| Miniproposals | ||||||||||
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| Operators | |
| Session leader(s): | Dmitri Mossessian |
| Physics operator(s): | Ron Parker |
| Engineering operator(s): | Unknown |
| Engineering Operator Run Comment |
| Purpose: MP282 Elm Studies/Parker/Mossessian/Lin/Schwartz |
| Session Leader Plans |
| Physics Operators Plans |
| Session Leader Summaries |
| Entered: Jul 7 2004 03:49:33:130PM |
| Author: Dmitri Mossessian |
| Run summary for Thursday, June 12 2003. MP 282 - triggering ELMs with current ramp. The purpose of this experiment is to check the idea that ELMs are "peeling" modes that are driven by high values of edge current (collisionless bootstrap current on tokamaks like DIII-D or JET). The edge current will be increased significantly if the plasma surface voltage is stepped up to its maximum value. To get a step in loop voltage we should program a fast current ramp. The problem is that at too high rate of current rise we loose control over the plasma. To avoid it we will try to run low elongation to achieve higher initial stability. The ELMs thoery predicts that the stability threshold for edge MHD depends on plasma shape. We will attempt to run moderately shaped plasma (low upper and lower triangularities) to lower the stability threshold. Results: The run started around 15:00 because of computer problems. We had only 10 useful shots. We menaged to changed plasma shape in such way that current ramp did not lead any more to plasma getting limited. Lowering elongation from 1.7 to 1.5 helped general stability. To lower the stability threshold for ELMs we decreased upper triangularity to 0.2. Since we needed high pedestal Te we dropped target density to 5e19. On shots with current ramp in H-mode phases (11 and 12) we did see some grassy ELMs which look somewhat different than ELMs seen without current ramp (shot 13). Also, shot 6 had a burst of large ELMs that might have been caused by current ramp. To obtain more definite results we need more shots. It is still possible to decrease plasma shaping (go to lower delta and elongation) and play with target density to achieve a compromize between pedestal temperature and amount of impurities in the plasma. Details: ---------------------------------------------------------------------------- 1030612004 mossessian SESSION_LEADER Jun 12 2003 3:52:29:786PM . . . . . . . . . . . . . . . . . . . . H-mode with not very steady RF between 3 and 4 MW. Ip=0.6MA, nl=0.6e20, Te_ped~400 eV Next shot - program current ramp starting at 0.95 s with 2 MA/s from 0.6 to 0.8 MA. Decrease elongation ---------------------------------------------------------------------------- 1030612005 mossessian SESSION_LEADER Jun 12 2003 3:55:02:133PM . . . . . . . . . . . . . . . . . . . . Plasma goes limited as soon as current starts ramping. Discovered that right gap is programed to be very small. Next shot - increase both inner and outer gap. ---------------------------------------------------------------------------- 1030612006 mossessian SESSION_LEADER Jun 12 2003 3:56:13:823PM . . . . . . . . . . . . . . . . . . . . H-mode survives current ramp. RF is tripping, but it looks like we got some ELMs during current ramp Next shot - decrease elongation. ---------------------------------------------------------------------------- 1030612007 mossessian SESSION_LEADER Jun 12 2003 3:58:53:340PM . . . . . . . . . . . . . . . . . . . . Similar to 6, but no signs of ELMs. With lower elongation plasma behaves better Next shot - move bot x-point out 1 cm to get lower deltas. ---------------------------------------------------------------------------- 1030612008 mossessian SESSION_LEADER Jun 12 2003 4:27:25:750PM . . . . . . . . . . . . . . . . . . . . Try to increase right gap some more - it is still too small during current ramp. On all shots starting from 7 Te_ped goes up to 500 eV at the beginning of H-mode but drops quickly to 200 eV or so, probably becase of radiated power. ---------------------------------------------------------------------------- 1030612010 mossessian SESSION_LEADER Jun 12 2003 4:31:21:143PM . . . . . . . . . . . . . . . . . . . . Shots 9 and 10 have several EDAish H-modes terminated by radiated power rise and/or Rf trips. Triangularities are low (delta_upper=.2, delta_lower=.47), elongation is 1.5 Pedestal cools down to 250 eV by the time current ramp starts. Next shot - move RF start to 0.9 (closer to current