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) Team XP review 1/11/08 Upgrades for 2008 Physics goals for 2008 Proposal for 2008 Possible concerns

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 cable shield GPI puffer BEaP B

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 I p ) try four electrode biasing +/-/+/- (V ExB 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 shot #plasma typebias voltage (1,2,3,4)comments 1OH, 0.8 MA, 4.5 kG0, 0, 0, 0recover #124688 2 same0, 0, +25, 0 3 same0, 0, +50, 0 4 same0, 0, +75, 0stop if near 30 amps 5 same0, 0, +100, 0stop if near 30 amps 6 same0, 0, 0, 0repeat shot #1 7 same+25, -25, +25, -25 8 same+50, -50, +50, -50 9 same+50, -50, +50, -50 10 same+75, -75, +75, -75 11 same+100, -100, +100, -100 12 same+25, -25, +25, -25try double probe bias 13 same+50, -50, +50, -50try double probe bias 14 same+75, -75, +75, -75try double probe bias 15 same+100, -100, +100, -100try double probe bias 16 same but with 1 NB+25, -25, +25, -25best case of above 17 same but with 1 NB+50, -50, +50, -50best case of above 18 same but with 1 NB+50, -50, +50, -50best case of above 19 same but with 1 NB+75, -75, +75, -75best case of above 20 same but with 1 NB+100, -100, +100, -100best case of above

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)