Alcator C-Mod Run 931008 Information

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Miniproposals
Miniproposal:
Date Filed:
Title:
First Author:
Session Leader:Bruce Lipschultz (shots 1-23)

Operators
Session leader(s):Bruce Lipschultz
Physics operator(s):John Goetz
Engineering operator(s):Vinny Bertolino,Joe Daigle,Frank Silva

Engineering Operator Run Comment
divertor gas puff

Session Leader Plans

Physics Operators Plans

Session Leader Summaries
Entered: Jul 7 2004 03:49:09:070PM
Author: To Be Determined

Session Leader summary for 931008

EO: Bertolino, Silva, Daigle
PO: Goetz
SL: Lipschultz

Run 931008 was in support of Mini-Proposal #032 - Gas Puffing in the Divertor.
The general aim of this mini-proposal is to explore the effect of gas puffing
at different poloidal points around the plasma. Is it more efficient to fuel the plasma from the inner
midplane or from the outer wall or someplace in the divertor? Does gas-puffing
of deuterium in the divertor increase the density there and have no
effect on the central plasma? Will injection of an impurity into
the divertor increase the radiation there without any bad effects on the
central plasma?

At this time there is only one gas puff tube that can be used for these studies.
It delivers gas into the private flux region of the divertor. Specifically, we
utilized tube number 9 which puts gas through a floor tile into the private
flux region. Because only one tube is available for todays run we will be
just comparing that gas puff to the 'regular' machine gas puff in terms of
effects on the central plasma and divertor. By varying the pressure in the
plenum behind this tube we can vary the flow rates from sub torr-l/sec to 50
torr-l/sec with D2. We will be working with SN dischages. See the ops log
for the specific plasma setup.

The run was troublesome in that we were not able to obtain reproducible plasmas.
It is not clear whether this is due to lack of ECDC prior to the run (20 minutes
instead of the customary 2 hrs) or the tile that later ended up on the TCI window
or some variations in the breakdown conditions. However I will not dwell on those
aspects. The shots of interest follow:

shot 11 nel_05=5.e19, Zeff=1.3 no gas puff
shot 13 nel_05=5.5e19, Zeff=1.2 1.5 PSI plenum pressure - 100ms pulse
shot 14 nel_05=5.->5.75e19, Zeff=1.1 5.6 psi plenum - 100 ms pulse
shot 17 nel_05=5.->6.2e19, Zeff=1.2 6.6 psi plenum - 200 ms pulse
shot 20 nel_05=5.->6.e19, Zeff=1.2 9 psi plenum - 200 ms pulse
shot 23 no puff,baseline, nel_05=4.3->4.e19, Zeff=1.4->2

The flow rate for shots 13, 14 & 17 were approximately
6, 15 and 26 tl/sec respectively. The H alpha
in the central plasma region was affected by these gas puffs proportional
to the density rise.
The Halpha from the divertor was strongly affected by the gas puff. This effect
was measured by Jim Terry &
Joe Snipes detector array on B-top which views the divertor. That
array is at the same toroidal location as the gas puff tube. There
were very large effects on the H gamma signal as measured by the UMd OMA which
was viewing the outer divertor surface at A-port.

Shots 17 & 20 were notable for an unusual occurence at ~ 600 ms. At that time
the radiation and density in the divertor region suddenly (within ms according
to Halpha measurements) rearranged their profiles. The Halpha emission went
from being peaked towards the inner divertor to peaked towards the outer
divertor. The UV bolometer and other div. bolos show similar behaviour.
The effects on the central plasma were also significant. The 2pi
bolometer signal shows a sudden increase, the main chamber Halpha drops and the
ratiomatic pressure increases. The sudden rise in radiated power may be related
to a moly injection. It is not clear whether this event is somehow dependent
on the gas puffing.

Starting shot 20 and thereafter, we tried (on Earl's suggestion) a pulse of
ICRF at breakdown to assist in breakdown and reproducibility of the discharges.
This pulse of rf was ~ 20 kW starting at 3 ms and lasting till ~ 7 ms after
the Halpha signal has started up. Since we had just 4 shots with this turned
on we cannot assess the usefullness of this technique (2 good shots out
of the last 4). However, it did not appear to have any deleterious effects.


