Miniproposals

Miniproposal: Date Filed: Title: First Author: Session Leader: Jim Terry (shots 1-23)

Engineering Operator Run Comment

Investigat volume recombination in the divertor under detached ohmic con

Session Leader Plans

Physics Operators Plans

Session Leader Summaries

Entered: Jul 7 2004 03:49:20:960PM

Author: To Be Determined

Run summary for 990528 PO - Ron Parker and Steve Wolfe SL - Jim Terry The purpose of the run was to investigate volume recombination in the divertor under detached ohmic conditions. The detailed issues we wanted to address were 1) the scaling of the recombination sink with plasma current, 2) T_e measurements in the recombining regions, 3) the effect of the bypass flaps on the detachment threshold, and 4) the existence of significant plasma in the private flux region when the outer strike point is deep in the slot. Unfortunately, this was not a productive run, and we were not successful in completing these goals. We did learn the following however: 1) The detachment threshold was higher than in the past for the 1 MA current. In the past the detachment threshold has been at NL_04~1.75e20. (See, for example, shot 980116024.) Today we got to NL_04=2.1e20 (shot 990528006) and the divertor was just beginning to detach (i.e. a death ray was observed). Thus for unknown reasons, the ohmic detachment threshold was higher today than in the past. 2) We observed extremely high densities on the outer divertor probes (up to 4.0e21 m-3 in the death ray - see OD probe 6 on shot 990528019) with the divertor still attached. These may be the highest measured on C-Mod to date. Thus, this represents an extension of the high-recycling regime. 3) We showed that the state of the bypass flaps DID affect the detachment threshold. For shot 990528020 with the flaps OPEN, the outer divertor went from partial to full detachment at 0.8-0.85 s, when NL_04 was 2.0e20. As stated above, shot 990528006 (with the flaps closed) got to 2.1e20 without detaching. 4) We got good Balmer spectra and Lyman radiative recombination spectra (for T_e) on shots 002, 004, 006, 019, and 020. A shot-by-shot accounting of the run is: 001 fizzle 002 Good shot (1 MA) - nl_04 to 1.8e20 - but no detatchment until current ramp down. Verified that McP, McP visible channels, B side, B top, A side, K bottom straight, K bottom RA reticons are working. 003 fizzle 004 Good shot - nl_04 to 1.8e20 - but no detatchment until current ramp down. 005 fizzle 006 Good shot (1 MA) - nl_04 to 2.13e20 - but no detatchment until current ramp down. 007 Disrupted at cross-over - 0.34 s 008 Disrupted at cross-over - 0.36 s 009 Plasma in big trouble after 0.17 s - finally disrupted at 0.495 s 010 Disrupted at 0.33 s 011 fizzle 012 ugly 1.0 MA plasma with multiple injections - survives to 0.86s 013 better 1.0 MA plasma with multiple injections - survives to 0.81s 014 good 0.7 MA plasma - ramps down 015 large Mo injections early - 700 kA, NL_04 ramps up to 1.2e20, then detaches on current rampdown 016 good 700 kA shot - decent D_0 Lyman spectrum 017 back to a 1.0 MA shot - disrupted at cross-over - 0.356 s 018 1.0 MA shot - disrupted from brigk at 0.674 s 019 good 1 MA shot - disrupted at 1.018 s at NL_04=2e20 020 good 1 MA shot with bypass flaps OPEN partial to full detachment around 0.8 s, disrupted at 1.030 s at NL_04=2.25e20 021 tried for 0.9 MA shot with bypass flaps OPEN - disrupted at 0.432 s 022 test 023 breaker pulled

