Miniproposals

Miniproposal: 028 Date Filed: 9/7/1993 Title: X-point Control of Diverted Plasmas First Author: John Goetz Session Leader: Robert Granetz (shots 1-23)

Engineering Operator Run Comment

diverted plasmas

Session Leader Plans

Physics Operators Plans

Session Leader Summaries

Entered: Jul 7 2004 03:49:10:790PM

Author: To Be Determined

Run summary for 940607 SL: R. Granetz PO: J. Goetz EC: V. Bertolino/J. Daigle The goal of this run was to develop good single-null lower x-point diverted discharges. "Good" means: 1) Not close to being double null 2) Good clearance (2+ cm) to both inner and outer limiters 3) Strike points below inner and outer divertor noses 4) Plasma center close to the midplane (for antenna coupling) 5) Stable elongation It turns out that with the new antennas, it is very difficult to get a plasma configuration that meets all of these criteria. By the last shot of the day (940607023), we achieved items 2,3, and 5, at least at Ip=0.6 MA. But we found that the easiest way to get this is by manually programming the shaping coil currents to be nearly up/down symmetric (i.e. EF2's, EF1's, and OH2's) and then moving the plasma centroid down to -1.5 cm below the midplane using the ZCUR feedback. The RF antenna was still able to couple >1 MW of power, but I don't know how the loading and performance compares in detail to a centered plasma. So item #4 may possibly be acceptably satisfied, but item #1 is probably not. To achieve item 1, we need to run a more asymmetric plasma, and we think this means that feedback with appropriate predictors/controllers for elongation must be developed, without screwing up the control of x-point position, inboard clearance, etc. We tried a little of this during the first part of this run, but we ended up with strongly triangular plasmas with an upper x-point near the inboard wall. Even if we decide that today's final plasma is an acceptable diverted configuration, without appropriate feedback, everything will have to be retuned when we raise Ip. Since I haven't gotten enough feedback yet from the divertor group, I don't know whether or not more discharge development is required for Thursday's divertor run. Despite the vacuum "incident" the evening before this run, we didn't have much more difficulty establishing plasma operation than any other recent run (3 fizzles, then a short disruptive shot, then we were on our way). There were, however, two separate episodes later in the run where the current rise was annoyingly lost, and minor tweaks to BR and BZ and/or reloading a previous shot brought it back.

