| Miniproposals | ||||||||||
|
| Operators | |
| Session leader(s): | Dmitri Mossessian |
| Physics operator(s): | Earl Marmar |
| Engineering operator(s): | Bill Cochran |
| Engineering Operator Run Comment |
| MP282A: Triggering ELMs by fast current Ramp-Up. Mossessian/Marmar/Coc |
| Session Leader Plans |
| Physics Operators Plans |
| Session Leader Summaries |
| Entered: Jul 7 2004 03:49:26:650PM |
| Author: To Be Determined |
| Run summary for 1010629: MP282A: Triggering ELMs by fast current ramp-up. SL: Dmitri Mossessian PO: Earl Marmar 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). One of the existing theories states, that these ELMs are "peeling" mode, driven by a large bootstrap current that is formed at the plasma edge during H-mode due to sharp pressure gradient in the pedestal region. According to the model, the ELM occurs when the edge current density exceeds a critical value. While in other tokamaks the bootstrap current is high enough to drive the modes, in C-Mod the current is significantly (by a factor of 2 or more) reduced by collisionality, which may explain the absence of ELMs in C-Mod plasmas. A simple experiment can be carried out that could produce results in support of the theory. If the reduction of the bootstrap current is expected to inhibit the type I ELMs, than the ELM can be triggered if one can provide sufficient edge current from a current ramp-up so that the edge current is comparable to the bootstrap current in the banana regime. Approach: The edge current will be increased significantly if the plasma surface voltage is stepped up to its maximum value. If the voltage is kept constant after that for a short period of time (100 ms), the edge current would be maintained at the value much higher than the bootstrap current can normally provide, while the total plasma current would not be affected significantly (at a max ramp rate of 1 MA/sec we'll get a 100 kA current rise, or 10% rise at 1 MA level). The voltage can be increased by a factor of 2 (from around 1 V to max value of 2 V), which should, at high edge temperature, provide values of edge current comparable to collisionless bootstrap. Therefore, the experiment would consist of programming a 100 msec long step in plasma current during steady state EDA H-mode. If ELM is triggered, it should be immediately seen on D-alpha signal, but also magnetic and other fluctuation diagnostics should be used to watch for MHD activity during current ramp-up. An attempt should be made to run at the lowest possible density and highest heating power to provide for high edge temperature and low collisionality. Results: Interesting and somewhat successful run. We started with .8 MA, 2.5 MW shots and current ramp to .95 MA at 2MA/sec. First 8 shots RF tripped right before the current ramp. On shot 9 we had nice EDA, 3 MW RF and observed QC mode increasing frequency from approx 50 kHz to 150 kHz following the current ramp up, and then decreasing back to 50 kHz at ramp down. Same picture on shot 10 and 12. No sign of QC mode changing character or any ELM-like activity is observed. The power was increased to 3.5 MW to get closer to grassy ELMs regime. Shot 1010629016 is a good example of grassy ELMs turning into EDA when power drops from 3.5 MW to 2.5 MW. However, the power goes down at the same time with the current, so the effect of the current remains unclear. On shot 18 RF stayed on throughout current ramp-up phase. The changing current seems to kill small ELMs that existed there prior to the ramp-up. The result is not clear