ERL主加速部#4号機
縦測定結果の報告
2011/12/2
ERL検討会ERL‐SCグループ 梅森健成、阪井寛志、佐藤昌史、沢村勝、篠江憲治、古屋貴章、Enrico Cenni

Specification for cERL main linac cavity• Eacc– Required Eacc is 30 MV for two cavities– But, operated with vector sum mode at first stage– Assuming 2x107coupling and maximum detuning of 50
Hz– Required maximum Eacc is ～20MV/m for a cavity• Q0 value– Larger Q0 value is desirable for He refrigerator– Target is 1x1010 at 15 MV/m

• Frequency– Frequency must be within mechanical tuner range(3mm = 900 kHz) at 2K, i.e. 1299.1~1300.0MHz– With good field flatness of > 98%

History for ERL 9‐cell #3/#4 cavities (for cERL)#3 cavity (1st)#3 cavity(2nd) #4 cavity (1st) #4 cavity(2nd)

Pre‐EP andEP‐1

5 um + 120um

5 um + 120um

Annealing

750 degree x
4hours750 degree x
4hoursPre‐tuning> 98%
flatness> 99 %
flatness> 98%
flatness> 98 %
flatness

EP‐250 um

20 um

50 um

30 um

HPR

5hours+ 5hours

7.5 hours+ 5 hours

6hours+ 5.5 hours

6 hours+ 5 hours

Baking> 110 degree,
48 hours> 110 degree, > 110 degree, > 110 degree,
48 hours
48 hours
48 hours

Vertical test(Done)(Done)

Assembly(Done)(Done)

#4 cavity 1st vertical test (10/27)• Initial (1.6‐1.8K), Passband(8pi),Final (1.7‐1.8K)•Max. Field 22.7 MV/m, quench at 1 cell equator• Q=1.4x1010(@15MV/m), 1.0x1010(@20MV/m)• X‐ray on set: (initial) 18MV/m → (final) 15MV/m• X‐ray at 20 MV/m: (initial) 3.7uSv/h → (final) 644 uSv/h

① 1 cell equator 264 deg(=224 for mapping)
After 1st vertical test

Local grinding

Defect was found after vertical test Defect disappeared after local
grinding
Bump
Height ~10um
Width ~200um

Bump
Height ~10um
Width ~200um

Local grinding② 8 cell equator 194 deg
After 1st vertical test

Defect was found after vertical test

After local grinding

Defect disappeared after local
grinding

③ 9 cell equator 102 deg
After vertical test

Defect was found after vertical test
Pit
Height 15~20um
Width ~200um

After local grinding

Defect disappeared after local
grindingPre‐tuning

Field flatness 98.5%

Frequencies of both end cells
are ~100kHz higher thanthose of center cells→ should be better flatnessafter EP-2(30um)

2nd EP‐2 for ERL‐9cell #4 cavity[before EP]• Degreasing (FM20) : 240min at ultrasound bath
• 60min at ultrasound bath with ultra‐pure water[EP]• Current density: 32 mA/cm^2• Amount of plishing: 30um
• Contained amount of Nb: 4.7 g/litter[After EP]• Degreasing (FM20) : 60min at ultrasound bath
• HPR: 6hour(flange open) + 5hour(flange close)Cavity surface after EP‐2
From LBP side

From SBP side

Cavity surface is generally fine.
Some defects, polished after EP-1 were seen. But edges
seem to be smooth.

Q‐T curve for ERL 9‐cell#3 and #4 cavity#3 cavity (1st VT)
1299.647 MHz(@2K)
17.5 nΩ#3 cavity (2nd VT)
1299.603 MHz(@2K)
16.6 nΩ#4 cavity (1st VT)
1299.717 MHz(@2K)
17.0 nΩ#4 cavity (2nd VT)
1299.640 MHz(@2K)
16.6 nΩResidual resistance
Includes loss at SUS
flangesQpickup for #3 and #4 cavities

Target of Qpickup 1e12Qpickup at 2K is OK, within 5～10%.

2K π‐mode measurement• Initial (1.6‐2.1K), Final (1.7‐1.8K)‐ At 3MV/m, Qo=1.5e10(1.8K) and Qo=1.1e10(2.1K)• Reached to 25 MV/m. Satisfied ERL spec.
• 1.4x1010(@15MV/m), 1.2x1010(@20MV/m)• No limitation up to 25MV/m

2K π‐mode (initial)

・Measured at temperature of 1.6～2.1K
・Reached to 25 MV/m
・Multipacting from 18 to 23 MV/m, accompanied by X‐rays.
・But they were processed. Radiation is also processed up to24 MV/m.
・Radiation was very small, 20uSV/h at 25MV/m.

2K π‐mode (final)・Measured at temperature of 1.7～1.8K
・Reached to 24 MV/m, without quenches.
・X‐ray on‐set was 22 MV/m・Radiation was very small, 4uSV/h at 24MV/m.

X-ray mapping system

・ Array of Si diode for X-ray detection and carbon resistor
for temperature measurement
・ They will rotate around cavity by using pulse motorX‐ray at 20 MV/m (final π‐mode)

No X‐rays were observed.

X‐ray at 24 MV/m (final π‐mode)

Small X‐ray signal around 2‐3 irisSummary• After 1st vertical test, several defects were found bysurface inspection. The cavity was repaired by grinding
such defects.
• Pre‐tuning and 30um EP‐2 were applied.
• 2nd vertical test was performed for ERL‐9cell #4 cavity.
• 25 MV/m was successfully reached.
• Qo=1.4e10(@15MV/m) and 1.2e10(@20MV/m)• Radiation was very small. Its final on‐set was 22MV/m.
• ERL specification was satisfied.
• This cavity will go for He jacket welding.