Physics Operator Summaries

Session Leader Comments
Jun 7 1994 10:04:17:200AM	940607001	Robert Granetz	No TF. Power supply was simply not enabled. Also, there was pretty bad 60 Hz on the OH1 as well.
Jun 7 1994 10:08:59:170AM	940607002	Robert Granetz	Fizzle. Crummy null, possibly due to large 60 Hz ripple (400 amps) on OH1. The engineers are going out there now to undo changes they made during the maintenance day yesterday. Next shot (in addition to fiddling with the OH1 supply), change pre-fill from 1.1 to 1.0e-5 torr.
Jun 7 1994 10:33:45:870AM	940607003	Robert Granetz	Fizzle. Oscillations in OH1 and OH2's are reduced substantially. Null looks so-so, but at least as good as last week. Next shot, tweak gain on OH1, but no important changes.
Jun 7 1994 10:41:14:160AM	940607004	Robert Granetz	Fizzle. Next shot, increase EF4 current by 10 amps to tweak Bz by less than 1 mT. Pre-fill is still at 1.0e-5 torr.
Jun 7 1994 10:56:55:030AM	940607005	Robert Granetz	Plasma, dirty disruptive. To be expected, given the vacuum event last night. On the mass spectrometer, H20 is equal to N2. Next shot, raise pre-fill from 1.0 to 1.2e-5.
Jun 7 1994 11:24:01:610AM	940607006	Robert Granetz	Plasma, getting better. Major disruption at 0.625 s. Ip=0.60 MA. Looks like we got to a kappa of 1.70, which probably caused the disruption. It was a downward VDE, with about 70 kA on the lower halo rogowski, but nearly 400 kA on the total of the divertor shunts. Next shot, program EF1U with +1500 more amps.
Jun 7 1994 11:48:41:540AM	940607007	Robert Granetz	Plasma. Good shot. Ip=0.60 MA, duration=1.11 s. There was a huge burst of impurities at 0.600 s, caused by the RF suddenly turning on to a level of 1 MW. The plasma was reasonably diverted from 0.6 to 0.65 s, but then by 0.7 s an upper x-point came in (close to the inboard wall), and triangularity went almost to unity. Next shot, lower plasma centroid by 1 cm from t=0.5 sec onward.
Jun 7 1994 12:10:03:160PM	940607008	Robert Granetz	Plasma. Disrupted upward at 0.825 s. Ip=0.60 MA. Only 40 kA of halo current. Got the -1 cm change in Z-centroid. This shot had an upper x-point for most of the shot, and no lower x-point. Next shot, put some negative current in EF1U, and move plasma centroid up from -1 cm to -0.5 cm.
Jun 7 1994 12:25:10:230PM	940607009	Robert Granetz	Fizzle. Next shot, remove the 10 amp change made to EF4 earlier in the run.
Jun 7 1994 12:45:14:000PM	940607010	Robert Granetz	Plasma. Ip=0.61 MA, duration=1.07 s. Several minor disruptions during the current rise, and several hesitations. Prf=1 MW. I don't think our unbalancing of the EF1's (starting with shot 007) was a good idea. Every shot since then has had an upper x-point. For the next shot, re-load shot 006 (which was the last one before we started playing with EF1U. Then make the following changes: Move Zcur to -0.005 m, and Subtract 10 amps from EF4.
Jun 7 1994 01:09:05:950PM	940607011	Robert Granetz	Plasma. Downward disruption at 0.77 s. Ip=0.6 MA. No RF this shot (well, it was at 20 kW). Plasma was nicely elongated from t=0.6 to 0.7 s, but then after 0.7 s it became too elongated and formed a double null. Next shot, lower plasma another 5 mm (from -0.005 to -0.010 m)
Jun 7 1994 01:29:52:090PM	940607012	Robert Granetz	Plasma. Disrupted downward at 0.68 s. Ip=0.60 MA. Plasma became disruptive at 0.6 s, which is when it becomes diverted. Next shot, move plasma outward by 1 cm (change Rcur from 0.67 to 0.68 m), starting at t=0.24 s.
Jun 7 1994 01:32:53:870PM	940607012	Robert Granetz	This plasma was a lower single null from t=0.62 onward, but there was not enough clearance on the inboard wall. The x-point RXL was okay, but the ZXL should be lowered a bit.
Jun 7 1994 02:00:17:350PM	940607013	Robert Granetz	Plasma. No disruptions. Ip=0.60 MA, duration=1.05 s. Getting a better lower x-point diverted plasma, starting at about 0.65 s. Next shot, put -400 amps more in both EF1U & L, in order to pull the lower separatrix farther down the divertor slot.
Jun 7 1994 02:09:46:920PM	940607014	Robert Granetz	Plasma. No disruptions. Ip=0.61 MA, duration=1.12 s. RF power reached 1 MW. Single lower null. Next shot, put -400 amps more in the EF1's to pull separatrix even more down the slot. Also extend shot length by 0.2 s.
Jun 7 1994 02:16:24:080PM	940607014	Robert Granetz	On second thought, I don't want any more negative changes in the EF1's, since we're already at an elongation of 1.7 on this shot. We will, however, extend the length of the shot by 0.2 s.
Jun 7 1994 02:50:46:320PM	940607015	Robert Granetz	Plasma. No disruptions. Ip=0.60 MA, duration=1.3 s. Prf=1.3 MW. Forms divertor around 0.6 s, pulls off of outboard limiter around 0.7 s, and is really good around 0.9 s. Next shot, put -300 amps in EF1L only. No change to EF1U. This is to shape the separatix into the slot even more.
Jun 7 1994 03:11:16:330PM	940607016	Robert Granetz	Plasma. Late disruption at 1.2 s. Ip=0.61 MA, duration=1.2 s. Prf=1.5-1.4 MW Lower x-point diverted, but it's still not exactly what we want. Next shot, move plasma from zcur=-1.0 cm to -0.5 cm.
Jun 7 1994 04:01:15:850PM	940607017	Robert Granetz	Fizzle. Next shot, reduce EF1 current by another 10 amps.
Jun 7 1994 04:00:45:870PM	940607018	Robert Granetz	Dud. Next shot, change BR by 0.5 mT.
Jun 7 1994 04:00:08:170PM	940607019	Robert Granetz	Plasma. Disrupted at 0.58 s, maybe because of kappa, but we're not sure. Ip=0.60 MA Next shot, remove the changes to EF2 made after shot 016.
Jun 7 1994 04:08:18:730PM	940607020	Robert Granetz	Fizzle. Null looks really awful. No problems with magnetics signals. Next shot, re-load shot 016 and change ZCUR to be -0.005 m.
Jun 7 1994 04:29:16:820PM	940607021	Robert Granetz	Plasma. Disrupted late at 1.03 s. Ip=0.61 MA. Next shot, change ZCUR to -1.5 cm, and turn on CLEARIN with setting of +1 cm.
Jun 7 1994 04:45:27:430PM	940607022	Robert Granetz	Plasma, but disrupted downwared at 0.57 s. Ip=0.6 MA. Disruption might have been due to kappa. Good clearance on both inboard and outboard limiters at the midplane. Plasma was limited near the nose of the inner divertor. Next shot, delay turn on of CLEARIN until 0.6-0.65 s.
Jun 7 1994 05:07:19:640PM	940607023	Robert Granetz	Plasma. No disruptions. Ip=0.61 MA, duration=1.26 s. Got the change in ZCUR, as programmed. Diverted plasma was pretty good, actually. Probably our best shot today.

