Alcator C-Mod Run 950523 Information

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Miniproposals
Miniproposal:078
Date Filed: 2/8/1995
Title:ICRF Heating in H-mode Plasmas
First Author:Yuichi Takase
Session Leader:Steve Golovato (shots 1-28)

Operators
Session leader(s):Steve Golovato
Physics operator(s):Joseph Snipes
Engineering operator(s):Vinny Bertolino,Joe Daigle

Engineering Operator Run Comment
icrf H-Modes

Session Leader Plans

Physics Operators Plans

Session Leader Summaries
Entered: Jul 7 2004 03:49:13:757PM
Author: To Be Determined
run summary - 950523
---------------------
SL: golovato
PO: snipes
EO: bertolino/daigle

The run was successful in that we attempted all of our ideas for improving the
quality (duration and h-factor) of the h-modes. It was not successful in actually
improving the quality. We began with shot 950505021, a good elm-free h-mode
shot at 1 MA, starting at nl_04=1.5e20. Once we got the d-port transmitter
to stop tripping, we had a shot much like 950505021 on shot 007. Our first idea
was to move the plasma in toward the antenna as we go into h-mode to maintain
the loading as best we could in order to keep the power as high as possible.
For shot 009, the outer gap was reduced from 2 to 1cm and the e-port h-mode loading
was increased from 1 to 1.7 ohms. This shot had multiple elm-free h-modes and
the highest stored energy of the day, 120kJ. Reducing the outer gap allowed
us to keep the power approximately constant through the L, elm-free and elmy
periods. However we did not extend the h-mode or increase the h-factor.
Reducing the outer gap to 5mm increased the e-port loading to 2.1 ohms but we
now got only one elm-free h-mode per shot rather than 3-4 with a 1cm gap
(see shot 012). Shot 14 had a constant 2cm gap and had 3 h-modes, much like
the shots where we reduced the outer gap.

For shots 16-22, we tried to increase triangularity and elongation as a means
of improving the h-modes. We had problems with early disruptions with these
configurations but shots 017 and 023 had 3 elm-free periods. D-port interupted
at the elm-free h-modes and we would then go back to l-mode. The rf would
recover and another elm-free period ensued. These elm-free h-modes were shorter,
25ish rather than 60ish ms, and started later in the rf pulse, 890 rather than
780 ms, when compared to the h-modes like shot 009. However, if we could have
avoided the interupts, they may have run longer.

For shots 27 and 28, we tried our last idea, reducing the inner gap to keep
the plasma in L-mode for the beginning of the rf pulse. Then the inner gap
was increased to get an h-mode transition in the preheated plasma. This
technique is used in some tokamaks to get better h-factors. We were able to
delay the h-mode until we increased the inner gap, but it wasn't clear that
we improved the h-mode. Unfortunately, on the last shot (028), d-port tripped
early. It may be debatable, but my impression is that the elm activity was
reduced (smaller elms and the density continued to increase at a lower rate
than elm-free) and we may have been able to hold this longer if the rf had
cooperated.

The session leader shot-to-shot summary can be found in the logbook under the
session_leader topic. Details on technical difficulties can be found in the
physics operator summary.

The shot summary was: 26 plasmas (5 early disruptions)
1 test shot
1 cryo magnet resistance fault


Physics Operator Summaries
Entered: Jul 7 2004 04:36:54:490PM
Author: To Be Determined
MP078A ICRF H-mode Run

Engineer in Charge: Vince Bertolino
Physics Operator: Joseph Snipes
Session Leader: Steve Golovato

One and a half hours of ECDC were performed in deuterium yesterday
evening. Then, another one and a half hours were performed early this
morning and another hour of ECDC in helium was performed just before the
run. The idea is to have several hours of ECDC in deuterium to clean away
impurities, followed by ECDC in helium to remove the deuterium from the
walls.

The program is to try to get high power, high H factor, long
duration, ICRF H-modes. The plan will be to start with shot 950505021 and
vary the outer gap to try to improve ICRF coupling during the H-mode.
Next, the upper and lower triangularity will be increased by reducing RXU
and RXL to try to improve the H-modes. Then there will be a scan in
elongation up to 1.8 and down to perhaps 1.5. Finally, an attempt will be
made to preheat an L-mode plasma before going into H-mode by first running
the plasma limited against the inner wall while heating with ICRF, then
pulling the plasma away from the inner wall to try to make the pre-heated
plasma go into H-mode while continuing ICRF heating.

