design of pm helicon arrays
DESCRIPTION
Design of PM helicon arrays. Optimization of the discharge tube Design of the permanent magnets Design of a multi-tube array Design and construction of a test chamber Antennas and the RF distribution system Experimental results Design of a compact module - PowerPoint PPT PresentationTRANSCRIPT
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Design of PM helicon arrays
UCLA
1. Optimization of the discharge tube
2. Design of the permanent magnets
3. Design of a multi-tube array
4. Design and construction of a test chamber
5. Antennas and the RF distribution system
6. Experimental results
7. Design of a compact module
8. Ideas for further improvements to be tested
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A commercial helicon etcher (PMT MØRI)
It required two heavy electromagnets with opposite currents.
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Previous experiment with 7 tubes
UCLA
ROTATING PROBE ARRAY
PERMANENT MAGNETS
3"
DC MAGNET COIL
18"
54 mm
2.4 mm
6.4 mm10 cm
2.5
cm
The “stubby” tube
It required a large electromagnet
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Plasmas merged; density is uniform
UCLA
Power scan at z = 7 cm, 5 mT A, 20 G, 13.56 MHz,
0.0
0.5
1.0
1.5
2.0
0 5 10 15 20 25 30R (cm)
N (
101
2 cm
-3) 3.0
2.5
2.0
1.5
1.0
P(kW)
7-tube m=0 array
ARGON
High density and uniformity were achieved
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A c o m p u t a t i o n a l p r o g r a m f o rH E L I C O N s a n d I C P s
V e r s i o n 1 . 0
A u t h o r : D o n a l d A r n u s h , w i t h F r a n c i s F . C h e nP r o g r a m m e r s : R i c k L a n , R a v a s h E l i a s s i
U C L AA
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Optimization of discharge tube: HELIC code
UCLAD. Arnush, Phys. Plasmas 7, 3042 (2000).
Radial profiles are arbitrary, but B and n must be uniform axially.
HELIC gives not only the wave fields but also R, the loading resistance.
a
b
c
AntennaLc
a b
h
Loop antenna
Helical antenna
B0
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The HELIC user interface
UCLA
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The Low-field Peak
UCLA
DENSITY vs. MAGNETIC FIELD4-cm tube, uniform field
0.0
0.5
1.0
1.5
2.0
0 20 40 60 80 100 120B (G)
n (1
012
cm
-3)
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Mechanism of the Low Field Peak
UCLA
0 1,r
z
ne nk
k B a k B
Basic helicon relations
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The peak is sensitive to the density profile
0
1
2
3
4
5
6
0 50 100 150 200 250 300
B (G)
R (
ohm
s)
Uniform
Flat with rolloff
Parabolic
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The peak depends on the boundary condition
0
1
2
3
4
5
6
7
8
0 50 100 150 200 250 300
B (G)
R (
ohm
s)
Insulating
Conducting
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The peak depends on distance from endplate
0
1
2
3
4
5
6
0 50 100 150 200 250 300
B (G)
R (
ohm
s)
5 cm
10 cm
No bdy
d
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The peak depends on the type of antenna
0
1
2
3
4
5
6
0 50 100 150 200 250 300
B (G)
R (
ohm
s)Loop, d = 10 cm
HH10, d = 10 cm
Nagoya III
Single loop: m = 0, bidirectionalHH (half-wavelength helical): m = 1, undirectionalNagoya Type III: m = 1, bidirectional
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Typical scan of Rp vs n, B
UCLA
0.0
0.5
1.0
1.5
2.0
2.5
1E+11 1E+12 1E+13n (cm-3)
R (
ohm
s)
1000464215100462210
B (G) d = 3", H = 2", 13.56MHz
Each point requires solving a 4th order differential equation >100 times.A typical scan takes ~ 3 hours on a PC.
