Status of 500-kV DC gun at JAEA

Status of 500-kV DC gun at JAEA

N. Nishimori, R. Nagai, R. HajimaJapan Atomic Energy Agency 　 (JAEA) M. Yamamoto, T. Miyajima, Y. Honda KEKH. Iijima, M. KurikiHiroshima UniversityM. Kuwahara, S. Okumi, T. NakanishiNagoya Univiersity

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

2Mar. 6, 2012 N. Nishimori, Jefferson Lab, Newport News, VA

3

Compact ERL (test facility)

Mar. 6, 2012 N. Nishimori, Jefferson Lab, Newport News, VA

Energy 35/245 MeVCurrent 10mAEmittance 0.1 – 1 mm ・ mrad

E gun (Installation by Oct. 2012 Beam generation by Mar. 2013)

superconductin

g accelerator

supercavity

LCS gamma-ray

exp. hall

electron beam

Mar. 6, 2012 4N. Nishimori, Jefferson Lab, Newport News, VA

HV terminal

segmentedinsulator

stem electrode

cathode

A 500 kV photocathode DC gun at JAEA

NEG pumps18,000 l/s

anode

gun chamber

Segmented insulator

ceramicstem

electrode

field emission stem electrode

guard rings6.8 MV/m

8.3 MV/m

1200

1000

800

600

400

200

0

-200

0 200 400 600

14.3 MV/m

radius (mm)

heig

ht (m

m)


stem electrode nose

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

gun chamber

beam axis

guard rings

500kV DC gun at JAEA

400mm in diam.

730mm

550kV Cockcroft Walton power supply

3.8 m

segmented insulator

SF6 tank

gun chamber made of titanium


1 m in diam.

Mar. 6, 2012

High voltage testing with a stem electrodestem electrode

dummy cup instead of cathode electrode

1143

.5 m

m

7N. Nishimori, Jefferson Lab, Newport News, VA

101.6

HV conditioning

0

100

200

300

400

500

600

0 20 40 60 80 100 120

appl

ied

volta

ge [-

kV]

time [hrs.]


4kV/hour

R. Nagai et al., “High-voltage testing of a 500-kV dc photocathode electron gun”, RSI. 81 033304 (2010).

550kV 190 ℃ baking for 8 hours start conditioning at 3x10-8[Pa] Vacuum pump: 1000L/s-TMP

Why slow conditioning ?

Because of radiation increase above 520kV

72 76 80 84 88

0

200

400

600

HV

(kV

)

time(hrs.)

102

1

10-2

Rad

iatio

n(S

v/h) at 500kV at 500kV

rapid increase and slow decrease every discharge

Conditioning with stem electrode (Oct. ’09)

Mar. 6, 2012 N. Nishimori, Jefferson Lab, Newport News, VA 9

1Sv=100rem

112 116 120 124 128

0

200

400

600

HV

(kV

)

time(hrs.)

102

1

10-2

Rad

iatio

n(S

v/h)


decrease of radiationat 500kV at 550kV


136 140 144 148 152

0

200

400

600

HV

(kV

)

time(hrs.)

102

1

10-2

Rad

iatio

n(S

v/h)

demonstration of 510 kV for eight hours

radiation similar to B.G. level



Cathode electrode: POISSON calculation

10.3 MV/m

cathode anode

100mm


6.7 MV/m

NEG

9.1 MV/mR=25

0

Mar. 6, 2012 13N. Nishimori, Jefferson Lab, Newport News, VA0 4 8

0

200

400

600

HV

(kV

)

time(hrs.)

Vac

uum

(Pa)

10-5

10-7

10-9

105

103

10

Rad

iatio

n(cp

m)

High voltage

Vacuum

GM survey meter

1x10-9Pa

Conditioning with cathode electrode (Jun. ’11)

112 116 120

0

200

400

600H

V(k

V)

time(hrs.)

Vac

uum

(Pa)

10-5

10-7

10-9

105

103

10

Rad

iatio

n(cp

m)

5004003002001000HV(kV)

0

4000

8000

12000

Rad

iatio

n(cp

m)

510kV

350kV

radiation spot


N. Nishimori, Jefferson Lab, Newport News, VAMar. 6, 2012 150 4 8

0

200

400

600

HV

(kV

)

time(hrs.)

Vac

uum

(Pa)

10-5

10-7

10-9

105

103

10

Rad

iatio

n(cp

m)

Vacuum (NEG reactivated without baking)

GM survey meter

HV

1x10-8Pa

Go up to 445kV within 1 hour

Conditioning after wiping cathode (Jun. ’11)

112 116 120

0

200

400

600H

V(k

V)

time(hrs.)

Vac

uum

(Pa)

10-5

10-7

10-9

105

103

10

Rad

iatio

n(cp

m)

found another local radiation from survey

3x10-9Pa

526kV


radiation spot

500480440420400 460HV(kV)

Rad

iatio

n(S

v/h)

0

20

40

60

80

100

1Sv=100rem

Possible local radiation sources found

17Mar. 6, 2012 N. Nishimori, Jefferson Lab, Newport News, VA

NEG

400L/s NEG holder

Polishing powder found in holes of NEG holder parts

0

200

400

500

HV

(kV

)

time(hrs.)

Rad

iatio

n(S

v/h)

Still suffered from field emission generated from cathode electrode

Status after removal of dust source (Feb. ’12)

400(8MV/m)

420 440 460 480 500(10MV/m)

0

2

4

6

8

10

12

0 2 4 6 8

radiation(Sv/h)

0

4

8

12

300

100

> 8hours without dischargeat 440kV

time(hrs.)0 2 4 6 8

time(hrs.)0 2 4 6 8

0.6hours at 480kV2hours at 460kV

HV

radiation

time(hrs.)0 2 4 6 8

0

200

400

500

HV

(kV

)

300

100

10-10

10-9

10-8

10-7 N2 equivalent pressure (P

a)8x10-10 Pa

HV

pressure


HV (kV)radiation spot

GM survey meter

1Sv=100rem

Gas conditioning with segmented insulator

stem electrode

field emission

2.6 MV/m on backside of ring8.3 MV/m on stem electrode


• 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

2.6MV/m

I-V curve of HV power supply without gas


0 500

HV (kV)

0100 200 300 400

0.4

-0.4

-0.2

0.0

0.2

100

50

150

200

HV

pow

er s

uppl

y cu

rren

t (

)

I (

)

I[A]=0.3312xHV[kV]-0.29HVPS current

deviation from fitting

Gun configuration


-500kV terminal

cathode

segmented insulatorpreparation

chamber

loadingchamber anode

1.5m transfer rod

1m transfer rod

HVchamber

e beam


Downstream beam line

22

solenoidElectron　gun

Window　,　Laser　shutterBeam　dump

Beam　profile　monitor

Bending　magnet laser

1.2　m　from　anode　to　bending　magnet0.7　m　from　bending　magnet　to　beam　profile　monitor


300 keV beam generation

23

• Beam profile on screen placed 1.9m downstream from anode.• 15nA@beam dump, laser power 1.4W@532nm, QE=2.5% • 5.7A@beam dump at maximum due to radiation from beam dump

High-Elow-E

top

bottom

diaphragm:4

2

High-Elow-E

top

bottom

diaphragm:8

Summary and Outlook

500kV gun statusScheduled 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

OutlookRepeated wiping with NEG reactivation might be a solution to 500kVGas conditioning with monitoring HVPS current carefullyBeam generation at > 400kV


Status of 500-kV DC gun at JAEA

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