Physics Operator Comments
Jun 7 1994 09:32:59:020AM		John Goetz	RUN 940607 The objective of this run is develop well controlled divertor discharges. 1. matched to the closed divertor 2. matched to the RF antennae The starting shot will be 940602927. This shot is the last, unfired shot from 940602. The only changes to this shot are to remove the gas puff near the end of the discharge.
Jun 7 1994 09:53:32:750AM	940607001	John Goetz	Shot 940607001 Fill pressure 1.1e-5 TF did not fire - supply was not enabled For Shot 940607002 try again
Jun 7 1994 10:17:25:530AM	940607002	John Goetz	Shot 940607002 Fizzle - lasting until 30+ msec null is very poor - Bz about 1mT too negative large 60Hz oscillation in OH1 before commutation For Shot 940607003 drop P_0 to 1.0e-5 engineers to change the OH1 gain in the power supply wait one shot to diagnose the null
Jun 7 1994 10:32:43:580AM	940607003	John Goetz	Shot 940607003 Fizzle - hit outer limiter at .016 null is as good as those on 940602 - which isn't saying much 60Hz oscillation in OH1 before commutation cured For Shot 940607004 P gain on IC_OH1 to 1.2 ( try and get to the programmed value a little sooner ) try again
Jun 7 1994 10:42:35:710AM	940607004	John Goetz	Shot 940607004 Fizzle - hit outer limiter at .016 null is as good as those on 940602 - which isn't saying much OH1 current reaches its target value earlier with no extra oscillation scatterplot shows Bz to be a bit too negative For Shot 940607005 IC_EF4 to -1020A from -1030A to bring up Bz at commutation
Jun 7 1994 10:58:17:630AM	940607005	John Goetz	Shot 940607005 dirty, disruptive plasma disruptions beginning at .116 - final disruption at 0.35 For Shot 940607006 raise fill pressure to 1.2e-5 in response to probable moly gettering on 006
Jun 7 1994 11:31:35:200AM	940607006	John Goetz	Shot 940607006 plasma - Ip=0.6 divertor begins to form after 0.55 disruption at 0.625 - going down kappa > 1.70 before disruption For Shot 940607007 IC_EF1U = 2000A from 0.4 to 0.78 ( try and hold down kappa ) IC_EF2U = -1000A @ 0.75 ( cancel radial field created by EF1U )
Jun 7 1994 11:53:37:850AM	940607007	John Goetz	Shot 940607007 plasma - Ip=0.6 - ramps all the way down divertor begins to form after 0.55 - double null kappa = 1.70 before disruption RF pulse from 0.6 to 0.75 For Shot 940607008 EF2_U_VOLT in RXL controller changed to 2e-3 ( from 4e-3) to help IC_EF2U controller ZCUR = -.01 @ 0.55 ( 0 @ 0.45 ) to get single null
Jun 7 1994 12:13:25:150PM	940607008	John Goetz	Shot 940607008 plasma - Ip=0.6 - disruption @ .825 mostly upper null divertor z-position oscillations - unstable at -1cm? For Shot 940607009 EF2_U_VOLT in RXL controller changed to 1e-3 ( from 2e-3) to help IC_EF2U controller ZCUR = -.005 @ 0.65 ( 0 @ 0.45 ) to help z-oscillations add 90V x .01sec pulse @ 0.5 on PULSE_GAS_1 IC_EF1U = 1500A from 0.4 to 0.78 ( was 2000A )
Jun 7 1994 12:48:43:780PM	940607009	John Goetz	Shot 940607009 fizzle - hit something at 0.013 Bz a little too positive - null looks good from 0. to .003 sec For Shot 940607010 IC_EF4 = -1030A ( was -1020 )
Jun 7 1994 12:50:30:520PM	940607010	John Goetz	Shot 940607010 plasma - successful rampdown kappa > 1.6 double null from 0.54sec on For Shot 940607011 give up and reload 940607006 - has symmetric EF1's ZCUR = -.005 IC_EF4 = -1030A add 90V x .012sec pulse @ 0.5 on PULSE_GAS_1
