting with the original CEBAF design, with variations for higher current in the two generations of JLab's free-electron laser (FEL), through two intermediate prototypes to the final high-performance module for the 12 GeV upgrade. Each of these represent fully engineered and tested configurations with a variety of specifications that could be considered for possible use in fourth generation light sources. Furthermore JLab has been actively pursuing advanced concepts for highcurrent high-efficiency cryomodules for next generation ERL based FEL's. These existing and proposed designs span the range from about 1mA single-pass to over 100 mA energy recovered current capability. Specialized configurations also exist for high-current non-energy recovered sections such as the injector region where very high RF power is required. We discuss the performance parameters of these existing and proposed designs and their suitability to different classes of fourth generation light sources.
WE206	First test results of half-reentrant single-cell superconducting cavities	407
	M. Meidlinger, J. Bierwagen, S. Bricker, C. Compton, T. Grimm, W. Hartung, M. Johnson, J. Popielarski, L. Saxton, R. York National Superconducting Cyclotron Laboratory P. Kneisel TJNAF E. Zaplatin Forschungszentrum Julich
	Particle physicists are on the verge of reaching a new frontier of physics, the Terascale, named for the teravolts of kinetic energy per particle required to explore this region. To meet the demand for more beam energy, superconducting cavities need to achieve higher accelerating gradients. It is anticipated that niobium cavities will reach a performance limit as the peak surface magnetic field approaches the critical magnetic field. "Low-loss" [1] and "reentrant" [2] 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. While these surface treatment methods have been effective for low-loss and reentrant single-cell cavity designs, it is not clear whether the same methods will be adequate for multi-cell versions. A "half-reentrant" cavity shape has been designed with RF parameters similar to the low-loss and reentrant cavities, but with the advantage that the same surface preparation should be reliable for multi-cell half-reentrant cavities. Two 1.3 GHz prototype single-cell half-reentrant cavities have been fabricated and tested at Michigan State University (MSU). One of the cavities was post-purified, etched via buffered chemical polishing, and tested at Thomas Jefferson National Accelerator Facility (TJNAF), reaching a maximum accelerating gradient of 35 MV/m. The halfreentrant cavity concept, design, fabrication, and first test results are presented.
	Slides(PDF)
WEP37	Nondistructive testing instrument of dished Nb sheets for SRF cavities based on squid technology	562
	Q. S. Shu, J. Susta, G. F. Cheng, I. Phipps AMAC Inc R. Selim, J. Mast Christopher Newport University P. Kneisel, G. Myneni JLab I. Ben-Zvi Brookhaven National Lab
	The performance of superconducting RF cavities used in accelerators can be enhanced by detecting micro particles and inclusions which are the most serious source of performance degradation. These defects prevent the cavities from reaching the highest possible accelerating fields. We have developed a SQUID scanning system based on eddy current technique that allows the scanning of curved Nb samples. This SQUID scanning system successfully located Tantalum defects about 100 um diameter in a flat Nb sample and was able to also locate the defects in a cylindrical surface sample. Most importantly, however, the system successfully located the defects on the backside of the flat sample and curved sample, both 3-mm thick. This system can be used for the inspection and detection of such defects during SRF cavity manufacturing.
TH102	Progress on large grain and single grain niobium - ingots and sheet and review of progress on large grain and single grain niobium cavities	728
	P. Kneisel JLab
	Large grain and single crystal niobium has been proposed several years ago as an alternative material to poly-crystalline niobium for superconducting cavities, exhibiting potential advantages such as "stream-lined" procedures, reduced costs and better reproducibility in performance. Several major laboratories have investigated the use of large grain and single crystal material in the past years and the niobium producing industry has responded in providing ingot material with enlarged grain sizes. Besides a large number of single cell and multi-cell cavities from large grain niobium, several single crystal cavities have been fabricated and tested with good performances. This contribution will review the progress since the SRF workshop in 2005 in material processing and handling and in cavity performances.
	Slides(PDF)