Miniproposals

Miniproposal: Date Filed: Title: First Author: Session Leader: Gerry Tinios (shots 1-20)

Engineering Operator Run Comment

plasma positioning with chopper

Session Leader Plans

Physics Operators Plans

Session Leader Summaries

Entered: Jul 7 2004 03:49:07:977PM

Author: To Be Determined

Summary for run 930624 Horne, Tinios. Summary of summary -- We learned the following things. 1) Probably the best way to get the bias current which EFC needs to operate properly is just to use I_bias = Vbias/R, where R is the series resistor, I_bias is the required bias current, and V_bias is the chopper output voltage with no feedback. In other words, program the chopper demand Vbias to be constant at the level which gives the required Ibias. A much more complicated and perhaps risky scheme is described below for shot 14. 2) With the above trick, add a second Z_cur to a wire (wire 3) and control the chopper with it. This is in addition to the z_cur predictor we have on wire 2, whose controller is OH2 and EF1. 3) The voltage programming on the chopper can and should be used to soften the start of the chopper. Ramping the demand voltage from full negative up to V_bias over 50 msec or so should allow the OH2 z_cur controller to correct the plasma position error introduced by putting I_bias into EFC. Best shot for EFC Z control -- 19, but gains need further tweaking. If anyone wants to pursue this next week, bring in your favorite shot, put z_cur on wire 3,bring up the CHOPPER.DAT scope and copy the PID and controller in. Adjust the chopper V preprogram and perhaps put steps in the PID to soften the turn-on. Long Summary This was the first attempt to use EFC with a plasma. The EFC is controlled by the chopper, which is powered by the EFC TMX supply. There is a resistor in series with the coil, which at the start of the run was set at about 0.1 ohm. At some point near the end of the run we dropped it to .03 ohms. The TMX supply was run under PLC control, 700 V, current limit at 1500 A. These parameters were arrived at during the previous run, when we ran the chopper after 0.4 seconds. Plan was to run chopper first under voltage programming, then current feedback, and finally vertical position feedback. Also, to begin by turning the chopper on late in the shot, then move the time earlier. Shot 1 today was a repeat of shot 930623017. Shot 2 move chopper start to 0.1 sec. Forgot to move TMX start; the chopper started chopping with bank uncharged, so when TMX turned on the chopper couldn't commutate. This would be a good shot to see effect of EFC on magnetics, since the current was flat (no chops) at about 1600 A. B_radial change of about 10 mT, which corresponds to about 1500 A on the cheat sheet. Shot 3 -- move the TMX to 0.05 sec, chopper chops again. Shot 4 demonstrated current feedback control, a programmed 1000 A pulse. For shot 5, added chopper to Z_cur controller, but had a series of un-related problems -- Shot 5 and 6 were fizzles, due to too much B_z see problem list. Shots 7-12 had problems of various sorts to do with EF3 not starting reproducibly -- the usual mixture of fizzles and fireworks, combined with a mild panic on shot 11 when a flux loop misbehaved in such a way as to mimic loss of current in EF3-U. Everybody's scar tissue itched, but the problem disappeared on later shots. Shot 13 finally worked, but the effect of the chopper is not at all obvious. For shot 14, tried to set up for real control. Basic idea -- 1) control Z_cur with chopper. 2) Program a bias current I_bias for the chopper. 3) As a controller for I_bias, use the EF2 power supplies. If the plasma moves, the chopper current changes to compensate, so the error in I_bias can be used as a slow z position indicator. Asymmetric ef2 currrents push the plasma in such a way as to force EFC back to the bias. The net effect is that the change in B_r initially produced by EFC ends up being produced by EF2. Shot fizzled, and the EF2 currents went wild trying to put current in the EFC coil. This scheme will only work (as programmed) if a plasma is present, though perhaps it could be modified to behave somehow. I think I=V/R is a much cleaner way to go. For shot 15, reload shot 13 and try the I=V/R scheme -- another z_cur predictor on wire 3 driving chopper. The shot ran, and the chopper behaved well. 16 and 17 were fizzles -- EF3 now realizes we moved it's start time earlier several shots ago. Shot 17 does show EFC bias current at 700 A or so -- about right for a max current of 1500 A. Tried compensating B_z with EF4, shot 18 was ok. The chopper programming was fine but the gain was too low to actually do anything significant. We had a delay here due to an alternator fault which we used to decrease the series resistor to .03 ohms. Increased gain on shot 19, where it's possible the chopper actually helped stabilize the plasma. This is nearly a proof-of-principle for the I=V/R scheme. Here we had a delay due to a a spontaneous reboot of SHAPE. When it became clear that shot 20 would be the last of the day, we raised the efc tmx from 700 to 900 V and the current limit to 2000 A. The chopper turn-on yanked the plasma vertically and terminated the shot. Comparison of 19 and 20 shows that at 30 msec, the shots are quite similar. They are displaced down by about 1 cm (ip_z = 5000, ip=100000). On shot 19, the chopper yanks the plasma up to about + .5 cm before settling down. On shot 20 the higher effective gain caused the chopper to push much more current, yanking the plasma out of the machine. It's possible that the chopper overcurrent protection told the TMX supply to invert early when the EFC current approached 3000 A -- compare the static voltage traces. I didn't discover this till after the supply was shut down so I can't read the fault indicators. Problems -- Usual Slow N2 pressure rise at beginning of run. Replaced an AFOL transmitter which was introducing a 400 A error into EFC_U rogowski. The inconsistent turn-on behavior of EF3 was implicated in several fizzles and runaway shots. Gwinn believes he has found a signature on the gate pulses and Rogowskies which indicates a problem in the supply. Unusual altermnator problem. Less unusual computer problem -- SHAPE reboot. Conclusions: Fix EF3, understand the gas, and try to open up our operating window between fizzles and runaways. Then try this again. Steve