and requires further analysis. We reversed the ramp on shot 19, starting from 1 MA plasma and going to .85 MA. PCI didn't work on last 3 shots (19-21), so it's not clear whether there was a QC mode on those shots, but ramp-down seems to trigger brief bursts of ELMs on all three shots. Shots for analysis: 1010629009 1010629010 1010629012 1010629016 1010629018 1010629019 1010629020 1010629021 Since no clear result was produced, but the initial results seem to be interesting, the miniproposal will be resubmitted with minor changes reflecting the gained experience. |
| Physics Operator Summaries |
| Entered: Jul 7 2004 04:37:13:567PM |
| Author: To Be Determined |
| ---------------------------------------------------------------------------- 1010629xxx marmar PHYSICS_OPERATOR Jun 29 2001 8:33:07:790AM . . . . . . . . . . . . . . . . . . . . Engineering setup for 1010629 MP282A: Triggering ELMs by fast current ramp-up. SL: Dmitri Mossessian PO: Earl Marmar Engineering setup: ECDC in D2 at 2.e-4 Torr overnight prior to run. We may require ECDC in D2 between shots Power systems as on 1010628017 RF: XMTR 1, main power on ONLY by 8:00 XMTR 2,3, 4 in RUN-ON started by 8:00 AM Gas setup: fill B-top with 6 psi of D2 Hybrid enabled (PG4) fill B-side lower with 1 psi of Ar Hybrid enabled (PG1) fill B-side upper with 30 psi of D2 Hybrid DISABLED (PG2) fill C-side with 30 psi of D2 Hybrid enabled (PG3) fill J-bottom with 30 psi of He Hybrid DISABLED (PG5) Enable the following gate valves: ECE, DNB, VUV Run starts at 09:00 and ends at 17:00 There may be a short delay at the beginning of the run during Mike Holland's visit, but the cell and power rooms should be locked up at the normal time. ----------------------------------------------------------------------------- Summary: The run went quite well from the physop point of view. The machine ran well (1 fizzle, B_R a little high). The current ramp ups caused some shape lurching (inner gap and triangularity). On the last shot we programmed a repetitive ramp, which worked well. Many shots disrupted during RF. We also had many shots with close to 4 MW of total power for substantial pulse lengths. Confinement was good on a number of shots, with H-factors approaching 2 in EDA at 800 kA plasma current. I added a gas puff during the H-mode, starting with shot 16, which didn't appear to hurt, and may have helped the RF. As a piggyback to the main MP, we injected Li pellets on a number of shots, and got good cigar images, both in H-mode and L-mode. The ablation images clearly show a systematic change in angle as the pellet penetrates from the edge to the core, starting near 10 degrees and going close to 0. Shot 13 is a good example. Scorecard: Plasmas 20 Fizzles 1 Duds 0 No power shots 0 Total cycles 21 _________________________________________________________________________________ 1010629xxx marmar PHYSICS_OPERATOR Jun 29 2001 9:34:31:370AM . . . . . . . . . . . . . . . . . . . . coldstart: logical name problem; spanna crashed yesterday. do a ccl remcam, and redo. 2'nd coldstart: no errors, all matrices respond. load from 1010628021; add current ramp starting at 1.0 second (up to 0.95 MA at 1.05, back to 0.8 MA by 1.2) ---------------------------------------------------------------------------- 1010629001 marmar PHYSICS_OPERATOR Jun 29 2001 9:58:55:160AM . . . . . . . . . . . . . . . . . . . . plasma got the current ramp, but we lost the H-mode (D faulted) ----------------------------------------------------------------------------- 1010629002 marmar PHYSICS_OPERATOR Jun 