We got off to a slow start due to some problems with the RF. We
also lost shot 3 to a cryo magnet resistance fault and shot 5 due to a
problem with the interferometer. The first part of the run was devoted to
scanning the outer gap. We found that even with 0.5 cm outer gap, the
H-modes were alright and that no clear improvement was made with larger
gaps. Since more power can be coupled with a smaller gap, we then remained
with a small gap. From shot 15, we increased the upper and lower
triangularity reaching values of about 0.6 for both. But, the H-mode
quality did not improve significantly. Indeed, there were indications at
the highest triangularities that the H-mode quality got worse. We changed
the elongation slightly in this process and found that a lower elongation
was somewhat worse, but that still needs to be explored further because
there was really very little change in the elongation. It proved difficult
to increase the triangularity further due to disruptions as the plasma
became limited on the nose of the divertor. It seems that it was a mistake
to center the plasma. Our best results were with ZCUR at -1.5 cm, but that
parameter was not really scanned.

In scanning the triangularity and the inner gap, shots 16 and 24
lost tuning of the RF and had no power.

The run was reasonably successful in that we achieved a number of
H-modes with a variety of magnetic configurations, but was unsuccessful in
achieving high H factors or long duration ELM-free H-modes. The best shots
had ELM-free H-modes of about 0.06 sec duration with an H factor of 1.3
(e.g., shot 9). It seems that higher triangularity is not a sufficient
condition for improving H-mode quality and that changes in recycling
accompanying the changes in triangularity make the H-modes worse.

Shot 1: OH test shot. O.K.
2: Copied shot 950505021. Prefill at 1.8 x 10^-5 Torr. Good shot.
Only one RF transmitter.
3: Added D from B top gas valve. Cryo magnet resistance fault. No
plasma.
4: Good shot. Added pulse gas 4 to increase the density to the
requested density of nl04 = 1.5 x 10^20 m^-2. Good shot. RF
still tripped on one transmitter, but we got 2.6 MW peak and it
went into an ELMy H-mode that was then maintained from 0.78 - 1.01

sec.
5: Bad shot. OH2L fault at 0.17 sec.
6: Good shot. ELMy RF H-mode from 0.78 - 1.03 sec. RF tripped again.
7: Raised EF4 pre-programmed current to 2 kA during flattop.
Good shot. RF up to 2 MW. Several ELM-free RF H-modes from 0.78 -
1.03 sec.
8: Ramped RCUR from 0.75 sec to 0.83 sec from 0.666 m to 0.67 m, then
remained at 0.67 m until 1.02 sec. Good shot. ELM-free RF H-mode
0.77 - 0.84 sec and ELMy H-mode from 0.88 - 0.91 sec.
9: Hard X rays at start up. Otherwise a good shot. RF up to almost
2.5 MW. ELM-free RF H-modes 0.78 - 0.84, 0.87-0.89, 0.93 - 0.95 sec.
10: Raised prefill to 2.1 x 10^-5 Torr. Moved RCUR out by another 2
mm from 0.83 to 1.02 sec. Good shot. ELM-free H-mode from 0.78 -
0.83 sec, then ELMy until 0.88 sec.
11: Bad shot. Moly very high at 0.1 sec. Got 2 MW of RF, but no
H-mode.
12: Good shot. ELM-free H-mode from 0.78 - 0.83 sec, then ELMy until
1.02 sec.
13: Moved RCUR to 0.664 from 0.83 to 1.02 sec. OH1 fault. Disrupted
at 0.31 sec. nl04 lost fringes at 0.3 sec causing the gas to go on
hard.
14: Try again. Good shot. ELM-free and ELMy RF H-modes from 0.78 - 1
sec.
15: Moved RXL in by 1 cm and RXU in by 2 cm to try to increase the
triangularity.
16: Moved RXL in by another 1 cm and RXU in by another 2 cm. Good
shot. NO RF. No H-mode.
17: Moved RXU in by another 2 cm, RXL out by 0.5 cm and ZXL down by
0.5 cm. Good shot. Big moly injection at 0.5 sec. Three
ELM-free RF H-modes from 0.88 - 1.02 sec.
18: Increased ZXU by 1 cm. Reduced elongation. Good shot. ELM-free RF
H-mode from 0.92 - 0.97 sec.
19: Decreased ZXU by 1 cm from 0.5 to 1.0 sec. Good shot. RF up to 2.4
MW. NO H-mode. The plasma was becoming nearly double null.
20: Increased ZCUR from -1.5 cm to 0. Increased ZXU by from 3.7 cm to
6 cm. Disrupted at 0.6 sec.
21: Moved ZCUR up by 1.5 cm to 0. ZXL down by 0.5 cm to - 3 cm. and
RXL out by 0.5 cm. Hard x rays at startup. Bad shot. Disrupted
at 0.53 sec.
22: Moved RXU out by 2 cm. Disrupted at 0.6 sec.
23: Reloaded shot 17. Good shot. 3 ELM-free RF H-modes.
24: Good shot. NO RF. No H-modes.
25: Good shot. RF H-mode from 0.8
26: Reloaded shot 9 but made steps in CLEARIN (-2cm) and RCUR (-1 cm)
to limit the plasma before H-mode at 0.9 sec. Bad shot. Disrupted
at 0.55 sec.
27: Decent shot. Some hard x rays early. Weak H-mode from 0.9 to 1.0
sec.
28: Good shot. RF tripped at the H-mode. H-mode from 0.9 - 0.96 sec.

