Alcator C-Mod Run 1000526 Information

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Miniproposals
Miniproposal:264
Date Filed: 4/3/2000
Title:Test of neutral point stability concept in Alcator C-Mod
First Author:Robert Granetz
Session Leader:Robert Granetz (shots 1-24)

Operators
Session leader(s):Robert Granetz
Physics operator(s):Jim Irby
Engineering operator(s):Bill Cochran,Gary Dekow

Engineering Operator Run Comment
MP 264 Neutral Point Vertical Stability.Nakamura,Granetz/Irby/Cochran/De

Session Leader Plans

Physics Operators Plans

Session Leader Summaries
Entered: Jul 7 2004 03:49:23:960PM
Author: To Be Determined
Run summary for Friday, 26 May 2000

MP 264 -- Test of neutral point stability concept in Alcator C-Mod

Session leaders: R. Granetz and Y. Nakamura
Physics operator: J. Irby
Engineering: G. Dekow

We ran a series of standard plasmas at a range of different heights
(keeping the elongation nearly constant by moving the x-point along with
the center), and disrupting them using double-barrel lithium pellet
injection. For plasmas with Z < +3 cm (measured with the core x-ray
arrays), the thermal quench led to a prompt loss of vertical stability,
with the plasma moving downwards. For plasmas with Z > +3.5 cm, the
thermal quench was followed by a prompt upward movement. But the last
three shots of the day (22, 23, 24) had Zcentroid set for +3.0, +3.0, and
+3.5 cm respectively, and showed clear signs of enhanced vertical
stability. For example, after the thermal quench on shot 22, the plasma
hung around for 8-9 ms before finally heading downward. In principle, this
is long enough for the power supplies to begin to have some useful
response, if they had been so programmed. The last shot of the day (shot
24) exhibited vertical stability for more than 20 ms after the pellet
injection, but we need to confirm that the pellets did indeed cause a full
thermal quench, not just a minor disruption.

Physics Operator Summaries
Entered: Jul 7 2004 04:37:11:037PM
Author: To Be Determined
Engineering Setup for 1000526

MP264 Neutral Point Vertical Stability

EO Cochran/Dekow
SL Nakamura/Granetz
PO Irby

Engineering setup:

Overnight ECDC stopping at 7:00am.

Power system setup as on 1000525001

Gas setup - fill B-top 6 psi of D2 Hybrid enabled
fill B-side lower 1 psi of Ar Hybrid enabled
leave B-side upper 2 psi of Kr Hybrid DISABLED
fill C-side 30 psi of D2 Hybrid enabled
leave J-bottom as is Hybrid DISABLED


The following gate valves should be enabled:

VUV
ECE

No RF is required for this run, but tests late in shot will be okay.


Results:

We got off to a good start in that the plasma ran very well for the
first shot. So there seemed to be no long lasting effect from
the disruption from yesterday or the broken flux loop at h-hor.
Following a fizzle on shot 2 we had 3 good plasmas as we tried to
get the pellet injector going, Kr gas levels set, and the plasma moved up
to the midplane. On shot 7 the pellet injector worked and disrupted
the plasma. On shots 8 and 9 we had duds. Tweak's to the fields may
have helped to get us back to a fizzle on shot 10. Finally on shot 11
we again got a plasma. However, we had probably pushed the density up
too much too early, and we lost the plasma before the pellet. We then
toggled between plasmas and fizzles until shot 17 when the plasma
finally lasted long enough to be killed by a pellet. We reduced the
density and Kr puff steadily to reach this point. We also raised ZCUR
during this time and managed to move the plasma over 3 cm above the
midplane. By shot 19 we had managed to get the plasma over 4 cm
above the midplane before the pellet caused a disruption. Shots
17 to 24 were good plasmas for completing MP264. All were disrupted
by the pellets.