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Matrices for optimizing discharge tube
UCLA
Vary the tube length and diameter Vary the RF frequency
Vary the pressure and frequency
Vary the endplate conductivity
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Vary H (endplate distance) for 3” diam
UCLA
0.0
0.5
1.0
1.5
2.0
2.5
1E+11 1E+12 1E+13n (cm-3)
R (
ohm
s)
H = 3 in.
H = 2 in.
H = 1 in.
100G, d = 3", 13.56 MHz
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Vary diam for H = 2” at 100G
UCLA
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
1E+11 1E+12 1E+13n (cm-3)
R (
ohm
s)
d = 4 in.
d = 3 in.
d = 2 in.
100G, H = 2", 13.56 MHzTube diameter
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Vary the frequency
UCLA
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
1E+11 1E+12 1E+13n (cm-3)
R (
ohm
s)
f = 27.12 MHz
f = 13.56 MHz
f = 2 MHz
D = 3", L = 2", 100G
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Not much variation with pressure
UCLA
0.0
0.5
1.0
1.5
2.0
2.5
1E+11 1E+12 1E+13n (cm-3)
R (
ohm
s)
1 mTorr
3 mTorr10 mTorr
D = 2", H = 1.5", 100G
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Vary the endplate material
UCLA
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
1E+11 1E+12 1E+13n (cm-3)
R (
ohm
s)
Conducting
Insulating
H = 2", D = 2", B = 80G
0.0
0.2
0.4
0.6
0.8
1E+11 1E+12 1E+13n (cm-3)
R (
ohm
s)
H = 1.5 in., conducting
H = 3.0 in., insulating
Initially, it seems that the conducting endplate is better. However, it is because the phase reversal at the endplate has changed, and the tube length has to be ~1/4 wavelength longer to get constructive interference. By changing H, almost the same R can be achieved.
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Relation of R to plasma density
UCLA
pin rf
p c
RP P
R R
7 1/ ½ 1.0 10 secsdN dt Snc n
c i eW E W W 101.1 10 WattsoutP n
Rp << Rc
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1E+11 1E+12 1E+13n (cm-3
)
R (
oh
ms)
100 G
63 G
40 G
25 G
16 G10 G
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Relation of R to plasma density
UCLA
pin rf
p c
RP P
R R
7 1/ ½ 1.0 10 secsdN dt Snc n
c i eW E W W 101.1 10 WattsoutP n
10
100
1000
1E+11 1E+12 1E+13n (cm-3)
Pin
(W
)1000
500
200
100
Loss
Prf (W)
Rp > Rc
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Final design
UCLA
2.120.25
4.00
2.25
Lesker QF50 cover plate
Lesker QF50 centering ringParker 2-330 Viton O-ring
Corning #237580 tubing, 63.5 mm OD, 4.8 mm wall
Parker 2-239 Viton O-ring
Dimensions are in inches
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The “New Stubby” tube
UCLA
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Design of PM helicon arrays
UCLA
1. Optimization of the discharge tube
2. Design of the permanent magnets
3. Design of a multi-tube array
4. Design and construction of a test chamber
5. Antennas and the RF distribution system
6. Experimental results
7. Design of a compact module
8. Ideas for further improvements to be tested
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Characteristics of permanent magnet rings
UCLA
Internal field
External field
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The B-field of annular PMs
UCLA
The field reverses at a stagnation point very close to the magnet.
Plasma created inside the rings follows the field lines and cannot be ejected.
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Optimization of magnet geometry
UCLA
Result: Field strength magnet volumeSpacing improves uniformity slightly
actual
actual
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The field of 4 stacked magnet rings
UCLA
-400
-300
-200
-100
0
100
200
-20 -15 -10 -5 0 5 10 15 20z (cm)
Bz
(G)
0.0
2.5
4.0
r (cm)
0
50
100
150
200
250
300
-20 -15 -10 -5 0 5 10 15 20z (cm)
|Bz|
(G
)
Calc.
Expt.
The internal and external fields at various radii. The individual rings can be seen at large radii.
Calibration of the calculated field with a gaussmeter.