Physics Operator Summaries
Entered: Jul 7 2004 04:36:50:457PM
Author: To Be Determined
Physics operator summary for 931008

EO: Bertolino, Silva, Daigle
PO: Goetz
SL: Lipschultz

Run 931008 was in support of Mini-Proposal #032 - Gas Puffing in the Divertor.
To this end SN discharges were run in deuterium and the divertor gas puff
system was used to put deuterium into the private flux region. The divertor
gas was puffed in at different times, for varying durations and varying supply
pressures. Results from this run will be provided by the Session Leader.

The run started with a reload of shot 931007029 which was the last shot of
the previous run, so hopefully all the bugs and offsets had been worked out
of PCS and the hybrid. Changes to this shot included extending the pulse gas
waveform to one second, changing the drawn plasma current, changing the
location of the x-point, and extending some voltage waveforms past one second.

The run was plagued with dirty startups. These startups were very disruptive
as indicated on all optical signals. Reconstruction of the vacuum ultraviolet
light showed that the discharges appeared to be well centered and well
controlled. Of the 14 plasmas obtained only six were acceptable for physics
purposes. These six survived the terrible startup and were good discharges
after .15s. It was probably just luck (good and/or bad) that allowed these
plasmas to go and the other eight to die a disruptive death. Attempts
to clean up the startup included moving the plasma out early and doing a scan
of fill pressure. Neither of these seemed to help. MARFES did not form on any
shots today and the density rises were quite rapid.

The variations in Bz and Br shot-to-shot and during the startup phase are
still with us. It is unclear as to whether these variations are meaningful
as the vacuum fields from a dud (012) were better than those from a plasma
(011). RF assisted breakdown was attempted today by pulsing approximately
20 kW at +.003s. The scorecard for RF assistance was three plasmas and one
fizzle. The canonical two hours of ECDC before the run today was plagued
with thermocouple problems that limited the cleaning to less than a hour.
This may have been the cause of the bad startups during the run.


Notes: RCUR was moved out in the beginning of the discharge to try and help
the startup. This technique was not successful.
The RXL and ZXL controllers were not moving the x-point in response
to the drawn position so the gain on the EF1 current controller
was turned down and this helped.
The gains on the slow ZCUR wire were fiddled with during the run and
the character of the low frequency oscillations was changed
for the better
Plasmas were obtained with the fill pressure as high as 1.5e-5 gauge.


Engineering today: Reliable operation at 5.2T and 600kA plasma current. Four
blown fuses in EF1 supply after shot 5. Broken EF1 lower conic heat shield
tile fell on TCI window ending the run early (window survived with a few
scratches). The tile was removed by the vacuum group and was found to be
radioactively 'cool'. Further analysis of the tile fragment will be carried
out.

Scorecard: 23 shots = 14 plasmas + 5 fizzles + 4 duds

Shot summary for Run 931008

Reload of 931007029

Changes:
extended PULSE_GAS_3 past .5 until 1s
extended V_EF3 until 1.3s
extended V_EF4 until 1.3s
S_RIN to 0. for all time (was -.02 after 1.)
S_IP = -580000 (rampdown from .8 to 1.3)
S_ZCUR ramps back to 0. @ 1s (was 1.4s)
P_ZCUR(2) = 1 @ .05s (was 2.5)
S_ZXL = -.005 after .6
S_RXL = -.005 after .6

