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A helicon source requires a DC magnetic field..

U. Wisconsin. A helicon source requires a DC magnetic field. UCLA. ...and is based on launching a circularly polarized wave in the plasma. UCLA. The antenna can be twisted to match the helicon's helical waveform. UCLA. The R-wave propagates to the right, and

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A helicon source requires a DC magnetic field..

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  1. U. Wisconsin A helicon source requires a DC magnetic field..

  2. UCLA ...and is based on launching a circularly polarized wave in the plasma

  3. UCLA The antenna can be twisted to match the helicon's helical waveform

  4. UCLA The R-wave propagates to the right, and the L-wave to the left (for this antenna helicity) But the L-wave is very weak, and this antenna is unidirectional

  5. Why do helicons ionize so well? Landau damping (1985) F.F. Chen, Plasma Phys. Control. Fusion 33, 339 (1991). This was disproved (1999) F.F. Chen and D.D. Blackwell, Phys. Rev. Lett. 82, 2677 (1999). Mode-coupling to TG modes (1996) K.P. Shamrai and V.B. Taranov, Plasma Sources Sci. Technol. 5, 474 (1996). Parametric excitation of ion acoustic waves (2005). B. Lorenz, M. Krämer, V.L. Selenin, and Yu.M. Aliev, Plasma Sources Sci.Technol. 14, 623 (2005). UCLA

  6. UCLA Two commercial helicon reactors The PMT (Trikon) MØRI source The Boswell source

  7. Distributed source: first attempt A 7-tube circular array. This failed to produce high density. Each tube with a solenoidal coil and helical m = +1 antenna UCLA

  8. Reason: Diverging field lines UCLA

  9. Distributed source: Second attempt This was better UCLA

  10. Distributed source: Third attempt The “stubby” tube This worked beautifully! But… UCLA

  11. Plasmas merged; density is uniform …but the size is limited by the single large electromagnet. UCLA

  12. Internal field External field Characteristics of permanent magnet rings UCLA

  13. External field Internal field Experiments with 7-cm diam tube UCLA

  14. Radial density profiles at Z1 and Z2 Upper probe x 1010cm-3 Lower probe Proof of principle: discharge in the external field gives much more plasma downstream. UCLA

  15. Optimization of magnet geometry actual Result: Field strength  magnet volume Spacing improves uniformity slightly actual UCLA

  16. Optimization of discharge tube: HELIC code D. 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. UCLA

  17. The low-field peak Typical HELIC result UCLA

  18. Relation of R to plasma density Rp << Rc UCLA

  19. Relation of R to plasma density Rp > Rc UCLA

  20. HELIC and expt. matrices varied a, L, f, p, endplate UCLA

  21. Examples: Tube diameter, frequency Larger diameter gives higher plasma resistance, but this is not practical. 13.56 MHz is much better than 2 MHz. UCLA

  22. Final design Very similar to “stubby” tube, designed by intuition! Only improvement is the metal top. A single NdFeB magnet UCLA

  23. The magnets are dangerous! Material: NdFeB Bmax = 12 kG Attractive force between two magnets 2 cm apart: 516 Newtons = 53 kG UCLA

  24. Wooden frame for safe storage UCLA

  25. Single tube, final configuration Radial density profiles at Z1 = 7.4 cm and Z2 = 17.6 cm below discharge. Radial Bz profiles at various distances below the magnet. Discharge tube UCLA

  26. Design of array The density at Z2 is summed over nearest tubes. For a single row, a distance L = 17.5 cm between two tubes gives less than 2% ripple in density. UCLA

  27. Computed uniformity n(x) for various y Half-way between rows 1/4-way between rows Directly under a row Beyond both rows

  28. An 8-tube linear test array UCLA

  29. The array source is vertically compact The magnets are to be stuck onto an iron plate, which holds them and also concentrates the flux. Once placed, the magnets cannot easily be moved, so for testing we use a wooden support. UCLA

  30. The wooden magnet frame is used in testing UCLA

  31. An 8-tube staggered array in operation UCLA

  32. Possible applications • Web coaters • Flat panel displays • Solar cells • Optical coatings A web coater UCLA

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