| Miniproposals | ||||||||||
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| Operators | |
| Session leader(s): | Martin Greenwald |
| Physics operator(s): | Robert Granetz |
| Engineering operator(s): | Bill Cochran |
| Engineering Operator Run Comment |
| MP# 233A Density Limits.Greenwald/Granetz/Cochran. |
| Session Leader Plans |
| Physics Operators Plans |
| Session Leader Summaries |
| Entered: Jul 7 2004 03:49:24:040PM |
| Author: To Be Determined |
| Run Plan mp 233a Density limits (H-mode task force) Session Leader - Greenwald Phys Op - Granetz mostly ============================ Plan: 1. scaling of pedestals/edge parameters near the density limit - in particular we will be varying Bt and Prf to try to get a wide range in beta. (The Rogers and Drake simulations have a significant dependence on the mhd alpha parameter.) 2. fluctuations near the density limit (both H/L and disruptive). The run follows the general approach of 980115 where we ran high density H-modes then ramped the current down to the density limit. The RF needs to be on steadily to the end of the shot. The plan is to start at 5.3T then move to 4.5T and finally to 6.0. The 6T shots will be ohmic and we will be looking at the disruptive limit only The outer gap should be in the range 1-1.5 cm so that we can get good data from the Lyman alpha array. ======================================================= Results: Not a very productive day. Start was delayed by 4 1/2 hours by a problem with a circuit board in a TF power supply cabinet. We lost the last 1/2 hour to a breaker fault. In between, we made a little progress on the mp. Early shots 007-010 were plagued with impurity injection. Speculating that the source was with the RF, we shut it down for shot 011. That shot lasted longer - the interferometer shut down half way through that shot. Starting with shot 012, we were able to extend the shot into the high density region. 013 and 014 had brief H-modes and disrupted roughly at 90% of the empirical limit. The H/L transition was at relatively low density. Shots 013 and 014 were also interesting in that they showed some modest density peaking toward as the limit was approached. We should look at the profiles. Note: Two puff valves were required to reach the density range of interest. ================================ Shots suitable for further analysis include: 1000606013 1000606014 |
| Physics Operator Summaries |
| Entered: Jul 7 2004 04:37:11:083PM |
| Author: To Be Determined |
| Physics operator summary for run 1000606: MP 233A -- Density limits Session leader: M. Greenwald Physics operator: R. Granetz Engineering operators: B. Cochran Summary: Once plasma operation began in the afternoon, things went pretty smoothly, at least from an operations standpoint. But the entire morning was spent trying to debug a faulty circuit board in one of the TF cabinets, and consequently we only had 9 plasmas. Most of these disrupted a little below the expected density limit (for example, shots 12 and 16), but shots 13 and 14 apparently reached the density limit. Brian got some interesting scanning probe data on shot 14 as well. The RF had difficulty coupling into the high densities. The run ended a little early due to a TF breaker problem. Scorecard: 9 plasmas 1 fizzles 0 duds 6 tests 0 aborted ---------- 16 total ------------------------------------------------------------------------------- Engineering setup for Tuesday, 06 June 2000: Overnight ECDC in D2, stopping 1-2 hours prior to the run. Run begins at 9:00 and ends at 17:00. Power system setup as on 1000602001 (last Friday morning), including fizzle delay settings Gas setup - fill B-top with 6 psi of D2 Hybrid enabled fill B-side lower with 1 psi of Ar Hybrid DISABLED leave B-side upper as is Hybrid DISABLED fill C-side with 30 psi of D2 Hybrid enabled leave J-bottom as is Hybrid DISABLED The following gate valves should be enabled, assuming no vacuum problems: ECE, VUV, DNB The first two shots will be a standard OH test and an EF4 test. ------------------------------------------------------------------------------- Run