1 P_0=1.2e-5 plasma
2 shift PULSE_GAS_3 +.003s (now @ -.008s) dud
3 P_0 = 1.5e-5 plasma
4 shift PULSE_GAS_3 +.005s (now @ -.003) & lower 1st point to 50V plasma
5 lower fueling between 0. and 1s plasma
6 reload PULSE_GAS_3 from 004 & shift -.005s (now @ -.008s) plasma
7 shift PULSE_GAS_3 -.002s (now @ -.01s) & raise first two points
to 55V & 45V fizzle
8 shift PULSE_GAS_3 +.002s (now @ -.008s) fizzle
9 make V_OH2's equal @ .002s (-35V) plasma
10 rasie fuel before .01s & lower after .1s plasma
11 P_ZCUR(2) = 2 @ .05s P_0 = 1.3e-5 plasma
12 S_ZXL = -.01 @ .6s S_RCUR = .68 all time dud
13 P_0 = 1.5e-5 S_IP = -600000 @ .95s plasma
14 Br offset = -1.75e-3 S_RCUR = .7 @ 0s & .68 @ .15s plasma
15 D_ZCUR(2) = 2 @ .5s P_ZCUR(2) = 1 @ .4 S_RCUR = .7 @ 0s &
.7 @ .1s & .68 @ .2s S_ZXL = -.01 @ .4 S_RXL = -.01
@ .4s divertor gas pulse @ .4s for .2s dud
16 P_0 = 1.7e-5 fizzle
17 Br offset now -2.25e-3 P_0 = 1.4e-5 plasma
18 P_ICEF1L = .25 @ .4s lower PULSE_GAS_3 after .5s P_0=1.5e-5 dud
19 IC_EF4 = -1025A (was -1015) P_0 = 1.6e-5 fizzle
20 IC_EF4 = -1015A P_0 = 1.4e-5 S_ZCUR = -.025 @ 1s
20 kW RF pulse @ .003s for .003s plasma
21 I_ZCUR(2) = 2 (was 1.5) plasma
22 P_0 = 1.5e-5 fizzle
23 P_0 = 1.2e-5 plasma

Session Leader Comments
Oct 8 1993 09:02:58:320AMBruce Lipschultz10/8/93

Session leader: Bruce Lipschultz
Physics Operator: John Goetz
Eng. Operator: Joe Daigle

Mini-proposal 32: Hydrogen gas puffing in the divertor.

This will be the first run utilizing the capillary gas puff
system. The goal of this mini-proposal is to compare the relative effect of H2
gas puffing at different poloidal locations; both in the divertor and
at other points around the plasma. For todays run only one tube is
operable, # 9 which pulses into the private flux region under the x-point.
Thart will limit todays run to comparing the effect of different flow
rates through that tube to the regular gas puff system (at A-side). We
may get to trying Ar puffing later in the day.

Oct 8 1993 09:15:39:630AM931008001Bruce LipschultzShot # 1:

This was a disruption @ 200 ms. We will lower the gas slightly and try
again.

Oct 8 1993 09:41:58:950AM931008002Bruce LipschultzShot # 3:

This was a fizzle. We are going to delay the gas.

Oct 8 1993 09:59:57:560AM931008004Bruce LipschultzShot # 4:

There was a disruption. The density was too high. We are going to lower
the gasp puff.

Oct 8 1993 10:29:54:640AM931008005Bruce LipschultzShot # 5:

There was a disruption around 500 ms. There were alot of hard x-rays.
The density was very high at the same time! We are going to move the
gas puff back earlier in time 5 ms and up the initial spike.

Oct 8 1993 10:47:59:010AM931008006Bruce LipschultzShot # 6:

There was a disruption around 170 ms. X-rays were reduced.
The density control was better! We are going to move the
gas puff back earlier in time another 2 ms and up the initial spike again..

Oct 8 1993 10:56:43:630AM931008007Bruce LipschultzShot # 7:

This was a fizzle. We will mnove the gas pulse time later.

Oct 8 1993 12:19:38:870PM931008011Bruce LipschultzShot # 11:

This is the first shot to last the programmed time. It barely made it
through the first 200 ms but seems fine after that. We will repeat this
shot with some minor changes. We will make our first try with the
divertor gas puff at 500 ms (for 100 ms) at 2 psi fill.

Oct 8 1993 12:32:35:520PM931008012Bruce LipschultzShot # 12:

Complete dud. We are going to raise the fill back to 1.5e-5.