Jun 7 1994 01:17:57:960PM	940607011	John Goetz	Shot 940607011 plasma - disruption at 0.767 disruptive beginning at 0.58 lower single null @ 0.6 - double null @ 0.7 For Shot 940607012 ZCUR = -.01 @ 0.6sec ( 0 @ 0.4 )
Jun 7 1994 01:31:14:880PM	940607012	John Goetz	Shot 940607012 plasma - disruption at 0.683 disruptive beginning at 0.58 lower single null @ 0.6 For Shot 940607013 RCUR = 0.68 from .25 to 0.9 - move x-pt out by moving plasma
Jun 7 1994 01:53:12:730PM	940607013	John Goetz	Shot 940607013 plasma - successful rampdown lower single null from 0.6 to 0.8 For Shot 940607014 RCUR = 0.67 from .25 to 0.4 and then 0.68 from 0.4 to 0.8 IC_EF1's to 225A from 0.49 to 1.0 to try and move strike points around
Jun 7 1994 02:19:32:490PM	940607014	John Goetz	Shot 940607014 plasma - successful rampdown lower single null from 0.6 to 0.8 kappa = 1.7 For Shot 940607015 extend flat-top until 1.0 sec by: draw Ip waveform to 1.0 draw Ip controller gain switches at 1.0 extend EF1's and EF2's until 1.5 sec PF invert times to 1.4; TF invert time to 1.2
Jun 7 1994 02:42:03:990PM	940607015	John Goetz	Shot 940607015 plasma - successful rampdown @ 1.0sec lower single null until 0.85 1.63 < kappa < 1.65 For Shot 940607016 RCUR = 0.68 all the way to 1.0 90V x .015 sec pulse added @ 0.7 to PULSE_GAS_1 100V x .015 sec pulse added @ 0.8 to PULSE_GAS_3 IC_EF1L = -100A (was +200) to try and move the strike points down the slot
Jun 7 1994 03:21:53:190PM	940607016	John Goetz	Shot 940607016 plasma - disruption during rampdown kappa = 1.6 from 0.6 to 1.0 gaps of ~2cm For Shot 940607017 IC_EF2U = -600A @ 0.7 (to try and keep upper x-point out of the machine) P gain for IC_EF2U = 0.5 from 0.5 to 1.2sec ZCUR = -.005
Jun 7 1994 03:25:18:320PM	940607017	John Goetz	Shot 940607017 fizzle - hit something at .016sec scatterplot says Bz a bit too positive For Shot 940607018 IC_EF4 = -1040A (was -1030) 100V x .01sec pulse added to PULSE_GAS_3 @ .45 sec
Jun 7 1994 03:40:15:440PM	940607018	John Goetz	Shot 940607018 DUD null is terrible - Br too positive For Shot 940607019 BR_0 offset = -3.0e-3 (was -2.5e-3)
Jun 7 1994 03:55:24:720PM	940607019	John Goetz	Shot 940607019 plasma - disrupts at 0.583 loss of vertical control starting at 0.55 was it the non-symmetric change in the EF2's from 017? For Shot 940607020 make the EF2's symmetric turn off the P gain on IC_EF2U @ 0.5
Jun 7 1994 04:12:40:820PM	940607020	John Goetz	Shot 940607020 fizzle null is awful - should never have broken down Br ramp from +2mT @ 0. to -2mT @ .015 For Shot 940607021 Punt! Reload of 940607016 ZCUR = -.005
Jun 7 1994 04:30:35:440PM	940607021	John Goetz	Shot 940607021 plasma - disruption at 1.033 single null @ 0.6 - double null @ .76 For Shot 940607022 ZCUR = -.015 CLEARIN = .01 @ .45sec P gain for CLEARIN is 1 @ 0.4
Jun 7 1994 04:49:36:650PM	940607022	John Goetz	Shot 940607022 plasma - disruption at .575 2 cm gap @ .42 sec - CLEARIN is working oscillation in z-position when plasma crosses -1 cm kappa is 1.6 at this time For Shot 940607023 CLEARIN = 0 @ .6sec & .01 @ .7sec P gain for CLEARIN is 0.5 @ .625 & 1 @ .65sec delay the turn-on of CLEARIN until the plasma is diverted
Jun 7 1994 05:13:42:640PM	940607023	John Goetz	Shot 940607023 plasma - successful rampdown z position well controlled but at -.02 fact learned from this shot - do not turn on CLEARIN until the plasma is ready to divert left gap of 3cm; right gap of 1.5-2cm RXL is under good control ZXL is slowly moving up kappa = 1.65 to 1.6 through the diverted time

