Alcator C-Mod Run 980115 Information

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Miniproposals
Miniproposal:166
Date Filed: 7/19/1996
Title:Density Limits in H-Mode MP No. 166
First Author:Martin Greenwald
Session Leader:Martin Greenwald (shots 1-27)

Operators
Session leader(s):Martin Greenwald
Physics operator(s):John Goetz
Engineering operator(s):Bill Cochran

Engineering Operator Run Comment
MP#166/GOETZ

Session Leader Plans

Physics Operators Plans

Session Leader Summaries
Entered: Jul 7 2004 03:49:17:820PM
Author: To Be Determined
Run Summary for 980115
Density Limits MP 166

Session Leader: Greenwald
Phys Op: Goetz

============================

Plan:

Toroidal Field: 5.7 (to avoid ECE cutoff)
Plasma Current: 0.4-1.0 MA
Working gas species: D2
RF: needed for at least the first half of the run.

This run was aimed toward investigating the H/L and disruptive density
limits in C-Mod. The general approach will be to start with scenarios
known to achieve high densities (3-4 x 10^20) at nominal currents
(0.8-1.0 MA); then to slowly ramp down the current thereby raising the
density limit parameter, n/Ia^2.

Bt was not ramped down until late in the current ramp in order
to allow gpc profile measurements.

==============================

Results:

We had reasonable success after a rocky start. With strong gas
puffing it was possible to hold the density near 4e20 as the
current was ramped down. On some shots, the RF faulted late;
for the early shots, this was due to the outer gap growing. After
this was corrected, some coupling problems remained but the sufficient
RF power was maintained on enough shots to get useful data.

In general we found strong deterioration in H-mode confinement at the
higher densities; both global and local parameters deteriorated toward
L-mode. Still clear transitions could be seen on the edge Te and xray
measurements. H/L transitions occurred at n/nlimit = 0.75-0.8.
Temperatures and stored energy continued to fall in the subsequent
L-mode phase, which were terminated by disruptions at n/nlimit =
0.9-1.1.

On one shot, 980115024, only 1 transmitter operated and the plasma
stayed in L-mode. The density apparently ran up to 5.7e20 (!) which
is the highest gas fueled discharge we have seen. Strong marfing was
detected so the density measurement might be suspect. (The density
from the YAG was similar, but nbogus from VB indicated much lower
densities. We may be able to estimate the density from ECE cutoff,
which was only mild.)

Sc injection late in the H-mode phase showed L-mode like confinement
(24 msec).

Shots suitable for further analysis include:

980115007
008
009
012
013
015
016
017
018
019
020
021
024
025
026
027

===================================







Physics Operator Summaries
Entered: Jul 7 2004 04:36:58:787PM
Author: To Be Determined
Physics operator summary for 980115

EO: Cochran
PO: Goetz
SL: Greenwald

Run 980115 was in support of MiniProposal 166 - Density Limits

This run is aimed toward investigating the H/L and disruptive density
limits in C-Mod. The general approach will be to start with scenarios
known to achieve high densities (3-4 x 10^20) at nominal currents
(0.8-1.0 MA); then to slowly ramp down the current thereby raising the
density limit parameter, n/Ia^2 If reproducible density limit phenomena
are observed, we will try to flatten the current at the lower value
in order to improve the measurements. The H->L and the disruptive density
limits were observed. See the session leader's report and the logbook
for further information.

Things learned today:
The fiducial used today had the gains for the slow ZCUR set to high.
This led to the first two attempts at fiducials resulting in early disruptions.
If a fiducial from pre-1998 is to be used, make sure the slow ZCUR gains have
been reduced to 0.7. The name of segment 4 has been changed to "1998 fiducial
980115003". There was one fizzle today - the urge to do something about it
was not resisted and a change of -.0003T in the Br offset cured the problem -
existent or non. Current rises were robust and breakdowns consistent. A
second gas valve was used to do heavy puffing. Thirty pounds of deuterium
were in the J-Bottom plenum and a puff from 0.5 to 1.5sec was used to raise
the density in conjuction with drawing a high density on NL04, i.e., 2.4e20.
Greater than 85Torr-l of deuterium was puffed on some shots. Very high
pressures were measured in the divertor, <170mTorr, and at the midplane,
<2mTorr. Current ramps were accomplished with ease - no problems. Most ramps
were <= 0.6MA/0.8sec.