Session Leader Comments
May 23 1995 08:48:28:170AMSteve Golovatorun 950523

goals - extend elm-free h-mode for longer times, get higher h-factors

(1) re-establish conditions of run 950505, using shot 950505021 as
the starting to start.

(2) reduce outer gap as we go into h-mode to maintain loading and
therefore power hopefully without degrading h-mode.

(3) produce more triangular configuration by moving upper x-point in.

(4) elongation scan, 1.8 to 1.5.

(5) maintain l-mode longer at high power to pre-heat before h-mode,
perhaps by holding plasma inner wall limited for some time and then
diverting during the rf pulse.

discharge cleaned in D and then He before run.

May 23 1995 09:18:12:190AM950523001Steve Golovatoshot 950523001 - test shot for oh coax connections.

May 23 1995 09:38:19:260AM950523002Steve Golovatoshot 950523002 - 1 MA, 1.5e20. rf pulse 0.75-1.sec
plasma. no h-mode. got 1MW, d-port tripped, would have had 2.5MW.

May 23 1995 09:52:44:530AM950523003Steve Golovatoshot 950523003 - adding b-top puff to get to requested density.
cryo magnet resistance fault, no plasma.

May 23 1995 10:08:58:810AM950523004Steve Golovatoshot 950523004 - plasma. d-port tripped again, like shot 002.
got elmy h-mode throughout rf pulse. 2.5MW before trip enough to get
into h-mode, 1MW later ehough to stay in.

May 23 1995 10:14:37:560AM950523005Steve Golovatoshot 950523005 - plasma. oh2l died at 170ms.

May 23 1995 10:47:10:490AM950523006Steve Golovatoshot 950523006 - plasma. same as shot 004, elmy h-mode throughout rf,
d-port trip. trips may be due to power supply overload in rf racks,
shold be fixed for next shot. we'll see.

May 23 1995 11:02:28:820AM950523007Steve Golovatoshot 950523007 - plasma. 4 elm-free periods. last after rf is off.
2MW, no trips.

May 23 1995 11:33:55:170AM950523008Steve Golovatoshot 950523008 - move plasma toward antenna as we go into h-mode.
moving 8mm from 750-830ms.

plasma. d-port tripped after 70ms. lose elm-free just after trip.

May 23 1995 11:36:06:410AM950523009Steve Golovatoshot 950523009 - plasma. no trip, 2.5MW. moving plasma keeps e-port
at 1.67 ohms, went to 1 ohm on shot 007, before we started moving
plasma, but h-mode not extended, peak voltage still 40kv, cannot raise
e-port power.

