Alcator C-Mod Run 930701 Information

Miniproposals

Miniproposal:

Date Filed:

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Session Leader: Steve Golovato (shots 1-32)

Operators
Session leader(s):	Steve Golovato
Physics operator(s):	Earl Marmar
Engineering operator(s):	Joe Daigle

Engineering Operator Run Comment
plasma run

Session Leader Plans

Physics Operators Plans

Session Leader Summaries

Entered: Jul 7 2004 03:49:08:040PM

Author: To Be Determined

Run Summary - July 1, 1993 run (930701)

Session leader - Golovato
Assistant leader - Marmar
Engineering leader - Daigle

The goals of the run were:

(1) Run in helium (pre-fill and puff) and make "good" plasmas.
(2) Move plasma out to be closer to antenna, Use helium if running well,
otherwise revert to hydrogen.
(3) Elongate and move plasma down to better match antenna shape.
(4) If everything is working, move the antenna in and observe antenna
probe and network analyzer outputs.

The run turned out to involve mainly breakdown studies, first in helium and
then in hydrogen. We did accomplish goal (3) and had a record current shot
(#24) of 430ka (non-thermal but not a complete runaway shot). By the end
of the run, we seemed to have found good running conditions, for shots 31
and 32. Helium ECDC for 1.75 hours preceeded the run. The first 13 shots
were in helium, the rest in hydrogen. The shot statsitics were:

Breakdown but no current buildup (fizzles)- 14 (12 in helium)
No breakdown (duds) - 2 (1 hardware, 1 too low gas)
Plasmas - 16 (all in hydrogen)

HELIUM OPERATION - We started with the hybrid setup for shot 930630019,
which included the new EF3 programming to improve its turnon consistency.
The fill gas was at 4.e-5 gauge, which is equivalent to 1.e-4 in hydrogen or
2.e-4 in nitrogen. The first few shots were spent adjusting EF4 to get
the right Bz at breakdown. We always got a flash but no buildup. EF3
was crossing -300a at 3ms (this is Wolfe's criteria for EF3) for the same
settings at which it crossed at 2ms the previous day. By shot 5 Bz looked
good. We did a gas scan from 4.e-5 to 1.e-5, where we lost the flash.
The breakdowns were late, around 7-8ms compared to 3-4ms the previous day,
but helium broke down readily and the magnetic configuration at breakdown
appeared correct for current buildup. EF3 was solid at -300a at 3ms.
The main observable difference compared to hydrogen was in the radiated power.
Typically the radiated power was 2-3 times higher than at the same time in a
good hydrogen shot or even a hydrogen fizzle. Hydrogen fizzles are usually
caused by too much gas or bad magnetics, neither of which appeared to be the
case for these helium shots. We never even achieved the "proto-plasma" state
in helium, only getting about 20ka. Several directions could be pursued to
get current buildup in helium:

(1) Use higher voltage breakdown, such as was used for the 930625 run
where Vloop was a few volts higher at breakdown than the 930630 run.
(2) Change the commutation resistors to get more Vloop. This will
likely necessitate adjustments of timing to get the null right.
(3) Try to get breakdown earlier, more like on 930630 and later this run
in hydrogen.

HYDROGEN OPERATION - We switched to hydrogen, both to make sure we could make
plasma with this configuration and to accomplish some of the other run goals.
The first hydrogen shot was good (#14). Thereafter, we had many disruptive
shots, typically with low current and high Zeff. Goal (2) was discarded
since the plasmas were already roughly full size radially (a=20cm).
Shots continued to be dirty with low current mixed, in with some non-thermal
shots (not full runaway shots) with record currents (430ka and 400ka).
Conditions were not very reproducible. Things improved on the last four
shots by moving the entire EF3 voltage programming 1ms earlier and adjusting
EF4 up a 25a. Now EF3 crossed -300a at <2ms and breakdowns occured around
3-4ms. However EF3 was no longer consistant, it was very early on shot 30,
which fizzled. During the series of hydrogen shots, the plasma was moved
down 2cm over the span of 125-200ms by programming zcur to move down 3cm.
It stayed at -2cm until OH2 runs out at about 260ms. On the last shot, the
elongation of 1.4 at 200ms was prolonged to 260ms by keeping EF1 current up
longer. This produced a plasma well-fitted to the antenna shape from about
190-260ms, as evidenced by roughly equal signals on the top, middle, and
bottom limiter probes, achieving goal (3) as time ran out.