001 Plasma
002 Fizzle
003 Plasma
004 Plasma
005 Plasma
006 Fizzle
007 Plasma -- pellet disruption
008 Dud
009 Dud
010 Fizzle -- late breakdown
011 Early disruption -- too much gas early
012 Fizzle
013 Plasma to 0.55 s
014 Fizzle
015 Plasma to 0.5 --- plasma moved up 17 mm
016 Fizzle
017 Plasma -- pellet disruption -- plasma 3 cm above midplane
018 Plasma -- pellet disruption
019 Plasma -- pellet disruption -- goes up
020 Plasma to pellet
021 Plasma to pellet
022 Plasma to pellet --- down
023 Plasma to pellet --- down
024 Plasma to pellet --- down

Plasmas 15
Fizzles 6
Duds 2

Total 24 shot cycles

Session Leader Comments
May 25 2000 12:41:26:200PMRobert GranetzRun plan for Friday, 26 May 2000

MP 264 -- Test of neutral point stability concept in Alcator C-Mod

Session leaders: R. Granetz, Y. Nakamura
Physics operator: J. Irby
Engineering:

Ip=0.8 MA
Bt=5.4 T
nl=1.e20 m-2

Puff krypton starting at t=0.3 s
Plenum pressure = 2 psi
Valve voltage = 100 volts
Pulse duration = 30 ms (we will probably increase this)

Lithium killer pellet injection (double Li pellets) should be set for t=0.6 s.

For the first part of the run, we want to try and run plasmas over a
very large range of ZMAGX (Z-coordinate of the magnetic axis),
specifically:

ZMAGX = 0, +5, -5, +10 cm (in that order)

This may prove to be very difficult indeed. In order to avoid hitting the
corners of the outer limiter, we will have to reduce the inner gap to 8-9 mm
and increase the outer gap to >= 3 cm for the highest ZMAGX. However, we
don't want the elongation to exceed 1.65, so the x-points will have to be
programmed accordingly.

For the second part of the run, Nakamura-san and I will pick the most
promising range of ZMAGX, and we would like to have a finer scan of ZMAGX
over that smaller range (with delta_ZMAGX = 5 mm initially, and probably
even finer if we see evidence of neutral point stability.

Most of the run will be ohmic. We may want some RF near the end of the
run IF things go incredibly well, but I don't expect that.
May 26 2000 09:43:55:873AM1000526001Robert GranetzShot 01 -- Plasma! Good shot. No pellet injection yet. No krypton.
May 26 2000 09:44:12:467AM1000526002Robert GranetzShot 02 -- Fizzle.
May 26 2000 10:00:24:513AM1000526003Robert GranetzShot 03 -- Plasma. Good shot. No pellet injected. No krypton.
Zmagx=-6.6 mm.

Next shot: turn on krypton, fire killer Li pellet at t=0.6 s.,
raise ZCUR and ZXL by 6-7 mm. Also program the
density to go very negative at t=0.6 s in order to try
and avoid shutting the gate valves.
May 26 2000 10:18:58:467AM1000526004Robert GranetzShot 04 -- Plasma. Good shot. No pellet came out of LPI.
Zmagx=-0.8 mm, Kappa=1.65 at t=0.6 s.
nl_04=0.86e20 m-2. Krypton was not seen

Note: krypton was mistakenly programmed
for t=1.3 s, not t=0.3 s.

Next shot: move krypton puff to t=0.3 s (30 ms pulse), and
try LPI again.
May 26 2000 10:45:03:950AM1000526005Robert GranetzShot 05 -- Plasma. Another good one. LPI still didn't give us a pellet.
Zmagx=0 mm,kappa=1.65. Krypton signal was weak.

Next shot: increase krypton puff from 30 to 50 ms. Watch
LPI gate valve at CHECK state.
May 26 2000 10:55:58:013AM1000526006Robert GranetzShot 06 -- Fizzle. The LPI gate valve did not automatically open, even though
it is enabled. John Rice used manual override to force it open before
the pulse. We may have to do this for the rest of the day.
May 26 2000 11:26:51:280AM1000526007Robert GranetzShot 07 -- Plasma. VDE due to Li pellet, followed by current quench. Not good
for our purposes.

Next shot: increase krypton pulse from 50 to 75 ms, and increase
density to nl_04=1.3e20m-2, and fire two LPI barrels simultaneously.
May 26 2000 11:35:01:153AM1000526008Robert GranetzShot 08 -- Dud.
May 26 2000 12:38:31:140PM1000526011Robert GranetzShot 11 -- Plasma. Good disruption at t=0.48 s, but due to natural causes.
Zmagx=-2.7 mm, kappa=1.63.

