Transcript Effect of Faraday shields on capacitive coupling

Effect of Faraday shields on capacitive coupling
D.D. Blackwell and F.F. Chen, 2D imaging of a helicon discharge,
Plasma Sources Sci. Technol. 6, 569 (1997)
No shield
With shield
m = +1 mode much stronger than m = –1
D.D. Blackwell and F.F. Chen, 2D imaging of a helicon discharge,
Plasma Sources Sci. Technol. 6, 569 (1997)
m = –1
m = +1
Development of a time-resolved energy analyzer
D.D. Blackwell and F.F. Chen, Time-resolved measurements of the EEDF in
a helicon plasma, Plasma Sources Sci. Technol. 10, 226 (2001)
vacuum feedt hrough
col lect or
fi lament
heater
-0- +12V
anode
ceramic cov ered wires
g rid
bias
-0- -200V
BN s pacers
RF modulated electron gun
for calibration
g ro un d ed h o us in g
2-electrode gridded analyzer
with RF response
Time-resolved EEDFs show no fast electrons
above a threshold of 10 -4
F.F. Chen and D.D. Blackwell, Upper limit to Landau damping in helicon
discharges, Phys. Rev. Lett. 82, 2677 (1999)
1 0 0 0 .0
60
3 .3 5 e V
40
1 0 .0
Ic (mA)
Electron current (mA)
1 0 0 .0
1 .0
20
0 .1
3.00 eV
0
0 .0
0
50
100
150
200
- 15
time (nsec)
-5
I-V swept by oscillating Vs
5
Vo lt s
15
25
I-V at two RF phases
3
1.2
Evolution of beam-created plasma
30
2
D is tanc e
I (mA)
R p ( )
20
0.8
fro m gu n
I (mA)
10
1
n o p la s m a
5 cm
10 cm
0
0
25
50
t (nsec)
75
100
20 cm
0.4
0
-180
-90
0
90
A n te n n a p h a s in g (d e g r e e s )
Loading resistance agrees with
calculations w/o L.D.
180
0.0
-150
-100
-50
0
Injecting
a current
causes
a
Volts
beam-plasma instability
50
ax ial p rob es
Development of an RF J-dot probe
D.D. Blackwell, T.G. Madziwa, D. Arnush, and F.F. Chen, Evidence for
matching
RF Po win
er Sa
uphelicon
ply
Trivelpiece-Gould
modes
discharge, LTP-106 (June, 2001)
circuit
p=3 mTorr, 20<B<50 Gauss, Prf<1kW, f=11 MHz
m =0 antenna
Return loop
Faraday shield
Evidence for Trivelpiece-Gould modes
D.D. Blackwell, T.G. Madziwa, D. Arnush, and F.F. Chen, Evidence for
Trivelpiece-Gould modes in a helicon discharge, LTP-106 (June, 2001)
14
14
12
10
10
8
Jz data
Bz data
n(r)
6
30G
(a )
12
J z (arb. units)
J z, B z (arb. units)
35G, 4E 11
8
11
n (10 )
6
3.5
4
4
2
2
0
0
3.0
no TG
-6
-4
-2
0
r (cm)
2
4
"Wings" are seen in Jz
but not in Bz.
6
-6
-4
-2
0
r (cm )
2
4
6
"Wings" are not predicted by
theory if TG modes are neglected.