| Miniproposals | ||||||||||
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| Operators | |
| Session leader(s): | Martin Greenwald,Martin Greenwald |
| Physics operator(s): | Steve Wolfe |
| Engineering operator(s): | Frank Silva |
| Engineering Operator Run Comment |
| pellet/coldwll run |
| Session Leader Plans |
| Physics Operators Plans |
| Session Leader Summaries |
| Entered: Jul 7 2004 03:49:08:523PM |
| Author: To Be Determined |
| Run Summary for August 17, 1993 This was the first run with the pellet injector. As such it was probably the most interesting and significant event for C-Mod to date. It was a good run with very few fizzles or duds. On a Tuesday! The injector performed well, firing pellets every time it was requested 22/22. On two shots, the pellets did not arrive at the plasma, indicating some minor internal alignment problem. We reached record plasma densities - line integral ne > 1.6 x 10^20 implying line average > 3 x 10^20. The first few shots were used to set up a target plasma. We were aiming for about .4 MA a long flat-top and n average about 1 x 10^20. Plasma shape and position were not considered critical - though we were looking for more or less constant conditions. Two pellet sizes were available on this day - with nominal particle contents of .5x10^20 (barrel #4) and 1.x10^20 (barrel #3); for the rest of this report I will refer to these as small and large pellets (Though these are the smallest two sizes of the four the injector can make). The barrels fired on each shot and the measured pellet velocity are stored signals and can be found in \fueling::barrels and \fueling::velocity. These are very sparse signals, with one point per pellet fired, thus when only one pellet is fired you have only one pair of pts in the signal and you can't plot it - it can still be retrieved however. Note that the time base for these signals is approximately (+/- 100 microseconds) the time at which the pellet reaches the plasma center. There is roughly 5 msec delay between the firing of the pellet valves and its arrival at the plasma. Velocities are typically near 1000 m/sec. On shot 5 we began pellet experiments by firing a single small pellet(barrel #4) into the plasma at .25 seconds. This raised the line integral density by about .2 x 10^20: This is approximately .4-.5 x 10^20 line averaged which is in rough agreement with the nominal pellet size which is .5 x 10^20 particles. The temperature, soft-xray emission, Zeff dropped as expected, and we saw bursts of hard xrays while the pellet was ablating (about 150 microseconds). A slight change in sawtooth period accompanies the pellets. There is also a burst of light, mostly hydrogen line emission, during ablation, Some diagnostics may see this in direct or reflected light. Note that since we are ionizing of order 10^20 particles in 10^-4 seconds, this light is very bright. Shots 7 and 10 were essentially repeats of shot 5. On shot 11 we switched to barrel #3 firing at the same time (.25 sec) The line integral density rise was then about .4 x 10^20, twice the size of the rise seen from barrel #4, in agreement with their relative sizes. Barrel #3 fires pellets with nominally 1.x10^20 particles. There was evidence that we had accessed the enhanced confinement mode. In particular the sawtooth period increased dramatically - conventional wisdom attributes this to current profile modification from accumulating impurities. The xray profile width narrows considerably from the same effect. There is considerable MHD activity which is seen on the xrays, tci, etc. On shot 14 we fired two pellets #4 at .25 sec and #3 at .28 seconds, line integral densities were above 1 x 10^20. This puts the line average over 2 x 10^20, note that the calculated density limit for these conditions is about 2.5x10^20. The plasma suffered a major disruption about .14 seconds later. Shots 15-17 were similar to shots 11-13 On Shot 17 we fired barrel #3 at .25 followed by #4 at .28. The line integral density reached 1.6 x 10^20, well in excess of the density limit. The plasma disrupted a few msec later resulting in the pumpout of all the density increment. Shots 18-23 were similar to shots 11-13 Shot 24 had both small and large pellets were fired at .25 sec. We reached a line integral density of 1.5 x 10^20 - which held over 1 x 10^20 for about .5 sec. Additional notes: The pellet tracker diagnostic worked well. The signals were slightly saturated on some early shots. After the cameras were stopped down we were able to get pellet trajectories. Marfes were a problem again. They may be corrupting some of the tci inner channels. The target plasma are dirty. There was a great deal of xray emission early in each shot, probably due to Mo. Since impurities accumulate in the enhanced confinement mode, we need to start with relatively clean plasmas. |