29 2001 10:10:26:503AM . . . . . . . . . . . . . . . . . . . . add derivative gain (3) to clearin at time of ramp ask for OH1 voltage increase at time of ramp increase target I_p during ramp (1e6 A) decrease prepuff by 4 msec (DNB firing at 0.6 s) disrupt at 0.78 (radiated power) ----------------------------------------------------------------------------- 1010629003 marmar PHYSICS_OPERATOR Jun 29 2001 10:30:52:833AM . . . . . . . . . . . . . . . . . . . . plasma disrupt just after 1 sec radiation went up, then programming changes probably pushed it over the top ----------------------------------------------------------------------------- 1010629004 marmar PHYSICS_OPERATOR Jun 29 2001 10:48:09:313AM . . . . . . . . . . . . . . . . . . . . reduce clearin derivative gain (1) reduce OH1 voltage preprog change at 1 sec plasma disrupt at 1.24 seconds, after the current ramp Got a ramp rate of about 2 MA/s ----------------------------------------------------------------------------- 1010629005 marmar PHYSICS_OPERATOR Jun 29 2001 11:41:32:660AM . . . . . . . . . . . . . . . . . . . . ECDC in D2 for 5 minutes before shot (P_fill=4e-4) plasma disrupt at 0.76 ----------------------------------------------------------------------------- 1010629006 marmar PHYSICS_OPERATOR Jun 29 2001 11:42:09:286AM . . . . . . . . . . . . . . . . . . . . turn off D port plasma disrupt at 0.97 ----------------------------------------------------------------------------- 1010629007 marmar PHYSICS_OPERATOR Jun 29 2001 12:09:26:046PM . . . . . . . . . . . . . . . . . . . . turn E-port off, D-port on plasma all the way through rampdown Got H-mode through the current ramp; D tripped during the ramp We're getting shape changes during the ramp (triangularity goes up, inner gap goes up) ----------------------------------------------------------------------------- 1010629008 marmar PHYSICS_OPERATOR Jun 29 2001 12:16:49:136PM . . . . . . . . . . . . . . . . . . . . Increase derivative gain on clearin (to 3) during I_p ramp and add a 5 mm jog; Increase prop gain on RCUR fizzle ----------------------------------------------------------------------------- 1010629009 marmar PHYSICS_OPERATOR Jun 29 2001 1:22:26:316PM . . . . . . . . . . . . . . . . . . . . no PCS changes plasma got the ramp, with RF in EDA Got a Li pellet at 1.7; cigar looks beautiful ----------------------------------------------------------------------------- 1010629010 marmar PHYSICS_OPERATOR Jun 29 2001 1:23:23:580PM . . . . . . . . . . . . . . . . . . . . reduce BR_0 offset by .5 mT plasma; good shot disrupt at 1.5 ----------------------------------------------------------------------------- 1010629011 marmar PHYSICS_OPERATOR Jun 29 2001 1:24:44:880PM . . . . . . . . . . . . . . . . . . . . decrease density (nl_zmeter to 0.3 from 0.45) aiming at nl_04=7e19 target plasma disrupt during I_p ramp at 1.09 ----------------------------------------------------------------------------- 1010629012 marmar PHYSICS_OPERATOR Jun 29 2001 1:50:29:513PM . . . . . . . . . . . . . . . . . . . . no pcs changes plasma ----------------------------------------------------------------------------- 1010629013 marmar PHYSICS_OPERATOR Jun 29 2001 2:12:46:096PM . . . . . . . . . . . . . . . . . . . . reduce argon puff by 5 msec plasma ----------------------------------------------------------------------------- 1010629014 marmar PHYSICS_OPERATOR Jun 29 2001 2:33:50:300PM . . . . . . . . . . . . . . . . . . . . change timing on clearin derivative gain plasma no obvious changes in shape lurches ----------------------------------------------------------------------------- 1010629015 marmar PHYSICS_OPERATOR Jun 29 2001 2:58:40:970PM . . . . . . . . . . . . . . . . . . . . increase CLEARIN derivative gain to 6 plasma ----------------------------------------------------------------------------- 1010629016 marmar PHYSICS_OPERATOR Jun 29 2001 3:21:52:723PM . . . . . . . . . . . . . . . . . . . . reduce prepuff by 3 msec increase target density (nl_zmeter to 0.37) turn off density feedback between 0.9 and 1.3 seconds; valve to 35 volt plasmas ----------------------------------------------------------------------------- 1010629017 marmar PHYSICS_OPERATOR Jun 29 2001 3:42:04:240PM . . . . . . . . . . . . . . . . . . . . increase H-mode puff level to 45 V on PG3. plasma disrupt at 1 second ----------------------------------------------------------------------------- 1010629018 marmar PHYSICS_OPERATOR Jun 29 2001 4:26:49:043PM . . . . . . . . . . . . . . . . . . . . reduce H-mode puff to 25 V plasma ----------------------------------------------------------------------------- 1010629019 marmar PHYSICS_OPERATOR Jun 29 2001 4:27:26:106PM . . . . . . . . . . . . . . . . . . . . program to 1 MA with ramp-down to 0.8 starting at 1.0 plasma disrupt shortly after current ramp-down ----------------------------------------------------------------------------- 1010629020 marmar PHYSICS_OPERATOR Jun 29 2001 5:19:51:483PM . . . . . . . . . . . . . . . . . . . . move RCUR out 1.5 mm plasma disrupt at 1.31 (Li pellet) ----------------------------------------------------------------------------- 1010629021 marmar PHYSICS_OPERATOR Jun 29 2001 5:21:03:593PM . . . . . . . . . . . . . . . . . . . . add multiple short I_p ramps plasma disrupt at 1.21 s got 2 ramps - |
| Session Leader Comments |
| Physics Operator Comments | |||
| Jun 29 2001 08:33:07:790AM | Earl Marmar | Engineering setup for 1010629 MP282A: Triggering ELMs by fast current ramp-up. SL: Dmitri Mossessian PO: Earl Marmar Engineering setup: ECDC in D2 at 2.e-4 Torr overnight prior to run. We may require ECDC in D2 between shots Power systems as on 1010628017 RF: XMTR 1, main power on ONLY by 8:00 XMTR 2,3, 4 in RUN-ON started by 8:00 AM Gas setup: fill B-top with 6 psi of D2 Hybrid enabled (PG4) fill B-side lower with 1 psi of Ar Hybrid enabled (PG1) fill B-side upper with 30 psi of D2 Hybrid DISABLED (PG2) fill C-side with 30 psi of D2 Hybrid enabled (PG3) fill J-bottom with 30 psi of He Hybrid DISABLED (PG5) Enable the following gate valves: ECE, DNB, VUV Run starts at 09:00 and ends at 17:00 There may be a short delay at the beginning of the run during Mike Holland's visit, but the cell and power rooms should be locked up at the normal time. | |
| Jun 29 2001 09:34:31:370AM | Earl Marmar | coldstart: logical name problem; spanna crashed yesterday. do a ccl remcam, and redo. 2'nd coldstart: no errors, all matrices respond. load from 1010628021; add current ramp starting at 1.0 second (up to 0.95 MA at 1.05, back to 0.8 MA by 1.2) | |
| Jun 29 2001 09:58:55:160AM | 1010629001 | Earl Marmar | plasma got the current ramp, but we lost the H-mode (D faulted) |
| Jun 29 2001 10:10:26:503AM | 1010629002 | Earl Marmar | add derivative gain (3) to clearin at time of ramp ask for OH1 voltage increase at time of ramp increase target I_p during ramp (1e6 A) decrease prepuff by 4 msec (DNB firing at 0.6 s) disrupt at 0.78 (radiated power) |
| Jun 29 2001 10:30:52:833AM | 1010629003 | Earl Marmar | plasma disrupt just after 1 sec radiation went up, then programming changes probably pushed it over the top |
