1. Status of 500-kV DC gun at JAEA
N. Nishimori, R. Nagai, R. Hajima
Japan Atomic Energy Agency　(JAEA)
M. Yamamoto, T. Miyajima, Y. Honda
KEK
H. Iijima, M. Kuriki
Hiroshima University
M. Kuwahara, S. Okumi, T. Nakanishi
Nagoya Univiersity

2. N. Nishimori, Jefferson Lab, Newport News, VA
Outline
Introduction (Compact ERL, a 500 kV DC gun)
High voltage conditioning of segmented insulator with a stem electrode
510kV for 8 hours after removing field emission site with current conditioning
High voltage conditioning with cathode electrode in place
Conditioning up to 526 kV by removing field emission site with wiping
Demonstration of 440kV for 8 hours (present status)
Plan of gas conditioning to remove field emission site
Beam generation at 300 kV
Summary and Outlook
Mar. 6, 2012
N. Nishimori, Jefferson Lab, Newport News, VA

3. Compact ERL (test facility)
E gun
(Installation by Oct. 2012
Beam generation by Mar. 2013)
exp. hall
Energy 35/245 MeV
Current 10mA
Emittance 0.1 – 1 mm・mrad
LCS gamma-ray
superconducting accelerator
supercavity
Mar. 6, 2012
N. Nishimori, Jefferson Lab, Newport News, VA

4. N. Nishimori, Jefferson Lab, Newport News, VA
A 500 kV photocathode DC gun at JAEA
HV terminal
segmented
insulator
stem electrode
gun chamber
cathode
anode
NEG pumps
18,000 l/s
electron beam
Mar. 6, 2012
N. Nishimori, Jefferson Lab, Newport News, VA

5. N. Nishimori, Jefferson Lab, Newport News, VA
1200
Segmented insulator
1000
Can guard ceramics against field emission generated from stem electrode.
Cannot diminish field emitter itself. Reliable way to remove field emitter still needs to be developed.
segmented insulator
800
600
6.8 MV/m
height (mm)
guard rings
400
guard rings
8.3 MV/m
field emission
stem electrode
200
stem electrode
14.3 MV/m
stem electrode nose
beam axis
gun chamber
-200
ceramic
200
400
600
Mar. 6, 2012
N. Nishimori, Jefferson Lab, Newport News, VA
radius (mm)

6. N. Nishimori, Jefferson Lab, Newport News, VA
500kV DC gun at JAEA
550kV Cockcroft Walton power supply
segmented insulator
SF6 tank
400mm in diam.
730mm
1 m
in diam.
3.8 m
gun chamber made of titanium
Mar. 6, 2012
N. Nishimori, Jefferson Lab, Newport News, VA

7. High voltage testing with a stem electrodemm
101.6 f
dummy cup instead of cathode electrode
Mar. 6, 2012
N. Nishimori, Jefferson Lab, Newport News, VA

8. N. Nishimori, Jefferson Lab, Newport News, VA
HV conditioning
Why slow conditioning ?
4kV/hour
190℃ baking for 8 hours
start conditioning at 3x10-8[Pa]
Vacuum pump: 1000L/s-TMP
550kV
Because of radiation increase above 520kV
R. Nagai et al., “High-voltage testing of a 500-kV dc photocathode electron gun”, RSI (2010).
Mar. 6, 2012
N. Nishimori, Jefferson Lab, Newport News, VA

9. Conditioning with stem electrode (Oct. ’09)
600
400
HV(kV)
200
102
rapid increase and slow decrease every discharge
1Sv=100rem
at 500kV
at 500kV 1
Radiation(mSv/h)
10-2 72 76 80 84 88
time(hrs.)
Mar. 6, 2012
N. Nishimori, Jefferson Lab, Newport News, VA 9

10. Conditioning with stem electrode (Oct. ’09)
600
400
HV(kV)
200
102
at 500kV
decrease of radiation
at 550kV 1
Radiation(mSv/h)
10-2
112
116
120
124
128
time(hrs.)
Mar. 6, 2012
N. Nishimori, Jefferson Lab, Newport News, VA 10

11. Conditioning with stem electrode (Oct. ’09)
600
400
demonstration of 510 kV for eight hours
HV(kV)
200
102 1
Radiation(mSv/h)
radiation similar to B.G. level
10-2
136
140
144
148
152
time(hrs.)
Mar. 6, 2012
N. Nishimori, Jefferson Lab, Newport News, VA 11

12. Cathode electrode: POISSON calculation
6.7 MV/m
cathode
100mm
anode
R=250
9.1 MV/m
10.3 MV/m
NEG
Mar. 6, 2012
N. Nishimori, Jefferson Lab, Newport News, VA

13. Conditioning with cathode electrode (Jun. ’11)
600
High voltage
400
HV(kV)
200
10-5
Vacuum
10-7
Vacuum(Pa)
10-9
1x10-9Pa
105
GM survey meter
103
Radiation(cpm) 10
Mar. 6, 2012
N. Nishimori, Jefferson Lab, Newport News, VA 4
time(hrs.) 8 13

14. N. Nishimori, Jefferson Lab, Newport News, VA
600
510kV
400
HV(kV)
200
radiation spot
10-5
12000
10-7
Vacuum(Pa)
8000
10-9
Radiation(cpm)
105
4000
350kV
103
Radiation(cpm)
100
200
300
400
500
HV(kV) 10
Mar. 6, 2012
112
116
time(hrs.)
120
N. Nishimori, Jefferson Lab, Newport News, VA 14