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For the designed tube, B ~ 60G is good
UCLA
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1E+11 1E+12 1E+13n (cm-3)
R (
oh
ms)
100.0
63.1
39.8
25.1
15.8
10.0
B(G) L=2", 1mTorr, conducting
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Proof of principle on 3” diam tube
UCLA
Gate Valve
To Turbo Pump
34 cm
36 cm
D
Z1
Z2
0
20
40
60
80
100
120
5 10 15 20 25 30 35 40z (cm)
Bz
(G)
B (0)231928
3338
D (cm)
-300
-250
-200
-150
-100
-50
0
50
100
150
0 5 10 15 20 25 30
z (cm)
Bz
(G)
Calculated
Measured
External field
Internal field
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Radial density profiles at Z1 and Z2
UCLA
0
2
4
6
8
10
-5 0 5 10 15 20r (cm)
n (
101
0cm
-3)
Z1, 40
Z1, 35
Z1, 30
Z1, 21
Z1, 1
D (cm)500W, 1mTorr
0
1
2
3
4
5
6
7
-5 0 5 10 15 20r (cm)
n (
101
0cm
-3)
Z2, 40
Z2, 35
Z2, 30
Z2, 21
Z2, 1
D (cm)
500W, 1 mTorr
Upper probe Lower probex 1010 cm-3
Proof of principle: discharge in the external field gives much more plasma downstream.
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The final design for 2” tubes
UCLA
12.7 cm
7.6 cm
PLASMA
Material: NdFeB
Bmax = 12 kG
Attractive force between two magnets 2 cm apart:
516 Newtons = 53 kg
The magnets are dangerous!
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Wooden frame for safe storage
UCLA
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Single tube, final configuration
UCLA
0
50
100
150
200
250
300
350
-4 -2 0 2 4r (cm)
Bz
(G)
56789101214
z (cm from midplane of magnet)
Radial Bz profiles at various distances below the magnet.
Discharge tube
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Design of PM helicon arrays
UCLA
1. Optimization of the discharge tube
2. Design of the permanent magnets
3. Design of a multi-tube array
4. Design and construction of a test chamber
5. Antennas and the RF distribution system
6. Experimental results
7. Design of a compact module
8. Ideas for further improvements to be tested
![Page 38: Design of PM helicon arrays](https://reader036.vdocuments.net/reader036/viewer/2022062301/56814748550346895db48624/html5/thumbnails/38.jpg)
Design of array
UCLA
The density at Z2 is summed over nearest tubes.
0
2
4
6
8
10
-5 0 5 10 15 20r (cm)
n (
10
11cm
-3)
Z1, single magnet
Z1, with neighbors
Z2, single magnet
Z2, with neighbors Radial density profilesat Z1 = 7.4 cm and Z2 = 17.6 cm below discharge.
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Computed uniformity n(x) for various y
0
1
2
3
4
5
6
7
8
-30 -20 -10 0 10 20 30x (cm)
n (
10
11 c
m-3
)
Sum
Row1
Row2
Avg: all y
y = 0
(a)
0
1
2
3
4
5
6
7
8
-30 -20 -10 0 10 20 30x (cm)
n (
10
11 c
m-3
)
Sum
Row1
Row2
Avg: all y
y = 7.5
(b)
0
1
2
3
4
5
6
7
8
-30 -20 -10 0 10 20 30x (cm)
n (
10
11 c
m-3
)
Sum
Row1
Row2
Avg: all y
y = 15
(c)
0
1
2
3
4
5
6
-30 -20 -10 0 10 20 30x (cm)
n (
10
11 c
m-3
)
Sum
Row1
Row2
Avg: all y
y = 22.5
(d)
Half-way between rows 1/4-way between rows
Directly under a row Beyond both rows
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A tube spacing of 7” is chosen
UCLA
0
2
4
6
8
10
12
15 20 25 30L (cm)
Rip
ple
(+
/- %
)
L = 17.5 cm gives < 2% ripple at 17 cm below source
For a single row, a distance L = 17.5 cm between two tubes gives less than 2% ripple in density.