Next shot: slow down the density rise a bit, and reduce the krypton
pulse from 75 to 65 ms.
May 26 2000 01:26:52:967PM1000526013Robert GranetzShot 13 -- Plasma. Disrupted at t=0.55 s, but it was a VDE, so we can't use it.

Next shot: raise ZCUR and ZXL by 3 cm, reduce density to nl=1.2e20 m-2.
LPI is still set to go at t=0.6 s, if the shot lasts that long. Also, reduce
krypton pulse another 5 ms (to 60 ms).
May 26 2000 01:58:20:670PM1000526015Robert GranetzShot 15 -- Plasma. Disrupted at t=0.50 s. Zcentroid was > +2.0 cm at the
time of the disruption. Current didn't begin quenching until
5 ms later. Plasma went down.

Next shot: reduce density to nl=1.0e20 m-2 and reduce krypton
pulse to 50 ms. No change to ZCUR.
May 26 2000 02:32:29:920PM1000526017Robert GranetzShot 17 -- Plasma. Two pellets fired simultaneously, hitting plasma at t=0.609 s.
Zxray=3.0 cm at that time. Pellet causes an upward VDE, which
then disrupts much later. Not good for our purposes.

Next shot: reduce krypton pulse to 35 ms.
May 26 2000 02:40:40:577PM1000526017 This shot might be good. Ip started to quench, but very slowly. Then, Current centroid starts to move upward from the position of Z=+0.035 cm at t=0.615 sec.
Equilibrium already is positioned above neutral point??
May 26 2000 02:57:48:920PM1000526018 Still downward going from Z=+2.5 cm of current centroid. Remember this shot as an important shot.
May 26 2000 02:58:52:560PM1000526018Robert GranetzShot 18 -- Plasma. Li pellets disrupted plasma at t=0.615 s. Prompt thermal quench after
pellets. Current quench delayed for 5 ms. Zxray=3.0 cm at the disruption.
Plasma went down.

Next shot: raiseZCUR by 20 mm,
raise ZXL by 20 mm,
decrease CLEARIN by 5 mm,
decrease RCUR by 2.5 mm.
May 26 2000 03:29:52:607PM1000526019Robert GranetzShot 19 -- Plasma. Zxray=+50 mm when pellet hits. Upward VDE followed much
later by current quench. Plasma switched to upper x-point just before
termination.

Next shot: repeat, but move ZXU up by 4 cm
May 26 2000 03:55:25:280PM1000526020Robert GranetzShot 20 -- Plasma. Zxray=+50 mm when the pellet hit. This one had a clear
thermal quench, with a quicker current quench.

Next shot: move plasma back to 2 cm above midplane.
(change ZCUR, ZXL, ZXU by -30 mm).
May 26 2000 04:05:00:920PM1000526021Robert GranetzShot 21 -- Plasma. Zxray=+20 mm when the pellet hit. Prompt thermal quench.
Plasma went down.

Next shot: set Z at +3 cm
(raise ZCUR, ZXL by 1 cm)
May 26 2000 04:28:16:857PM1000526022Robert GranetzShot 22 -- Plasma. Zxray=+3.0 when pellet hit. Prompt thermal quench.
This one stayed on the midplane for 8 ms before moving down!!!

Next shot: repeat, no changes. Check for robustness
May 26 2000 04:47:14:467PM1000526023Robert GranetzShot 23 -- Plasma. Zxray=+3.0 cm when pellets hit. This shot also exhibited
enhanced stability, but not as much as the previous one. Plasma
went down.

Next shot: raise ZCUR, ZXL by 4 mm.
May 26 2000 05:08:42:810PM1000526024Robert GranetzShot 24 -- Plasma. Amazingly stable!! Zxray=+3.5 cm when the pellets hit.
Thermal quench spike is smaller than normal. Plasma stays near
midplane for more than 20 ms! Eventually it went down.

