Alcator C-Mod Run 930804 Information

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Miniproposals
Miniproposal:
Date Filed:
Title:
First Author:
Session Leader:Brian Labombard (shots 1-29)

Operators
Session leader(s):Brian Labombard
Physics operator(s):John Goetz
Engineering operator(s):Steve Fairfax

Engineering Operator Run Comment
Goetz MP#016 SOL Charac.

Session Leader Plans

Physics Operators Plans

Session Leader Summaries
Entered: Jul 7 2004 03:49:08:273PM
Author: To Be Determined
Operator Summary of Run 930804

Session Leader: Labombard
Physics Operator: Goetz
Eng. Operator: Fairfax

The goal of this run was to follow MP016 - Scrape-off Layer Characterization I
In order to accomplish this goal, a low, outside, and fat plasma was
required. This was so that the fast scanning probe (FSP) could reach the last
closed flux surface (LCFS). To this end, plasmas were created that allowed
some of the physics goals to be met. The session leader will create a run
summary of his own.

Vacuum conditions: A 35 degree overnight bake and 2 hours of
hydrogen ECDC (0600 - 0800) were performed prior to the run.
Base pressure was 6e-7 before the run started at 1100.

Aux. systems: The EFCL proportional valve was replaced before the run in an
attempt to remedy the 930803 cooling problem. This fix was not
successful and lead to a delay in the beginning of the run due to
a late start on the cooling.

Power supplies: The delay allowed OH1 tests to be performed. Shots 001 to 008
were used to try and isolate the OH1 oscillations. Best results were
obtained with both OH1 cabinets operational.

Plasma control: The run needed low plasmas and thus the ZCUR controller was
of primary interest. With no chopper available the controller
consisting of OH2's and EF1's was used. This controller could not
stop the plasma from oscillating once it reached -2 cm. A variety of
P and D gains were tried but the minimum oscillation obtained was just
less than 1 cm. Of secondary importance to the run was moving the
plasma out. The RCUR controller consisting of OH1, OH2's and EF3's
was used. This controller worked better when the IC_OH1 and the V_EF3
demands were changed to help out. Acceptable elongations for the FSP
were obtained by changing the V_OH2L & V_OH2U demands by 4V (more
positive).

Plasma creation: After the power supply tests the first shot went well. The
next shot was a fizzle. The fill pressure was lowered to 1.e-5 and the
next eight shots were acceptable. The line-averaged density dropped
throughout this sequence. This led to shots 019 & 020 which were hard
x-ray dominated. The fill was increased to 1.8e-5 and the next six
shots went, although overgassing pushed the last few into multiple
disruptions. A WARNING to operators: watch the density
carefully. It appears that the reservoir of particles in the
walls empties quickly. Hard x-rays early in the shot and density
dips were taken care of with puffing of gas but need a watchful eye.


Score-card:
8 engineering shots
17 "good" shots
2 hard x-ray shots
2 fizzles
--
29 total shots

Record current levels were achieved on shots 011, 012, and 014 (603 kA).

Physics Operator Summaries

Session Leader Comments
Aug 4 1993 09:00:48:340AMBrian LabombardSession Leader: B. LaBombard Physics Operator: John Goetz
Engineers: Bertolino, Fairfax
Todays run focusses on continuing MP#016 - 'Scrape of Layer Characterization I'
We plan on starting from 930803007, customizing the equilibrium for maximum
fast-scanning probe penetration: Z_CUR at < -2 cm, Kappa > 1.3, R_CUR increased
(value adjusted depending on equilibrium).
The RF limiter has been positioned at R=.95., the antenna at R=.98
The time of maximum probe insertion will be initially set to .225 ms
The maximum probe insertion coordinates are now R=0.74 Z=-0.26 meters. (1cm
deeper than run of 930728)
Wall conditioning: Overnight bake at 35 degrees C following by approx 2 hours of ECDC.

Aug 4 1993 09:35:14:080AM930804001Brian LabombardPower Test

Aug 4 1993 09:48:35:370AM930804002Brian LabombardPower Test Again

Aug 4 1993 10:42:30:800AM930804003Brian LabombardPower Test Again

Aug 4 1993 10:42:40:590AM930804004Brian LabombardPower Test Again

Aug 4 1993 10:43:15:920AM930804005Brian LabombardPower Test Again

Aug 4 1993 10:43:25:730AM930804006Brian LabombardPower Test Again

Aug 4 1993 10:43:41:560AM930804007Brian LabombardPower Test Again

Aug 4 1993 10:53:45:910AM930804008Brian LabombardPower Test Again

Aug 4 1993 11:23:25:520AM930804009Brian LabombardFirst attempt for plasma.

Not bad for a start. Ip = 435 ka

Aug 4 1993 11:37:40:180AM930804010Brian LabombardTry for better controlled position.

Flash only.

Aug 4 1993 11:52:24:620AM930804011Brian LabombardIp=525 kA
Position is still jumping around

Aug 4 1993 12:11:15:480PM930804012Brian LabombardTry to fix jumping position.

Got plasma again. Ip=595ka!

Aug 4 1993 12:34:01:030PM930804013Brian LabombardPlasma again.