15. Conditioning after wiping cathode (Jun. ’11)
600 HV
400
Go up to 445kV within 1 hour
HV(kV)
200
10-5
Vacuum (NEG reactivated without baking)
10-7
Vacuum(Pa)
1x10-8Pa
10-9
105
GM survey meter
103
Radiation(cpm) 10
Mar. 6, 2012
N. Nishimori, Jefferson Lab, Newport News, VA 4
time(hrs.) 8 15

16. N. Nishimori, Jefferson Lab, Newport News, VA
600
526kV
400
HV(kV)
200
radiation spot
10-5
10-7
100
1Sv=100rem
Vacuum(Pa) 80
10-9 60
3x10-9Pa
Radiation(mSv/h)
105 40
found another local radiation from survey 20
103
Radiation(cpm)
400
420
440
460
480
500
HV(kV) 10
Mar. 6, 2012
112
116
time(hrs.)
120
N. Nishimori, Jefferson Lab, Newport News, VA 16

17. Possible local radiation sources found
NEG
400L/s NEG holder
Polishing powder found in holes of
NEG holder parts
Mar. 6, 2012
N. Nishimori, Jefferson Lab, Newport News, VA

18. Status after removal of dust source (Feb. ’12)
Still suffered from field emission generated from cathode electrode 12
1Sv=100rem
500
10-7 10
400 8 HV
10-8
HV(kV)
300
Radiation(mSv/h) 6
N2 equivalent pressure (Pa)
pressure
200 4
10-9
100
8x10-10 Pa 2
10-10 2 4 6 8
400
(8MV/m)
420
440
460
480
500
(10MV/m)
time(hrs.)
GM survey meter
HV (kV)
radiation spot
500 12
400 HV 8
300
> 8hours without discharge
at 440kV
2hours at 460kV
0.6hours at 480kV
HV(kV)
radiation(mSv/h)
200 4
radiation
100 2 4 6 8 2 4 6 8 2 4 6 8
Mar. 6, 2012
N. Nishimori, Jefferson Lab, Newport News, VA
time(hrs.)
time(hrs.)
time(hrs.) 18

19. Gas conditioning with segmented insulator
10-9Pa, 10mA would produce the same amount of ion with 10-3 Pa, 10nA
Ion back-bombardment would be ~10-6 of field emission current for 10-3 Pa He gas.
No field emission from stem electrode, but some emission from backside of guard rings.
Still be careful about damage on ceramics by field emission.
Measurement of HV power supply current with high accuracy.
HVPS current with gas should be equal to that without gas.
guard rings
field emission
stem electrode
2.6MV/m
2.6 MV/m on backside of ring
8.3 MV/m on stem electrode
Mar. 6, 2012
N. Nishimori, Jefferson Lab, Newport News, VA

20. I-V curve of HV power supply without gas
200
I[mA]=0.3312xHV[kV]-0.29
0.4
HVPS current
150
0.2
HV power supply current (mA)
100
0.0
DI (mA)
-0.2 50
deviation from fitting
-0.4
100
200
300
400
500
HV (kV)
N. Nishimori, Jefferson Lab, Newport News, VA
Mar. 6, 2012

21. N. Nishimori, Jefferson Lab, Newport News, VA
Gun configuration
-500kV terminal
segmented
insulator
preparation
chamber
1.5m
transfer rod HV
chamber
cathode
loading
chamber
anode
e beam 1m
transfer rod
Mar. 6, 2012
N. Nishimori, Jefferson Lab, Newport News, VA

22. N. Nishimori, Jefferson Lab, Newport News, VA
Downstream beam line
Electron gun
solenoid
Beam profile monitor
Bending magnet
laser
Beam dump
Window , Laser shutter
1.2 m from anode to bending magnet
0.7 m from bending magnet to beam profile monitor
Mar. 6, 2012
N. Nishimori, Jefferson Lab, Newport News, VA 22

23. N. Nishimori, Jefferson Lab, Newport News, VA
300 keV beam generation
top
top
low-E
High-E
low-E
High-E f2
bottom
bottom
diaphragm:4
diaphragm:8
Beam profile on screen placed 1.9m downstream from anode.
dump, laser power QE=2.5%
dump at maximum due to radiation from beam dump
Mar. 6, 2012
N. Nishimori, Jefferson Lab, Newport News, VA 23

24. N. Nishimori, Jefferson Lab, Newport News, VA
Summary and Outlook
500kV gun status
Scheduled to be installed by Oct. 2012
HV test with a stem electrode: 510kV (500kV) for 8 hours without any discharge after removal of FE site by current conditioning for 50 hours
HV test with a cathode electrode: 440kV (430kV) for 8 hours without any discharge. FE site cannot be removed by current conditioning so far.
Vacuum: 8x10-10 [Pa] N2 equivalent in HV chamber with HV on
Beam generation at 300kV
Outlook
Repeated wiping with NEG reactivation might be a solution to 500kV
Gas conditioning with monitoring HVPS current carefully
Beam generation at > 400kV
Mar. 6, 2012
N. Nishimori, Jefferson Lab, Newport News, VA