Engineering, computing, and diagnostics today:
RF CAMAC had troubles today. These were traced to a cable that was
added last night. This cable was acting like an antenna and bringing noise
into the decoder. A disk on JUKBOX died or was seriously ill. This led to
logbook and BigBoard troubles that access this disk. Two hours were lost due
to these troubles. The heavy gas puffing today led to gate-valve closures
after almost all shots. In fact the set point on the TCI was exceeded during
shots and the set point was doubled.

Scorecard: 27 shots = 26 plasmas + 1 fizzles + 0 dud + 0 eng. duds + 0 test

Shot summary for Run 980115:

coldstart hybrid - all matrices respond
Load from 980107005 and turn off segment 2 and turn on segment 4
to get a fiducial

Shot change result
____ _____ ______
1 see above plasma - disr. @ .56

2 see above plasma - disr @ .52 - growing vertical
instability

3 draw P and D gains on wire 2 to fiducial - runs o.k. - no oscillation
1.0 @ 0.1sec and 0.7 @ .25sec

4 turn off seg 4; turn on seg 2 plasma - Bt=5.8T - RF CAMAC troubles
draw TF to -160kA (5.7T)

5 55min wait for RF fix; plasma - Bt=5.7T - RF CAMAC o.k.
TF to -157kA

6 100Vx22ms on PG1 plasma

7 Ip ramp [0.7,1.0]->[1.5,0.6] plasma - no disruption! - 1 EDA
Bt ramp down @ 1.5; extend
waveforms and gain to 1.5; PG5
triangle puff [.5,75]->[1,0]

8 PG5=[.5,75]->[1.5,40] plasma - 1 EDA - shrinking elongation

9 extend CLEARIN waveform to 1.5; plasma - growing o.gap after 1.0sec
IP=[0.7,1.0]->[1.5,0.5]

10 RCUR=[1.0,.666]->[1.5,.668]; plasma - H->L transition; o.gap better
NL04=1.5e20

11 PG5=[0.5,90]->[1.5,50] plasma - H->L transition

12 IP=[0.7,1.0]->[1.5,0.4]; plasma - 1 EDA - o.gap increasing still
RCUR=[0.8,.666]->[1.5,.67]

13 IP=[0.7,1.0]->[1.5,0.4]; plasma - 1 EDA - o.gap increases after
RCUR=[0.8,.666]->[1.5,.672] 1.2sec

14 RCUR=[0.8,.666]->[1.5,.677]; fizzle - Br a tad too positive?
NL04=2.6e20

15 BR_0 offset = .0057 plasma - disr. @ 1.2; lots of gas
>85Torr-l delivered

16 NL04=2.4e20; PG5=[0.5,75]-> plasma - disr. @ 1.44; stays in H-mode
[1.5,40] density is falling from 2.3 to 2.0e20

17 PG5=[0.5,80]->[1.5,50] plasma - disr. @ 1.37; stays in H-mode
density falling from 2.4->2.1e20

18 PG5=[0.5,80]->[1.5,80]; plasma - disr. @ 1.32; stays in H-mode
NL04=2.5e20 density only from 2.4->2.2e20

19 PG5=[0.5,90]->[1.5,90] plasma - disr. @ 1.41; RF stays on

20 IP=[0.7,-0.9]->[1.5,-0.2] plasma - disr. @ 1.15; density actually
increases

21 no changes plasma - disr. @ 1.13; density increase
H->L transition @ 0.87

22 no changes plasma - disr. @ 1.16; density increase
H->L transition @ 0.87

23 IP=[0.7,-0.8]->[1.5,-0.1] plasma - disr. @ 1.13; H->L @ 0.8
170mTorr in the divertor

24 IP=[0.7,-0.8]->[1.5,-0.4]; plasma - disr. @ 1.34; L-mode
PG5=[.5,75]->[1.3,75]

25 no changes plasma - disr. @ 1.36; H->L @ 0.86

26 PG5=[.5,65]->[1.3,65]; plasma - disr. @ 1.41; H->L @ 0.93
NL04=2.4e20

27 no changes plasma - disr. @ 1.44: H->L @ .88

Session Leader Comments
Jan 15 1998 08:34:12:110AMMartin GreenwaldRun Plan for 980115
Density Limits MP 166
Session Leader: M. Greenwald
Physics Operator: J. Goetz


Toroidal Field: 5.7 (to avoid ECE cutoff)
Plasma Current: 0.4-1.0 MA
Working gas species: D2
RF: needed for at least the first half of the run.