Physics Operator Summaries

Entered: Jul 7 2004 04:37:01:427PM

Author: To Be Determined

Run Plan for 28 May 1999 Session Leader: J. Terry Physics Operator: R. Parker Engineering Preparations: 1 Hour ECDC in D2 Prior to run, with an hour between end of ECDC and beginning of run. Power Supply Setup: Same as in shot 990521011 Gas Setup: Fill B-Top with 6 psi of D2, Hybrid enabled Fill B-Side Lower with 1 psi Ar, Hybrid DISABLED Fill B-Side Upper with 30 psi D2, Hybrid DISABLED Fill C-Side with 30 psi D2 Hybrid enabled Fill J-Bottom with 30 psi D2 Hybrid DISABLED** **CAUTION: J-Bottom valve has a through-leak. If base pressure rises above 1e-7 Torr when plenum is filled, do not continue filling and instead evacuate line. Gate Valves: ECE, VUV Enabled Run Purpose: Investigate volume recombination in the divertor under detached ohmic cond- itions. Detailed Objectives: 1. Determine scaling of the recombination sink with current; 2. T_e measurements in recombining regions; 3. Determine the effect of bypass flaps on detachment threshhold, and 4. Determine if significant plasma exists in the private flux region when the outer strike point is deep in the slot. Run Plan: Start with shot 990521011 but with BT constant at 5.4 T and a different density program, namely nl_04=1.4e20 at 0.6 s ramping to 2.0e20 by 1.1 s. After establishing this plasma, increase n-ramp to reach nl_04 greater than 2.5e20 by 1.1 s. The density at which detachment occurs will be determined, with flaps closed (~5 shots). The above will be repeated with flaps open (~2 shots). The plasma current will be increased to 1.2 MA and the density ramps repeated, increasing the maximum density until nl_04 exceeds 3.0e20 (Gulp!). The recom- bination sink, the densities and temperatures will be measured and the extent of the recombination region observed. (~7 shots). Then the "slot-divertor" part of the run begins. Shot 990429003 (0.8 MA) will be loaded. This shot begins with a "slot" outer divertor but evolves to a "ver- tical target" divertor. The density at first will be just low enough for the the outer leg to be attached (nl_04~1e20). The second density will be such that the outer leg is attached (nl_04~1.7e20). The third density (nl_04~2e20) should behigh enough for the outer divertor to be deeply detached. Each of the three densities will be run only once with the flappers open and once with the flap- pers closed. (~10 shots) Run Summary: The run began with reasonable shots, following the run plan. Some fizzles were encountered. In shot 5 an unbalance between OH2 U and L was noted and corrected. Whether it was a cause of the fizzles is not clear, but the discharge initiation was more reliable after this change. Unfortunately, another problem developed in shot 7, namely an early disruption. Disruptions then plagued the run for the remaining shots. By lowering the current, e.g., to 700 kA as in shot 14, the disruptions coould be avoided. But this was not part of the run plan. The current was increased again successfully in shots 19 and 20, but disruptions occured just after inversion. Then on shot 21 the TF inverted after a disruption and crowbarred. A blown fuse was replaced in the TF supply. Shot 22 was a TF test, followed by shot 23 during which the breakers pulled early. EF 4 supply had single-phased and a number of SCR's (4?) had to be re- placed. Since replacing the SCR's would take more time than was left in the run, the run was terminated. Overall this was a disappointing run which produced few of the shots required for the run plan.

Session Leader Comments
May 28 1999 08:08:31:810AM		Jim Terry	The purpose of the run is to investigate volume recombination in the divertor under detached ohmic conditions. The detailed issues we want to address are 1) the scaling of the recombination sink with plasma current, 2) T_e measurements in the recombining regions, 3) the effect of the bypass flaps on the detachment threshold, and 4) the existence of significant plasma in the private flux region when the outer strike point is deep in the slot. The run plan is as follows: Load shot 990521011 (1 MA), but with Bt constant at 5.4 T and a different density program. We want nl_04=1.4e20 at 0.6 s ramping to 2.0e20 by 1.1 s. After making the above plasma successfully, increase the density ramp to reach nl_04>2.5e20 by 1.1 s. Measure the density at which the divertor detaches. (Bypass flaps closed) (~5 shots) Repeat the above shot(s) with the bypass flaps open. Again measure the density at which the divertor detaches. (~2 shots) Increase the plasma current to 1.2 MA. Repeat the density ramps, increasing the max density shot-by-shot until nl_04 is > 3.0e20. Measure the recombination sink, the densities and temperatures in the recombination regions and observe the extent of the recombination region. (~7 shots) For the "slot-divertor" part of the run, load shot 990429003 (0.8 MA). This shot begins with a "slot" outer divertor, but evolves to a "vertical" divertor target. Run this shot at three densities. The first (with nl_04~1e20) is to be low enough that the outer divertor leg is attached. The 2nd density (nl_04~1.7e20) is such that the outer divertor is detached. The third density (nl_04~2e20) should be high enough for the outer divertor to be deeply detached. Each of the three densities will be run once with the flappers closed and once with the flappers open. (~10 shots)
May 28 1999 04:50:12:590PM		Jim Terry	The spectroscopic diagnostic setup is; McPherson (VUV) and McPherson visible chords are looking at inner nose. Visible channels are D_a, D_b, fiber 3 to the Chromex. The Chromex is looking at K bottom, K top, McP fibers. The K bottom reticon filters are D_a and D_b. U Md is looking at four of the A bottom "tangential" divertor fibers and K bottom 13. It will be looking at D_a. B side, B top, and A side reticons are looking at D_a as usual. The Fabry-Perot is looking at D_a from K top fiber 4.
May 28 1999 08:30:42:107AM	990528001	Jim Terry	fizzle
May 28 1999 08:55:19:577AM	990528002	Jim Terry	Good shot - nl_04 to 1.8e20 - but no detatchment until current ramp down. I verified that McP, McP visible channels, B side, B top, A side, K bottom straight, K bottom RA are working.
May 28 1999 08:55:36:920AM	990528003	Jim Terry	fizzle
May 28 1999 09:41:07:577AM	990528004	Jim Terry	Good shot - nl_04 to 2.0e20 - but still no detatchment until current ramp down.
May 28 1999 09:41:18:403AM	990528005	Jim Terry	fizzle
May 28 1999 10:19:51:467AM	990528006	Jim Terry	Good shot - nl_04 to 2.13e20 - still no detatchment until current ramp down. -
May 28 1999 10:20:24:280AM	990528007	Jim Terry	Disrupted at cross-over - 0.34 s
May 28 1999 10:36:09:610AM	990528008	Jim Terry	Disrupted at cross-over - 0.36 s
May 28 1999 11:07:23:530AM	990528009	Jim Terry	Plasma in trouble after .17 s, finally disrupted at 0.495 s.
May 28 1999 11:08:24:560AM	990528010	Jim Terry	disrupted at 0.33 s.
May 28 1999 11:38:00:700AM	990528012	Jim Terry	multiple injections - ugly plasma which survives to 0.86s
May 28 1999 12:11:43:810PM	990528013	Jim Terry	multiple injections - somewhat better plasma - survives to 0.81s
May 28 1999 12:13:39:200PM	990528014	Jim Terry	716 kA plasma - looks good, ramps down
May 28 1999 12:39:04:327PM	990528015	Jim Terry	large Mo injections early - 700 kA, NL_04 ramps to 1.2e20, then detaches on current rampdown
May 28 1999 12:57:06:153PM	990528016	Jim Terry	good 700 kA shot - decent D_0 Lyman spectrum
May 28 1999 01:12:22:403PM	990528017	Jim Terry	tried 1 MA shot - disrupted at cross-over - 0.356 s
May 28 1999 01:29:36:747PM	990528018	Jim Terry	try for 1 MA shot - disrupted from brick at 0.674 s
May 28 1999 01:43:01:530PM	990528019	Jim Terry	good 1 MA shot - disrupted at 1.018 s at NL_04=2e20
May 28 1999 02:10:40:310PM	990528020	Jim Terry	good 1 MA shot with bypass flaps OPEN partial to full detachment around 0.8 s, disrupted at 1.030 s at NL_04=2.25e20
May 28 1999 02:32:41:890PM	990528021	Jim Terry	try for 0.9 MA shot with bypass flaps OPEN disrupted at 0.432 s

