Magnetron Discharge Characteristics Magnetron Discharge Characteristics

for the improvement of IEC Performancefor the improvement of IEC Performance

T. Mizutani, A. Nagafuchi, M. Imoto, K. Masuda, H. Toku, K. Nagasaki, K. Yoshikawa

Institute of Advanced Energy, Kyoto University

The 5th US-Japan Workshop on IEC Neutron SourcesOct. 9-10, 2002

cathodemade of TaI.D. : 50 mmO.D. : 60 mm

thickness : 0.3 mm

IECF device

6 ringstransparency： 96%

Vacuum chamber (anode）SUS 304

I.D. : 340 mmthickness：3 mm

D2

Objectives (1)

So farIons were produced mainly by glow discharge.

P, V, and I can not be chosen as independent variables.

A beam-background colliding fusion was dominant.

To get higher neutron production rate

Low P, high V, and large Ioperation is required.

A beam-beam colliding fusion would be dominant.

Simulation study predicts N∝I 3 [1]M. Ohnishi, et al., “Correlation between potential well structure and neutron production in inertial electrostatic confinement fusion”, Nucl. Fusion 5 (1997) 611-619.

[1]

.

.

Objectives (2)

To attain a low pressure operationUsing external ion sources

However

Most of them complicate the IECF device.

For the applications including a portable neutron sourceFor the applications including a portable neutron source,,the device has to be compact and simple.the device has to be compact and simple.

In this study,we propose use ofmagnetron discharge plasmas as an ion source.

The device is composed of extremely compact and simple instruments.

Magnetron discharge

50 mm

155

Max 3000 gauss (Sm-Co)

N

S

Principle of magnetron discharge

IEC chamber

Magnet for magnetron discharge Application to IEC

IEC discharge with equator magnet array

IEC chamber

0 10 20 30 40 500

5

10

15

20

25

30

35

He

IIEC

= 40 mA const.

VIE

C [

kV ]

P [ mTorr ]

With magnet W/O

The magnets doesn’t have much effect on the discharge characteristics.Electrons reach the chamber without crossing magnetic field and carrying out ExB drift.

Instruments for magnetron discharge with an anode

120 mm

φ1 mmTa wire

N

S

135 mm105 mm

A permanent magnet array (ring array)

An additional ring anode in the chamber

Schematic diagram for magnetron discharge with an anode

H230 mm NSN

S

camera

BE

H2

0 5 10 15 20 25 30 35 400

100

200

300

400

500

600

Ia = 300 mA

100 mA

D2

Ia = const.

Va [

V ]

P [ mTorr ]

Magnetron discharge with an anode (V IEC = 0 V)

Secondary electrons by ion impact with the chamber are needed for the magnetron discharge maintenance.

down to 10 mTorr

The magnetron discharge was maintained at 10 mTorr.

Large Ia is needed as P decreases.

Va doesn’t depend on P.

To maintain magnetron discharge, sufficient Ia is needed

0 100 200 300 400 5000

100

200

300

400

500

600

P = 10 mTorr

15 mTorr

D2

P = const.

Va [

V ]

Ia [ mA ]

0 5 10 15 20 25 300

200

400

600

800

30 mA

IIEC

= 80 mA

D2

Va

[ V]

Ia= 300 mA

P [ mTorr ]

Magnetron discharge was maintained at lower P with glow discharge.

IEC discharge was maintained at lower pressure than that only glow discharge.High voltage couldn’t be applied to the IEC cathode.

I a = 300 mA, I IEC = 30, 80 mA const.

down to 2.3 mTorr

Major part of ions is provided from magnetron discharge.

0 5 10 15 20 25 300

2

4

6

8

30 mA

IIEC

= 80 mA

D2

Ia = 300 mA

P [ mTorr ]V

IEC [k

V ]

Electrons from glow discharge relate to the magnetron discharge.

Glow/Magnetron hybrid dischargewith an anode

0 100 200 300 400 500 6000

2

4

6

8P = 10 mTorr

D2

Ia

VIE

C[k

V]

IIEC

20mA 40mA 60mA 80mA

I IEC

Ia＝ 0.35 0.45

V IEC increases as Ia decreases.

I IEC is provided only from magnetron discharge.

I IEC

Iameans ion extraction efficiency.

When about 40 % of magnetron discharge current is extracted to

the IEC cathode, it can’t be maintained.

Assumption

[ mA ]

Glow/Magnetron hybrid dischargewith an anode

The number of ions provided to the IEC cathode decreases.

Magnetron discharge with an anode

IonSecondary electron

Secondary electrons are needed to maintain magnetron discharge. A part of ions have to go to the chamber.It’s difficult to extract major part of ions to the IEC cathode.

0 10 20 30 40 500

500

1000

1500

2000

2500

3000

3500

4000

B [

Gau

ss ]

D [ mm ]

N SNS

5 mm

NS

Max 7000 Gauss (Nd-Fe-B)

D

B

anod

eca

thod

e

Magnetron discharge with an anode and cathode

5 mm

BE

anod

eca

thod

e

0 1 2 3 4 5 6 7 8 9 100

200

400

600

800

1000

1200

1400

1600H

2

Va

[ V ]

P [ mTorr ]Magnetron discharge ignition

Magnetron discharge with an anode and a cathode (V IEC = 0 V)

down to 0.07 mTorr

0 400 800 1200 16000

1

2

3

4

5

Va

[ V ]

Ia

Ig

Ic

H2

P = 1 mTorr const.I a,

I g,I c [

mA

]

Magnetron discharge current increases as the anode voltage increases

Magnetron discharge with an anode and a cathode (V IEC = 0 V)

Glow/Magnetron hybrid discharge with an anode and a cathode

P = 10 mTorr, I IEC = 10 mA P = 10 mTorr, I IEC = 30 mA

0 400 800 1200 16000.0

2.5

5.0

7.5

0

5

10

15

I,I

,I [

mA

]

VIE

C [

kV ]

Va [ V ]

0 400 800 1200 16000.0

2.5

5.0

7.5

0

5

10

15

I a,I g,

I c [ m

A ]

VIE

C [

kV ]

Va [ V ]

Ia

Ig

Ic

VIEC

H2

Magnetron discharge current increases as Va increases, and V IEC decreases.

The number of ions provided to the IEC cathode increases.

ag

c

This effect is more significant with lower I IEC (Left side).

Glow/Magnetron hybrid discharge with an anode and a cathode

0 5 10 15 200

5

10

15

20

25

I a,I g,

I c [ m

A ]

Ia

Ig

Ic

H2

P [ mTorr ]

Va = 1500 V, I IEC = 10 mA const.

Magnetron current decrease as pressure decreases. Then V IEC increases.

0 5 10 15 200

5

10

15

20

25

withoutmagnetron discharge

VIE

C [

kV ]

IEC/magnetron Hybrid discharge

H2

P [ mTorr ]

Glow + Magnetron

Glow

The number of ions provided to the IEC cathode decreases.

Pressure was reduced by use of magnetron discharge at the same V IEC and I IEC.

Conclusions

Magnetron discharge plasma with an anode and a cathode is maintained at the pressure of 0.07 mTorr.

In the IEC/magnetron hybrid discharge, magnetron discharge plasma serves as an ion source. As a result, lower pressure operation can be attained than glow discharge.

Evaluate an effect of magnetron discharge on the neutron production rate.

Optimize the configuration of the magnetron discharge system.

Future works