| 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. | |
| 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. | |