plan: MP# 233A -- Density limits SL: M. Greenwald PO: R. Granetz (and maybe J. Irby ?) Ramp current down dynamically to get density limit disruptions. Get probe fluctuation measurements and pedestal profile measurements as the density limit is reached. Do this at three fields (5.3, 4.5, 6.0 T), keeping q95 the same (Ip=1.0, 0.85, 1.15 MA respectively). Have RF power from D and E antennas for 5.3 and 4.5 T shots to get H-modes, and subsequent H-L transitions just prior to density limit disruptions. High density is desired (nebar=4-5e20 m-3 or more). Outer gap=1.0-1.5 cm. Note: keep Btor flattopped (except for usual waggles for ECE) until after the density limit is reached. Then rampdown Btor at the restricted rate of 75-100 kA/s. ------------------------------------------------------------------------------- Overnight ECDC in D2 was done, stopping 2 hours prior to the run Hybrid coldstart done; no errors found Loaded 1000602014 and set current to 1.0 MA, starting rampdown at t=0.70 s, with dIp/dt=-0.9 MA/s. Btor=5.3 T (constant until t=1.5 s). nl_04=2.0e20 m-2. RCUR changed to give outer gap = 13 mm. ------------------------------------------------------------------------------- Shot 01 -- Test; Usual Tuesday OH coax test. Coax Resis (uohm) ---- ------------ OH1 0.42 OH2U 0.21 OH2L 0.29 Irby says 'Go'. Shot 02 -- Test; No-power cycle. This was supposed to be an EF4 shunt test, but there was a problem with a PLC controlling communication with the alternator. Shot 03 -- Test; EF4 shunt test under PLC control. Looks good. There's a problem with an IOC fault in one of the TF cabinets. We are having a delay while Bill Cochran checks it out. Shot 04 -- Test; 50 kA TF-only, under PLC control. All okay during the current pulse, but the IOC fault popped up again after the shot. We'll have another delay while the engineers continue looking into the problem. Jim Irby will be substituting for me from 12-14:00 today. That change will start now, prior to shot 05. Shot 05 -- Test; 50 kA TF-only test under PLC control. Okay. Shot 06 -- Test; 100 kA TF-only test under PLC control. Okay. Shot 07 -- Plasma. Disrupted at t=0.99 s, during the current rampdown. Next shot: increase pre-fill puff by 3 ms. Granetz returns as physop. Shot 08 -- Plasma. Disrupted at t=0.97 s, during the current rampdown. Outer gap was 2 cm and increasing. I think it may have been going vertically unstable. This was not a density limit disruption. Next shot: decrease outer gap by 1 cm (increase RCUR by 5 mm). This will also help any vertical stability problem. Also increase nl_04 to 2.4e20 m-2. Shot 09 -- Plasma. Disrupted at t=0.94 s. This was a thermal quench, due to some impurity problem. Next shot: tweak CLEARIN to keep both gaps more constant during the rampdown. Also fill J-bottom plenum with 30 psi of D2, but don't enable the valve yet. Shot 10 -- Plasma. Disrupted at t=0.98 s. This was another thermal quench, but not a density limit disruption. Next shot: no RF. Also tweak RCUR/outer gap a little more. Also add 3 ms to pre-fill puff to compensate for the DNB, which will now remain closed for the rest of the run. Shot 11 -- Plasma. Disrupted at t=1.29 s, when Ip got down to 0.44 MA. TCI has no signal after t=0.8 s. This was an ohmic shot. Outer gap grows to 3 cm. Next shot: turn RF back on. Program a 1 cm outward ramp in RCUR. Enable J-bottom valve, using preprogrammed waveform. Also add 2 ms more to pre-fill puff. Shot 12 -- Plasma. Disrupted at t=1.13 s. Density was higher, but RF faulted early without any clear H-mode. Outer gap was steady at 1 cm. J-bottom valve gave gas, but it's voltage doesn't show up on the digitizer. Next shot: repeat, with only minor tweaks to CLEARIN. Shot 13 -- Plasma. Disrupted at t=1.14 s when Ip=0.59 MA. Outer gap is 6-10 mm. Inner gap=14-16 mm. RF faulted early again. Density was nearly at the expected density limit. H-mode would have done it easily. Next shot: repeat, no PCS changes. Shot 14 -- Plasma. Disrupted at t=1.14 s when Ip=0.56 MA. This might have been at the density limit. RF needs more tweaking. Brian fired the A scanning probe at 0.6, 0.8, and 1.05 s. Next shot: repeat, no PCS changes. Shot 15 -- Fizzle. Next shot: add 10 amps to IC_EF4. Shot 16 -- Plasma. Disrupted at t=1.05 s when Ip=0.64 MA. Didn't quite make it to the density limit. After this shot, a motor in one of the TF mechanical breakers was found to have burned up. That forced us to end the run early. |