| Physics Operator Summaries |
| Entered: Jul 7 2004 04:36:50:317PM |
| Author: To Be Determined |
| Operations Summary for Run 930817 Session Leader: Greenwald Physics Operator: Wolfe Assistant Operator: Terry Engineering Operator: Silva Primary: MP#009 Pellet Injection Piggy-Back: MP#022 Cold Walls The goal of the run was to test pellet fueling. The secondary goal was to evaluate operation with cold (-40C) walls. Both goals were achieved. Discharge cleaning was carried out as usual, after which the vessel and coil pockets were cooled toward -40C. "Average" vessel temperature for the first plasma attempt was -28C, and reached -36C during the run. The 28 peak began slowly rising during cooldown, and remained somewhat higher than normal throughout the run. H-port and K-port pumpout lines had a large pressure excursion (outer seal opening) during the cooldown which then recovered. Starting point for the run was based on 930812023 (Ip=400:450kA, nel = 3.8e19). It was necessary to recalculate the filament and FLUXIHH predictors to account for the replacement of the BP17_BC coil by BP17_DE. Small adjustments were made to gas programming during the day. The only changes to the equilibrium were extending the time the plasma was programmed low to 600msec, and extending the negative current on EF4 similarly. Fill pressure was started at 1.2e-5, as on 8/12. This was lowered to 1.0e-5 when the pellet operation started to compensate for the expected gas influx; while the lower pressure worked fine, it was eventually raised back to 1.1e-5 on shot 11 (to reduce hards) and to 1.2e-5 on shot 20, following a dud. Pellets were fired at around 250 and/or 280msec beginning on shot 5. Most worked, although the post-pellet phases of the later, larger pellet shots eventually disrupted at between 350 and 500msec (non-pellet shots had been running over 600msec) The timing of the pellets was into the limited phase of the discharge, which diverted around 300:350msec. The target density on shot was raised to 6.7e19 (integral ndl) by bridging the pulses on the A-side valve, ie holding the valve at 90V from 140:210 msec; the pellet at 255 raised this to 1.6e20, or nbar around 3e20. This seemed to exceed the density limit; the shot finally disrupted around 350msec. The target density was lowered to around 4.2e19 for the rest of the run, by dropping the A-side programming to 60V from 155 to 210msec. Cold wall operation did not cause any noticeable problems, despite the somewhat elevated N2 level. Whether it helped or not is not clear; this was the best Tuesday run in recent memory, but we were running based on a well behaved shot from a high-consistency run from last week. Problems: -------- There was another sump/dewar backup problem prior to the run; no vacuum problem this time. There may have been a similar problem during the run, as it was noted that the TV view under the dewar was conpletely obscured by vapor around 16:00. The chopper was not functioning from the beginning of the run till shot 14. The first plasma attempt (shot 2) was killed off at 40msec by the fact that the chopper failed to chop and caused the plasma to go screaming up.The plasmas were not seriously unstable without it, although there were some vertical oscillations which were cured when the chopper was put back online. The problem was traced to a loose wire at the control cabinet. There was a delay due to a logbook problem at shot 22; SYSTEM SERVICE REQUEST Errors on Make Entry, and apparently on the automatic entries. TWF got us back in operation, but it wasn't clear what caused the problem. We lost one (maybe two) shots around 16:30 because we had to evacuate the building for a fire alarm. The alarm was apparently caused by welding going on in the old computer room. Scorecard: ---------- Tests 2 (#1,8) Duds 1 Fizzles 1 (100kA in 40msec-Chopper malfunction) Good 20 -- Total 24 |
| Session Leader Comments | |||
| Aug 17 1993 11:12:40:580AM | 930817005 | Jim Terry | First D_2 pellet attempt at 250 ms. Definite success.