Physics Operator Summaries

Session Leader Comments
Jun 24 1993 03:17:11:600PM		Gerry Tinios	Physics Op: S. Horne Assist Op.: G. Tinios Engineering Op: V. Bertolino Commutation resistors: OH1 : 65.3 mOhms OH2U : 12.8 OH2L : 13.2 EF1U : 120.4 EF1L : 119.3 EF2U : 45.4 EF2L : 46.0 Goal: Control vertical instability with the chopper
Jun 24 1993 09:37:36:680AM	930624001	Gerry Tinios	Start with shot 930623017 from yesterday. EFC-rogowski AFOL transmitter was replaced, so the EFC current offset from yesterday shoud be fixed. Limits on EFC-chopper voltage trace set to [-1000.,1000.] Start with negative EFC-chopper demand voltage so as to smooth out the kicking in of the EFC without having to program the EFC-TMX. Log of partial pressure of mass-28: -8.58 (normal cool leak?) Fill pressure: 4.e-5 like yesterday. Dispupted at 184 msec. Not many hard X-rays. EFC-current offset is zero.
Jun 24 1993 09:47:50:480AM	930624002	Gerry Tinios	Same as previous shot, only the EFC was moved into plasma time. Zero current demand on EFC. Two -1000. EFC-chopper voltage demand pulses drawn at 0.1. Oops, forgot to change the EFC-TMX-timing. So, this was the same as last shot. Disrupted after 200msec. Diverted after 160msec.
Jun 24 1993 10:00:48:000AM	930624003	Gerry Tinios	Try again. EFC-TMX starttime was set at 0.1sec. Plasma diverted after 150msec. We lost it at 180msec.
Jun 24 1993 10:28:09:790AM	930624004	Gerry Tinios	EF2U current was reduced by 300A after 0.1 sec. We are EFC-current-programming now: 1kA 10msec pulse applied at 0.16sec. Again, negative voltage is applied to chopper just before turning on. We lost the plasma at 0.18sec again. Feedback control on EFC-current seems to work.
Jun 24 1993 10:50:05:430AM	930624005	Gerry Tinios	Reduce P-gain on EFC current from 4 to 2. Reduce controller on EFC-current from 0.2 to 0.05 Program a 500A bias current for EFC starting at 0.15sec Conncect EFC to Z-controller. A fizzle.
Jun 24 1993 10:56:06:580AM	930624006	Gerry Tinios	Exactly the same as previous shot. Fizzle again. Too much vertical field.
Jun 24 1993 11:04:55:090AM	930624006	Gerry Tinios	Some oscillation appears at the EF3 current signal after the chopper is turned on.
Jun 24 1993 11:21:05:320AM	930624007	Gerry Tinios	EF3 set to turn on 1msec later. Plasma, sparks. Too much vertical field this time! Runaway shot, lasted until 370msec. Many hard X-rays. No EF3 current oscillations this time.
Jun 24 1993 11:35:02:680AM	930624008	Gerry Tinios	Moved EF3 back by 1msec to how it was two shots ago. Got plasma. Disrupted at 220msec. Lots of x-rays. No EF3 current oscillations this time either.
Jun 24 1993 11:48:37:800AM	930624009	Gerry Tinios	Move EF3 back another msec. Reduce late puff to half the voltage. Plasma died at 160msec. Current reached 400kA. Substantial X-rays still.
Jun 24 1993 12:08:45:210PM	930624010	Gerry Tinios	Raise the fill pressure to 4.5e-5. Plasma died at 140 msec. Was diverted upwards at 130 msec according to FFIT. Two disruptions.
Jun 24 1993 12:16:50:610PM	930624011	Gerry Tinios	Increase fill pressure to 5e-5. Prescribed Z-position changed to 0. Fizzle.
Jun 24 1993 12:43:20:940PM	930624011	Gerry Tinios	The F12 flux loop seems to have some integrator-related problem.
Jun 24 1993 01:02:23:240PM	930624012	Gerry Tinios	Repeat previous shot, but reduce EF1 currents by 1kA, so as to reduce elongation. EF1L crowbared. F12 flux loop problem did not appear this time. Plasma died at 180msec.
Jun 24 1993 01:40:50:500PM	930624013	Gerry Tinios	Chopper P-gain on Z-Curr wire raised from 2.e-3 to 1.e-2.
Jun 24 1993 02:08:37:610PM	930624014	Gerry Tinios	EFC-current is now being controlled by EF2U,L antisymmetric configuration. (+,-0.2 V/A gain). P_gain set at 2. Z-curr controlled by EFC. P-gain increased from 0.5 to 1. D-gain decreased form 2 to 0.5. Chopper was set to start at 30 msec. Bias current is 500 A as before. Chopper voltage demand goes from -1000 at 30msec back to 0 at 35msec. Fizzle. Died before 20 msec.
Jun 24 1993 02:31:51:690PM	930624015	Gerry Tinios	Loaded shot 13 and made the following changes: The chopper was taken out of wire 2. Another wire (3) was added to control Z-curr by means of the chopper. Wire 3 kicks in at 30 msec.
Jun 24 1993 03:38:25:510PM	930624015	Gerry Tinios	Fill pressure was 4.5e-5
Jun 24 1993 03:36:46:480PM	930624016	Gerry Tinios	P-gain on wire 3 raised from 1 to 3, because it was observed in the previous shot that EFC was hardly used. D-gain on wire 2 (Z-curr control by coils other than EFC reduced from 2 to 1. Alternator had a problem. The extra time was used to change the EFC-resistor from 0.1 to 0.033 Ohms.
Jun 24 1993 03:38:45:420PM	930624016	Gerry Tinios	Fill pressure was 5e-5
Jun 24 1993 03:48:24:620PM	930624016	Gerry Tinios	EFC was voltage preprogramming was set at -500 V.
Jun 24 1993 03:53:36:010PM	930624017	Gerry Tinios	Same as previous shot, only fill pressure was set at 4e-5 and EFC voltage preprogramming was moved to -200 V starting at 30msec. EFC bias current was 700 A.
Jun 24 1993 04:10:08:430PM	930624018	Gerry Tinios	Increase EF4 current by 30 A to buck out some of the vertical field during breakdown. Turned off feedback control on EFC current. EFC voltage preprogramming will hopefully give us the desired bias current. Fill pressure : 4e-5
Jun 24 1993 04:28:16:800PM	930624019	Gerry Tinios	Fill pressure set at 4.5e-5 P-gain on wire 3 was increased to 5.
Jun 24 1993 04:58:59:510PM	930624020	Gerry Tinios	EFC is tapered in more gently. EFC voltage preprogramming goes from 0 to -200 between 30 and 50 msec. Chopper bank voltage was increased to 900 V. P-gain on wire 3 was doubled (from 5 to 10). SHAPE spontaneously rebooted while INITing this shot. Had to abort and reINIT, when it was finished rebooting.

