Alcator C-Mod Run 930617 Information

Miniproposals

Miniproposal:

Date Filed:

Title:

First Author:

Session Leader: Yuichi Takase (shots 1-14)

Operators
Session leader(s):	Yuichi Takase
Physics operator(s):	Steve Horne
Engineering operator(s):	Frank Silva

Engineering Operator Run Comment
Improved plasma control

Session Leader Plans

Physics Operators Plans

Session Leader Summaries

Entered: Jul 7 2004 03:49:07:913PM

Author: To Be Determined

Summary of run 930617.

The goals for this run:

1) Shift the plasma down by 1cm to match the antenna/limiter.
(The antenna/limiter are centered approx. 1cm below the nominal midplane.)
The limiter probes, magnetics, and soft x-ray will be used to verify
vertical position control.
2) Continue with yesterday's work on producing a diverted plasma.
Start from the plasma obtained at the end of goal 1) and start
pulling the lower null (and maybe the upper null too).

The run started with a series of operational problems:

Attempt was made to ECDC before the run, but a control logic "feature"
(when the TF control is in the REMOTE mode, PEI will not turn on in the
TEST state) prevented PEI from turning on. The PLC logic was modified
to allow ECDC in the TEST state with TF in the REMOTE mode.

Shortly after magnet cooling has started, a leak appeared (nitrogen peak
jumped up by an order of magnitude). C port side inner seal was purged
with He (it was being pumped). ECDC was run for about 15 minutes,
terminated by a periscope overtemp fault. Cooling for the F port
periscope (vacuum cleaner) was found to be turned off.

A second attempt to cool the machine resulted in another nitrogen leak.
This time we tried to locate the leak by leak checking while the leak was
still open (i.e., with cooling on). The bottom vertical ports D and G
were iced up and the heaters which are supposed to be on were found to be
unplugged. Working under the igloo while cooling is on is almost impossible
because of leaking liquid nitrogen and oxygen depletion.
Leak checking (with Ar) was inconclusive.

Further cooling of the machine resulted in a third leak (at least the
correlation of the leak with cooling is reproducible). The leak usually
seals itself, at least partially. By this time (12:40) the base pressure
was 1.8e-6 and the partial pressures were reading 6e-10 for mass 18 and
7e-10 for mass 28 on the RGA. We slowed the cooling as precaution (it is
not clear that helped).

Results of the run:

3 fizzles -- shot 001 probably because of too much gas;
shots 005 and 006 because of EF3 "front porch" problem
1 gas test -- no power supplies, test for gas puff (works fine)
4 runaway shots -- partially because of late EF3 ramp (caused by fix to
the "front porch" problem), partially low prefill;
shots 007, 008, 010, 011
5 good shots -- verified vertical position control

It is pretty clear that the gas settings (prefill and puff) must be
adjusted carefully in response to the changing wall conditions. We
started with the "recommended" fill pressure based on yesterday's run
successfully, but a change in plasma startup (unintentional change
in EF3 ramp) resulted in runaway discharges. Runaway discharges do
nasty things to the limiter (or whatever the high energy electrons hit
--- it may not always be the rf limiter!) and we know that molten Moly
getters water pretty well. We had to increase both the prefill and
gas puff substantially (we ended up with a prefill of 5.5e-5 to 6e-6)
to get good shots back. By the end of the run we got some good-looking
discharges (shots 012-014). These shots had low radiated power and Zeff
(we got Earl's Zeff to go below 1!), and according to FFIT, q* of about 5
(Ip=365kA for shots 012 and 013).

The vertical position was programmed to ramp from z=0 to z=z_prog from
t=0.1s to 0.15s, then held steady at z=z_prog, where z_prog was varied
from 0 to -3cm. After about 0.26sec, we lose the plasma downward. This
is about when we run out of OH2. According to the soft x-ray z centroid,
the plasma is a little above the midplane (z=+0.5cm) when z_prog=0cm
(shot 003) and moves down to z=-2cm when z_prog=-3cm (shot 014) and
there is about 25msec delay from the programmed waveform. z_cur from
ffit agrees with the x-ray z centroid except for shot 003. The ratio
between the bottom probe and the top probe varies from 0.02 (shot 003)
to 0.8 (shot 014).

The conclusion is that the vertical position control works. It could use
some fine tuning, however, because there is a discrepancy between what
you program in and what you really get.

We never got a chance to investigate goal 2).

