Experimental Comparison at KEK of High Gradient Performance of Different Single Cell Superconducting Cavity Designs. F. Furuta, K. Saito, T. Saeki, H.

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.

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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 ]

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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

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RE Qo @ 2KQo

Eacc [MV/m]

Eacc,max = 52.4MV/mQo = 1.21E10

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LL Qo @ 2KQo

Eacc [MV/m]

Eacc,max = 47.3MV/mQo = 1.13E10

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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

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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!

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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.

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LL cavity

EP(30um)+HPR(UPW)re-evacuationre-HPR(UPW)warm-up onlyre-evacuation

Qo

Eacc[MV/m]

Reproducibility

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RE cavity

re-evacuationre-HPR(UPW)re-evacuationwarm-up onlyHPR(UPW)

Qo

Eacc[MV/m]

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Temperature dependence of Eacc max

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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

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Field Emission Analysis

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1.5 10-11

2 10-11

2.5 10-11

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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

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Hcr

[O

e]

t (=T/Tc)

Hcr Nb CornellTESLA-like KEK singleLL single cellReentrant single cellIchiro single cell

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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

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Qo

Qo

Eacc[MV/m]

World record!

Eacc=53.5 MV/m Qo =0.78e10

IS cavity #4