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
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
GPIpuffer
BEaP
B
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 ?)
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 imageslook 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)
Approximate Shot Sequence
shot # plasma type bias voltage (1,2,3,4) comments
1 OH, 0.8 MA, 4.5 kG 0, 0, 0, 0 recover #124688
2 same 0, 0, +25, 0
3 same 0, 0, +50, 0
4 same 0, 0, +75, 0 stop if near 30 amps
5 same 0, 0, +100, 0 stop if near 30 amps
6 same 0, 0, 0, 0 repeat 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, -25 try double probe bias
13 same +50, -50, +50, -50 try double probe bias
14 same +75, -75, +75, -75 try double probe bias
15 same +100, -100, +100, -100 try double probe bias
16 same but with 1 NB
+25, -25, +25, -25 best case of above
17 same but with 1 NB +50, -50, +50, -50 best case of above
18 same but with 1 NB +50, -50, +50, -50 best case of above
19 same but with 1 NB +75, -75, +75, -75 best case of above
20 same but with 1 NB +100, -100, +100, -100 best case of above
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 bolometerno increase in Ptot in 2007 run
• Floating double-probe operation with voltage transients ?
(review before implementation)
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