| Jun 29 2001 10:48:09:313AM | 1010629004 | Earl Marmar | reduce clearin derivative gain (1) reduce OH1 voltage preprog change at 1 sec plasma disrupt at 1.24 seconds, after the current ramp Got a ramp rate of about 2 MA/s |
| Jun 29 2001 11:41:32:660AM | 1010629005 | Earl Marmar | ECDC in D2 for 5 minutes before shot (P_fill=4e-4) plasma disrupt at 0.76 |
| Jun 29 2001 11:42:09:287AM | 1010629006 | Earl Marmar | turn off D port plasma disrupt at 0.97 |
| Jun 29 2001 12:09:26:047PM | 1010629007 | Earl Marmar | turn E-port off, D-port on plasma all the way through rampdown Got H-mode through the current ramp; D tripped during the ramp We're getting shape changes during the ramp (triangularity goes up, inner gap goes up) |
| Jun 29 2001 12:16:49:137PM | 1010629008 | Earl Marmar | Increase derivative gain on clearin (to 3) during I_p ramp and add a 5 mm jog; Increase prop gain on RCUR fizzle |
| Jun 29 2001 01:22:26:317PM | 1010629009 | Earl Marmar | no PCS changes plasma got the ramp, with RF in EDA Got a Li pellet at 1.7; cigar looks beautiful |
| Jun 29 2001 01:23:23:580PM | 1010629010 | Earl Marmar | reduce BR_0 offset by .5 mT plasma; good shot disrupt at 1.5 |
| Jun 29 2001 01:24:44:880PM | 1010629011 | Earl Marmar | decrease density (nl_zmeter to 0.3 from 0.45) aiming at nl_04=7e19 target plasma disrupt during I_p ramp at 1.09 |
| Jun 29 2001 01:50:29:513PM | 1010629012 | Earl Marmar | no pcs changes plasma |
| Jun 29 2001 02:12:46:097PM | 1010629013 | Earl Marmar | reduce argon puff by 5 msec plasma |
| Jun 29 2001 02:33:50:300PM | 1010629014 | Earl Marmar | change timing on clearin derivative gain plasma no obvious changes in shape lurches |
| Jun 29 2001 02:58:40:970PM | 1010629015 | Earl Marmar | increase CLEARIN derivative gain to 6 plasma |
| Jun 29 2001 03:21:52:723PM | 1010629016 | Earl Marmar | reduce prepuff by 3 msec increase target density (nl_zmeter to 0.37) turn off density feedback between 0.9 and 1.3 seconds; valve to 35 volt plasmas |
| Jun 29 2001 03:42:04:240PM | 1010629017 | Earl Marmar | increase H-mode puff level to 45 V on PG3. plasma disrupt at 1 second |
| Jun 29 2001 04:26:49:043PM | 1010629018 | Earl Marmar | reduce H-mode puff to 25 V plasma |
| Jun 29 2001 04:27:26:107PM | 1010629019 | Earl Marmar | program to 1 MA with ramp-down to 0.8 starting at 1.0 plasma disrupt shortly after current ramp-down |
| Jun 29 2001 05:19:51:483PM | 1010629020 | Earl Marmar | move RCUR out 1.5 mm plasma disrupt at 1.31 (Li pellet) |
| Jun 29 2001 05:41:13:000PM | 1010629021 | Earl Marmar | add multiple short I_p ramps plasma disrupt at 1.21 s got 2 ramps |
| Engineering Operator Comments | ||||
| Shot | Time | Type | Status | Comment |
| 1 | 09:35:52:200AM | Plasma | Ok | |
| 2 | 09:59:53:533AM | Plasma | Ok | |
| 3 | 10:18:43:190AM | Plasma | Ok | |
| 4 | 10:34:50:057AM | Plasma | Ok | |
| 5 | 11:04:40:743AM | Plasma | Ok | |
| 6 | 11:23:45:600AM | Plasma | Ok | |
| 7 | 11:44:47:337AM | Plasma | Ok | |
| 8 | 12:11:51:270PM | Plasma | Ok | |
| 9 | 12:24:46:913PM | Plasma | Ok | |
| 10 | 12:45:49:103PM | Plasma | Ok | |
| 11 | 01:11:37:017PM | Plasma | Ok | |
| 12 | 01:31:09:860PM | Plasma | Ok | |
| 13 | 01:55:44:163PM | Plasma | Ok | |
| 14 | 02:17:52:603PM | Plasma | Ok | |
| 15 | 02:44:52:510PM | Plasma | Ok | |
| 16 | 03:07:56:467PM | Plasma | Ok | |
| 17 | 03:27:57:670PM | Plasma | Ok | |
| 18 | 03:49:05:140PM | Plasma | Ok | |
| 19 | 04:09:15:720PM | Plasma | Ok | |
| 20 | 04:32:11:880PM | Plasma | Ok | |
| 21 | 04:59:25:500PM | Plasma | Ok | |