Saxton L.

Paper	Title	Page
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.
TUP67	Niobium Quarter-Wave Resonator Development for a Heavy Ion Re-accelerator	296
	W. Hartung, J. Bierwagen, S. Bricker, C. Compton, T. Grimm, M. Johnson, F. Marti, J. Popielarski, L. Saxton, R. C. York Michigan State University A. Facco INFN-LNL E. Zaplatin FZ Juelich
	A superconducting linac is being designed for reacceleration of exotic ions produced by the Coupled Cyclotron Facility at Michigan State University (MSU). The re-accelerator beam line will include a cyclotron gas stopper, a charge breeder, a normal conducting radio-frequency quadrupole, and two types of superconducting quarterwave resonators (QWRs) for re-acceleration to energies of up to 3 MeV per nucleon, with the option of additional acceleration to 12 MeV per nucleon as a future upgrade. Both QWR types are based on existing cavities that are presently used at INFN-Legnaro. The second QWR (optimum beta = 0.085, 80.5 MHz) was previously designed and prototyped as a collaborative effort between Legnaro and MSU. The first QWR (optimum beta = 0.041, 80.5 MHz) is very similar to the corresponding QWR in use at Legnaro, but with a larger beam aperture. Separation between the cavity vacuum and the cryostat insulation vacuum is also implemented to reduce the risk of particulate contamination. Structural analysis of the QWRs is being done in collaboration with FZ Juelich. The beta = 0.041 QWR design and prototyping effort is discussed in this paper.
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.
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