May 23 1995 11:56:35:640AM950523010Steve Golovatoshot 950523010 - moving plasma in 4mm more, to 5mm from about 9mm
from 750-830ms. got hards last shot, raising prefill.

plasma. d-port tripped after 100ms. 1st elm-free period not extended.
e-port loading stays up at 2.1 ohms. power doesn't droop during
elm-free periods.

May 23 1995 12:19:03:230PM950523011Steve Golovatoshot 950523011 - raising e-port power since loading is higher.

plasma. lots of moly earlier. odd (dirty?) plasma. no h-mode.
e-port interupts after 100ms.

May 23 1995 12:35:28:300PM950523012Steve Golovatoshot 950523012 - plasma. still have moly early, but got one
elm-free h-mode period, then went into elmy h-mode for rest of
rf pulse.

May 23 1995 12:48:51:320PM950523013Steve Golovatoshot 950523013 - 5mm gap seems worse, only get one elm-free h-mode.
try larger gap, go back to shot 007 but program gap to stay at 2cm
after rf turns on (instead of decreasing to 1.6cm) by moving rcur
in by 2mm.

plasma, early disruption.

May 23 1995 01:06:32:510PM950523014Steve Golovatoshot 950523014 - plasma. 3 h-modes. no better, no worse.

May 23 1995 01:27:31:460PM950523015Steve Golovatoshot 950523015 - go back to moving plasma out to 1cm outer gap
during rf. start to increase triangularity. moving rxu in 2cm and
rxl in 1cm.

plasma. delta_u=0.37, delta_l=0.59, R_gap=2->1cm; 4 h-modes.

May 23 1995 01:48:46:560PM950523016Steve Golovatoshot 950523016 - trying to get more triangularity.
moving rxu in another 2cm and rxl in 1cm.

plasma. delta_u=0.36, delta_l=0.64, R_gap=2->1cm; no RF (mistuned).

May 23 1995 02:01:29:770PM950523017Steve Golovatoshot 950523017 - trying to get more triangularity.
moving rxu in another 2cm, and rxl out 0.5cm and zxl down 0.5cm.

plasma. delta_u=0.57, delta_l=0.65, R_gap=2->1cm; 3 H-modes.
D-port RF trips on H-mode transitions.

May 23 1995 02:30:56:880PM950523018Steve Golovatoshot 950523018 - trying to get more elongation.
moving zxu up 1cm. (got lower elongation)

plasma. delta_u=0.46, delta_l=0.64, kappa=1.65, R_gap=2->1cm; 1 H-mode (late).
RF trips on H-mode transition.

May 23 1995 02:44:17:010PM950523019Steve Golovatoshot 950523019 - trying to get more elongation.
moving zxu down 2cm.

plasma. delta_u=0.66, delta_l=0.64, kappa=1.68, R_gap=2->1cm; no H-mode (late).

May 23 1995 02:55:41:150PM950523020Steve Golovatoshot 950523020 - zcur up to midplane, +1.5cm. zxu up by 2.3cm.

plasma, disrupted early, nose limited.

May 23 1995 03:22:18:230PM950523021Steve Golovatoshot 950523021 - move lower x-point out off of nose.

plasma, hards, early disruption.

May 23 1995 03:28:27:230PM950523022Steve Golovatoshot 950523022 - last shot had upper x-point on inner wall. move
rxu out by 2cm and try again. raise prefill.

plasma, early disruption. doesn't want to run like this.
go back to shot 017, tune to avoid interupts.

May 23 1995 03:48:16:640PM950523023Steve Golovatoshot 950523023 - return to shot 017.

plasma, like shot 017, rf still interupts at h-mode transition.

May 23 1995 03:58:45:980PM950523024Steve Golovatoshot 950523024 - repeat for fsp, laser blowoff.

plasma. rf interupting throughout.

May 23 1995 04:23:24:940PM950523025Steve Golovatoshot 950523025 - retune and try once more.

plasma, one h-mode at 1sec. got lase blowoff durig h-mode.

May 23 1995 04:31:46:790PM950523026Steve Golovatoshot 950523026 - go back to shot 009, move to inner wall between
700-750ms, keeping in l-mode. move back out to 2cm inner gap,
1.cm outer gap between 850-900ms to divert, get h-mode. good luck!

plasma, disrupted early. may be nl_04 problem again. alternately,
we're railing the ef2's, or both.

