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Experimental Comparison at KEK of High Gradient Performance of Different Single Cell Superconducting
Cavity Designs.
F. Furuta, K. Saito, T. Saeki, H. Inoue, Y. Morozumi, T. Higo, Y. Higashi, H. Matsumoto, S. Kazakov, H. Yamaoka, K. Ueno,
Y. Kobayashi, aR. S. Orr and bJ. Sekutowicz,
KEK, aUniv. of Toronto/JSPS, bDESY
EPAC 2006 MOPLS084
1
Abstract We have performed a series of vertical tests of three different designs of single cell Niobium superconducting cavities at 2 degrees Kelvin. These tests aimed at establishing that an accelerating gradient of 45 MV/m could be reached in any of the designs, while using the standard KEK surface preparation. The designs tested were the Cornel re-entrant shape (RE), the DESY/KEK Low Loss shape (LL), and the KEK ICHIRO series. The cavities underwent surface preparation consisting of centrifugal barrel polishing, light chemical polishing,electropolishing, and final a high-pressure water rinse. All three kinds cavities were used in a series of vertical tests to investigate details of the surface treatment. When using ultra-pure water for the high pressure rinse, the LL cavity reproducibly exceeded a gradient of 45 MV/m, the RE design reproducibly reached a gradient of between 50 MV/m and 52 MV/m, and three of the six ICHIRO cavities reached a gradient of between 45 MV/m and 51 MV/m.
0
500
1000
1500
2000
2500
3000
0.2 0.4 0.6 0.8 1
Hcr
[O
e]
t (=T/Tc)
Hcr(t) = A*[1- t4] : A=1750 +- 150 Oe
Hcr Nb-cornell
Hcr Nb-KEK
High gradient limitation of Type-2 SRF cavity
H crRF (Oe) = 1750 150 [1 t 4 ]
2
TESLA LL RE IS
Diameter [mm] 70 60 66 61
Ep/Eacc 2.0 2.36 2.21 2.02
Hp/Eacc [Oe/MV/m] 42.6 36.1 37.6 35.6
R/Q [W] 113.8 133.7 126.8 138
G[W] 271 284 277 285
Eacc max 41.1 48.5 46.5 49.2
Principle of 50MV/m Cavity shape designs with low Hp/Eacc
TTF: TESLA shapeReentrant (RE): Cornell Univ. Low Loss(LL): JLAB/DESYIchiro ー Single(IS): KEK
from J.Sekutowicz lecture Note
3
10 9
10 10
10 11
0 10 20 30 40 50 60
RE Qo @ 2KQo
Eacc [MV/m]
Eacc,max = 52.4MV/mQo = 1.21E10
10 9
10 10
10 11
0 10 20 30 40 50 60
LL Qo @ 2KQo
Eacc [MV/m]
Eacc,max = 47.3MV/mQo = 1.13E10
10 9
10 10
10 11
0 10 20 30 40 50 60
ICHIRO Qo @ 2KQo
Eacc [MV/m]
Eacc,max = 51.4MV/mQo = 0.777E10
Ichiro Single
Low Loss
Reentrant Diameter [mm] 60
Ep/Eacc 2.36
Hp/Eacc [Oe/MV/m] 36.1
R/Q [W] 133.7
G[W] 284
Eacc max 48.5
Diameter [mm] 66
Ep/Eacc 2.21
Hp/Eacc [Oe/MV/m] 37.6
R/Q [W] 126.8
G[W] 277
Eacc max 46.5
Diameter [mm] 61
Ep/Eacc 2.02
Hp/Eacc [Oe/MV/m] 35.6
R/Q [W] 138
G[W] 285
Eacc max 49.2
Done the Principle proof of the 50MV/m 4
Eacc vs. Year
10
20
30
40
50
60
70
Eac
c,m
ax [
MV
/m]
Date [Year]'91 '00'95 '05'93 '97 '03
High pressuer water rinsing
(HPR)
Electropolshing(EP)
+ HPR + 120OC Bake
New Shape
Chemical Polishing
RE, LL, IS shape
'99 '07
2nd Breakthrough!
1st Breakthrough!
5
Reentrant@ 2kTreatment Eacc,max Qo @ Eacc,max Re-evacuation 51.2 0.59E10Re-HPR(UPW) 52.3 0.97E10Re-evacuation 51.9 1.11E10Warm-up only 52.4 1.21E10Re-HPR(UPW) 50.0 0.98E10Eacc max Ave. 51.6MV/m, Std. 1.0 MV/m Q0 = Ave. 0.97e10, Std. 0.24e10
Low Loss @ 2KTreatment Eacc,max Qo @ Eacc,maxEP(30um)+HPR(UPR) 46.5 1.20E10Re-evacuation 47.3 1.13E10Re-HPR(UPR) 46.6 1.50E10Warm-up only 45.0 1.03E10Re-evacuation 44.0 1.20E10
Eacc max Ave. 45.9MV/m, Std. 1.3MV/m , Qo Ave. 1.21e10, Std. 0.18 e10
HPR and evacuation were repeated.
108
109
1010
1011
0 10 20 30 40 50
LL cavity
EP(30um)+HPR(UPW)re-evacuationre-HPR(UPW)warm-up onlyre-evacuation
Qo
Eacc[MV/m]
Reproducibility
108
109
1010
1011
0 10 20 30 40 50 60
RE cavity
re-evacuationre-HPR(UPW)re-evacuationwarm-up onlyHPR(UPW)
Qo
Eacc[MV/m]
6
Temperature dependence of Eacc max
108
109
1010
1011
0 10 20 30 40 50 60
RE cavity
Qo(2K)Qo(1.8K)Qo(1.7K)Qo(1.5K)
Qo
Eacc[MV/m]
Eacc / Qo @Temp52.31 / 9.67e9 @2.0K51.65 / 1.27e10 @1.91K52.46 / 1.53e10 @1.73K52.73 / 1.48e10 @1.64K
7
Field Emission Analysis
-5 10-12
0
5 10-12
1 10-11
1.5 10-11
2 10-11
2.5 10-11
0 20 40 60 80 1 102 1.2 102
RE cavityLL cavityIS caity
d(1/Qo)
Ep[MV/m]
cavity FE onset
RE 60 39
LL 30 45
IS 16 49
:field enhancement factor
Field enhancement factor of IS shape is very small. 8
0
500
1000
1500
2000
2500
3000
0.2 0.4 0.6 0.8 1
Hcr
[O
e]
t (=T/Tc)
Hcr Nb CornellTESLA-like KEK singleLL single cellReentrant single cellIchiro single cell
9
RF critical field analysis
H crRF (Oe) = 1750 150 [1 t 4 ]
New shapes
Summary
Proof of reproducibility was done.
See poster MOPLS087
New cavity shapes with low Hp/Eacc made a breakthrough in high gradient of 50MV/m.
From the analysis of field enhancement factor it was also shown that the high gradient performance of IS shape is superior to other shapes.
Establishment of recipe is ongoing
Cavities prepared by KEK recipe
Mean=44.3MV/m, Sigma=6.9
by R.S.Orr
10 108
109
1010
1011
0 10 20 30 40 50 60
Qo
Qo
Eacc[MV/m]
World record!
Eacc=53.5 MV/m Qo =0.78e10
IS cavity #4