2. Commercial helicon sources need heavy magnets
and cannot cover large substrates
The PMT (Trikon) MØRI source

3. Solution 1: Use distributed sources
Experiment at PMT,
ca 1995
However, still need a large electromagnet

5. Solution 2: Use permanent magnets
Material: NdFeB
Bmax = 12 kG
The magnets are dangerous!
The innovation involves two parts:
1. Novel use of PMs
2. Use of the low-field peak effect.
UCLA

6. The field of annular permanent magnets
Internal field
External field
Plasma created inside the rings follows the field lines and cannot be ejected.
The field reverses at a stagnation point very close to the magnet.

7. Proof of principle on 3” diam tube
External field
Internal field
The bottom curve is when the tube is INSIDE the magnet

8. Mechanism of the Low Field Peak
Constructive interference of reflected wave
Basic helicon relations
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9. Design of discharge tube: maximize the loading resistance
Low-field peak
Calculations are done using the HELIC code of D. Arnush

10. Final design of “stubby” discharge tube

11. Medusa 2: An 8-tube linear test array
Top view
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12. The array source is vertically compact
Side view
Probe ports
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.
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13. Wooden frame for safe storage
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14. The wooden magnet frame is used in testing
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15. Antenna connections UCLA
For CW operation, all connections were solidly soldered, and RG/393 teflon-insulated cable was used. Cable connectors cannot take the startup voltage.
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16. Matching circuit for N tubes in parallel
The problem with array sources is that the cable lengths cannot be short. The match circuit cannot be close to all the tubes.
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17. There is a “sweet spot” for tube design when RF is considered.
Matching sets limits on antenna inductance and cable lengths.
There is a “sweet spot” for tube design when RF is considered.
C1, C2 for N=8, L = 0.8mH, Z1 = 110 cm, Z2 = 90 cm

18. A water-cooled, 50-W, low resistance, rectangular transmission line

19. Medusa 2 in operation
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20. Density profiles across the chamber
3.5
Compact configuration, 3kW
Side Langmuir probe
<< 4” below tubes
<< 7” below tubes
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21. Density profiles across the chamber7 -7 14
Staggered configuration, 3kW
Bottom probe array
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22. Density profiles along the chamber
Staggered configuration, 3kW
Bottom probe array
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23. Density profiles along the chamber
Compact configuration, 3kW
Bottom probe array
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24. A compact, stackable module
The match circuit fits on top of the array