DEVELOPMENTS OF 700-MHZ 5-CELL SUPERCONDUCTING CAVITIES FOR APT Page: 2 of 3
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3 SURFACE TREATMENT AND
PREPARATION AT LANL
After delivery to LANL, the cavities were chemically
etched again with a standard BCP (Buffered Chemical
Polishing) solution of 1:1:2 . Then, they were rinsed
with high-pressure deionized water at -950 psi in a class-
100 clean room and assembled with couplers, flanges and
vacuum valve. Once sealed in the clean room, the cavity
was moved to a measurement room, set on the cryostat
insert, and pumped down and leak checked. Before
cooled down, the cavities were baked at 150 0C for 48
hours. It should be noted that no cavities were baked at
temperatures higher than this before testing.
4 TEST RESULTS
Figure 2 shows the Q-E curves of all the cavities. The
tests conducted at TJNAF are marked as JLAB with the
legend. The data for Eleanore cavity between 4 MV/m
and 11.5 MV/m are missing since we could not take the
final data due to damage to the driving coupler cable. As
for the LANL cavity, there were difficulties in performing
the final equator weld in the middle cell and we found the
Qo drop shown in Fig. 2 was caused by some defect at this
equator from heating detected by a temperature sensor.
Before the LANL cavity was tested, low-field Q> obtained
at LANL were lower than that recorded by TJNAF. We
have been investigating the cause of these differences.
Rinsing process right after BCP might have contributed to
the better Q> since the LANL cavity was filled with DI
water and kept overnight before HPR (High Pressure
At LANL, the available RF power was limited to - 250
W. Degradation of Q due to field emission limited
performance, although it appeared that most of the
cavities would have quenched at fields slightly higher
than their maximum fields due to heating at defects or
heating by electron bombardment on the surface. At
TJNAF, however, they stopped measurement of the AES
cavity so as not to damage the driving coupler cable.
Germaine and Sylvia cavities were limited by quench.
Best results of all the APT 5-cell cavities (up to 1/29/01)
K XXX- Quench
D + +
_ r~r -5- -.
1.E+08a I f 4
0 2 4 6 8 10 12 14
Figure 2: Vertical test results of all six 5-cell cavities developed for APT. Test temperature was 2 K.
The results shown in Fig. 2 are the best results for each
cavity. Some cavities needed extra chemical etching
(100-200 m), RF processing and/or helium processing,
although processing did not take more than a few hours.
The problem we have to solve to get higher gradients for
the next project such as AAA, that would want to operate
at F cc as high as 10 MV/m is, field emission.
Unfortunately, we have not had good diagnostic tools,
such as temperature and X-ray mapping of the cavity, to
determine the loss distribution inside the cavity and
identify the cause of Qo drops.
6 FUTURE PLANS
We are planning to identify the
emissions that appear in most of the
temperature and X-ray mapping system
causes of field
cavities using a
o AES (12/21/00)@JLAB
A Ayako (9/27/00)
X Eleanore (12/6/00)
* Germaine (4/12/00)@JLAB
* Sylvia (8/3/00)@JLAB
+ Sylvia (11/1/00)
o LANL (1/18/01)
* APT Spec.
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TAJIMA, T.; MONTOYA, D. I & AL, ET. DEVELOPMENTS OF 700-MHZ 5-CELL SUPERCONDUCTING CAVITIES FOR APT, article, June 1, 2001; New Mexico. (digital.library.unt.edu/ark:/67531/metadc717507/m1/2/: accessed December 16, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.