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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