1. Measurement results of cavity gradient degradiation of cERL Main Linac cryomodule under beam operation
Hiroshi Sakai, Takaaki Furuya, Masato Sato, Kenji Shinoe, Kensei Umemori, Kazuhiro Enami(KEK), Masaru Sawamura (JAEA), Enrico Cenni (Sokendai)
8 pages
Main linac cryomodule set in cERL
Cryostat
HOM absorber
Tuner
9-cell cavity
Specifications
RF frequency: 1.3 GHz
Input power : 20 kW CW (SW)
Eacc: 　　 MV/m
Unloaded-Q:　　Q0 > 1*1010
Beam current : max 100mA (HOM-damped cavity)
Input couplers
Onset of radiation
ERL target
Summary of performance of cryomodule test in 2012
Vc=16 MV was achieved.
Vc= MV could be kept for more than 1 hour
Onset of radiation due to field emission: 8-10 MV/cavity
Degradation
2012.Dec
2011.Nov
Vertical Test 1
After installation to module (Vc = 1.038Eacc)
TTC CR mini-workshop (2014.Nov.12-Nov.14)

2. Target and status of Compact ERL (cERL) in 2013 & 2014
Due to the large field emission, we set the beam energy to 20MeV
Energy：20MeV　　(ML:16.7MeV(8.36MV+8.36MV)+Inj 3.3MeV)
Beam current：1.3GHz 10uA current (CW) with Energy recovoery
Initial target of cERL
　　　　　　　　　　　2013
　　　　　　　　2014 6 7 8 9 10 11 12 1 2 3 4 5
Magnet setting & alignment
NEG coating chamber
Injector beam commissioning
5.5MeV
Vacuum chamber setting
Cool down aging
Cool down to 2K
Beam commissioning
(1/30 – 3/14)
Beam commissioning
(5/22 – 6/20)
Return loop beam comissining（12/16-12/20）
History of cooling (2013.Nov.-Dec.)
Keep 3K/h(avoid HOM damper crakcking)
cERL return loop
commisisioning
Upper ML cavity temp
Lower ML cavity temp 2K
High power test
(each cavity )
High power test
（total:injector & ML）
LBP :Upper HOM damper temp
SBP : Middle HOM damper temp
LBP : Lower HOM damper temp
1 week
Normal operation of beam and/or high power test
start cooling (9:00～12:00) to 2K。13:00～22:00(or24:00) ,2Kkeep＆study, midnight & weekend 4K keep

3. Profile of field emission
First beam operation in 2013 Dec. (Screen shot of field emission and this effect)
When we shorten the gate width to 10us, we could not see the field emission.
Profile of field emission
Screen shot of field emission of 8.3MV of ML1 & 8.3MV of ML2 8.3MV with gate width of 100ms of CCD camera. We could see the profile of field emission.
screen
e- beam
20MeV
Main linac cryomodule
Beam profile
We could acceralate the beam without HOM damper effect and/or coupler kick.
No field emission effect was observed during beam operaion.
After that, we could see the beam profile without field emission effect with 10us gate width of CCD.

4. What happened during long term beam operation to cavities (radiation & cavity performance)
We set two types of radiation monitor. (radiation monitor (ALOKA), PIN profile monitor) near the beam axis.
Radiation measurement during beam operation with 20MeV for 3 weeks. We found sudden jump after 2weeks operation.
No6
Radiation monitor
#3 cavity（lower）ML2
#4 cavity（upper） ML1
No5
Radiation monitor
Keep 8.57MV of each cavity every daytime
1week
Increase radiation(No.6) e-
Radiation (mSv/h)
No.5
16 PIN diodes
Q degradation & change of PIN diodes
Lower cavity 16 PIN diodes
We met Q degradation during beam operation.
PIN profile were also increased totally.
Fatal Q decrease like crack of Hom damper was observed
Same timing response
2013.Dec.12 (same as 2012.Dec.)
Operation
voltage
Lower PIN
Vc=10MV
Upper PIN
Decrease Q0
during operation
Cavity voltage
No6
2012.Dec.
No5
Lower PIN
2014.Mar.10
Upper PIN
2014.Feb—Mar.
Vc=10MV
1hour

5. Apply pulse processing
ML1 Vc
During beam operation, we apply pulse processing in order to eliminate the field emission source by applying high field.
Measured voltage(digital)(Vc)
Sudden high peak
1hour
100ms Vc
Pulse processing
Base:8.57MV
Upper PIN diode
Duty 10Hz 4ms [peak:11MV] (pulse)
QL ~ 1*10^7  t ½ = 1ms , 4ms is larger t ½
When we applied pulse processing, we could see the decreasing of PIN signal individually.  pulse processing works well
Pulse processing applied　(10Hz 4ms) 8.5MV+2.5MV(pulse)
　　　ML1:15min + 1hour
ML2:15min + １hour
Pulse processing was effective for both cavities. (ML1: 8.57MV & ML2:8.57MV)
Upper radiation(No.5) 38.7mSv/h (2/25 21:00)  20.48mSv/h (2/26 21:47)
Lower radaition(No.6) 133mSv/h (2/25 21:00)  77.9mSv/h (2/26 21:47)
Radiation reduced to half by pulse processing. Now pulse aging works for reducing field emission during beam operation. We plan to try He processing end of beam operation (first try at V.T)

