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Possibilities for a next-generation spheromak experiment

Author: Bick Hooper
Requested Type: Poster Only
Submitted: 2006-12-22 19:55:14

Co-authors: H. S. McLean, C. A. Romero-Talamás, R. D. Wood, L. L. LoDestro, J. M. Moller

Contact Info:
LLNL
PO Box 808
Livermore, CA   94551
USA

Abstract Text:
SSPX experiments and resistive MHD modeling suggest options for a next-generation experiment. Results to date include [1]:

• Magnetic fluctuations are now <1% when the q-profile does not cross low-order rational surfaces in the spheromak core, yielding good energy confinement. [2]
• Plasma current and magnetic field decay slowly; initial experiments suggest that the they can be rebuilt periodically by high current pulses. [3]
• Modeling predicts that flux amplification, typically 2-3 in SSPX, can be increased to >50 by actively reducing the bias (“ABR”) after spheromak formation, reducing edge ohmic losses proportionally. ABR is also predicted to improve stability and energy confinement.
• Modeling of neutral-beam experiments planned for SSPX [1] suggest it may provide a path to hotter plasmas.

Next-generation spheromak geometries and scenarios which build on these results are examined to improve plasma parameters, explore additional stability control, and examine other physics issues. A strawman scenario includes:

• Increasing the dimensions by a factor of two, resulting in a flux conserver radius of 1 m and major radius of ~ 0.6-0.7 m.
• Increasing the pulselength by a factor of 10 to ~ 0.1 sec or more.
• Operation with a thin-wall flux conserver with feed-back control of the tilt and shift modes.
• Separating the confinement and field-building phases of operation:
– Changing the helicity injector (“gun”) to allow the bias flux to be varied during the discharge, thereby increasing flux amplification during the confinement phase, increasing the plasma volume, reducing the power losses in the edge plasma, and reducing heating of the gun electrodes.
– Rebuilding the spheromak flux with helicity injection using periodic high-current pulses.
• Options for current-profile control experiments during the confinement phase, with the goal of optimizing stability and confinement.

Work supported by U.S. DOE under Contract No. W-7405-ENG-48 at UC LLNL.
[1] R. D. Wood, this meeting.
[2] H. S. McLean, et al., Phys. Plasmas 13, 056105 (2006).
[3] S. Woodruff, et al., Phys. Rev. Letters 93, 205002 (2004).

Characterization: A1,E3

Comments:
Place with SSPX Posters See abstract by H. S. McLean for order.