End of run

Physics Operator Comments
May 26 2000 08:05:28:280AMJim IrbyLoaded From Shot 1000525001 into PCS
Load/Clean

Did cold start
All matrices respond


May 26 2000 08:55:08:530AM1000526001Jim IrbyPlasma attempt

Good plasma: 1.8 seconds


Time (ms): 0 5 10 25
----------------------------------------
Ip (kA): -0.5378 -10.9144 -21.2911 -70.6028
dIp/dt (kA/ms): -1.2728 -2.2890 -2.2912 -4.9605
pressure (mTorr): 0.0701 0.0693 0.0686 0.0663
Bz0 (mT): -2.1371 -0.0507 2.1299 18.2750
Br0 (mT): -0.8776 -0.6591 -0.6274 -2.1093

May 26 2000 09:26:20:700AM1000526002Jim IrbyRemoved Bt waggle

Load/clean

Enabled LPI gatevalve

Fizzle

Time (ms): 0 5 10 25
----------------------------------------
Ip (kA): 2.0564 -13.5086 -23.8852 -23.9079
dIp/dt (kA/ms): -1.3988 -2.5444 -1.6532 -0.0011
pressure (mTorr): 0.0717 0.0717 0.0701 0.0717
Bz0 (mT): -2.5893 -0.8996 1.4001 15.4748
Br0 (mT): -0.6517 -1.0558 -1.0211 -1.7497



May 26 2000 09:39:52:153AM1000526003Jim IrbyReduced pre-puff by 3 ms

Others suggest Bz0 may be a little too negative

Plasma: 1.81 s

Time (ms): 0 5 10 25
----------------------------------------
Ip (kA): 2.0564 -13.5086 -29.0962 -83.5963
dIp/dt (kA/ms): -1.2716 -3.0531 -2.6705 -5.5963
pressure (mTorr): 0.0634 0.0627 0.0627 0.0592
Bz0 (mT): -2.0211 0.2854 1.6257 18.1806
Br0 (mT): -0.3590 -0.5888 -0.8174 -2.2970

H_to_D low at 2 to 3%

May 26 2000 10:27:25:983AM1000526004Jim IrbyEnabled Kr for John and Bob
Pellet expected at 0.6 s

Raised ZCUR from -0.015 to -0.009 after 0.4 s
Raised ZXL 5 to 6 mm

Made nl04 go negative at 0.6 s to keep too much gas from getting
into the machine after the disruption

Nice plasma, but no pellet

OH coax looks good

Bob got ZCUR, ZXL, and kappa he wanted

Didn't see Kr --- I had programming wrong on pg2




May 26 2000 10:44:10:983AM1000526005Jim Irbypg2 now programmed for 0.30 to 0.33 s --- should see Kr

Good shot: Still no pellet

No much Kr

May 26 2000 10:57:43:670AM1000526006Jim IrbyIncreased Kr puff: 0.3 to 0.35 s

Fizzle

The LPI gatevalve had to be forced open at its PLC

Time (ms): 0 5 10 25
----------------------------------------
Ip (kA): 2.0564 -16.1027 -26.4794 -23.8852
dIp/dt (kA/ms): -1.6543 -2.7976 -1.9075 -0.1260
pressure (mTorr): 0.0641 0.0641 0.0648 0.0641
Bz0 (mT): -1.6925 0.2140 1.8623 16.2503
Br0 (mT): -0.5055 -0.4742 -0.7893 -1.4648

May 26 2000 11:22:57:200AM1000526007Jim IrbySet +0.0003 Tesla offset on BR0 to 0.0000

Good Plasma

Pellet kills it

Still small Kr signal

Time (ms): 0 5 10 25
----------------------------------------
Ip (kA): -0.5378 -13.5086 -26.4794 -78.3626
dIp/dt (kA/ms): -1.3988 -2.9248 -2.7976 -5.7235
pressure (mTorr): 0.0648 0.0648 0.0634 0.0599
Bz0 (mT): -1.6066 0.2966 0.8075 17.4968
Br0 (mT): -0.7461 -1.1337 -0.6535 -2.3579

BR0 looks a little better
May 26 2000 11:39:19:390AM1000526008Jim IrbyIncreased Kr puff another 25 ms: 0.300 to 0.375

