Compton C.

Paper	Title	Page
TUP05	Crystal Orientation Effects During Fabrication of Single or Multi-Crystal NB SRF Cavities	111
	D. Baars, T. R. Bieler, A. Zamiri, F. Pourboghrat, C. Compton Michigan State University
	Single and large-grain Nb SRF cavities are of interest due to possible reduction of cost and problems associated with inconsistent texture and surface finish among batches of rolled polycrystalline Nb sheet. The effect of crystal orientation on dislocation density, surface quality, and recrystallization after plastic deformation and e-beam welding was investigated, as understanding of their interrelations is needed. These were evaluated for three samples of different orientations at steps similar to those in typical cavity forming, with deformation modeled using a crystal plasticity approach. Initial dislocation density was higher than expected, increased with deformation, after welding was reduced in recovered areas, and was similar to initial density in recrystallized grains; there was also evidence that Nb has a higher tolerance for dislocations than other metals. Surface quality depends on a complex relation of crystal orientation, slip system activity, and prior surface treatment. Recrystallization nucleated outside the melt pool, and the new orientations grew both epitaxially into the weld as it solidified, and away until heat and time were insufficient to continue growth.
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.
	Slides(PDF)
WEP01	Studies of alternative techniques for niobium cavity fabrication	429
	C. Compton, D. Baars, T. Bieler, J. Bierwagen, S. Bricker, W. Hartung, D. Pendell, R. York Michigan State University L. Cooley, H. Jiang, B. Kephart Fermilab
	Alternative fabrication techniques for superconducting radio frequency (SRF) cavities are being investigated. The main goals are to reduce cavity fabrication costs and expand possibilities for advanced cavity designs. At present, SRF cavities are fabricated via deep drawing of parts from sheet material and electron beam welding (EBW) to join the parts together. EBW produces welds of high quality, but the procedures are costly and timeconsuming. Alternative technologies being explored include tungsten inert gas (TIG) welding of Nb, hydroforming of Nb, and electron-beam free form fabrication (EBFFF) of Nb. If techniques can be developed which do not degrade the Nb purity, TIG welding could reduce or eliminate the need for EBW. Hydroforming could also be an alternative to deep drawing and EBW. As has been demonstrated by several other groups, complete cavities can be hydroformed from Nb tubes in one step using internal pressure and outer dies. Hydroforming of cavities in an industrial setting is presently being explored. EBFFF is a new technique for forming parts from wire stock with an electron beam. Though it may not be suitable for fabrication of a complete cavity, EBFFF could be used to produce tubes for hydroforming or parts for drift tube cavities. Additionally, the possibility of producing single crystal tubes using EBFFF is being explored.