6. Cavity performance under beam operation of cERL (2014.Jan-Jun.)
DA/A ~ 0.02%
DF ~ 0.02deg
ML1 Vc
ML2 Vc
FPGA
Virtex5-FX
8 hours
8 hours
Piezo voltage
uTCA
1kHz
piezo
ML1 vac
ML2 vac
Microphinics pk-pk = 7Hz
Piezo feedback works well
He return gas (52W:static+inj+ML)
Normal decay time~ 1ms
オシロの絵(trip)
Pt : yellow
8 hours
Very fast
He pressure (3kPa+-10Pa)
He level
50us
We operated from 13:00-22:00 under 2K cooling. Vc keep 8.57MV for 2 cavities. 1 trip (burst) was usually observed (Pref ITL).
We have enough cooling power and keep to 2K
stably with injector & main linac by cryogenic

7. Present status (May to June 2014)
Operation Vc
Operation Vc
During beam operation
During beam operation
Q0 values were measured by He gas flow ratio by keeping CW field.We met Q degradation during beam operation. But we keep same performance within error bars after degradation from May to June in 2014 by trying pulse processing every 2 weeks. We continue to see the cavity performance on next beam operation.

8. Summary
We met the Q degradation & radiation increase during beam operation.
We can reduce pulse processing pragmatically.
In beam operation, we kept stable operation by using digital feedback system.
Several trips were observed on a half year.
Now we keep stoping the cavity degradiation by using several pulse processing. And we will try He processing to much reduce the field emission source.
We continue to see the cavity performance on next beam operation.

9. backup

10. Setup of high power test at cERL
30kWIOT
16kW Solid State AMp
Setup of high power test at cERL
Radiation sensor (下流)
#4 cavity（upper）
Radiation sensor　（上流）
#3 cavity（lower）
QL :
1.31*10^7(上流decay)
1.01*10^7(下流,decay)
場所は少し違う
PIN radiation profile monitor set around beam axis
Si PIN diode set around beam axis
16 Si PIN diodes at each position
#3 cavity（lower）
#4 cavity（upper）
SBP side
LBP3
LBP4
SBP3
SBP4
LBP side
２０１２年から設置しており、これで前回の放射線の比較を行う。

11. Digital LLRFによる空洞安定性(total 20MeV時の安定性)
FPGA
Virtex5-FX 入射 空洞
主空洞

12. 冷却中の主空洞Alignment 今回は１側から覗いた。 ４or8が精度が出にくい。 冷凍機側0.2-0.5mm (ここがエラーがでかい)
h 1-4
入力カプラー側
0.7mm
h 5-8
2012年の冷却時の
変化のデータ
下側1.0mm
Summary of displacements of targets and cavities between RT to 2K
Horizontal (mm)
Vertical
(mm)
Target 1-4 (Average)
-0.11
-1.06
Target 5-8 (Average)
0.87
-0.37
Average movement of cavity center (from target 5-8)
0.39
v 1-4
下側0.2mm
途中ずれたか？
大体前回を再現している。
v 5-8
空洞中心の変化は0.4mm程度

13. Next case (6/12)
79mSv/h  250mSv/h  400mSv/h (final)　(upper cavity)

14. ML1 Pulse aging (6/14)
ML2 pulse aging start Vc = 8.6MV+1.9MV (4ms,10Hz, pulse)
ALOKA ML1
0:29 ML1 : Vc=0MV ML2 Vc=8.57MV GV close ALOKA No5 459 mSV/h, No6 204mSv/h
2:22 ML1 Vc=0MV ML2 Vc=8.57MV GV close ALOKA NO5 1.31mSv/h (much reduce) ALOKA No mSv/h (half)

15. Ring 16 PIN diodes were set on both jacket sides
to compare the radiation profile with rotating mapping
Typical example of chaging How to know the profile and radiation source on cryomodule test ?
#4 cavity before jacket welding for cERL
Field emission (F.E) electron run along cavity axis.
We think angular distribution of F.E preserved and detected outside of jacket near both end.
-mode 22MV/m Q0=8.0*10^9
Q-E curve of 1st #4 cavity V.T
Xray onset start 14MV/m
Peak at 360°
22MV/m x-ray rotating mapping
Broad Peak at 180°
Peak at 360°
22MV/m x-ray mapping by both jacket PIN diodes
Broad Peak at 180°
Radiation profile were detected from both direction by a ring of 16 PIN diodes and agree well with x-ray angular distribution of rotating mapping.
16 PIN can detect radiation profile during cryomodule test.

16. Detail radiation profile measurement
Sudden burst event was observed under keeping field of 14.5MV
After burst
Before burst #3
(lower)
#4 cav #4
(upper )
Field decreased
・Radiation pattern was changed from V.T
・Radiation pattern also changed after X-ray burst
・Another new radiation sources were produced during assembly work and high power test.