Increased density request from 0.9 to 1.3e20

Dud

Gas okay

BZ0 more positive



Time (ms): 0 5 10 25
----------------------------------------
Ip (kA): 2.0564 -13.5086 -23.8852 -21.2911
dIp/dt (kA/ms): -1.5260 -2.2890 -0.7630 -0.2566
pressure (mTorr): 0.0648 0.0656 0.0641 0.0648
Bz0 (mT): -1.0936 0.3731 1.5217 14.5904
Br0 (mT): -1.2292 -0.7294 -0.9634 -1.8883

May 26 2000 11:54:17:357AM1000526009Jim IrbyMade early EF4 a little more negative: -1260 to -1280 Amps

Dud

Time (ms): 0 5 10 25
----------------------------------------
Ip (kA): -0.5151 -16.0800 -23.8852 -21.2911
dIp/dt (kA/ms): -1.5249 -2.2912 -0.7652 -0.3826
pressure (mTorr): 0.0648 0.0634 0.0663 0.0663
Bz0 (mT): -2.3981 -0.6464 1.9522 14.9115
Br0 (mT): -1.1526 -1.2937 -1.2470 -2.0869

Gas still okay

Wolfe suggests Br0 too negative
May 26 2000 12:15:23:483PM1000526010Jim IrbyAdded 0.001 Tesla offset to Br0

Fizzle -- late breakdown

Time (ms): 0 5 10 25
----------------------------------------
Ip (kA): -0.5378 -16.1027 -26.4794 -23.8852
dIp/dt (kA/ms): -1.5260 -2.6693 -2.1618 0.1260
pressure (mTorr): 0.0634 0.0627 0.0641 0.0599
Bz0 (mT): -1.5840 0.0121 1.8813 15.3566
Br0 (mT): -0.0841 -0.0043 0.0078 -0.8251

Tweak to Br0 worked

May 26 2000 02:51:32:437PM1000526011Jim IrbyPCL Repeat

Early Disruption: 0.487 s

Radiated power rises starting around 350 ms

Density rise probably too fast


Time (ms): 0 5 10 25
----------------------------------------
Ip (kA): 2.0564 -16.1027 -29.0735 -83.5736
dIp/dt (kA/ms): -1.7825 -3.1791 -2.6693 -5.4670
pressure (mTorr): 0.0634 0.0648 0.0641 0.0566
Bz0 (mT): -2.7204 -0.2488 1.1715 16.6034
Br0 (mT): 0.0724 -0.3026 0.2596 -0.8731

May 26 2000 12:46:48:780PM1000526012Jim IrbyDropped density rise before 0.45 s
Reduced Kr puff by 10 ms

Load/clean

Fizzle


Time (ms): 0 5 10 25
----------------------------------------
Ip (kA): 2.0564 -16.1027 -31.6677 -26.5021
dIp/dt (kA/ms): -1.5249 -3.1802 -1.6554 -0.0033
pressure (mTorr): 0.0648 0.0663 0.0663 0.0663
Bz0 (mT): -3.0769 0.3146 1.3245 14.8759
Br0 (mT): -0.2919 0.3178 -0.0314 -0.8550


May 26 2000 01:11:26:547PM1000526013Jim IrbyBr0 offset reduced to 0.3 from 1.0 mT

Plasma to 0.55 s

Marfe on inner wall working its way to the top of the machine


Time (ms): 0 5 10 25
----------------------------------------
Ip (kA): 2.0564 -16.1027 -29.0735 -73.1742
dIp/dt (kA/ms): -1.7803 -3.0520 -2.4150 -5.5952
pressure (mTorr): 0.0641 0.0634 0.0648 0.0592
Bz0 (mT): -2.3823 0.2891 1.8142 17.0042
Br0 (mT): -0.4146 -0.8361 -0.7526 -1.8549
May 26 2000 01:35:01:857PM1000526014Jim IrbyZCUR raised 30 mm
ZXL raised 30 mm
NL04 request dropped from 1.3 to 1.2e20
Kr gas puff reduced 5 ms

Fizzle


Time (ms): 0 5 10 25
----------------------------------------
Ip (kA): -0.5378 -16.1255 -29.0735 -23.9079
dIp/dt (kA/ms): -1.7826 -2.7976 -1.6520 0.0011
pressure (mTorr): 0.0656 0.0641 0.0663 0.0656
Bz0 (mT): -2.6872 -0.9644 1.3899 15.1687
Br0 (mT): -0.1169 -0.6173 -0.5345 -1.8274
May 26 2000 01:50:29:903PM1000526015Jim IrbyRepeat