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Design of PM helicon arrays
UCLA
1. Optimization of the discharge tube
2. Design of the permanent magnets
3. Design of a multi-tube array
4. Design and construction of a test chamber
5. Antennas and the RF distribution system
6. Experimental results
7. Design of a compact module
8. Ideas for further improvements to be tested
![Page 42: Design of PM helicon arrays](https://reader036.vdocuments.net/reader036/viewer/2022062301/56814748550346895db48624/html5/thumbnails/42.jpg)
An 8-tube linear test array
UCLA
165 cm
53.3 cm
17.8
17.8
17.8
17.8 cm73.7 cm
8.9 cm
x
y
Top view
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Possible applications
UCLA
• Web coaters• Flat panel displays• Solar cells• Optical coatings
A web coater
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The array source is vertically compact
UCLA
The magnets can be made in two pieces so that they hold each other on an aluminum sheet.
Once placed, the magnets cannot easily be moved, so for testing we use a wooden support.
165 cm
30 cm
15 cm
Side view
Probe ports
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The wooden magnet frame is used in testing
UCLA
64"
21"
3.5"
12"
Wooden magnet support
2.00
5.00
3.75
2.5
24 ea. 2.5 x 5.5 x 1/2"4 ea. 2.5 x 64 x ¾”
1 ea. 21 x 64 x 1/2”16 ea. 1/4” diam dowels
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Water and RF connections
UCLA
These will be shown in detail later
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An 8-tube staggered array in operation
UCLA
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Design of PM helicon arrays
UCLA
1. Optimization of the discharge tube
2. Design of the permanent magnets
3. Design of a multi-tube array
4. Design and construction of a test chamber
5. Antennas and the RF distribution system
6. Experimental results
7. Design of a compact module
8. Ideas for further improvements to be tested
![Page 49: Design of PM helicon arrays](https://reader036.vdocuments.net/reader036/viewer/2022062301/56814748550346895db48624/html5/thumbnails/49.jpg)
Antennas
UCLA
The antennas are m = 0 loops made of three turns of 1/8” diam copper tubing.
The reason for m = 0 is that m = 1 antennas are too long, and much of the plasma is lost by radial diffusion before exiting the tube. The antenna must be close to the exit aperture and be tightly wound onto the tube.
The helicon wave pattern for m = 0 is a peculiar one but theory is straightforward. The wave changes from pure electromagnetic to pure electrostatic in each half cycle.
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The RF system
UCLA
The critical elements are the junction box and the transmission lines.
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Antenna connections (1)
UCLA
The antennas must be connected in parallel with cables of equal length.
The first trial was to use standard RG/8U cables and N connectors.
These arced and overheated.
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Reason that RF connectors don’t work
UCLA
0
1000
2000
3000
4000
5000
6000
0 50 100 150 200 250 300 350 400Watts
Vol
ts p
-p
V p-p
Fit
0
2
4
6
8
10
12
14
0 50 100 150 200 250 300 350 400Watts
Am
ps r
ms
I rms
Fit
High voltages and currents occur when there is NO PLASMA; that is, before breakdown or when the plasma disrupts. Then, if the RF power on a tube is set for 400W, the peak-to-peak voltage can be 5kV, and the rms current can be 12A. Once the discharge is on, the RF power goes into the plasma rather than into the cables and connectors.
![Page 53: Design of PM helicon arrays](https://reader036.vdocuments.net/reader036/viewer/2022062301/56814748550346895db48624/html5/thumbnails/53.jpg)
Antenna connections (2)
UCLA
In the second try, all connections were solidly soldered, and RG/393 teflon-insulated cable was used. This method works for CW operation in experiment
but may be marginal for industrial use.