Physics Operator Comments

Engineering Operator Comments
Shot	Time	Type	Status	Comment
1	09:10:50:640AM	Plasma	Ok	300ka plasma -- no faults
2	09:37:07:620AM	Plasma	Ok	320ka plasma
3	09:49:29:210AM	Plasma	Ok	310ka plasma
4	10:16:14:760AM	Plasma	Ok	320ka plasma
5	10:35:14:040AM	Plasma	Ok	fizzle
6	10:48:50:270AM	Plasma	Ok	fizzle
7	11:07:59:300AM	Plasma	Ok	350ka plasma
8	11:22:59:460AM	Plasma	Ok	350ka plasma -- no faults
9	11:38:19:440AM	Plasma	Ok	410ka plasma -- no faults
10	11:50:13:510AM	Plasma	Ok	360ka plasma
11	12:12:35:260PM	Plasma	Ok	fizzle
12	12:45:25:810PM	Plasma	Ok	comm fault ef1l -- fuses ok
13	01:04:37:450PM	Plasma	Ok	360ka plasma -- no faults
14	01:47:01:980PM	Plasma	Ok	fizzle
15	02:20:35:280PM	Plasma	Ok	320ka plasma -- no faults
16	02:36:49:560PM	Plasma	Ok	fizzle
17	03:49:28:890PM	Plasma	Ok	fizzle
18	04:05:49:750PM	Plasma	Ok	350ka plasma
19	04:19:46:680PM	Plasma	Ok	320ka plasma -- no faults
20	04:34:53:890PM	Plasma	Ok	140ka plasma -- no faults