Design and Prototype Progress toward a Superconducting Crab Cavity Cryomodule for the APS Page: 2 of 3
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Proceedings of IPAC'10, Kyoto, Japan
Figure 2: Baseline model (left) for the vertical cold test
prototype. EDM wire is cutting (right bottom) on the bulk
niobium plate with the "Y" contour for the half
waveguide wall. The right, top picture shows the
simulated "Y" cut on an aluminum template.
MULTIPACTORING AND LORENTZ
3-D multipactoring simulations were performed on both
single-cell structures using Omega3P/Track3P , see
Fig. 3. The results are similar for both cases which imply
that the multipactoring regions are common to both and
are not enhanced by the damper design. The most
dangerous 2nd order, one-point multipactoring is located
near the cavity equator along the squashed surface. The
impact energy is approximately 1318 eV and
corresponds to a crabbing voltage level of >0.35 MV and
a maximum surface magnetic field of >66.3 mT in the
baseline structure. All electrons with a higher impact-
energy are associated with higher-order (3~5)
multipactoring and are considered less dangerous. Based
on experimental benchmarks of other cavity (e.g., a
TE011 mode cavity) and the test result in Fig. 1, we
believe that the multipactoring of the single-cell cavity
designs are not hard limits and can be processed away.
Lorentz force detuning (LFD) was investigated to
validate experimental data as well as to consider its effect
on the tight phase tolerance required to assure that the
SPX system is transparent to the remainder of the APS
storage ring. A non-uniform niobium shell thickness of
the cavity was shown to cause a large LFD , but the
addition of waveguide groups reduces this effect.
An LFD value of 22.4-29.8 Hz/(MV/m)2, depending on
structural constraints, was obtained in an ANSYS
simulation for the baseline design. At 0.5 MV deflecting
voltage, the folded resonance peak, with a loaded Q of
1.2E6, is tilted over its -3dB bandwidth (-1.17 kHz, in
Fig. 4). A fast digital self-excited loop control can be used
to quickly recover from an RF trip without requiring
cavity stiffeners .
CRYOSTAT AND COOLING DESIGN
The SPX cavity likely can be integrated into an old
800 er - ;+
j W , 'On-cell damper only - *
o OM +Y WOdampers o * :
f I o +
-I" I X4U
4a u 9
E E a
20 480 *
30 40 50 o 70
Maximum Surface Magnetric Field (mT)
+ Oncexii damper Qfly
o LoM+Y G damp~ert
2rd order MP, one-pa rt
3d order MP o-port..
Sinhorder MP re-peirt..
020 025 830 835 040 045 050
Crabbing Voltage (MV)
Figure 3: 3-D simulation results of multipactoring in
single-cell SPX cavities from Omega3P/Track3P.
-5 -LFD due to 29.8
Figure 4: Structural deformation of the baseline SPX
cavity due to the Lorentz force (insert) and the resultant
detuning of the cavity resonance (blue curve).
CEBAF C100-style helium vessel with only three
convolutions of bellows. The end-plates of the helium
contaimment around each cavity could be constructed
simply from the waveguide end-groups during fabrication,
see Fig. 5. The conductive cooling effect will be
confirmed by 3-D RF-thermal simulations.
A 1-D RF-thermal model has been developed to
determine the proper Nb flange and 50K heat station
07 Accelerator Technology
T07 Superconducting RF
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Haipeng Wang, Guangfeng Cheng, Gianluigi Ciovati, James Henry, Peter Kneisel, Robert Rimmer, Gary Slack, Larry Turlington, Geoff waldschmidt, Alireza Nassiri. Design and Prototype Progress toward a Superconducting Crab Cavity Cryomodule for the APS, article, May 1, 2010; Newport News, Virginia. (digital.library.unt.edu/ark:/67531/metadc837204/m1/2/: accessed December 11, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.