In the end, it would have been nice to try helium with an earlier breakdown
time, as was achieved in hydrogen at the end of the run. It might work.
The other key may be the higher radiated power in helium, we may need more
power early to burn through. It is not clear whether the many high Zeff,
low current shots were related to the helium discharge cleaning and helium
operation, or the late breakdown. Some shots got stuck at about 20ka for a
while before taking off, looking similar to the helium shots (see shots 16
and 27). I think we could achieve helium operation with another day of trying.
Matching the plasma to the antenna shape seems straightforward. We also pushed
the density up with gas puffing, getting above 6.e19 during the matched phase
(190-260ms) on shot 32. The higher edge density during the "shark fin" on
shot 32 is also advantageous for coupling, though Zeff also goes up during the
shark fin.

There were no engineering problems. One shot was lost because OH1 did not
commutate, but no problem was found and the subsequent shots worked fine.
It is advantageous to run the LN2 pump at 34 Hz to avoid cryo holding
up the shot cycle. No leaks were opened with this rate of cooling.

Physics Operator Summaries

Session Leader Comments

Jul 1 1993 09:09:22:430AM Earl Marmar Today's run: RF coupling studies in helium.

Specific goals:

1) Run in helium and make "good" plasmas.

2) Move plasma out to be close to antenna. Use He if running well, otherwise revert to
hydrogen.

3) Elongate and move down a little to better match the antenna shape.

4) If everything is working, move the RF antenna in a little.

Jul 1 1993 09:14:19:450AM 930701001 Earl Marmar Today's run: RF coupling studies in helium.

Starting from shot 930630019, but with Ip feedback turned off and EF4 turn-on
earlier; gas puff also tweaked and moved earlier (starts at -12 msec).

Pfill (gauge) = 4.0e-5

Result: Fizzle; Got slightly +ve vertical field at commutation. EF4 was a bit high and
EF3 was a bit late.

Jul 1 1993 09:39:16:980AM 930701002 Earl Marmar Lower fill pressure to 3.0e-5 and try again.

Result: Fizzle. Same problem with vertical field.

Jul 1 1993 09:48:32:950AM 930701003 Earl Marmar Lower fill pressure to 2.5e-5
Lowered EF4 from 725 to 702 A.

Result: Fizzle. Bz better but still slightly +ve.

Jul 1 1993 10:01:27:360AM 930701003 Earl Marmar Lowered EF4 from 702 to 653 A.

Result: Fizzle. Bz looks good.

Jul 1 1993 10:15:56:250AM 930701005 Earl Marmar Lowered fill pressure to 2.0e-5

Result: Fizzle. Bz still looks OK. Slightly more Prad at breakdown.

Jul 1 1993 10:32:17:270AM 930701006 Earl Marmar Lowered fill pressure to 1.5e-5

Result: Fizzle.

Jul 1 1993 10:49:05:200AM 930701007 Earl Marmar Lowered fill pressure to 1.2e-5

Result: Fizzle

Jul 1 1993 10:55:59:980AM 930701008 Earl Marmar Lowered fill pressure to 1.0e-5

Result: Dud

Jul 1 1993 11:10:53:770AM 930701008 Earl Marmar Lowered fill pressure to 1.0e-5

Result: Dud

Jul 1 1993 11:11:23:420AM 930701009 Earl Marmar Lowered fill pressure to 1.8e-5

Result: Fizzle

Jul 1 1993 11:37:50:160AM 930701010 Earl Marmar Fill pressure to 2.2e-5

Result: Fizzle

Jul 1 1993 11:39:33:390AM 930701011 Earl Marmar Fill pressure to 4.0e-5

Result: Fizzle

Jul 1 1993 11:58:07:840AM 930701012 Earl Marmar Fill pressure to 2.0e-5
EF3 voltage reduced from -1300 to -1200 V

Result: Fizzle

Jul 1 1993 12:09:18:960PM 930701013 Earl Marmar Fill pressure 2.0e-5
EF3 voltage reduced from -1200 to -1100 V