This run is aimed toward investigating the H/L and disruptive density
limits in C-Mod. The general approach will be to start with scenarios
known to achieve high densities (3-4 x 10^20) at nominal currents
(0.8-1.0 MA); then to slowly ramp down the current thereby raising the
density limit parameter, n/Ia^2 If reproducible density limit phenomena
are observed, we will try to flatten the current at the lower value
in order to improve the measurements.

Bt should not be ramped down until late in the current ramp in order
to allow gpc profile measurements. Fluctuation measurements should
also be made with a fast window near the H/L, disruption time.
(Reflectometery measurements might be particularly useful.)

If flattops near the limit can be obtained, we will want to
inject impurities (Sc) to measure impurity particle confinement.



Detailed plan.

Start with shot 980107005, when established, begin an Ip rampdown
starting at 0.75 sec. This ramp should take Ip to 0.5 mA at 1.5 sec.
(At this point, the shot can resume the normal end of shot rampdown
rate.

If/when density limit disruptions are seen, we can modify the Ip
waveform to lower the ramp rate near the disruption time.

Subsequent shots will scan the initial density/gas p
Jan 15 1998 09:00:08:650AM980115001Martin Greenwaldattempt at fiducial
disruption at 0.56 sec
Jan 15 1998 09:09:52:750AM980115002Martin GreenwaldSame as shot 1
Jan 15 1998 11:40:59:570AM980115003Martin GreenwaldFiducial attempt
Good shot, but RF power reads only .5 and 1. MW
camac problem

Decent H-mode
Jan 15 1998 11:40:29:380AM980115004Martin GreenwaldGood Shot
data system reads only ~1MW on RF - camac problem
probably twice that

Decent H-mode EDA
nebar reaches 3.8e20
Jan 15 1998 11:43:09:830AM980115005Martin GreenwaldAttempt to repeat 980107005
only 1.2 MW on RF (for real this time)
Decent EDA H-mode, but strong impurity accumulation
Jan 15 1998 12:04:53:160PM980115006Martin Greenwald3 H-mode periods
first from .5 to .9 sec
H ~ 1.5
moderate EDA, Pdiv ~ 30mT
Jan 15 1998 12:10:25:110PM980115007Martin GreenwaldGood shot
Current rampdown starts at .7, reaches 0.6 MA at 1.5 sec
reach 0.55 x nlimit
stored energy, tau, H all sag
Prad never exceeds 40%
Jan 15 1998 12:25:29:650PM980115008Martin GreenwaldSimilar to previous shot
a bit more gas puffing
radiation lower
Jan 15 1998 12:34:45:530PM980115009Martin GreenwaldSimilar to previous shot
RF power extended, runs now from 0.4 - 1.4 sec
2 MW
n/nlimit reaches 0.6
Jan 15 1998 12:55:19:670PM980115010Martin Greenwaldsimilar but with impurity injection at .78
drops out of H-mode briefly
Jan 15 1998 01:02:56:510PM980115011Martin Greenwaldsimilar again
still problems keeping rf coupled late
outer gap grows near end of current ramp
n/nlimit still no higher than .6
Jan 15 1998 01:09:33:570PM980115011Martin Greenwaldfast window moved late
poloidal detachment seen - shark fin
just before end of shot disruption