Increases seen on H_alpha, visible brems., TCI at that time. Increase on TCI ch. 5 is about 2e19. Decrease seen in ECE temp. at that time. |
| Aug 17 1993 11:02:38:260AM | 930817006 | Jim Terry | D_2 pellet attempt at 250 ms. Nothing seen in the plasma. Pellet (probably slushy)
seen on time-of-flight diodes. |
| Aug 17 1993 11:06:09:170AM | 930817007 | Jim Terry | D_2 pellet attempt at 250 ms. Definite pellet at 255 ms.
Plasma current max is 0.42 MA. |
| Aug 17 1993 12:21:16:880PM | 930817010 | Jim Terry | Good discharge, Plasma current max of 0.43 MA.
Pellet attempt at 250 ms. Good pellet. Hard x-rays increased somewhat from last shot. Shark fin begins at about 550 ms. |
| Aug 17 1993 12:40:30:070PM | 930817011 | Jim Terry | Good discharge, plasma current max 0f 0.43 MA.
Pellet attempt (next larger size - nominally 1e20 particles) at 250 ms. Good pellet. delta Nel was 4.2e19. Pellet slows the sawtooth period; large MHD prior to each subsequent sawtooth. Hard x-rays decreased significantly from last shot. |
| Aug 17 1993 01:04:37:600PM | 930817012 | Jim Terry | Good discharge, Plasma current max 0f 0.43 MA.
Pellet attempt (size - nominally 1e20 particles) at 250 ms. Good pellet. Delta Nel on channel 5 is again 4.2e19. Pellet slows the sawtooth period; large MHD prior to each subsequent sawtooth. Shark fin begins at 500 ms. |
| Aug 17 1993 01:46:48:030PM | 930817014 | Jim Terry | Discharge disrupted at 420 ms. Plasma current max of 0.44 MA.
Large MHD after 335 ms. Attempt for 2 pellets at 250 and 280ms. Tiny pellet at 250 ms, bigger pellet at 280 ms. |
| Physics Operator Comments | |||
| Aug 17 1993 08:35:47:050AM | Steve Wolfe | Run 930817
MP 009 Pellet Injection / Piggyback Cold Walls) Session Leader : [g] Physics Op: wolfe Start from 930812023; update all Ip-type predictors to account for new BP17 loop Walls will be at -40C (they are at -5.0 at 08:35) | |
| Aug 17 1993 11:15:43:550AM | Jim Terry | We are beginning this run with 'cold' walls (part of MP 022). We start with the
vessel temp. at -31 deg.C with a set pt of 40 deg. C. If this temperature changes significantly during the run, it will be noted according to shot. | |
| Aug 17 1993 09:02:04:730AM | 930817001 | Steve Wolfe | Data System test
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| Aug 17 1993 09:40:14:860AM | 930817002 | Steve Wolfe | Vessel avg temp = -28C
Small N2 leak = 5.7e-10 on RGA Result: Fizzle EFC didn't chop. It lasted until almost 50msec. EFC almost certainly killed it-- xray centroid says it went screaming up. |
| Aug 17 1993 11:08:08:070AM | 930817002 | Jim Terry | Fizzle - about 40 ms long.
Chopper did not function properly - did not chop. Until further notice; RF limiter is at R=96.0, antenna is at R=98.0 cm |
| Aug 17 1993 11:08:52:340AM | 930817003 | Jim Terry | Plasma current max is 0.40; pulse length is about 700 ms.
Prefill was 1.2e-5 Torr. Again the chopper did not commutate. For this shot it's charging voltage was changed to -400 V and it's turn-on was delayed to 600 ms. 'Z_meter' INCAA digitized only for the 1st 100 ms. Vertically unstable after about 500 ms. Low hard x-rays. |
| Aug 17 1993 11:09:44:120AM | 930817004 | Jim Terry | Plasma current max is 0.42; pulse length is about 730ms.
