The progress in developing superconducting third harmonic cavity Page: 2 of 3
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support posts, will be slightly modified for the 3.9 GHz
Figure 3: Layout of the cryostat.
The cavity string will be assembled at Fermilab but the
cryomodule will be pre -assembled to check the fit of all
components, disassembled, and then shipped to DESY for
final assembly. Ultimately, the cryomodule will be
installed in DESY's TTF in 2007.
COLD TEST RESULTS
Test of the 3-cell cavity.
The first niobium 3 -cell prototype was built to test
cavity performances and develop tooling and technology.
There are no HOM or main coupler s on this cavity. The
first results of th e cold tests were reported in [5 -6]. A
brief test history is shown in Table 1.
Table.1: History of cold tests of the 3-cell cavity
BCP; HT; HPWR Test results
o treatment R=2000nSi, Ea=5.6 MV/m
CP-140pm; R=60n5i, Ea=11.5 MV/m; X-ray
CP-30pm; HPR: 3x30 R=70nSi; E=12.5 MV/m; X-ray
PWR:lhrs, movable R=60nSi;E=12.8MV/m;NoX-ray
CP:20pm;HPR:7x90' =15MV/m - coupler problem
CP:5pm; HPR-2hrs R=6 nf ; Ea=19MV/m; NoX-ray
ake: 48hrs@120C R=16 n5i, E=19MV/m; NoX-ray
CP:lOpm;HPR:2.5hrs R=58 nf ; Ea=12MV/m, X-ray
PR:6.5 hrs, movable R=15n5i;Ea-19MV/m; NoX-ray
Initially the cavity was etched -140 pm inside
(measured by etching rate, not frequency) and 20 pm
outside and then treated l0hrs at 600 C. The first test
showed a field emission problem, which was fixed after
appropriate high pressure rinsing. The b est achieved
residual surface resistance was 6 n&2 (measured at 1.4 K).
Typical resistance at 1.8 K of -50 n&2 corresponds
Q0-6.e+9. The c avity was quenched at accelerating
gradient of -19 MV/m (surface peak magnetic field o f
-105mT) and this threshold can be explained by thermal
breakdown model [ 9]. The 9 -cell cavity will have a
gradient of -21MV/m for the same surface magnetic field
achieved in the 3-cell cavity. This is well above design
gradient of 14MV/m. We are planning to use this cavity
as a reference cavity to check performances of the
buffered chemical polishing ( BCP) and high pressure
water rinsing (HPWR) facilities.
Test results of the 9-cell cavity
The first 9 -cell Nb cavity (prototype) failed during the
deep BCP. After -130pm etch a hole developed in one of
the HOMs coupler s, which has thinner wall thickness
than in the final design. Cavity No. 2 was successfully
manufactured, tuned and tested after BCP, high
temperature treatment (lOhrs at 600 K) and HPWR.
Initial measurements show ed a very high residual
resistance Rres=3000 n&2. After operating with high fields
in "7t" and "0" modes, the residual resistance dropped off
-5 times to - 600 n&2. After processing at high field level
during the rest of the day, the next day showed a residual
resistance of -80 n &2. Processing was done at pulsed
power 120 W and different duty factor from 1% to CW.
Additional high field processing for 2 more days
improved residual resistance to 40 n &2. The h istory of
RvsT measurements is shown in figure 4.
In the cavity tests we observed strong multipactor ing
which causes Q -slope at small field le vel. After high
Figure 4: Resistance vs. Tc/T. Measurements
were done in a few cold tests.
fields "processing" Q improved for small fields and the
multipacting level shifted from -0.5 MV/m acceler ating
gradient to - 2.5 MV/m. In pulsed regime accelerating
gradient was -8-11 MV/m, limited by available RF power
due to low Q. Some DC current was observed from pick-
up antenna at the gradient higher than 10 MV/m (fig. 5).
-- Rs, 06.06.06
--Rs, 06 06.09
5 TclT 6
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Solyak, Nikolay; Edwards, Helen; Foley, Mike; Gonin, Ivan; Harms, Elvin; Khabiboulline, Timergali et al. The progress in developing superconducting third harmonic cavity, article, June 1, 2006; Batavia, Illinois. (https://digital.library.unt.edu/ark:/67531/metadc889800/m1/2/: accessed March 22, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.