10 kHz osc. seen on magnetics
Jan 15 1998 01:27:25:120PM980115012Martin Greenwaldn/nlimit reaches 0.7 (0.85 using nlimit pro)
rf coupling and hmode lost immediately after
Jan 15 1998 01:32:51:610PM980115013Martin Greenwaldslightly faster rampdown
reach n/nlimit of 0.88 with nlimit pro
Jan 15 1998 01:41:01:530PM980115014Martin Greenwaldfizzle
Jan 15 1998 02:29:12:710PM980115015Martin Greenwaldreach n/nlimit of 0.8 at H/L, 0.9 in Lmode
Jan 15 1998 02:29:39:630PM980115016Martin Greenwaldreach n/nlimit 0.8 at H/L, 0.9 in Lmode
Jan 15 1998 02:30:17:920PM980115017Martin Greenwaldreach n/nlimit 0.78 at H/L, 0.92 in Lmode
Jan 15 1998 02:41:09:810PM980115018Martin Greenwaldreach n/nlimit 0.8 at H/L, 0.92 in Lmode
Jan 15 1998 03:04:05:550PM980115019Martin Greenwaldreach n/nlimit 0.8 at H/L , 1.08 in L-mode
Jan 15 1998 03:21:42:270PM980115020Martin Greenwaldlower max Ip to 0.9 MA and ramp down to 0.2
n/nlimit reaches 0.76 at H/L 1.0 in L-mode
Jan 15 1998 03:48:02:190PM980115021Martin Greenwaldn/nlimit reaches 0.78 at H/L, 1.0 at L-mode disruption
Jan 15 1998 03:46:18:280PM980115022Martin Greenwalddensity lost at end of shot - gate valve closes
Jan 15 1998 05:52:38:870PM980115024Martin Greenwald1 transmitter only, no H-mode
very high (apparent density) 5.7e20 (!)
corresponds to n/nlimit = 1.5
Jan 15 1998 05:28:38:870PM980115025Martin Greenwalddensity lost when gate valve closes early
set point adjusted after this shot

n/nlimit = 0.75 at H/L transition
Jan 15 1998 04:59:24:530PM980115026Martin Greenwaldreach n/nlimit 0.76 at H/L, 1.05 in L-mode
Jan 15 1998 05:08:20:310PM980115027Martin Greenwaldreaches n/nlimit = 0.75 at H/L and 1.1 in L-mode at disruption

Physics Operator Comments
Jan 15 1998 08:13:08:040AMJohn GoetzRun Plan for 980115
MP #166 Density Limits

Engineering setup:
ECDC in D2 for a few hours in the morning
begin as on 980107005, except TF current limit set to
183kA (approximately 6T+ headroom)
TF under hybrid control
Gas setup - fill K-side with 30 PSI of D2, hybrid enabled
fill B-top with 6 PSI of D2, hybrid enabled
fill B-side-lower with 2 PSI of Ar, hybrid enabled
fill J-bottom with 30 PSI of D2 hybrid disabled

ECE gate valve enabled; others if diagnosticians are ready.

Physics to be done:
Toroidal Field: 5.7 (to avoid ECE cutoff)
Plasma Current: 0.4-1.0 MA
Working gas species: D2
RF: needed for at least the first half of the run.

This run is aimed toward investigating the H/L and disruptive density
limits in C-Mod. The general approach will be to start with scenarios
known to achieve high densities (3-4 x 10^20) at nominal currents
(0.8-1.0 MA); then to slowly ramp down the current thereby raising the
density limit parameter, n/Ia^2 If reproducible density limit phenomena
are observed, we will try to flatten the current at the lower value
in order to improve the measurements.

Bt should not be ramped down until late in the current ramp in order
to allow gpc profile measurements. Fluctuation measurements should
also be made with a
Jan 15 1998 08:14:46:420AMJohn GoetzBeginning of 980115

Coldstart hybrid - all matrices respond
load 980107005 - turn off segment 2
turn on segment 4 to get a fiducial loaded
Jan 15 1998 09:07:49:090AM980115001John GoetzShot 001
Plasma
disrupts @ 0.56
Jan 15 1998 09:08:44:910AM980115002John GoetzShot 002
no changes

Plasma
disrupts @ 0.52
turns out the gains on the slow ZCUR (wire 2) were not reduced for this
fiducial shot so a growing vertical instability got both of these
shots
Jan 15 1998 09:25:47:240AM980115003John GoetzShot 003
draw both the D and P gains on wire 2 (slow ZCUR) to the following waveform:
gain = 1.0 @ 0.1sec
gain = 0.7 @ 0.25sec