Engineering Operator Comments
Shot	Time	Type	Status	Comment
1	09:49:26:260AM	Plasma	Bad	tf not enabled -- did not fire
2	10:01:22:900AM	Plasma	Ok	oh1 has 60Hz
3	10:19:31:580AM	Plasma	Ok	no faults
4	10:31:47:220AM	Plasma	Ok	no faults
5	10:48:13:550AM	Plasma	Ok	no faults
6	11:09:31:310AM	Plasma	Ok	no faults
7	11:32:16:900AM	Plasma	Ok	no faults
8	11:53:04:260AM	Plasma	Ok	no faults
9	12:17:47:280PM	Plasma	Ok	no faults
10	12:31:19:790PM	Plasma	Ok	oh1 comm fail in inversion
11	12:54:57:110PM	Plasma	Ok	No faults
12	01:14:59:580PM	Plasma	Ok	NO faults.
13	01:33:58:120PM	Plasma	Ok	No faults.
14	01:53:38:870PM	Plasma	Ok	No faults.
15	02:18:09:710PM	Plasma	Ok	oh1 comm. fault
16	02:38:15:240PM	Plasma	Ok	no faults Initially camac hybrid problem
17	03:14:25:020PM	Plasma	Ok	dud No faults.
18	03:26:33:650PM	Plasma	Ok	Dud no faults
19	03:41:40:930PM	Plasma	Ok	No faults.
20	04:00:16:720PM	Plasma	Ok	Dud no faults.
21	04:14:23:570PM	Plasma	Ok	No faults
22	04:35:31:540PM	Plasma	Ok	No faults.
23	04:56:45:680PM	Plasma	Ok	No faults