Result: Fizzle

Jul 1 1993 12:45:14:880PM 930701014 Earl Marmar Switching back to hydrogen fill and pulse
EF3 back to -1300V
Pulse gas program from shot 930630019
Fill pressure 4.5e-5

Result: Good shot. 350 kA. nel4=3.4e19

Jul 1 1993 01:05:56:840PM 930701015 Earl Marmar Changed Rcur to move plasma out 1 cm between 150 and 200 msec

Result: OK. quite disruptive

Jul 1 1993 01:14:04:730PM 930701016 Earl Marmar Fill pressure to 4.0e-5

Result: 170 kA, died at 180 ms.

Jul 1 1993 01:31:50:750PM 930701017 Earl Marmar Removed Rcur change.
Changed Zcur to -1.5 between 150 and 200 ms.

Result: 250 kA. Plasma did respond to Zcur change; disruption at 230 ms

Jul 1 1993 01:47:28:900PM 930701018 Earl Marmar Fill pressure = 3.7e-4 (this was also true for shot 17)
Changed Zcur to -2.5 between 125 and 200 ms.
Using gas puff from 930625025 with lower middle puff.

Result: Good shot. 280 kA. First diruption at 330 ms. Zcur responded, got about
-1.5 cm on soft X-rays.

Jul 1 1993 02:04:54:720PM 930701019 Earl Marmar Changed Zcur to -3 cm between 125 and 200 ms.
Middle gas puff a little earlier and a bit bigger.
EF3 to -1200 from -1300 V.

Result: 180 kA. Disrupt at 188.

Jul 1 1993 02:13:25:270PM 930701020 Earl Marmar Decreased initial gas puff, middle gas puff earlier.

Result: Good shot. 280 kA, first disrupt at 337 ms. nel4=4e19, Zeff=2.

Jul 1 1993 02:18:39:630PM 930701020 Earl Marmar Decreased initial gas puff, middle gas puff earlier.

Result: Good shot. 280 kA, first disrupt at 337 ms. nel4=4e19, Zeff=2.

Jul 1 1993 02:32:02:510PM 930701021 Earl Marmar Tweaks on gas puff

Result: Dud. No commutation on OH1.

Jul 1 1993 02:42:52:700PM 930701022 Earl Marmar Try again

Result: 150 kA, disrupt at 96 ms, possibly too much early gas puff.

Jul 1 1993 03:02:47:040PM 930701023 Earl Marmar Reduce first gas puff.

Result: Slightly better. 200 kA, first disrupt at 105 kA

Jul 1 1993 03:16:51:470PM 930701024 Earl Marmar Delayed EF3 by 1 msec

Result: Very disruptive. Non-thermal. Hard Xray = 25 Volts. New current record
Ip=430 kA.

Jul 1 1993 03:45:13:060PM 930701026 Earl Marmar Move EF3 earlier by 1 msec (back to where it was for shots 23 and earlier).
EF3 demand reduced to -1060 from -1200 V.

Result: Non-thermal. 400 kA, lots of hards, bright spot on limiter at end of shot,
no obvious gettering of water.

Jul 1 1993 03:58:02:170PM 930701027 Earl Marmar Increased EF3 demand to -1150 V.
Fill pressure = 4.0e-5

Result: 150 kA, disruptive

Jul 1 1993 04:05:04:000PM 930701028 Earl Marmar loaded EF3 voltage and EF4 current from 930630019

Result: fizzle. Bz possibly a little to close to 0.

Jul 1 1993 04:23:09:070PM 930701029 Earl Marmar moved EF3 voltage programming earlier by 1 msec

result: good shot. 330 kA. Disruptive after 185 ms. Z_eff ~ 1.3

Jul 1 1993 04:34:41:020PM 930701030 Earl Marmar lowered fill pressure to 3.7e-5
lowered second gas puff

Result: fizzle. EF3 came on about .5 msec earlier, breakdown was later and there
was too much Bz.

Jul 1 1993 04:55:17:100PM 930701031 Earl Marmar Raised EF4 from 725 to 750 Amps

Result: good shot. 310 kA. Sawtoothing. First disruption at 340 ms. nel4=4.8e19.
Z_eff ~ 1.2

Jul 1 1993 06:11:40:540PM 930701032 Earl Marmar Changed EF1 to maintain elongation later in the shot.