Physics Operator Summaries

Session Leader Comments

Jun 17 1993 09:13:02:630AM Yuichi Takase The plan was to ECDC before the run.
This did not happen because of TORVAC-TF communication problems (we think).
During this process some He and some Ar got into the vessel by accident (Frank
was not aware what gas was in which plenum).
A leak opened up (nitrogen) around 8:45. Cooling was stopped to allow access
into the cell to look for any obvious problems (like a frosted port).

Jun 17 1993 09:48:18:530AM Yuichi Takase C port (horizontal) is now purged with He (was being pumped before).
Will ECDC before the run starts.
Currently working on the TORVAC-TF communication problem.

Jun 17 1993 10:24:31:390AM Yuichi Takase ECDC problem was a logic problem which did not allow PEI to turn on
in the TEST state if the TF control cabinet is in REMOTE mode.
The logic was changed to allow ECDC in the TEST state with TF in the
REMOTE mode.
Discharge cleaned for about 15 minutes (tripped on periscope temp.
because the vacuum cleaner was off).
Resumed cooling at 10:20.

Jun 17 1993 10:34:00:690AM Yuichi Takase Today's run objectives:

1. Reproduce 930616022, and try to lower z by 1cm to match the limiter/antenna.
(The limiter/antenna are centered 1cm below the midplane.)

2. Reproduce 930616028, and continue with yesterday's work on diverted plasma.

Jun 17 1993 11:01:27:810AM Yuichi Takase Nitrogen leak again.
Will try to identify the leak.
D and G port bottom underneath the machine are iced up.
The heaters which are supposed to be on were found unplugged.

Jun 17 1993 12:48:49:280PM Yuichi Takase At 12:40 base pressure 1.8e-6,
partial pressure on RGA 6.e-10 (18), 7.e-10 (28). 1.8e-8 (2).
Fill pressure for shot 001 set at 3.8e-5

Jun 17 1993 01:55:38:500PM 930617001 Steve Horne All commutation resistors and timing same as yesterday.
First shot = shot 22 from yesterday,930616022.
Gas: 3.8 fill, B Top.

Result: Fizzle. Probably too much gas? Next shot -- drop
fill to 3.5.

shot 2 worked. For shot 3, the following:
1) load shot 930616028
2) remove argon puff
3) remove the current programming on ef1 and ef2 which was used to make a divertor.

Jun 17 1993 01:56:03:120PM 930617002 Steve Horne All commutation resistors and timing same as yesterday.
First shot = shot 22 from yesterday,930616022.
Gas: 3.8 fill, B Top.

Result: Fizzle. Probably too much gas? Next shot -- drop
fill to 3.5.

shot 2 worked. For shot 3, the following:
1) load shot 930616028
2) remove argon puff
3) remove the current programming on ef1 and ef2 which was used to make a divertor.

Jun 17 1993 02:04:01:740PM 930617003 Steve Horne
For shot 3, the following:
1) load shot 930616028
2) remove argon puff
3) remove the current programming on ef1 and ef2 which was used to make a divertor.

Result:
It worked. For next shot, program z_cur to go
from 0 to -.01 over times .1 to .15

Jun 17 1993 02:23:30:310PM 930617004 Steve Horne For this shot, program z_cur to go
from 0 to -.01 over times .1 to .15

Result -- xray centroid at about -.003 this shot, compared to +.005 last
shot. For next shot, reduce P gain on ef1 drawn currents, to allow
z control to be more effective.

Jun 17 1993 09:28:08:840PM 930617006 Yuichi Takase Shots 005 and 006 fizzled because of EF3 front porch.
Set EF3 bias to +100V before t=0 for shot 007.

Jun 17 1993 09:30:33:220PM 930617008 Yuichi Takase Shots 007 and 008 were runaway shots.
Fill pressure was 3.5e-5 for shot 007, 3.8e-5 for shot 008.

Jun 17 1993 03:57:41:790PM 930617009 Steve Horne For this shot, raise gas to 3.8e-5
Result: Still lots of hard x-rays.
For next shot, a gas test -- no power supplies, just gas pulse
to test the valve.

Jun 17 1993 04:03:13:930PM 930617009 Steve Horne For this shot,(9) a gas test -- no power supplies, just gas pulse
to test the valve.
Result: seems ok.
For next shot, gas at 4.5e-5

Jun 17 1993 04:12:51:860PM 930617010 Steve Horne For this shot,(10) gas at 4.5e-5
Result:Better, but still lots of x-rays. For shot 11, raise gas at 30 msec
from 50 to 80 volts.

