1. Performance Degradation cERL Injector Cryomodule
and
Performance Recovery in
cERL Injector Cryomodule
Eiji Kako
(KEK, Japan)

2. cERL Injector Section 500 kV DC Gun 2K Cold Box Gate valve Buncher
Cavity
X-ray detector
Faraday cup
Screen monitor
Lower
Center
Upper
Collimator
No.1
Faraday cup
Screen monitor
No.2
No.3
Injector Cryomodule
Merger Section
Ion pump
Specification
7.0 MV/m x 3 cavity
Total Vacc : 5 MV

3. Assembly of Injector Cryomodule
History of cool-down cycles
Year
2012
2013
2014
2015
2016
Assembly of Injector Cryomodule
1st cool-down
2nd cool-down
3rd cool-down
4th cool-down
5th cool-down
6th cool-down
7th cool-down
8th cool-down
9th cool-down
10th cool-down 4 6 9
Low RF power tests of Injector Cryomodule 1
High RF power tests of Injector Cryomodule 4
Beam commissioning
of Injector section at 5 MeV 5 7 11
High RF power tests of Main Linac Cryomodule
Beam commissioning of Main Linac section 1 3
Beam commissioning of Re-circular ring 4 6
Beam operation at 20 MeV, ~10 mA 1 4
LCS experiments 5 6
Beam operation at 20 MeV, ~100 mA 1 3
Beam operation at 20 MeV, ~1 mA

4. Severe increase of x-ray radiation level
> 100 mSv/h
Jump
Jump
#1 Cavity
#2 Cavity
#3 Cavity
Total : 5 MV
(Ave. 7.0 MV/m)
Quench

5. Performance degradation in long term beam operation for 3 years
Eacc = 7.0 MV/m
individual cavity
Eacc = 7.0 MV/m
individual cavity
Observations
Degradation firstly initiated in #3 cavity close to merger section.
Then, contamination area seems to have gradually extended toward #2 cavity and #1 cavity.
Qo values in #3 cavity dramatically degraded after June 11th , together with heavy x-ray radiation.
Field emitted electrons, which run away from #3 cavity, were accelerated by #2 and #3 cavities.
These electrons went toward upper stream and collided with cathode surface of DC-gun.

6. Pulsed RF conditioning for performance recovery
CW 30 kW
Klystron
CW 300 kW
Klystron
QL interlock
< 0.8 x QL(normal)

7. Performance recovery by pulsed RF conditioning

8. Questions ?? How do you clean warm components?
Gate valves
Ion pump
Beam position monitor
Screen monitor
Faraday cup
Collimator
Beam pipes
(Charge-up of insulator)
Where dust particles come from?