May 23 1995 04:50:22:180PM950523027Steve Golovatoshot 950523027 - try again.

plasma. got h-mode when plasma moved off inner wall, as planned.

May 23 1995 05:03:37:220PM950523028Steve Golovatoshot 950523028 - move to inner wall 50ms earlier, extend rf pulse
50ms to 1.05s.

plasma. got h-mode when plasma diverted but d-port tripped, lost
h-mode early.

Physics Operator Comments
May 23 1995 09:39:52:580AM950523002Joseph SnipesShot 2
Copied shot 950505021 with no changes. Good shot. RF with only one
transmitter. No H-mode.

May 23 1995 09:46:03:830AM950523003Joseph SnipesShot 3
Cryo magnet resistance fault. No plasma.

May 23 1995 09:58:07:410AM950523003Joseph SnipesShot 3
Cryo magnet resistance fault. No plasma.

May 23 1995 10:10:32:620AM950523004Joseph SnipesShot 4
Added pulse gas 4 to increase the density to the requested density of nl04 =
1.5 x 10^20 m^-2. Good shot. RF still tripped on one transmitter, but we got
2.6 MW peak and it went into an ELMy H-mode that was then maintained from
0.78 - 1.01 sec.

May 23 1995 10:15:33:250AM950523005Joseph SnipesShot 5
Bad shot. OH2L fault at 0.17 sec.

May 23 1995 10:48:19:380AM950523006Joseph SnipesShot 6
Try again. TF invert time set to 1.1 sec. Good shot. ELMy RF H-mode from 0.78
- 1.03 sec.

May 23 1995 10:58:40:350AM950523007Joseph SnipesShot 7
Raised EF4 pre-programmed current to 2 kA during flattop. Good shot. RF up
to 2 MW. Several ELM-free RF H-modes from 0.78 - 1.03 sec.

May 23 1995 11:24:33:900AM950523008Joseph SnipesShot 8
Ramped RCUR from 0.75 sec to 0.83 sec from 0.666 m to 0.67 m, then remained
at 0.67 m until 1.02 sec. Good shot. ELM-free RF H-mode 0.77 - 0.84 sec and
ELMy H-mode from 0.88 - 0.91 sec.

May 23 1995 11:37:19:320AM950523009Joseph SnipesShot 9
Hard X rays at start up. Otherwise a good shot. RF up to almost 2.5 MW.
ELM-free RF H-modes 0.78 - 0.84, 0.87-0.89, 0.93 - 0.95 sec.

May 23 1995 12:00:57:860PM950523010Joseph SnipesShot 10
Raised prefill to 2.1 x 10^-5 Torr. Moved RCUR out by another 2 mm from
0.83 to 1.02 sec. Good shot. ELM-free H-mode from 0.78 - 0.83 sec, then ELMy
until 0.88 sec.

May 23 1995 12:13:27:030PM950523011Joseph SnipesShot 11
One more time. Bad shot. Moly very high at 0.1 sec. Got 2 MW of RF, but no
H-mode.

May 23 1995 12:37:43:230PM950523012Joseph SnipesShot 12
Raised early gas before 0.1 sec to try to smooth out the jump in requested
density at the segment switch. Good shot. ELM-free H-mode from 0.78 - 0.83
sec, then ELMy until 1.02 sec.

May 23 1995 12:54:38:910PM950523013Joseph SnipesShot 13
Moved RCUR to 0.664 from 0.83 to 1.02 sec. OH1 fault. Disrupted at 0.31 sec.
nl04 lost fringes at 0.3 sec causing the gas to go on hard.

May 23 1995 01:10:31:370PM950523014Joseph SnipesShot 14
Try again. Good shot. ELM-free and ELMy RF H-modes from 0.78 - 1 sec.

May 23 1995 01:26:36:910PM950523015Joseph SnipesShot 15
Moved RXL in by 1 cm and RXU in by 2 cm to try to increase the triangularity.
Good shot. ELM-free and ELMy RF H-modes from 0.79 - 1.01 sec.

May 23 1995 01:45:25:610PM950523016Joseph SnipesShot 16
Moved RXL in by another 1 cm and RXU in by another 2 cm. Good shot. NO RF.
No H-mode.