Plasma
looks like a fiducial
OH2 - EFC oscillation is gone
rename segment 4 to "1998 fiducial (980115003)"
Jan 15 1998 10:08:26:700AM980115004John GoetzShot 004
turn off segment 4 - turn on segment 2
draw TF waveform to -160kAmps (5.7T) in segments 1 and 2

Plasma - EDA H-mode transition @ 0.52
got 5.79T
problems with RF CAMAC - hard and/or software - for this shot and shot 003
pause to enter cell and investigate
Jan 15 1998 11:40:29:840AM980115005John GoetzShot 005
TF current = -157kA in segments 1 and 2
55 minute wait to fix RF CAMAC

Plasma
got 5.70T
problem with logbook and BigBoard
Jan 15 1998 11:58:23:070AM980115006John GoetzShot 006
JUKBOX disk problem caused 57minute delay
100V x 22msec pulse of argon on PG1

Plasma - 3 EDA H-modes

Jan 15 1998 12:08:34:180PM980115007John GoetzShot 007
draw in Ip ramp: 1.0MA @ 0.7sec -> 0.6MA @ 1.5sec
begin Bt ramp down @ 1.5sec
extend waveforms and gains to handle 1.5sec pulse length
draw triangle waveform on PG5: 75V @ 0.5sec -> 0V @ 1.0sec

plasma
no disruption!!
1 long EDA (from 0.5 to 1.2sec)
Jan 15 1998 12:25:56:670PM980115008John GoetzShot 008
draw trapezoid waveform on PG5: 75V @ 0.5sec -> 40V @ 1.0sec

plasma
one long EDA - decreasing density
elongation is shrinking - missed the CLEARIN waveform during the waveform
extension of a few shots ago


Jan 15 1998 12:41:55:730PM980115009John GoetzShot 009
extend CLEARIN waveform to 1.5sec
IP = [0.7,1.0] -> [1.5,0.5]sec,MA

plasma (down to 0.5MA @ 1.5sec)
shape fixed, but outer gap is growing after 1.0sec (caused high reflected power
trip at 1.3sec)

Jan 15 1998 12:53:59:990PM980115010John GoetzShot 010
fool the gap with RCUR = [1.0,.666] -> [1.5,.668]sec, m
NL04 = 1.5e20

plasma - H->L transition in the middle of this one
outer gap drift not as bad as before; remains <= 2cm

Jan 15 1998 01:04:39:650PM980115011John GoetzShot 011
PG5 = [0.5,90] -> [1.5,50] sec,V

plasma - H->L transition in this one also
RF tripping at 1.2sec on this one
Jan 15 1998 01:19:27:540PM980115012John GoetzShot 012
IP = [0.7,1.0] -> [1.5,0.4] sec,MA
RCUR = [0.8,.666] -> [1.5,.670] sec,m - to try and help the RF with the outer gap

plasma - disrupts @ 1.46
one EDA H-mode
outer gap still increasing (plasma radius shrinking)
Jan 15 1998 01:34:59:300PM980115013John GoetzShot 013
IP = [0.7,1.0] -> [1.5,0.3] sec,MA
RCUR = [0.5,.666] -> [1.5,.672] sec,m - to try and help the RF with the outer gap

plasma - disrupts @ 1.45
one EDA H-mode
gap shrinks only after 1.2sec
Jan 15 1998 01:49:03:410PM980115014John GoetzShot 014
RCUR = [0.5,.666] -> [1.5,.677] sec,m - to try and help the RF with the outer gap
NL04 = 2.6e20 after 0.6sec

fizzle - Br a tad too positive??
Jan 15 1998 02:03:47:910PM980115015John GoetzShot 015
RCUR = [0.5,.666] -> [1.5,.677] sec,m - to try and help the RF with the outer gap
NL04 = 2.6e20 after 0.6sec
BR_0 offset = .0057

plasma - disrupts @ 1.2sec
RF trips @ 0.95
lots of gas around - > 85Torr-l delivered through K-side and J-Bottom
outer gap looks o.k.
Jan 15 1998 02:17:10:090PM980115016John GoetzShot 016
PG5 = [0.5,75] -> [1.5,40] sec,V
NL04 = 2.4e20 after 0.6sec