![Page 54: Design of PM helicon arrays](https://reader036.vdocuments.net/reader036/viewer/2022062301/56814748550346895db48624/html5/thumbnails/54.jpg)
Connections (3): a rectangular transmission line
UCLA
.25
0.70
ground
ground
HV RF
water in
water out
water at HV
1 1 10
000
cosh ( / ) cosh ( / ) 377 cosh ( / )
44 4r r r
h d h d h dZ
c
0 30ln(2 / )Z h d
For w >> h, we find
![Page 55: Design of PM helicon arrays](https://reader036.vdocuments.net/reader036/viewer/2022062301/56814748550346895db48624/html5/thumbnails/55.jpg)
Impedance for various pipe diameters
UCLA
0
20
40
60
80
100
120
140
0 1 2 3 4 5 6h (in.)
Z0 (W
)0.25
0.375
0.5
0.625
0.75
0.875
1.0050W
d (in.)
For Z0 = 50W, h ~ 3/4”, but exactly 50W is not necessary
![Page 56: Design of PM helicon arrays](https://reader036.vdocuments.net/reader036/viewer/2022062301/56814748550346895db48624/html5/thumbnails/56.jpg)
Transmission line construction (1)
UCLA
![Page 57: Design of PM helicon arrays](https://reader036.vdocuments.net/reader036/viewer/2022062301/56814748550346895db48624/html5/thumbnails/57.jpg)
Transmission line construction (2)
UCLA
10.50
3.50
4.00
24.50
3.50
14.00
17.50
1.50
60.00
![Page 58: Design of PM helicon arrays](https://reader036.vdocuments.net/reader036/viewer/2022062301/56814748550346895db48624/html5/thumbnails/58.jpg)
Transmission line construction (3)
UCLA
0.25
1.25
![Page 59: Design of PM helicon arrays](https://reader036.vdocuments.net/reader036/viewer/2022062301/56814748550346895db48624/html5/thumbnails/59.jpg)
Transmission line (4): water connections
UCLA
TOP SHEET
BOTTOM SHEET
14.00 14.0022.00
14.00 14.0022.00
7.007.00 7.007.507.507.007.007.00
28.50
1.50
1.50
8.50
8.50
No high voltage is applied along a water line.
![Page 60: Design of PM helicon arrays](https://reader036.vdocuments.net/reader036/viewer/2022062301/56814748550346895db48624/html5/thumbnails/60.jpg)
Pictures (1)
UCLA
![Page 61: Design of PM helicon arrays](https://reader036.vdocuments.net/reader036/viewer/2022062301/56814748550346895db48624/html5/thumbnails/61.jpg)
Pictures (2)
UCLA
![Page 62: Design of PM helicon arrays](https://reader036.vdocuments.net/reader036/viewer/2022062301/56814748550346895db48624/html5/thumbnails/62.jpg)
Pictures (3)
UCLA
![Page 63: Design of PM helicon arrays](https://reader036.vdocuments.net/reader036/viewer/2022062301/56814748550346895db48624/html5/thumbnails/63.jpg)
Design of the matching circuitUCLA
T 2 R2 X 2 B2 R(T 2 R)
C1 R
BC2
1
T 2(X B)
Z ZL cos(kz) j sin(kz)
cos(kz) jZL sin(kz)
“Standard” circuit “Alternate” circuit
Analytic formulas from Chen. The important part is that the impedance changes with cable length.
F.F. Chen, Capacitor tuning circuits for inductive loads, UCLA Rept. PPG-1401 (unpublished) (1992); F.F. Chen, Helicon Plasma Sources, in "High Density Plasma Sources", ed. by Oleg A. Popov (Noyes Publications, Park Ridge, NJ), Chap. 1 (1995)
![Page 64: Design of PM helicon arrays](https://reader036.vdocuments.net/reader036/viewer/2022062301/56814748550346895db48624/html5/thumbnails/64.jpg)
Adapted to N tubes in parallel
UCLA
R, L
R, L
R, L
R, L
PS
N loads
Z2 - short cables
Distributor
Z1Z2
Z1 - long cable
C1C2
Matching ckt. 50W
The problem with array sources is that the cable lengths cannot be short. The match circuit cannot be close to all the tubes.