Aug 4 1993 12:55:47:590PM930804014Brian LabombardMoving gas pulse program up to .110 msec (40 msec earlier)

Early density dip filled in. Record current, 602 kA

Aug 4 1993 01:09:50:030PM930804015Brian LabombardMoving gas pulse program up to .110 msec (40 msec earlier)

Early density dip filled in. Record current, 602 kA
Probe Signal shows LCFS signature?

Aug 4 1993 01:26:46:550PM930804016Brian Labombard510 kA Runaway shot

Aug 4 1993 01:46:13:560PM930804017Brian LabombardChange gas program.

Less hards.

Aug 4 1993 02:02:35:410PM930804018Brian LabombardSame setup

Very nice shot.
Probe fully inserted.

Aug 4 1993 02:13:30:310PM930804019Brian LabombardSame setup

540 kA Disruption at 200 msec - narrowly missing probe.

Aug 4 1993 02:24:58:880PM930804020Brian LabombardFill pressure raised to 1.2e-5
Fueling increased.
Very ugly shot. Serious hards.

Aug 4 1993 02:41:59:330PM930804021Brian LabombardFill pressure raised to 1.8e-5
Walls are depleted of gas?
Looking for a fizzle to load walls.

Good Plasma!!

Aug 4 1993 02:58:29:960PM930804022Brian LabombardLooking for higher density now.
Fill pressure at 1.8e-5
Increased pulsed gas.

Good shot . NeL = 5.4e19

Aug 4 1993 03:18:54:830PM930804023Brian LabombardAdd another burst of pulsed gas.

Nice. NeL = 6.0e19

Aug 4 1993 03:46:57:710PM930804024Brian LabombardAttempting to increase elongation. Same gas.

kappa peaks at about 1.4

Aug 4 1993 04:07:09:030PM930804025Brian LabombardIncreased R_CUR to .67
Attempted to increase elongation some more.

kappa = 1.5, Nel=5.0e19

Aug 4 1993 04:21:05:190PM930804026Brian LabombardDecrease elongation. More pulsed gas


Too much gas. Very ugly. Diverted. Disruptions.

Aug 4 1993 04:40:30:490PM930804027Brian LabombardReload gas programming from shot 25, and tweeked pulsed gas 3 spikes
Pellet to be fired at .425 msec

Flash only. Lots of gas in torus. 1mtorr/sec pressure rise.

Aug 4 1993 04:48:55:650PM930804028Brian LabombardSet prefill to 1.6e-5

Ugly, ugly. Disruptions.

Aug 4 1993 05:40:03:780PM930804029Brian LabombardReloading shot 18
Fill gas at 1.3e-5

Very good shot!! Ip=519 kA, NeL=4.9e19
Probe fully inserted. Edge profile data looks good.

Physics Operator Comments

Engineering Operator Comments
ShotTimeTypeStatusComment
109:32:05:000AMTestOkoh1 front only -- ok
209:44:44:990AMTestOkoh1 rear only ok
309:56:11:070AMTestOkOH1 12-pulse test good; ripple is 1/2 of 6-pulse
410:06:13:540AMTestOkOH1 Voltage limit PLC control test OK
510:16:00:150AMTestOkOH1, OH2 test PLC control OK; ripple slightly higher
610:27:13:060AMTestOkOH1 and OH2 under hybrid control OK
710:37:45:900AMTestOkNormal current OH1 and OH2 hybrid control
810:48:16:450AMTestOkRepeat of last shot
911:22:47:230AMPlasmaOkGood plasma shot; OH ripple excellent
1011:27:10:080AMPlasmaOkFizzle
1111:39:46:590AMPlasmaOkNew plasma cuurent record; 520 kA
1211:54:46:650AMPlasmaOkNew record. 590 kA; result of tuning out early minor disruptions
1312:21:06:130PMPlasmaOkNice Plasma. 540 kA
1412:39:20:500PMPlasmaOkNew record; 600 kA
1512:55:56:180PMPlasmaOkLow early density; minor disruption at 70 msec when EF1 crowbar is fired
1601:11:31:060PMPlasmaOkposition errors but otherwise OK
1701:28:37:780PMPlasmaOkfirst probe scan with good overtrace.
1801:47:24:200PMPlasmaOkProbe at last closed flux surface this shot
1902:02:51:630PMPlasmaOkNasty hard x-ray shot with major disruption
2002:18:31:800PMPlasmaOkRunaway shot
2102:32:12:840PMPlasmaOkBetter shot
2202:47:13:480PMPlasmaOkNice plasma; student taking flash picture during shot scared everyone!
2303:03:02:650PMPlasmaOkVery clean shot
2403:21:25:910PMPlasmaOkslightly higher kappa using OH2 I-prog
2503:48:16:040PMPlasmaOkGood shot with better kappa
2604:08:16:520PMPlasmaOkcontinuously disrupting
2704:26:32:720PMPlasmaOkFizzle. Pellet injector filled torus to >30e-4 Torr
2804:39:55:020PMPlasmaOkdisruptive shot; confusion about whether pellet should be allowed to fir
2904:52:49:570PMPlasmaOkGood shot from reloaded shot 18