ramp). Lower target to 4e19 - we are actually getting 6e19 when asking for 5e19 ---------------------------------------------------------------------------- 1030612011 mossessian SESSION_LEADER Jun 12 2003 4:48:21:243PM . . . . . . . . . . . . . . . . . . . . The grass in the first H-mode whet pedestal is hot (~600 eV) may be driven by current rise. The density is down, so pdestal is warmer at the same RF power. Lower strik point may be a little too high. Next shot - RXL down 2 cm and ZXL in 1 cm to move the strike point into the divertor. ---------------------------------------------------------------------------- 1030612012 mossessian SESSION_LEADER Jun 12 2003 4:56:46:986PM . . . . . . . . . . . . . . . . . . . . The small ELms are again there, although with smaller amplitude. Next shot - get rid of the current ramp. ---------------------------------------------------------------------------- 1030612013 mossessian SESSION_LEADER Jun 12 2003 5:14:35:726PM . . . . . . . . . . . . . . . . . . . . There are still some grassy fluctuations in H-alpha in the first H-mode, but they look different. No clear conclusion can be made out of these data, but we may be getting close to the expected (or unexpected) result. More shots are needed. |
| Physics Operator Summaries |
| Entered: Jul 7 2004 04:37:18:350PM |
| Author: Ron Parker |
| Engineering Setup & Run Plan for Thursday, June 12, 2003 PURPOSE: MP282 Elm Studies Session Leader: Mossessian Physop: Parker RF Leaders: Y. Lin, C. Schwartz ENGINEERING SETUP ECDC in D2 @ 2e-4 Torr Overnight prior to run,stopping at 7:00. 60 C Bake Run Starts at 9:00 AM and Ends at 5:00 PM Power Systems as on 1030605028 Gas setup: Fill B-Top with 6 psi of D2 hybrid enabled (PG4) Fill B-side lower with 1 psi Ar Hybrid enabled (PG1) Fill B-side upper with 10 psi D2 Hybrid Disabled (PG2) fill C-side with 30 psi D2 Hybrid enabled (PG3) ICRF: Transmitters 1, 2, 3 and 4 in Run On by 8:00 AM. Enable the ECE and DNB gate-valves, assuming no vacuum problems RUN PLAN 1. We'll start with a discharge with Ip=0.6 MA, target nl=0.6e20, RF power high as practical. 2. Then we'll establish a good EDA H-mode with low collisionality, hot pedestal. 3. We'll program current ramp at rate of 2 MA/s at a time when H-mode is estab- lished and loop voltage is stabilized. 4. The elongation will be decreased by moving ZXL up. We may need to shift RXL at the same time to avoid moving strike points out of the divertor nodse. Also, moving ZXU up (shifting upper X-point higher) may help decreasing elongation and make plasma more stable. 5. We'll try two scenarios - starting current ramp during H-mode or applying RF after the ramp starts. 6. We'll scan plasma triangularity to move ELM stability boundary. Run Summary The run began 5.5 hours late due to a problem with the DAQ A computer. Thanks to a heroic workaround effort by Josh, we managed to get things going by ~ 2:30.In spite of the late start, the run proved worthwhile as most of the run plan was accomplished, except step 5. The machine ran exceptionally well with 11 plasma shots set up and run; one disruption, no duds and no fizzles. |
| Session Leader Comments | |||
| Jun 12 2003 03:52:29:787PM | 1030612004 | Dmitri Mossessian | H-mode with not very steady RF between 3 and 4 MW. Ip=0.6MA, nl=0.6e20, Te_ped~400 eV Next shot - program current ramp starting at 0.95 s with 2 MA/s from 0.6 to 0.8 MA. Decrease elongation |
| Jun 12 2003 03:55:02:133PM | 1030612005 | Dmitri Mossessian | Plasma goes limited as soon as current starts ramping. Discovered that right gap is programed to be very small. Next shot - increase both inner and outer gap. |
| Jun 12 2003 03:56:13:823PM | 1030612006 | Dmitri Mossessian | H-mode survives current ramp. RF is tripping, but it looks like we got some ELMs during current ramp Next shot - decrease elongation. |
| Jun 12 2003 03:58:53:340PM | 1030612007 | Dmitri Mossessian | Similar to 6, but no signs of ELMs. With lower elongation plasma behaves better Next shot - move bot x-point out 1 cm to get lower deltas. |
| Jun 12 2003 04:27:25:750PM | 1030612008 | Dmitri Mossessian | Try to increase right gap some more - it is still too small during current ramp. On all shots starting from 7 Te_ped goes up to 500 eV at the beginning of H-mode but drops quickly to 200 eV or so, probably becase of radiated power. |