| Session Leader Comments | |||
| Jun 6 2000 09:06:54:827AM | Martin Greenwald | Plan: 1. scaling of pedestals/edge parameters near the density limit - in particular we will be varying Bt and Prf to try to get a wide range in beta. (The Rogers and Drake simulations have a significant dependence on the mhd alpha parameter.) 2. fluctuations near the density limit (both H/L and disruptive). The run follows the general approach of 980115 where we ran high density H-modes then ramped the current down to the density limit. The RF needs to be on steadily to the end of the shot. The plan is to start at 5.3T then move to 4.5T and finally to 6.0. The 6T shots will be ohmic and we will be looking at the disruptive limit only The outer gap should be in the range 1-1.5 cm so that we can get good data from the Lyman alpha array. | |
| Jun 6 2000 09:08:18:623AM | Martin Greenwald | Background: Earlier work[1] has suggested that the tokamak density limit can be explained fully only by consideration of transport effects. While there is little dispute about the final stages of a density limit collapse - edge cooling via radiation then shrinkage of the current channel leading to MHD instability and disruption - theories based on edge power balance physics alone can not explain important aspects of density limit phenomenology. In particular, the power balance theories predict a density limit with strong dependence on input power and on impurity content. Neither of these dependences are generally observed. These classes of theories also have difficulty explaining the robustness of the density limit with respect to plasma configuration, divertor topology, or operational regime. Finally there is data from Alcator C, TEXT, and MTX (nee Alcator C) which show degradation of particle confinement or enhanced fluctuations in the vicinity of the limit. The work by Drake and Rogers suggest a specific turbulence mechanism for this phenomenon. The simulations show a boundary, above which fluctuations increase dramatically from nominal ``L'' mode levels. This boundary has somewhat complex parametric dependence but has much in common with the empirical limit derived in reference [1]. The edge pressure gradient is an important parameterization for the computationally derived boundary - thus we propose a power scan as part of this mp. We note in passing, the rough agreement with the L/H threshold of simulations carried out with the same code [4]. Recent studies by LaBombard [2] have suggested that the edge diffusivity increases strongly with local collisionality. Since the edge temperature is roughly fixed by parallel transport, this correlation is consistent with an increase in transport as the density is increased. A number of machines have reported a degradation in H-mode confinement as the density limit is approached. This effect apparently sets in at lower densities for P $\sim$ P$_{THRESHOLD}$. So far, C-Mod H-modes have been in this regime. With additional RF power we should be able to access the regime with P $>>$ P$_{THRESHOLD}$. [1] M. Greenwald, et al., ``A New Look at Density Limits'', Nuclear Fusion 28 12 (1988) 2199 [2] LaBombard, 1999 APS [3] Rogers and Drake, Phys. Rev. Letters 79 229 (1997) [4] Hubbard et al, ``Measurements of the High Confinement Mode Pedestal Region on Alcator C-Mod'' Phys. Plasmas, 5 (1998) 1744. | |
| Jun 6 2000 01:31:10:607PM | 1000606007 | Martin Greenwald | First plasma shot after long delay for TF control electronics problem disrupts at .95 sec 2 MW on RF H-mode Lots of little injectins nice striations on the fast camera |
| Jun 6 2000 01:46:54:077PM | 1000606008 | Martin Greenwald | Disrupts before 1 second again |