Prefill was 1.2e-5 Torr. Again the chopper did not commutate. For this shot it's charging voltage was changed to -1000 V, and its turn-on was at t=0. Vertically unstable after about 500 ms. Low hard x-rays. Vessel temperature was -32 deg. C. After the shot the set pt. was dropped to -50 deg. C. |
| Aug 17 1993 11:11:37:780AM | 930817005 | Jim Terry | Plasma current max is 0.42; pulse length is about 740ms.
Prefill was 1.0e-5 Torr. First D_2 pellet attempt at 250 ms. Increases seen on H_alpha, visible brems., TCI at that time. Increase on TCI ch. 5 is about 2e19. Decrease seen in ECE temp. at that time. Again the chopper did not commutate. Vertically unstable after about 500 ms. Low hard x-rays. Vessel temperature was -39 deg. C. Set pt returned to -40 deg. C. |
| Aug 17 1993 11:14:45:800AM | 930817006 | Jim Terry | Plasma current max is 0.42; pulse length is about 740ms.
Prefill was 1.0e-5 Torr. D_2 pellet attempt at 250 ms. No pellet at that time. Changes in pulsed gas programming: Pulsed gas valve 2 programming at 47 and 100 ms changed from 27 V to 20 V. Pulsed gas valve 1 (Argon) programming set to open valve at 0 ms instead of 100 ms. Vessel temperature was -34 deg. C. |
| Aug 17 1993 11:05:17:350AM | 930817007 | Jim Terry | Plasma current max is 0.42; pulse length is about 740ms.
Prefill was 1.0e-5 Torr. D_2 pellet attempt at 250 ms. Definite pellet at 255 ms. Plasma current max is 0.42 MA. Prefill is still 1.0e-5 torr. Changes in pulsed gas programming: Pulsed gas valve 2 programming shortened by 30 ms. Pulsed gas valve 3 (A side) programming extended to 0.77 s at a level of 33 V. Vessel temperature was -34 deg. C. |
| Aug 17 1993 11:44:11:770AM | 930817008 | Jim Terry | TMX-chopper test only. No plasma attempted.
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| Aug 17 1993 11:58:21:420AM | 930817008 | Jim Terry | Result of the TMX-chopper test was that the commutation bank was charging
properly. Thus that does not seem to be the problem. |
| Aug 17 1993 12:10:05:690PM | 930817009 | Jim Terry | There was a long (about 50 min) delay between this shot and the previous plasma
attempt (Shot 930817007). This was to allow cell entry. Good discharge, Plasma current max 0f 0.43 MA. Pellet attempt at 250 ms. No pellet. |
| Aug 17 1993 12:19:51:680PM | 930817010 | Jim Terry | On the pulsed gas valve 3 programming a 65 V pulse between 500 and 550 ms
was added. Good discharge, Plasma current max 0f 0.43 MA. Pellet attempt at 250 ms. Good pellet. Hard x-rays increased somewhat from last shot. Shark fin begins at about 550 ms. |
| Aug 17 1993 12:38:05:950PM | 930817011 | Jim Terry | Prefill raised to 1.1e-5 Torr.
On the pulsed gas valve 3 programming, we removed the 65 V pulse between 500 and 550 ms. Good discharge, Plasma current max 0f 0.43 MA. Pellet attempt (next larger size - nominally 1e20 particles) at 250 ms. Good pellet. Pellet slows the sawtooth period; large MHD prior to each subsequent sawtooth. Hard x-rays decreased significantly from last shot. |
| Aug 17 1993 12:59:12:490PM | 930817012 | Jim Terry | Prefill still 1.1e-5 Torr.
Extend the "down" time on ZCUR to 650 ms. Extend EF4 reverse voltage programming (at -400 V) until 635 ms. This successfully held the plasma low 'til the end of the shot. Good discharge, Plasma current max 0f 0.43 MA. Pellet attempt (size - nominally 1e20 particles) at 250 ms. Good pellet. Pellet slows the sawtooth period; large MHD prior to each subsequent sawtooth. Shark fin begins at 500 ms. |
| Aug 17 1993 01:17:50:390PM | 930817013 | Jim Terry | Prefill still 1.1e-5 Torr.