Jun 17 1993 04:54:39:470PM 930617012 Steve Horne For this shot (12), raise fill pressure from 4.5e-5 to 6e-5 and pray.
That worked. Many enthusiastic sounds from the peanut gallery.
Low Z eff, high current, "giant sawteeth", etc.
For next shot (13), drop gas to 5.5e-5

Jun 17 1993 09:34:51:660PM 930617012 Yuichi Takase B_z ramp was delayed for previous runaway shots (007, 008, 010, 011)
because of the higher positive bias for EF3.
EF3 ramp was moved 1msec earlier for shot 012.

Jun 17 1993 05:00:35:350PM 930617013 Steve Horne For this shot (13), drop gas to 5.5e-5
Also for thios shot, drew plasm z position at - 2 cm.
We got a nicely controlled 1 cm motion.
For next shot, ask for -3 cm.

Jun 17 1993 05:34:48:750PM 930617014 Steve Horne For this shot, ask for -3 cm.
Got around -2 cm.
The limiter probes were balanced.
This was last shot.

Jun 17 1993 05:38:28:200PM 930617014 Steve Horne Leader: Takase
Slogger: Horne
Plan: Move the Z position down to match the
plasma to the RF limiter shape. Use the probes
on the limiter to estimate the shape -- try to
make the top and bottom probes match, approximately.