| Jun 12 2003 04:31:21:143PM | 1030612010 | Dmitri Mossessian | Shots 9 and 10 have several EDAish H-modes terminated by radiated power rise and/or Rf trips. Triangularities are low (delta_upper=.2, delta_lower=.47), elongation is 1.5 Pedestal cools down to 250 eV by the time current ramp starts. Next shot - move RF start to 0.9 (closer to current ramp). Lower target to 4e19 - we are actually getting 6e19 when asking for 5e19 |
| Jun 12 2003 04:48:21:243PM | 1030612011 | Dmitri Mossessian | The grass in the first H-mode whet pedestal is hot (~600 eV) may be driven by current rise. The density is down, so pdestal is warmer at the same RF power. Lower strik point may be a little too high. Next shot - RXL down 2 cm and ZXL in 1 cm to move the strike point into the divertor. |
| Jun 12 2003 04:56:46:987PM | 1030612012 | Dmitri Mossessian | The small ELms are again there, although with smaller amplitude. Next shot - get rid of the current ramp. |
| Jun 12 2003 05:14:35:727PM | 1030612013 | Dmitri Mossessian | There are still some grassy fluctuations in H-alpha in the first H-mode, but they look different. No clear conclusion can be made out of these data, but we may be getting close to the expected (or unexpected) result. More shots are needed. |
| Physics Operator Comments | |||
| Jun 12 2003 12:31:41:633PM | 1030612001 | Ron Parker | The run today has been delayed by computer problems - DAQ A. So far the delay has been 3.5 hours. Josh has implemented a workaround and now, at 12:30, it looks hopeful that the rest of the run can be salvaged. |
| Jun 12 2003 01:40:34:387PM | 1030612001 | Ron Parker | Problems continue with the computer. Run continues to be delayed. |
| Jun 12 2003 02:00:03:800PM | 1030612001 | Ron Parker | It appears that we may be ready for plasma shots. The first shot will be a no-power shot. |
| Jun 12 2003 02:24:43:467PM | 1030612001 | Ron Parker | The first shot was a no-power shot. However no gas was pulsed into chamber even though hybrid seemed to function properly. The issue is being investigated. Next shot will repeat the no-power test. |
| Jun 12 2003 02:30:34:350PM | 1030612002 | Ron Parker | Test shot was successful --apparently. Shot 3 will be a plasma shot. |
| Jun 12 2003 02:42:07:440PM | 1030612003 | Ron Parker | Shot 3 was the first plasma shot and ran well. Next shot: Repeat with 600 kA, 0.6e20 nl |
| Jun 12 2003 02:47:52:870PM | 1030612003 | Ron Parker | Bouquets to Josh for getting us going today! |
| Jun 12 2003 03:29:50:153PM | 1030612004 | Ron Parker | Shot ran well. Next shot will have a current ramp beginning at 0.95 s and lasting until 1.05 s. The delta I will be 200 kA. also the upper and lower X points will be raised by 2 cm. |
| Jun 12 2003 03:31:16:390PM | 1030612005 | Ron Parker | Shot ran well with current ramp, but became limited. In next shot, delta sep will be increased by 1 cm. |
| Jun 12 2003 03:42:48:167PM | 1030612006 | Ron Parker | Shot 6 ran well with no limited mode. In next shot, both x-points will be raised 2 cm. |
| Jun 12 2003 03:52:41:460PM | 1030612007 | Ron Parker | Shot 7 ran well, next shot will have reduced triangularity with both x-points move out 1 cm. |
| Jun 12 2003 04:08:43:260PM | 1030612008 | Ron Parker | Shots continue to run well. Next shot: outer gap increased by 6 mm. |
| Jun 12 2003 04:23:23:823PM | 1030612009 | Ron Parker | Shots running well. Next shot: lower target density to 0.5e20, move RXU and RXL out 1 cm |
| Jun 12 2003 04:32:49:913PM | 1030612010 | Ron Parker | Shot 10 ran well, but target density did not come down. For next shot, target density will be lowered to 4e19. |
| Jun 12 2003 04:57:06:017PM | 1030612011 | Ron Parker | Shot 11 ran well. |
| Jun 12 2003 05:10:06:737PM | 1030612012 | Ron Parker | Shot 12 ran well, but disrupted. Next shot: identical but no current ramp. |
| Jun 12 2003 05:10:49:690PM | 1030612013 | Ron Parker | Shot 13 ran well, with no current ramp. There was some change in ELM behavior. End of run. |
| Engineering Operator Comments | ||||
| Shot | Time | Type | Status | Comment |
| 1 | 02:01:47:660PM | Test | Ok | Cycle test |
| 2 | 02:25:11:610PM | Test | Ok | Cycle test |
| 3 | 02:35:58:433PM | Plasma | Ok | |
| 4 | 02:54:13:313PM | Plasma | Ok | |
| 5 | 03:13:13:133PM | Plasma | Ok | |
| 6 | 03:29:42:247PM | Plasma | Ok | |
| 7 | 03:42:48:667PM | Plasma | Ok | |
| 8 | 03:56:56:980PM | Plasma | Ok | |
| 9 | 04:09:55:510PM | Plasma | Ok | |
| 10 | 04:22:56:133PM | Plasma | Ok | |
| 11 | 04:35:42:320PM | Plasma | Ok | |
| 12 | 04:48:42:070PM | Plasma | Ok | |
| 13 | 05:01:25:303PM | Plasma | Ok | |