| Jun 6 2000 02:09:32:607PM | 1000606009 | Martin Greenwald | just about the same as the previous 2 shots |
| Jun 6 2000 02:47:22:263PM | 1000606010 | Martin Greenwald | same again - maybe killed by discrete injections |
| Jun 6 2000 02:57:41:857PM | 1000606011 | Martin Greenwald | RF turned off for this shot lasts til 1.3 seconds interferometer not working |
| Jun 6 2000 03:18:34:857PM | 1000606012 | Martin Greenwald | RF back on, but trips early lasts til 1.13 seconds very brief H-mode L-mode density near limit at disruption (0.85) |
| Jun 6 2000 04:33:22:543PM | 1000606013 | Martin Greenwald | Short RF pulse again Short H-mode essentially reaches density limit density peaking seen toward end of shot |
| Jun 6 2000 04:33:05:390PM | 1000606014 | Martin Greenwald | Similar to shot 13 scanning probe inserted density peaking seen toward end of shot |
| Jun 6 2000 04:13:28:263PM | 1000606015 | Martin Greenwald | fizzle |
| Physics Operator Comments | |||
| Jun 6 2000 09:04:54:200AM | Robert Granetz | Engineering setup for Tuesday, 06 June 2000: Overnight ECDC in D2, stopping 1-2 hours prior to the run. Run begins at 9:00 and ends at 17:00. Power system setup as on 1000602001 (last Friday morning), including fizzle delay settings Gas setup - fill B-top with 6 psi of D2 Hybrid enabled fill B-side lower with 1 psi of Ar Hybrid DISABLED leave B-side upper as is Hybrid DISABLED fill C-side with 30 psi of D2 Hybrid enabled leave J-bottom as is Hybrid DISABLED The following gate valves should be enabled, assuming no vacuum problems: ECE, VUV, DNB The first two shots will be a standard OH test and an EF4 test. | |
| Jun 6 2000 09:05:09:607AM | Robert Granetz | Run plan: MP# 233A -- Density limits SL: M. Greenwald PO: R. Granetz (and maybe J. Irby ?) Ramp current down dynamically to get density limit disruptions. Get probe fluctuation measurements and pedestal profile measurements as the density limit is reached. Do this at three fields (5.3, 4.5, 6.0 T), keeping q95 the same (Ip=1.0, 0.85, 1.15 MA respectively). Have RF power from D and E antennas for 5.3 and 4.5 T shots to get H-modes, and subsequent H-L transitions just prior to density limit disruptions. High density is desired (nebar=4-5e20 m-3 or more). Outer gap=1.0-1.5 cm. Note: keep Btor flattopped (except for usual waggles for ECE) until after the density limit is reached. Then rampdown Btor at the restricted rate of 75-100 kA/s. | |
| Jun 6 2000 09:05:22:623AM | Robert Granetz | Overnight ECDC in D2 was done, stopping 2 hours prior to the run Hybrid coldstart done; no errors found Loaded 1000602014 and set current to 1.0 MA, starting rampdown at t=0.70 s, with dIp/dt=-0.9 MA/s. Btor=5.3 T (constant until t=1.5 s). nl_04=2.0e20 m-2. RCUR changed to give outer gap = 13 mm. | |
| Jun 6 2000 09:14:36:937AM | 1000606001 | Robert Granetz | Shot 01 -- Test; Usual Tuesday OH coax test. Coax Resis (uohm) ---- ------------ OH1 0.42 OH2U 0.21 OH2L 0.29 Irby says 'Go'. |
| Jun 6 2000 09:28:50:607AM | 1000606002 | Robert Granetz | Shot 02 -- Test; No-power cycle. This was supposed to be an EF4 shunt test, but there was a problem with a PLC controlling communication with the alternator. |
| Jun 6 2000 09:53:52:153AM | 1000606003 | Robert Granetz | Shot 03 -- Test; EF4 shunt test under PLC control. Looks good. |
| Jun 6 2000 09:54:25:607AM | 1000606003 | Robert Granetz | There's a problem with an IOC fault in one of the TF cabinets. We are having a delay while Bill Cochran checks it out. |
| Jun 6 2000 10:46:30:857AM | 1000606004 | Robert Granetz | Shot 04 -- Test; 50 kA TF-only, under PLC control. All okay during the current pulse, but the IOC fault popped up again after the shot. We'll have another delay while the engineers continue looking into the problem. |
| Jun 6 2000 11:55:56:297AM | 1000606004 | Robert Granetz | Jim Irby will be substituting for me from 12-14:00 today. That change will start now, prior to shot 05. |
| Jun 6 2000 02:02:38:763PM | 1000606005 | Robert Granetz | 50 kA TF test. Looks good (This is really Jim Irby substituting for Granetz.) |