Physics Operator Comments
May 28 1999 08:40:54:873AM	990528001	Ron Parker	990528001 Shot was a fizzle. Diagnosis: BR too neagative. Changed offset from .001 to .003.
May 28 1999 08:42:32:810AM	990528002	Ron Parker	990528002 Shot ran as programmed. Density fell a little short of 2e20. n_04 gain increased from 4 to 8.
May 28 1999 09:00:04:670AM	990528003	Ron Parker	990528003 A fizzle, with no obvious cause. No changes for next shot.
May 28 1999 12:00:11:793PM	990528004	Ron Parker	Shot 990528004 Shot ran as programmed
May 28 1999 09:51:37:467AM	990528005	Ron Parker	990528005 Shot was a fizzle. Unbalance in OH2 U and L noted and removed. Pulse gas B-side Upper enabled for next shot. Programming same as for C-side.
May 28 1999 12:05:20:030PM	990528006	Ron Parker	Shot 990528006 Pulse gas B-side upper had not been programmed. Shot ran as programmed
May 28 1999 10:16:19:170AM	990528007	Ron Parker	shot 7: Wolfe taking over for Parker. Increase density program by .2e20, load changes to NL04 control and B-side upper voltage (didn't make it in last time) Move ZXL and RXL down and in by another .005m Result: Early disruption, at crossover. Let's back off on this a bit.
May 28 1999 10:37:56:810AM	990528008	Steve Wolfe	Shot 8: Reduce Pulse gas 2 pre-program to zero before .6sec, and reduce early NL_04 density program. Leave RXL, ZXL changes in place. Result, another early disruption. Density is lower, that's not the problem? Next shot, go back to segment 2 from shot 6, which went.
May 28 1999 10:52:45:810AM	990528009	Steve Wolfe	Shot 9: go back to segment 2 from shot 6, which went. This shot has square-wave pre-programming only on pg2, nl_04 controller only to pg3. Result: Disruption at .5 sec, current is driven down to 275ka at .23sec, then recovers! Looks like a massive injection at .17sec. We need some disruption recovery time.
May 28 1999 11:11:32:687AM	990528010	Steve Wolfe	Shot 10: Re-run that one, and hope it improves. Result: Another disruption, before crossover. Looks like a vertical instability this time. Next shot: Try a fiducial-like shot (segment 3).
May 28 1999 11:22:55:843AM	990528011	Steve Wolfe	Shot 11: Try a 1MA fiducial-like shot (segment 3). fizzle. - well, at least it didn't disrupt! Next shot: Repeat
May 28 1999 11:39:45:700AM	990528012	Steve Wolfe	Shot 12: Try a 1MA fiducial-like shot (segment 3). Disrupts at 0.84 - vertical instability. Lots of little injections. Next shot: CLEARIN from -.008 to -.010
May 28 1999 12:06:20:420PM	990528013	Ron Parker	Shot 990528013 Similar to last shot, disrupts at 0.8 s. Erratic current rise. Loaded shot 990527005 into Segment 3 for next shot.
May 28 1999 12:28:11:827PM	990528014	Ron Parker	Shot 14 ran as programmed, without disruption.
May 28 1999 12:27:03:437PM	990528015	Ron Parker	Shot 9905280015 Shot ran without major disruption, still at 700 kA. Density ramped up to 1.3e20. Moly (?) injection at about t=0.4 s.
May 28 1999 12:54:04:747PM	990528016	Ron Parker	Shot 990528016 Ran as programmed, less disruptive. For next shot, return to programming for Shot 990528006, without B side upper valve. TF Flat top extended to 1.4 s.
May 28 1999 01:30:17:700PM	990528017	Ron Parker	Shot 990528017 Bad disruption on current rise. For next shot changed time of CLEARIN flattop (to .008 m) -- from 0.35 s to 0.5 s.
May 28 1999 01:33:49:310PM	990528018	Ron Parker	Shot 990528018 Major disruption again, but delayed from point of disruption in last shot. Disruption occured at about 0.65 s.
May 28 1999 01:41:22:217PM	990528019	Ron Parker	Shot 990528019 disrupted again, but made it to inversion. Still problems with current ramp phase.
May 28 1999 02:05:22:793PM	990528020	Ron Parker	Shot 990528020 Shot ran, again disrupting just after inversion. Troubles again during rampup. Next shot: same as 20 except 900 kA.
May 28 1999 02:39:49:233PM	990528021	Ron Parker	Shot 990528021 Shaky current ramp, followed by major disruption at about 0.43 s. TF inverted, then crowbared. One blown fuse found in TF convertors.
May 28 1999 03:33:18:733PM	990528022	Steve Wolfe	Shot 22: TF test at 50kA Next shot, load seg 2 of 990429014 and change density to 1.5e20 at .6sec.
May 28 1999 04:35:30:483PM	990528023	Steve Wolfe	Shot 23: Load seg 2 from 990429014, a 800kA plasma with an initial slot. Change nl_04 to 1.5e20. Hold your breath and cross your fingers. Result:Breakers pulled early. EF4 fault. It looks like the supply single-phased, and the bus rog signals are screwy - big imbalance, and ramps on up through 4sec, like the integrator failed? Irby points out that the integrator behaves this way when there is non-zero signal on them when the gate turns on. In this case there were shorted SCR's in the EF4 which caused sinusoidal currents from -infinity (relative to the gate at -2sec.) Run terminated because repairs to EF4 will take >1hour