Plasma to 0.5 s

Marfe again

Made it up to about 17 mm above the midplane

Time (ms): 0 5 10 25
----------------------------------------
Ip (kA): 2.0564 -16.1027 -29.0735 -78.3853
dIp/dt (kA/ms): -1.7814 -3.0520 -2.2890 -5.5953
pressure (mTorr): 0.0634 0.0634 0.0648 0.0592
Bz0 (mT): -2.5322 -0.5808 1.7483 15.8963
Br0 (mT): -0.4209 -0.8656 -0.8559 -2.0497
May 26 2000 02:06:47:280PM1000526016Jim IrbyDensity request reduced to 1.0e20
Kr gas puff reduced 10 ms: 0.3 to 0.35 s

Fizzle

Time (ms): 0 5 10 25
----------------------------------------
Ip (kA): 2.0564 -16.1027 -31.6677 -26.4794
dIp/dt (kA/ms): -1.7825 -3.1791 -2.0358 -0.2566
pressure (mTorr): 0.0641 0.0648 0.0648 0.0620
Bz0 (mT): -1.5863 -0.3119 1.7471 15.3359
Br0 (mT): -0.5785 -0.5644 -0.4760 -1.7344
May 26 2000 02:33:23:950PM1000526017Jim IrbyPCS Repeat

Plasma --- killed by pellet

Plasma moves up 3 cm or so before it's lost
May 26 2000 02:52:02:857PM1000526018Jim IrbyKr puff reduced to 35 ms

Plasma -- pellet takes it out

H_to_D staying low: 2 to 3%




May 26 2000 03:20:25:013PM1000526019Jim IrbyRaised ZCUR another 20.0 mm
Raised ZXL another 20.0 mm
Clearin reduced by 5.0 mm
RCUR reduced by 2.5 mm

load/clean

Plasma to pellet time --- disrupts up

Plasma goes 46 mm above midplane!



May 26 2000 03:37:17:420PM1000526020Jim IrbyAdded 40mm to ZXU

Load/clean

Plasma to pellet

Disrupted up

May 26 2000 04:00:09:310PM1000526021Jim IrbyReduced ZCUR by 30 mm
Reduced ZXL by 30 mm
Reduced ZXU by 30 mm

Load/clean

Plasma to pellet

Disruption guys pretty happy


May 26 2000 04:50:54:000PM1000526022Jim IrbyZCUR up 10 mm
ZXL up 10 mm

Load/clean

Jim Terry reported that he is NOT seeing Cu

Plasma to pellet --- down

May 26 2000 04:45:47:263PM1000526023Jim IrbyRepeat

Plasma to pellet --- goes down

May 26 2000 05:01:30:653PM1000526024Jim IrbyZCUR up 4 mm
ZXL up 4 mm
ZXU up 4 mm

Load/Clean

Plasma to pellet

Done............

Engineering Operator Comments
ShotTimeTypeStatusComment
108:49:04:547AMPlasmaOk
209:13:59:937AMPlasmaOk
309:29:36:890AMPlasmaOk
410:03:53:013AMPlasmaOk
510:29:07:933AMPlasmaOk
610:51:01:310AMPlasmaOk
711:12:49:310AMPlasmaOk
811:31:56:983AMPlasmaOk
911:47:54:763AMPlasmaOk
1012:05:02:467PMPlasmaOk
1112:25:03:640PMPlasmaOk
1212:41:56:217PMPlasmaOk
1301:02:10:047PMPlasmaOk
1401:23:40:030PMPlasmaOk
1501:43:08:187PMPlasmaOk
1602:01:45:513PMPlasmaOk
1702:18:57:263PMPlasmaOk
1802:37:58:653PMPlasmaOk
1903:11:46:187PMPlasmaOk
2003:30:27:717PMPlasmaOk
2103:50:23:653PMPlasmaOk
2204:11:22:420PMPlasmaOk
2304:35:20:780PMPlasmaOk
2404:54:40:340PMPlasmaOk