![Page 65: Design of PM helicon arrays](https://reader036.vdocuments.net/reader036/viewer/2022062301/56814748550346895db48624/html5/thumbnails/65.jpg)
C1, C2 for N=8, L = 0.8H, Z1 = 110 cm, Z2 = 90 cm
UCLA
0
200
400
600
800
1000
1200
0 50 100 150 200Z1 (cm)
C (
pF)
C1(S)
C2(S)
0
200
400
600
800
1000
1200
1400
1600
0 50 100 150 200Z2 (cm)
C (
pF)
C1(S)
C2(S)
0
200
400
600
800
1000
1200
1400
1600
1800
2000
0.5 1 1.5 2 2.5 3 3.5 4 4.5 5R (ohms)
C (
pF)
C1(S)
C2(S)
0
200
400
600
800
1000
1200
1400
1600
0 0.5 1 1.5 2 2.5 3L (uH)
C (
pF)
C1(S)
C2(S)
![Page 66: Design of PM helicon arrays](https://reader036.vdocuments.net/reader036/viewer/2022062301/56814748550346895db48624/html5/thumbnails/66.jpg)
Variation with the number of tubes N
UCLA
0
200
400
600
800
1000
1200
1400
1600
1800
2000
0 0.5 1 1.5 2 2.5L (uH)
C1
(pF
)
8
6
4
2
1
N
0
100
200
300
400
500
600
700
800
0 0.2 0.4 0.6 0.8 1 1.2 1.4
L (uH)
C2
(pF
)
8
6
4
2
1
N
Note that it is not possible to match to 1 or 2 tubes with the same length cables used for 8 tubes.
![Page 67: Design of PM helicon arrays](https://reader036.vdocuments.net/reader036/viewer/2022062301/56814748550346895db48624/html5/thumbnails/67.jpg)
Design of PM helicon arrays
UCLA
1. Optimization of the discharge tube
2. Design of the permanent magnets
3. Design of a multi-tube array
4. Design and construction of a test chamber
5. Antennas and the RF distribution system
6. Experimental results
7. Design of a compact module
8. Ideas for further improvements to be tested
![Page 68: Design of PM helicon arrays](https://reader036.vdocuments.net/reader036/viewer/2022062301/56814748550346895db48624/html5/thumbnails/68.jpg)
Experimental layout
UCLA
Staggered configuration
Compact configuration
Four probe positions
![Page 69: Design of PM helicon arrays](https://reader036.vdocuments.net/reader036/viewer/2022062301/56814748550346895db48624/html5/thumbnails/69.jpg)
Effect of B-field strength (magnet height D)
UCLA
0
5
10
15
20
4 5 6 7 8 9 10 11
D (in)
n (
10
11 c
m-3
)
3kW2kW
Staggered, 20mTorrZ1 level, x=0", y=3.5"
0
1
2
3
4
4 5 6 7 8 9 10 11
D (in)
R(W
)
2kW3kW
Staggered, 20mTorr
Variation of density with D
Variation of loading resistance with D
![Page 70: Design of PM helicon arrays](https://reader036.vdocuments.net/reader036/viewer/2022062301/56814748550346895db48624/html5/thumbnails/70.jpg)
Variation with RF power and Ar pressure
UCLA
0
5
10
15
20
25
30
0 20 40 60 80 100 120 140 160 180 200 220
P (mTorr)
n (1
01
1 c
m-3
)
3kW2kW
StaggeredZ1 level, x=0", y=3.5", D=7"
0
5
10
15
20
25
1.6 2 2.4 2.8 3.2 3.6 4 4.4 4.8 5.2
PRF (kW)
n (
10
11 c
m-3
)
Z1 levelZ2 level
Staggered, 20mTorr x=0", y=3.5", D=7"
Variation of density with RF power
Variation of density argon pressure
![Page 71: Design of PM helicon arrays](https://reader036.vdocuments.net/reader036/viewer/2022062301/56814748550346895db48624/html5/thumbnails/71.jpg)
Density jump inside the tube
UCLA
0.01
0.1
1
10
100
0 50 100 150 200 250 300 350 400
Power per tube (W)
n (
10
11 c
m-3
)
0.10
0.50
1.00
Meas.