Oct 8 1993 12:52:54:140PM931008013Bruce LipschultzShot # 13:

Good shot. We will just move the plasma off the inner wall earlier in
time for the next shot

Oct 8 1993 01:14:22:350PM931008014Bruce LipschultzShot # 14:

Good shot. We appear to be getting some effect on the divertor plasma from
the gas puff; the density as measured by the probes goes up and the
divertor bolo signals increwase. There does not seem to be any effect on the
central plasma at this point. If anything there appears to be a decrease in
density in the central plasma. For the next shot we will increase the
divertor gas pulse time from 100 to
200 ms. and move the pulse time .5 to .4 seconds. It shows up in the
divertor around 50 ms later.
Argon was turned on for shot 14.

Oct 8 1993 01:37:35:960PM931008015Bruce LipschultzShot # 15:

Dud

Oct 8 1993 01:38:46:500PM931008016Bruce LipschultzShot # 16:

fizzle - we will lower the fill for the next shot.

Oct 8 1993 02:08:03:470PM931008017Bruce LipschultzShot # 17:

Good shot. The gas puff was at 450 ms for 200 ms. The H alpha and
probe signals drop suddenly at ~ 600 ms. There seems to be an increase
in the SXR emission from the main plasma at that time (also bolos). We
don't understand this drop in divertor signals which is during the gas puff.
The next shot will be with increase gas fill and extend the divertor
gas puff to 300 ms.

Oct 8 1993 02:10:09:750PM931008018Bruce LipschultzShot # 18:

dud.

Oct 8 1993 02:29:44:450PM931008019Bruce LipschultzShot # 19:

Fizzle. We seem to be oscillating between too much gas and too little.
For the next shot we will try something new - pulse ~ 100kW of ICRF
for 3 ms starting at 3ms after commutation. We hope this will assist
in making a consistent brakedown.

Oct 8 1993 02:54:39:790PM931008020Bruce LipschultzShot # 20:

Good shot. We will turn off the divertor gas puff for the next shot to
see the difference without it. The rf lasted from 4.5 to 7 ms after
commutation. There was 20kW net into the machine. We will keep that
happening for the next shot.

Oct 8 1993 03:21:19:650PM931008022Bruce LipschultzShot # 22:

Fizzle. We will lower the fill for the next shot.

Oct 8 1993 03:38:56:330PM931008023Bruce LipschultzShot # 23:

Good shot. The divertor gas puff was delayed till after the shot to get
a baseline on the plasma. The density decreased as expected. We will
up the divertor gas puff magnitude for the next shot, putting it back to 400
ms.

There appears to be something blocking part of the CO2 beam for the
2-color intereferometer. The O2 level is too high to get into the cell
to investigate. We will try to go in after the enxt shot with the
O2 monitor if the objject is still there.

Physics Operator Comments

Engineering Operator Comments
ShotTimeTypeStatusComment
108:58:58:950AMPlasmaOkPlasma shot O.K.
209:17:50:790AMTestOkPlasma shot dud
309:32:06:270AMTestOkfizzel
409:48:45:330AMPlasmaOkPlasma shot OK.
510:06:04:420AMPlasmaBadEF1 fuse loss 4 fuses
610:34:59:750AMPlasmaOkGood shot
710:49:53:010AMPlasmaOkPlasma shot Fizzle
811:05:16:780AMPlasmaOkPlasma shot no faults fizzle.
911:27:37:330AMPlasmaOkno faults
1011:46:50:640AMPlasmaOkno faults
1112:00:09:010PMPlasmaOkno faults
1212:20:39:250PMPlasmaOkno faults
1312:35:17:140PMPlasmaOkno faults
1412:52:54:010PMPlasmaOkPlasma shot OK.
1501:12:02:330PMPlasmaOkPlasma shot dud no faults.
1601:27:46:500PMPlasmaOkPlasma pulse no faults fizzle.
1701:44:38:010PMPlasmaOkplasma shot no faults.
1802:02:51:390PMPlasmaOkPlasma shot no faults
1902:18:04:920PMPlasmaOkPlasma pulse no faults fizzle.
2002:34:34:660PMPlasmaOkPlasma shot no faults.
2102:53:43:300PMPlasmaOkPlasma shot no faults.
2203:08:58:160PMPlasmaOkno faults
2303:23:44:480PMPlasmaOkno faults