Result: decent shot. 280 kA. Sawtoothing. Disrupts at 280 ms.
kappa stayed up at ~1.4 until 250 ms.
nel4=6.7e19, with shark fin.
Z_eff ~ 1.2 before shark fin.

Physics Operator Comments

Engineering Operator Comments

Shot Time Type Status Comment

1 08:56:07:310AM Plasma Ok Plasma shot no faults.

2 09:29:26:170AM Plasma Ok Plasma shot No faults

3 09:41:11:190AM Plasma Ok Plasma shot No faults

4 09:55:35:040AM Plasma Ok Plasma shot no faults.

5 10:08:51:420AM Plasma Ok Plasma shot no faults

6 10:25:04:570AM Plasma Ok Plasma shot no faults.

7 10:40:09:180AM Plasma Ok Plasma shot no faults

8 10:53:27:930AM Plasma Ok Plasma shot no faults.

9 11:08:24:370AM Plasma Ok Plasma shot no faults.

10 11:23:22:210AM Plasma Ok plasma shot no faults

11 11:35:17:160AM Plasma Ok no faults

12 11:50:44:190AM Plasma Ok no faults

13 12:04:41:550PM Plasma Ok no faults

14 12:23:51:770PM Plasma Ok no faults

15 12:46:30:510PM Plasma Ok Plasma shot No faults.

16 01:00:34:260PM Plasma Ok no faults

17 01:17:31:640PM Plasma Ok plasma shot no faults

18 01:35:50:740PM Plasma Ok no faults

19 01:50:42:440PM Plasma Ok plasma shot no faults

20 02:03:18:870PM Plasma Ok no faults

21 02:20:04:720PM Plasma Ok no faults -- oh1 didn't comm.

22 02:34:34:160PM Plasma Ok plasma shot no faults

23 02:46:51:610PM Plasma Ok no faults

24 03:00:19:160PM Plasma Ok plasma shot 430ka No faults.

25 03:16:47:230PM Plasma Ok Plasma shot No faults.

26 03:27:31:220PM Plasma Ok plasma shot 400KA No faults.

27 03:47:50:110PM Plasma Ok no faults

28 03:59:44:100PM Plasma Ok plasma shot no faults

29 04:13:02:240PM Plasma Ok plasma shot no faults

30 04:27:38:680PM Plasma Ok Plasma shot no faults.