Rc (W)
compared with theory for various circuit resistances Rc
![Page 72: Design of PM helicon arrays](https://reader036.vdocuments.net/reader036/viewer/2022062301/56814748550346895db48624/html5/thumbnails/72.jpg)
Deployment of movable probe array
UCLA
![Page 73: Design of PM helicon arrays](https://reader036.vdocuments.net/reader036/viewer/2022062301/56814748550346895db48624/html5/thumbnails/73.jpg)
An linear array of 15 probes
UCLA
0.375Ó
19.75Ó
4.0"0.25Ó
H. Torreblanca, Multitube helicon source with permanent magnets, Thesis, UCLA (2008).
![Page 74: Design of PM helicon arrays](https://reader036.vdocuments.net/reader036/viewer/2022062301/56814748550346895db48624/html5/thumbnails/74.jpg)
Density profiles across the chamber (1)
UCLA
0
4
8
12
16
20
-8 -6 -4 -2 0 2 4 6 8y (in)
n (1
011 c
m-3
)
Z1, x = 0Z1, x = 3.5Z2, x = 0Z2, x = 3.5
.
Staggered3kW, D=7", 20mTorr 0 3.5
Staggered configuration, 3kW
Side Langmuir probe
![Page 75: Design of PM helicon arrays](https://reader036.vdocuments.net/reader036/viewer/2022062301/56814748550346895db48624/html5/thumbnails/75.jpg)
UCLA
0
2
4
6
8
10
-8 -6 -4 -2 0 2 4 6 8y (in)
n (1
011 cm
-3)
Z1, x = 0Z1, x = 3.5Z2, x = 0Z2, x = 3.5
Compact 3kW, D=7", 20mTorr
0 3.5
Compact configuration, 3kW
Side Langmuir probe
Density profiles across the chamber (2)
![Page 76: Design of PM helicon arrays](https://reader036.vdocuments.net/reader036/viewer/2022062301/56814748550346895db48624/html5/thumbnails/76.jpg)
UCLA
0
1
2
3
4
5
-8 -6 -4 -2 0 2 4 6 8y(in)
n (1
011 c
m-
- 70714
x (in)Staggered3kW, D=7", 20mTorr
Density profiles across the chamber (3)
0 7-7 14
Staggered configuration, 3kW
Bottom probe array
![Page 77: Design of PM helicon arrays](https://reader036.vdocuments.net/reader036/viewer/2022062301/56814748550346895db48624/html5/thumbnails/77.jpg)
UCLA
Density profiles across the chamber (4)
Compact configuration, 3kW
Bottom probe array
0
2
4
6
8
10
-8 -6 -4 -2 0 2 4 6 8
y(in)
n (1
011 c
m-
-70714
Compact3kW, D=10", 20mTorr
x (in)0 7-7 14
![Page 78: Design of PM helicon arrays](https://reader036.vdocuments.net/reader036/viewer/2022062301/56814748550346895db48624/html5/thumbnails/78.jpg)
UCLA
0
1
2
3
4
5
-8 -6 -4 -2 0 2 4 6 8 10 12 14 16x(in)
n (
10
11 c
m-
-3.503.5
Staggered, 3kW, D=7", 20mTorr y (in)
Density profiles along the chamber (1)
Staggered configuration, 3kW
Bottom probe array
![Page 79: Design of PM helicon arrays](https://reader036.vdocuments.net/reader036/viewer/2022062301/56814748550346895db48624/html5/thumbnails/79.jpg)
UCLA
0
1
2
3
4
5
-8 -6 -4 -2 0 2 4 6 8 10 12 14 16x(in)
n (
10
11 c
m-
-3.503.5
Staggered, 3kW, D=7", 20mTorr y (in)
Density profiles along the chamber (2)
Compact configuration, 3kW
Bottom probe array
![Page 80: Design of PM helicon arrays](https://reader036.vdocuments.net/reader036/viewer/2022062301/56814748550346895db48624/html5/thumbnails/80.jpg)
Calibration of the collector array
UCLA
0
1
2
3
4
5
6
7
8
9
10
-8 -6 -4 -2 0 2 4 6 8y (in)
n (1
011 cm
-3)
LP, x = 0LP, x = 3.5LP over Al, x = 0LP over Al, x = 3.5ICC, x=0ICC, x=3.5