| Jun 6 2000 02:03:03:577PM | 1000606006 | Robert Granetz | 100 kA TF shot (This is really Jim Irby substituting for Granetz.) |
| Jun 6 2000 02:04:19:700PM | 1000606007 | Robert Granetz | Plasma to 0.995 seconds Looks like current rise is a little fast (This is really Jim Irby substituting for Granetz.) |
| Jun 6 2000 01:52:53:047PM | 1000606008 | Robert Granetz | Added 3 ms to pg4 width --- a little more prepuff Plasma to 0.97 s (This is really Jim Irby substituting for Granetz.) |
| Jun 6 2000 01:53:06:920PM | 1000606008 | Robert Granetz | Granetz returns as physop |
| Jun 6 2000 01:56:24:687PM | 1000606008 | Robert Granetz | Shot 08 -- Plasma. Disrupted at t=0.97 s, during the current rampdown. Outer gap was 2 cm and increasing. I think it may have been going vertically unstable. This was not a density limit disruption. Next shot: decrease outer gap by 1 cm (increase RCUR by 5 mm). This will also help any vertical stability problem. Also increase nl_04 to 2.4e20 m-2. |
| Jun 6 2000 02:19:24:653PM | 1000606009 | Robert Granetz | Shot 09 -- Plasma. Disrupted at t=0.94 s. This was a thermal quench, due to some impurity problem. Next shot: tweak CLEARIN to keep both gaps more constant during the rampdown. Also fill J-bottom plenum with 30 psi of D2, but don't enable the valve yet. |
| Jun 6 2000 02:50:55:763PM | 1000606010 | Robert Granetz | Shot 10 -- Plasma. Disrupted at t=0.98 s. This was another thermal quench, but not a density limit disruption. Next shot: no RF. Also tweak RCUR/outer gap a little more. Also add 3 ms to pre-fill puff to compensate for the DNB, which will now remain closed for the rest of the run. |
| Jun 6 2000 03:02:19:123PM | 1000606011 | Robert Granetz | Shot 11 -- Plasma. Disrupted at t=1.29 s, when Ip got down to 0.44 MA. TCI has no signal after t=0.8 s. This was an ohmic shot. Outer gap grows to 3 cm. Next shot: turn RF back on. Program a 1 cm outward ramp in RCUR. Enable J-bottom valve, using preprogrammed waveform. Also add 2 ms more to pre-fill puff. |
| Jun 6 2000 03:21:55:670PM | 1000606012 | Robert Granetz | Shot 12 -- Plasma. Disrupted at t=1.13 s. Density was higher, but RF faulted early without any clear H-mode. Outer gap was steady at 1 cm. J-bottom valve gave gas, but it's voltage doesn't show up on the digitizer. Next shot: repeat, with only minor tweaks to CLEARIN. |
| Jun 6 2000 03:37:29:730PM | 1000606013 | Robert Granetz | Shot 13 -- Plasma. Disrupted at t=1.14 s when Ip=0.59 MA. Outer gap is 6-10 mm. Inner gap=14-16 mm. RF faulted early again. Density was nearly at the expected density limit. H-mode would have done it easily. Next shot: repeat, no PCS changes. |
| Jun 6 2000 04:01:29:983PM | 1000606014 | Robert Granetz | Shot 14 -- Plasma. Disrupted at t=1.14 s when Ip=0.56 MA. This might have been at the density limit. RF needs more tweaking. Brian fired the A scanning probe at 0.6, 0.8, and 1.05 s. Next shot: repeat, no PCS changes. |
| Jun 6 2000 04:17:59:390PM | 1000606015 | Robert Granetz | Shot 15 -- Fizzle. Next shot: add 10 amps to IC_EF4. |
| Jun 6 2000 05:00:05:950PM | 1000606016 | Robert Granetz | Shot 16 -- Plasma. Disrupted at t=1.05 s when Ip=0.64 MA. Didn't quite make it to the density limit. After this shot, a motor in one of the TF mechanical breakers was found to have burned up. That forced us to end the run early. |
| Engineering Operator Comments | ||||
| Shot | Time | Type | Status | Comment |
| 1 | 09:09:56:497AM | Test | Ok | OH Coax Test |
| 2 | 09:22:03:293AM | Test | Bad | Alternator PLc Fault during Init. |
| 3 | 09:34:29:403AM | Test | Ok | EF4 Shunt Test |
| 4 | 10:33:10:843AM | Test | Ok | TF 50 KA Test |
| 5 | 12:48:50:640PM | Test | Ok | 50ka TF test only |
| 6 | 01:02:16:250PM | Test | Ok | 100ka TF test only |
| 7 | 01:17:45:390PM | Plasma | Ok | |
| 8 | 01:39:51:560PM | Plasma | Ok | |
| 9 | 02:05:44:013PM | Plasma | Ok | |
| 10 | 02:25:06:810PM | Plasma | Ok | |
| 11 | 02:47:27:140PM | Plasma | Ok | |
| 12 | 03:07:47:420PM | Plasma | Ok | |
| 13 | 03:27:47:543PM | Plasma | Ok | |
| 14 | 03:49:02:310PM | Plasma | Ok | |
| 15 | 04:10:29:200PM | Plasma | Ok | |
| 16 | 04:27:06:420PM | Plasma | Ok | |