31 04:39:40:730PM Plasma Ok plasma shot no faults

32 04:56:56:730PM Plasma Ok plasma shot no faults

Session Leader Comments
Jul 1 1993 09:09:22:430AM		Earl Marmar	Today's run: RF coupling studies in helium. Specific goals: 1) Run in helium and make "good" plasmas. 2) Move plasma out to be close to antenna. Use He if running well, otherwise revert to hydrogen. 3) Elongate and move down a little to better match the antenna shape. 4) If everything is working, move the RF antenna in a little.
Jul 1 1993 09:14:19:450AM	930701001	Earl Marmar	Today's run: RF coupling studies in helium. Starting from shot 930630019, but with Ip feedback turned off and EF4 turn-on earlier; gas puff also tweaked and moved earlier (starts at -12 msec). Pfill (gauge) = 4.0e-5 Result: Fizzle; Got slightly +ve vertical field at commutation. EF4 was a bit high and EF3 was a bit late.
Jul 1 1993 09:39:16:980AM	930701002	Earl Marmar	Lower fill pressure to 3.0e-5 and try again. Result: Fizzle. Same problem with vertical field.
Jul 1 1993 09:48:32:950AM	930701003	Earl Marmar	Lower fill pressure to 2.5e-5 Lowered EF4 from 725 to 702 A. Result: Fizzle. Bz better but still slightly +ve.
Jul 1 1993 10:01:27:360AM	930701003	Earl Marmar	Lowered EF4 from 702 to 653 A. Result: Fizzle. Bz looks good.
Jul 1 1993 10:15:56:250AM	930701005	Earl Marmar	Lowered fill pressure to 2.0e-5 Result: Fizzle. Bz still looks OK. Slightly more Prad at breakdown.
Jul 1 1993 10:32:17:270AM	930701006	Earl Marmar	Lowered fill pressure to 1.5e-5 Result: Fizzle.
Jul 1 1993 10:49:05:200AM	930701007	Earl Marmar	Lowered fill pressure to 1.2e-5 Result: Fizzle
Jul 1 1993 10:55:59:980AM	930701008	Earl Marmar	Lowered fill pressure to 1.0e-5 Result: Dud
Jul 1 1993 11:10:53:770AM	930701008	Earl Marmar	Lowered fill pressure to 1.0e-5 Result: Dud
Jul 1 1993 11:11:23:420AM	930701009	Earl Marmar	Lowered fill pressure to 1.8e-5 Result: Fizzle
Jul 1 1993 11:37:50:160AM	930701010	Earl Marmar	Fill pressure to 2.2e-5 Result: Fizzle
Jul 1 1993 11:39:33:390AM	930701011	Earl Marmar	Fill pressure to 4.0e-5 Result: Fizzle
Jul 1 1993 11:58:07:840AM	930701012	Earl Marmar	Fill pressure to 2.0e-5 EF3 voltage reduced from -1300 to -1200 V Result: Fizzle
Jul 1 1993 12:09:18:960PM	930701013	Earl Marmar	Fill pressure 2.0e-5 EF3 voltage reduced from -1200 to -1100 V Result: Fizzle
Jul 1 1993 12:45:14:880PM	930701014	Earl Marmar	Switching back to hydrogen fill and pulse EF3 back to -1300V Pulse gas program from shot 930630019 Fill pressure 4.5e-5 Result: Good shot. 350 kA. nel4=3.4e19
Jul 1 1993 01:05:56:840PM	930701015	Earl Marmar	Changed Rcur to move plasma out 1 cm between 150 and 200 msec Result: OK. quite disruptive
Jul 1 1993 01:14:04:730PM	930701016	Earl Marmar	Fill pressure to 4.0e-5 Result: 170 kA, died at 180 ms.
Jul 1 1993 01:31:50:750PM	930701017	Earl Marmar	Removed Rcur change. Changed Zcur to -1.5 between 150 and 200 ms. Result: 250 kA. Plasma did respond to Zcur change; disruption at 230 ms
Jul 1 1993 01:47:28:900PM	930701018	Earl Marmar	Fill pressure = 3.7e-4 (this was also true for shot 17) Changed Zcur to -2.5 between 125 and 200 ms. Using gas puff from 930625025 with lower middle puff. Result: Good shot. 280 kA. First diruption at 330 ms. Zcur responded, got about -1.5 cm on soft X-rays.
Jul 1 1993 02:04:54:720PM	930701019	Earl Marmar	Changed Zcur to -3 cm between 125 and 200 ms. Middle gas puff a little earlier and a bit bigger. EF3 to -1200 from -1300 V. Result: 180 kA. Disrupt at 188.
Jul 1 1993 02:13:25:270PM	930701020	Earl Marmar	Decreased initial gas puff, middle gas puff earlier. Result: Good shot. 280 kA, first disrupt at 337 ms. nel4=4e19, Zeff=2.
Jul 1 1993 02:18:39:630PM	930701020	Earl Marmar	Decreased initial gas puff, middle gas puff earlier. Result: Good shot. 280 kA, first disrupt at 337 ms. nel4=4e19, Zeff=2.
Jul 1 1993 02:32:02:510PM	930701021	Earl Marmar	Tweaks on gas puff Result: Dud. No commutation on OH1.
Jul 1 1993 02:42:52:700PM	930701022	Earl Marmar	Try again Result: 150 kA, disrupt at 96 ms, possibly too much early gas puff.
Jul 1 1993 03:02:47:040PM	930701023	Earl Marmar	Reduce first gas puff. Result: Slightly better. 200 kA, first disrupt at 105 kA
Jul 1 1993 03:16:51:470PM	930701024	Earl Marmar	Delayed EF3 by 1 msec Result: Very disruptive. Non-thermal. Hard Xray = 25 Volts. New current record Ip=430 kA.
Jul 1 1993 03:45:13:060PM	930701026	Earl Marmar	Move EF3 earlier by 1 msec (back to where it was for shots 23 and earlier). EF3 demand reduced to -1060 from -1200 V. Result: Non-thermal. 400 kA, lots of hards, bright spot on limiter at end of shot, no obvious gettering of water.
Jul 1 1993 03:58:02:170PM	930701027	Earl Marmar	Increased EF3 demand to -1150 V. Fill pressure = 4.0e-5 Result: 150 kA, disruptive
Jul 1 1993 04:05:04:000PM	930701028	Earl Marmar	loaded EF3 voltage and EF4 current from 930630019 Result: fizzle. Bz possibly a little to close to 0.
Jul 1 1993 04:23:09:070PM	930701029	Earl Marmar	moved EF3 voltage programming earlier by 1 msec result: good shot. 330 kA. Disruptive after 185 ms. Z_eff ~ 1.3
Jul 1 1993 04:34:41:020PM	930701030	Earl Marmar	lowered fill pressure to 3.7e-5 lowered second gas puff Result: fizzle. EF3 came on about .5 msec earlier, breakdown was later and there was too much Bz.
Jul 1 1993 04:55:17:100PM	930701031	Earl Marmar	Raised EF4 from 725 to 750 Amps Result: good shot. 310 kA. Sawtoothing. First disruption at 340 ms. nel4=4.8e19. Z_eff ~ 1.2
Jul 1 1993 06:11:40:540PM	930701032	Earl Marmar	Changed EF1 to maintain elongation later in the shot. Result: decent shot. 280 kA. Sawtoothing. Disrupts at 280 ms. kappa stayed up at ~1.4 until 250 ms. nel4=6.7e19, with shark fin. Z_eff ~ 1.2 before shark fin.