Compact, 2kW D=10", 20mTorr
0
1
2
3
4
5
6
7
8
9
10
-8 -6 -4 -2 0 2 4 6 8y (in)
n (1
011 cm
-3)
LP, x = 0LP, x = 3.5LP over Al, x = 0LP over Al, x = 3.5ICC, x = 0ICC, x = 3.5
Compact, 3kW, D=10", 20mTorr
0
1
2
3
4
5
-7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7
y(in)
LP/(
LP o
ver
Al)
x=0x=3.5
0
1
2
3
4
5
-7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7
y(in)
LP/IC
C
x=0x=3.5
![Page 81: Design of PM helicon arrays](https://reader036.vdocuments.net/reader036/viewer/2022062301/56814748550346895db48624/html5/thumbnails/81.jpg)
Design of PM helicon arrays
UCLA
1. Optimization of the discharge tube
2. Design of the permanent magnets
3. Design of a multi-tube array
4. Design and construction of a test chamber
5. Antennas and the RF distribution system
6. Experimental results
7. Design of a compact module
8. Ideas for further improvements to be tested
![Page 82: Design of PM helicon arrays](https://reader036.vdocuments.net/reader036/viewer/2022062301/56814748550346895db48624/html5/thumbnails/82.jpg)
A compact, 8-tube module
UCLA
28.00
7.00 7.00 14.00
TOP VIEW OF ONE MODULE END VIEW
5.50
![Page 83: Design of PM helicon arrays](https://reader036.vdocuments.net/reader036/viewer/2022062301/56814748550346895db48624/html5/thumbnails/83.jpg)
Stacked modules for large-area coverage
UCLA
![Page 84: Design of PM helicon arrays](https://reader036.vdocuments.net/reader036/viewer/2022062301/56814748550346895db48624/html5/thumbnails/84.jpg)
Match circuit fits on top of module
UCLA
![Page 85: Design of PM helicon arrays](https://reader036.vdocuments.net/reader036/viewer/2022062301/56814748550346895db48624/html5/thumbnails/85.jpg)
Design of PM helicon arrays
UCLA
1. Optimization of the discharge tube
2. Design of the permanent magnets
3. Design of a multi-tube array
4. Design and construction of a test chamber
5. Antennas and the RF distribution system
6. Experimental results
7. Design of a compact module
8. Ideas for further improvements to be tested
![Page 86: Design of PM helicon arrays](https://reader036.vdocuments.net/reader036/viewer/2022062301/56814748550346895db48624/html5/thumbnails/86.jpg)
Ferrites for better coupling
UCLA
The RF energy outside the antenna is wasted.
Perhaps it can be captured with a ferrite cover.
![Page 87: Design of PM helicon arrays](https://reader036.vdocuments.net/reader036/viewer/2022062301/56814748550346895db48624/html5/thumbnails/87.jpg)
Untested ideas
UCLA
One-piece ceramic tube
Ferrite transformer coupling
![Page 88: Design of PM helicon arrays](https://reader036.vdocuments.net/reader036/viewer/2022062301/56814748550346895db48624/html5/thumbnails/88.jpg)
![Page 89: Design of PM helicon arrays](https://reader036.vdocuments.net/reader036/viewer/2022062301/56814748550346895db48624/html5/thumbnails/89.jpg)
Varying the magnet shapes and spacings
UCLA
Varying the ID and OD of PMs shows that B depends mainly on total volume of magnet.
This shows that not much uniformity is lost if the magnet spacing is zero