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XP #802 - Biased Electrodes

XP #802 - Biased Electrodes. S.J. Zweben, R.J. Maqueda, L. Roquemore, R.J. Marsala, Y. Raitses, R. Kaita, C. Bush R.H. Cohen, D.D. Ryutov, M. Umansky (LLNL). • Upgrades for 2008 • Physics goals for 2008 • Proposal for 2008 • Possible concerns. Team XP review 1/11/08.

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XP #802 - Biased Electrodes

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  1. XP #802 - Biased Electrodes S.J. Zweben, R.J. Maqueda, L. Roquemore, R.J. Marsala, Y. Raitses, R. Kaita, C. Bush R.H. Cohen, D.D. Ryutov, M. Umansky (LLNL) • Upgrades for 2008 • Physics goals for 2008 • Proposal for 2008 • Possible concerns Team XP review 1/11/08

  2. Hardware Upgrades for 2008 • Two positive supplies increased from ~10 A to ~30 A • Added radial array of probes to measure local SOL • Will now have fast camera views of BEaP electrodes radial probe array GPI puffer B cable shield BEaP

  3. BEaP Goals for 2008 • Measure effect of increased positive bias (x3 in I, x2 in V) • Measure effect on local SOL with new radial probe array • View effects of biasing on D light near BEaP electrodes • Evaluate effect of double-probe biasing (floating electrodes) • Evaluate effects during NBI and RF (via piggy-backing ?)

  4. BEaP XP for 2008 (~1/2 day) Repeat #124688, I=0.8 MA, B=4.5 T, outer gap ~5 cm -> 1 cm 1st hour: single-electrode voltage scan up to +100 V (≤ 30 A) monitor local array, local D light at BEaP, GPI images look for effects on plasma (impurities, radiation, divertor) after this, check probe-GPI correlations for alignment 2nd hour: optimize alignment based on shots #1-5 (i.e. adjust Ip) try four electrode biasing +/-/+/- (VExB outward at array) 3rd hour: reconfigure for double-probe biasing (pending review) 4th hour: repeat best case, or try with NBI (using ~5 cm gap)

  5. Approximate Shot Sequence

  6. Possible Concerns • Electrode heating: P(2008) ≤ 3 kW @ 50% for 0.2 sec => maximum T (surface) ~ 75 ºC during shot => maximum T (bulk) ≤ 40 ºC after shot => should be no problem with melting • Arcing: will look at electrode currents and fast camera • Impurity influx: will monitor iron with SPRED and Ptot with bolometer no increase in Ptot in 2007 run • Floating double-probe operation with voltage transients ? (review before implementation)

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