Engineering Operator Comments
Shot	Time	Type	Status	Comment
1	08:56:07:310AM	Plasma	Ok	Plasma shot no faults.
2	09:29:26:170AM	Plasma	Ok	Plasma shot No faults
3	09:41:11:190AM	Plasma	Ok	Plasma shot No faults
4	09:55:35:040AM	Plasma	Ok	Plasma shot no faults.
5	10:08:51:420AM	Plasma	Ok	Plasma shot no faults
6	10:25:04:570AM	Plasma	Ok	Plasma shot no faults.
7	10:40:09:180AM	Plasma	Ok	Plasma shot no faults
8	10:53:27:930AM	Plasma	Ok	Plasma shot no faults.
9	11:08:24:370AM	Plasma	Ok	Plasma shot no faults.
10	11:23:22:210AM	Plasma	Ok	plasma shot no faults
11	11:35:17:160AM	Plasma	Ok	no faults
12	11:50:44:190AM	Plasma	Ok	no faults
13	12:04:41:550PM	Plasma	Ok	no faults
14	12:23:51:770PM	Plasma	Ok	no faults
15	12:46:30:510PM	Plasma	Ok	Plasma shot No faults.
16	01:00:34:260PM	Plasma	Ok	no faults
17	01:17:31:640PM	Plasma	Ok	plasma shot no faults
18	01:35:50:740PM	Plasma	Ok	no faults
19	01:50:42:440PM	Plasma	Ok	plasma shot no faults
20	02:03:18:870PM	Plasma	Ok	no faults
21	02:20:04:720PM	Plasma	Ok	no faults -- oh1 didn't comm.
22	02:34:34:160PM	Plasma	Ok	plasma shot no faults
23	02:46:51:610PM	Plasma	Ok	no faults
24	03:00:19:160PM	Plasma	Ok	plasma shot 430ka No faults.
25	03:16:47:230PM	Plasma	Ok	Plasma shot No faults.
26	03:27:31:220PM	Plasma	Ok	plasma shot 400KA No faults.
27	03:47:50:110PM	Plasma	Ok	no faults
28	03:59:44:100PM	Plasma	Ok	plasma shot no faults
29	04:13:02:240PM	Plasma	Ok	plasma shot no faults
30	04:27:38:680PM	Plasma	Ok	Plasma shot no faults.
31	04:39:40:730PM	Plasma	Ok	plasma shot no faults
32	04:56:56:730PM	Plasma	Ok	plasma shot no faults