Engineering Operator Comments
Shot	Time	Type	Status	Comment
1	08:14:14:793AM	Plasma	Ok	No Faults
2	08:27:03:467AM	Plasma	Ok	No Faults
3	08:44:55:357AM	Plasma	Ok	No Faults
4	09:08:32:200AM	Plasma	Ok	No Faults
5	09:28:10:013AM	Plasma	Ok	No Faults
6	09:52:55:170AM	Plasma	Ok	No Faults
7	10:13:21:890AM	Plasma	Ok	No Faults
8	10:31:29:293AM	Plasma	Ok	No Faults
9	10:45:51:857AM	Plasma	Ok	No Faults
10	11:03:30:157AM	Plasma	Ok	No Faults
11	11:17:49:280AM	Plasma	Ok	(null)
12	11:32:02:420AM	Plasma	Ok	No Faults
13	11:45:59:483AM	Plasma	Ok	No Faults
14	12:04:11:780PM	Plasma	Ok	No Faults
15	12:20:57:407PM	Plasma	Ok	No Faults
16	12:40:35:140PM	Plasma	Ok	No Faults
17	12:56:27:170PM	Plasma	Ok	No Faults
18	01:18:09:890PM	Plasma	Ok	No Faults
19	01:36:28:733PM	Plasma	Ok	No Faults
20	01:56:22:110PM	Plasma	Ok	(null)
21	02:12:41:187PM	Plasma	Bad	TF fault IOC ,self power circuit fired
22	03:31:34:827PM	Test	Ok	TF test only, 50kamps plc control
23	03:49:00:403PM	Plasma	Bad	EF4 Fault type 1, fuse loss