plasma - disrupts @ 1.44sec
stays in H-mode, but the density is falling from 2.3->2.0e20
outer gap fine
Jan 15 1998 02:29:22:670PM980115017John GoetzShot 017
PG5 = [0.5,80] -> [1.5,50] sec,V

plasma - disrupts @ 1.37sec
stays in H-mode, but the density is falling from 2.4->2.1e20
transmitter drop @ 1.1
Jan 15 1998 02:42:02:920PM980115018John GoetzShot 018
PG5 = [0.5,80] -> [1.5,80] sec,V
NL04 = 2.5e20

plasma - disrupts @ 1.32sec
stays in H-mode, but the density is better; only from 2.4->2.2e20
transmitter drop @ 1.06
Jan 15 1998 03:04:54:170PM980115019John GoetzShot 019
PG5 = [0.5,90] -> [1.5,90] sec,V

plasma - disrupts @ 1.41sec
stays in H-mode, but the density still falls from 2.4->2.2e20
RF stays on!
Jan 15 1998 03:22:12:310PM980115020John GoetzShot 020
IP = [0.7,-0.9] -> [1.5,-0.2] sec,MA

plasma - disrupts @ 1.15sec
H->L transition moves earlier in time
the density actually rises during the H-mode this time
RF trip in L-mode
Jan 15 1998 03:30:37:120PM980115021John GoetzShot 021
give the RF another try

plasma - disrupts @ 1.13sec
H->L transition @ 0.87sec
the density actually rises during the H-mode this time
RF trip in L-mode
Jan 15 1998 03:42:37:100PM980115022John GoetzShot 022
no changes

plasma - disrupts @ 1.16sec
H->L transition @ 0.88sec

Jan 15 1998 04:00:56:430PM980115023John GoetzShot 023
IP = [0.7,-0.8] -> [1.5,-0.1] sec,MA

plasma - disrupts @ 1.13sec
injection @ 0.29sec; big one, probably molybdenum
H->L transition @ 0.8sec

Jan 15 1998 04:11:05:170PM980115024John GoetzShot 024
IP = [0.7,-0.8] -> [1.5,-0.4] sec,MA
PG5 = [0.5,75] -> [1.3,75] sec,V

plasma - disrupts @ 1.34sec
injection @ 0.29sec; small one, probably molybdenum
1 transmitter; L-mode all the way
NL04 of 3.5e20!!

Jan 15 1998 04:30:20:700PM980115025John GoetzShot 025
no changes

plasma - disrupts @ 1.36sec
2 transmitters - H->L @ 0.86

Jan 15 1998 04:50:12:170PM980115026John GoetzShot 026
NL04 = 2.4e20
PG5 = [0.5,65] -> [1.3,65] sec,V

plasma - disrupts @ 1.41
H -> L transition @ 0.93



Jan 15 1998 05:14:51:650PM980115027John GoetzShot 027
no changes
inject scandium

plasma - disrupts @ 1.44
H -> L transition @ 0.88
small Sc injection @ 0.8



Engineering Operator Comments
ShotTimeTypeStatusComment
108:51:34:940AMPlasmaOkno faults
209:02:48:220AMPlasmaOk
309:17:42:510AMPlasmaOk
409:35:26:140AMPlasmaOk
611:43:07:680AMPlasmaOk
712:00:11:430PMPlasmaOk
812:12:53:420PMPlasmaOk
912:27:04:460PMPlasmaOk
1012:40:44:410PMPlasmaOkno faults plasma
1112:56:01:250PMPlasmaOk
1201:09:38:870PMPlasmaOk
1301:24:25:810PMPlasmaOk
1401:38:34:030PMPlasmaOk
1501:50:31:870PMPlasmaOk
1602:07:19:670PMPlasmaOk
1702:20:55:740PMPlasmaOk
1802:34:52:570PMPlasmaOk
1902:57:25:900PMPlasmaOk
2003:14:52:450PMPlasmaOk
2103:25:39:670PMPlasmaOk
2203:38:05:200PMPlasmaOk
2303:51:55:600PMPlasmaOk
2404:03:26:800PMPlasmaOk
2504:19:45:630PMPlasmaOk
2604:44:18:270PMPlasmaOk
2704:57:33:550PMPlasmaOk