Physics Operator Comments

Engineering Operator Comments

Shot Time Type Status Comment

1 01:33:52:090PM Test Bad

2 01:34:08:620PM Test Bad

3 01:51:55:790PM Test Bad

4 02:12:02:440PM Plasma Ok 320ka plasma -- no faults

5 02:25:57:750PM Plasma Ok no flash -- no faults

6 02:44:51:660PM Plasma Ok no faults, no flash

7 03:19:15:480PM Plasma Ok no faults --350ka plasma

8 03:43:49:980PM Plasma Ok no faults -- -- plasma

9 03:55:11:260PM Test Ok testing torvac

10 04:05:22:030PM Plasma Ok plasma -- no faults

11 04:17:26:500PM Plasma Ok plasma -- no faults

12 04:35:00:360PM Plasma Ok no faults -- plasma

13 04:51:29:520PM Plasma Ok plasma -- no faults

14 05:03:02:690PM Plasma Ok plasma -- no faults

Session Leader Comments
Jun 17 1993 09:13:02:630AM		Yuichi Takase	The plan was to ECDC before the run. This did not happen because of TORVAC-TF communication problems (we think). During this process some He and some Ar got into the vessel by accident (Frank was not aware what gas was in which plenum). A leak opened up (nitrogen) around 8:45. Cooling was stopped to allow access into the cell to look for any obvious problems (like a frosted port).
Jun 17 1993 09:48:18:530AM		Yuichi Takase	C port (horizontal) is now purged with He (was being pumped before). Will ECDC before the run starts. Currently working on the TORVAC-TF communication problem.
Jun 17 1993 10:24:31:390AM		Yuichi Takase	ECDC problem was a logic problem which did not allow PEI to turn on in the TEST state if the TF control cabinet is in REMOTE mode. The logic was changed to allow ECDC in the TEST state with TF in the REMOTE mode. Discharge cleaned for about 15 minutes (tripped on periscope temp. because the vacuum cleaner was off). Resumed cooling at 10:20.
Jun 17 1993 10:34:00:690AM		Yuichi Takase	Today's run objectives: 1. Reproduce 930616022, and try to lower z by 1cm to match the limiter/antenna. (The limiter/antenna are centered 1cm below the midplane.) 2. Reproduce 930616028, and continue with yesterday's work on diverted plasma.
Jun 17 1993 11:01:27:810AM		Yuichi Takase	Nitrogen leak again. Will try to identify the leak. D and G port bottom underneath the machine are iced up. The heaters which are supposed to be on were found unplugged.
Jun 17 1993 12:48:49:280PM		Yuichi Takase	At 12:40 base pressure 1.8e-6, partial pressure on RGA 6.e-10 (18), 7.e-10 (28). 1.8e-8 (2). Fill pressure for shot 001 set at 3.8e-5
Jun 17 1993 01:55:38:500PM	930617001	Steve Horne	All commutation resistors and timing same as yesterday. First shot = shot 22 from yesterday,930616022. Gas: 3.8 fill, B Top. Result: Fizzle. Probably too much gas? Next shot -- drop fill to 3.5. shot 2 worked. For shot 3, the following: 1) load shot 930616028 2) remove argon puff 3) remove the current programming on ef1 and ef2 which was used to make a divertor.
Jun 17 1993 01:56:03:120PM	930617002	Steve Horne	All commutation resistors and timing same as yesterday. First shot = shot 22 from yesterday,930616022. Gas: 3.8 fill, B Top. Result: Fizzle. Probably too much gas? Next shot -- drop fill to 3.5. shot 2 worked. For shot 3, the following: 1) load shot 930616028 2) remove argon puff 3) remove the current programming on ef1 and ef2 which was used to make a divertor.
Jun 17 1993 02:04:01:740PM	930617003	Steve Horne	For shot 3, the following: 1) load shot 930616028 2) remove argon puff 3) remove the current programming on ef1 and ef2 which was used to make a divertor. Result: It worked. For next shot, program z_cur to go from 0 to -.01 over times .1 to .15
Jun 17 1993 02:23:30:310PM	930617004	Steve Horne	For this shot, program z_cur to go from 0 to -.01 over times .1 to .15 Result -- xray centroid at about -.003 this shot, compared to +.005 last shot. For next shot, reduce P gain on ef1 drawn currents, to allow z control to be more effective.
Jun 17 1993 09:28:08:840PM	930617006	Yuichi Takase	Shots 005 and 006 fizzled because of EF3 front porch. Set EF3 bias to +100V before t=0 for shot 007.
Jun 17 1993 09:30:33:220PM	930617008	Yuichi Takase	Shots 007 and 008 were runaway shots. Fill pressure was 3.5e-5 for shot 007, 3.8e-5 for shot 008.
Jun 17 1993 03:57:41:790PM	930617009	Steve Horne	For this shot, raise gas to 3.8e-5 Result: Still lots of hard x-rays. For next shot, a gas test -- no power supplies, just gas pulse to test the valve.
Jun 17 1993 04:03:13:930PM	930617009	Steve Horne	For this shot,(9) a gas test -- no power supplies, just gas pulse to test the valve. Result: seems ok. For next shot, gas at 4.5e-5
Jun 17 1993 04:12:51:860PM	930617010	Steve Horne	For this shot,(10) gas at 4.5e-5 Result:Better, but still lots of x-rays. For shot 11, raise gas at 30 msec from 50 to 80 volts.
Jun 17 1993 04:54:39:470PM	930617012	Steve Horne	For this shot (12), raise fill pressure from 4.5e-5 to 6e-5 and pray. That worked. Many enthusiastic sounds from the peanut gallery. Low Z eff, high current, "giant sawteeth", etc. For next shot (13), drop gas to 5.5e-5
Jun 17 1993 09:34:51:660PM	930617012	Yuichi Takase	B_z ramp was delayed for previous runaway shots (007, 008, 010, 011) because of the higher positive bias for EF3. EF3 ramp was moved 1msec earlier for shot 012.
Jun 17 1993 05:00:35:350PM	930617013	Steve Horne	For this shot (13), drop gas to 5.5e-5 Also for thios shot, drew plasm z position at - 2 cm. We got a nicely controlled 1 cm motion. For next shot, ask for -3 cm.
Jun 17 1993 05:34:48:750PM	930617014	Steve Horne	For this shot, ask for -3 cm. Got around -2 cm. The limiter probes were balanced. This was last shot.
Jun 17 1993 05:38:28:200PM	930617014	Steve Horne	Leader: Takase Slogger: Horne Plan: Move the Z position down to match the plasma to the RF limiter shape. Use the probes on the limiter to estimate the shape -- try to make the top and bottom probes match, approximately.

Engineering Operator Comments
Shot	Time	Type	Status	Comment
1	01:33:52:090PM	Test	Bad
2	01:34:08:620PM	Test	Bad
3	01:51:55:790PM	Test	Bad
4	02:12:02:440PM	Plasma	Ok	320ka plasma -- no faults
5	02:25:57:750PM	Plasma	Ok	no flash -- no faults
6	02:44:51:660PM	Plasma	Ok	no faults, no flash
7	03:19:15:480PM	Plasma	Ok	no faults --350ka plasma
8	03:43:49:980PM	Plasma	Ok	no faults -- -- plasma
9	03:55:11:260PM	Test	Ok	testing torvac
10	04:05:22:030PM	Plasma	Ok	plasma -- no faults
11	04:17:26:500PM	Plasma	Ok	plasma -- no faults
12	04:35:00:360PM	Plasma	Ok	no faults -- plasma
13	04:51:29:520PM	Plasma	Ok	plasma -- no faults
14	05:03:02:690PM	Plasma	Ok	plasma -- no faults