Extend the "down" time on ZCUR to 650 ms. Good discharge, Plasma current max 0f 0.43 MA. Pellet attempt (size - nominally 1e20 particles) at 250 ms. Good pellet. Shark fin begins at 500 ms. Vessel temperature now -36 deg. C |
| Aug 17 1993 01:39:57:840PM | 930817014 | Jim Terry | Prefill still 1.1e-5 Torr.
Chopper is fixed - now chopping as programed. Programmed pulsed gas valve 2 to give a 50 V pulse at 1 sec for calibration of the machine pressure gauges. Good discharge, Plasma current max 0f 0.44 MA. Attempt for 2 pellets at 250 and 280ms. Tiny pellet at 250 ms, bigger pellet at 280 ms. Vessel temperature is still -36 deg. C. |
| Aug 17 1993 01:55:56:750PM | 930817015 | Jim Terry | Prefill still 1.1e-5 Torr.
Chopper programmed to turn go from -1000 V at 30 ms to 0 V at 80 ms. Chopper operational. Removed the gas pulse at 1 sec (from pulsed gas valve 2). Good discharge. Plasma current max 0f 0.44 MA. Large MHD between 305 and 327 ms. Attempt for 1 pellet at 250 ms. Good pellet at 250 ms. Vessel temperature is still -36 deg. C. |
| Aug 17 1993 02:22:25:820PM | 930817016 | Jim Terry | Prefill still 1.1e-5 Torr.
Chopper charging voltage changed from 400 to 700 V. Increased the width of the 1st 3 pulses on pulsed gas valve 3 from 2 ms to 8 ms. This doubled the H_alpha sig (at K port). Density (channel 5) didn't increase. Good discharge. Plasma current max 0f 0.44 MA. Attempt for 1 pellet at 250 ms. Good pellet at 250 ms. Vessel temperature is still -36 deg. C. |
| Aug 17 1993 02:22:45:490PM | 930817016 | Jim Terry | Prefill still 1.1e-5 Torr.
Chopper charging voltage changed from 400 to 700 V. Increased the width of the 1st 3 pulses on pulsed gas valve 3 from 2 ms to 8 ms. This doubled the H_alpha sig (at K port). Density (channel 5) didn't increase. Good discharge. Plasma current max 0f 0.44 MA. Attempt for 1 pellet at 250 ms. Good pellet at 250 ms. Vessel temperature is still -36 deg. C. |
| Aug 17 1993 02:44:52:370PM | 930817017 | Jim Terry | Prefill still 1.1e-5 Torr.
Pulsed gas valve 3 programmed at 90 V from 140 'til 210 ms. This saturated the H_alpha sig (at K port). Density (channel 5) increased from 3.8 to 5.5 e19 at that time. RF limiter moved into 95.0 cm. Calibration gas pulse (80 V) at 1 sec from pulsed gas valve 3 (A side). Discharge disrupted at about 350 ms. Plasma current max 0f 0.42 MA. Attempt for 1 pellet at 250 ms. Good pellet at 250 ms. Density after the pellet went to 1.62e20 ! Vessel temperature is still -36 deg. C. |
| Aug 17 1993 03:03:07:160PM | 930817018 | Jim Terry | Prefill still 1.1e-5 Torr.
Pulsed gas valve 3 programmed at 60 V from 155 'til 210 ms. Density (channel 5) was back to 4.2e19 at that time. RF limiter at 95.0 cm. Calibration gas pulse (80 V) at 1 sec from pulsed gas valve 3 (A side). Discharge disrupted at about 475 ms. Plasma current max of 0.43 MA. MHD from about 315 ms to 330 ms. Attempt for 1 pellet at 250 ms. Good pellet at 250 ms. Density after the pellet went to 1.1e20 Channel 5 TCI. |
| Aug 17 1993 03:14:41:720PM | 930817019 | Jim Terry | Dud!
Prefill still 1.1e-5 Torr. RF limiter at 95.0 cm. |
| Aug 17 1993 03:34:03:610PM | 930817020 | Jim Terry | Prefill raised to 1.2e-5 Torr.