May 23 1995 01:53:51:730PM950523017Joseph SnipesShot 17
Moved RXU in by another 2 cm, RXL out by 0.5 cm and ZXL down by 0.5 cm. Good
shot. Big moly injection at 0.5 sec. Three ELM-free RF H-modes from 0.88 -
1.02 sec.

May 23 1995 02:25:23:230PM950523018Joseph SnipesShot 18
Increased ZXU by 1 cm from 0.5 to 1.0 sec. This reduced the elongation.
Good shot. ELM-free RF H-mode from 0.92 - 0.97 sec.

May 23 1995 02:45:48:280PM950523019Joseph SnipesShot 19
Decreased ZXU by 2 cm from 0.5 to 1.0 sec. Good shot. RF up to 2.4 MW. NO
H-mode. The plasma was becoming nearly double null.

May 23 1995 02:58:42:940PM950523020Joseph SnipesShot 20
Increased ZCUR from -1.5 cm to 0. Increased ZXU by from 3.7 cm to 6 cm.
Disrupted at 0.6 sec.

May 23 1995 03:24:21:510PM950523021Joseph SnipesShot 21
Moved ZCUR up by 1.5 cm to 0. ZXL down by 0.5 cm to - 3 cm. and RXL out by
0.5 cm. Hard x rays at startup. Bad shot. Disrupted at 0.53 sec.

May 23 1995 03:44:49:310PM950523022Joseph SnipesShot 22
Moved RXU out by 2 cm. Bad shot. Disrupted at 0.6 sec.

May 23 1995 04:24:44:690PM950523023Joseph SnipesShot 23
Reloaded shot 17. Good shot. 3 ELM-free RF H-modes from 0.9 - 1.03 sec.

May 23 1995 04:25:45:280PM950523024Joseph SnipesShot 24
Good shot. NO RF. NO H-mode.

May 23 1995 04:42:00:660PM950523025Joseph SnipesShot 25
Good shot. RF H-mode from 0.98 - 1.02 sec.

May 23 1995 04:53:17:520PM950523026Joseph SnipesShot 26
Bad shot. Disrupted at 0.55 sec.

May 23 1995 04:57:49:280PM950523027Joseph SnipesShot 27
Decent shot. Some hard x rays early. Weak H-mode from 0.9 to 1.0 sec.

May 23 1995 05:27:31:890PM950523027Joseph SnipesShot 26
Reloaded shot 9. Changed CLEARIN and RCUR to put in steps from 0.7 to 0.9 sec
moving CLEARIN in by 2 cm and RCUR in by 1 cm to limit the plasma during RF
to preheat the H-mode that may come after the plasma returns to diverted.

May 23 1995 06:26:19:250PM950523028Joseph SnipesShot 28
Good shot. RF tripped at the H-mode. H-mode from 0.9 - 0.96 sec.

Engineering Operator Comments
ShotTimeTypeStatusComment
109:14:49:930AMTestOkoh coax test
209:25:53:800AMPlasmaOk
309:41:08:120AMPlasmaBadmag resist fault in check
409:55:15:710AMPlasmaOkcomm faults after disruption
510:09:51:310AMPlasmaBadoh2l comm fault early
610:28:46:170AMPlasmaOk
710:50:46:130AMPlasmaOk
811:07:37:080AMPlasmaOk
911:20:48:860AMPlasmaOk
1011:42:02:560AMPlasmaOk
1112:00:15:630PMPlasmaOkcomm fault after disruption
1212:15:37:630PMPlasmaOk
1312:37:50:710PMPlasmaBadoh1 ioc/shoot through
1412:55:12:160PMPlasmaOk
1501:12:29:810PMPlasmaOk
1601:27:25:610PMPlasmaOk
1701:45:36:010PMPlasmaOk
1802:09:24:820PMPlasmaOk
1902:27:53:380PMPlasmaOk
2002:46:05:960PMPlasmaOk
2103:07:33:260PMPlasmaOk
2203:25:46:290PMPlasmaOk
2303:38:05:620PMPlasmaOk
2403:53:54:940PMPlasmaOk
2504:07:04:420PMPlasmaOk
2604:25:04:910PMPlasmaOk
2704:38:32:840PMPlasmaOkComm Fault OH2L went first.
2804:54:14:790PMPlasmaOk