RF limiter at 95.0 cm. Plasma disrupted at 525 ms. Decent discharge through the pellet injection. Shark fin begins at 450 ms. Attempt for 1 pellet at 250 ms. Good pellet. |
| Aug 17 1993 03:56:02:400PM | 930817021 | Jim Terry | Prefill still at 1.2e-5 Torr.
RF limiter at 95.0 cm. Plasma disrupted at 412 ms. Decent discharge through the pellet injection, unhappy after the pellet. Attempt for 1 pellet at 250 ms. Good pellet. |
| Aug 17 1993 04:29:55:800PM | 930817022 | Jim Terry | Prefill still at 1.2e-5 Torr.
Removed the last 4 gas puffs (into plasma) starting at about 330 ms from gas valve 3. Removed the calibration gas puff from valve 3 at 1 s. RF limiter back to R=96.0 cm. RF antenna back to R=98.0 cm Good shot lasting 612 ms. Plasma current max was 0.43 MA. Attempt for 1 pellet at 250 ms. Good pellet. |
| Aug 17 1993 04:54:21:630PM | 930817023 | Jim Terry | Prefill still at 1.2e-5 Torr.
RF limiter at R=96.0 cm. Shot disrupted at 450 ms - good until 2nd pellet. Plasma current max was 0.44 MA. Attempt for 2 pellets at 250 ms and 280 ms. Both were successfull, although the 2nd one caused the plasma to go bad. Strong MHD from about 295 ms to 320 ms. Vessel temperature still -36 deg. C. |
| Aug 17 1993 05:08:20:320PM | 930817023 | Jim Terry | Prefill still at 1.2e-5 Torr.
RF limiter at R=96.0 cm. Shot disrupted at 365 ms - good until pellet injection. Plasma current max was 0.44 MA. Attempt for 2 pellets both at 250 m. Both were successful. Chan5 on TCI and visible brems. stay high for 50 ms after the injection. Vessel temperature still -36 deg. C. |
| Engineering Operator Comments | ||||
| Shot | Time | Type | Status | Comment |
| 1 | 08:37:58:430AM | Test | Ok | data system test |
| 2 | 09:25:47:600AM | Test | Ok | fizzel/ efc chopper o/c |
| 3 | 09:46:51:630AM | Plasma | Ok | plasma good shot |
| 4 | 10:03:01:540AM | Plasma | Ok | plasma |
| 5 | 10:21:06:770AM | Plasma | Ok | pellet shot |
| 6 | 10:41:49:500AM | Plasma | Ok | pellet |
| 7 | 10:59:13:430AM | Plasma | Ok | pellet |
| 8 | 11:41:31:340AM | Test | Ok | efc chopper test |
| 9 | 11:55:21:650AM | Plasma | Ok | plasma |
| 10 | 12:12:51:920PM | Plasma | Ok | pellet/plasma |
| 11 | 12:28:16:620PM | Plasma | Ok | big pellet |
| 12 | 12:49:28:540PM | Plasma | Ok | plasma |
| 13 | 01:10:13:050PM | Plasma | Ok | bigger pellet |
| 14 | 01:31:32:610PM | Plasma | Ok | plasma |
| 15 | 01:48:07:370PM | Plasma | Ok | chopper now operational |
| 16 | 02:09:48:090PM | Plasma | Ok | plasma |
| 17 | 02:29:01:260PM | Plasma | Ok | plasma |
| 18 | 02:49:03:720PM | Plasma | Ok | sparks |
| 19 | 03:08:55:280PM | Plasma | Ok | fizzel |
| 20 | 03:24:16:270PM | Plasma | Ok | show shot for pacer |
| 21 | 03:41:35:140PM | Plasma | Ok | plasma |
| 22 | 04:20:44:330PM | Test | Bad | |
| 23 | 04:29:58:380PM | Plasma | Ok | disruption, torvac gauges off |
| 24 | 04:56:41:840PM | Test | Bad | |