Attempt: Reproduce ELMy H-mode from 1101214029
Result: EDA H-mode. Starting density is too high.
Looking for nebar before L-H of 1.2--1.3e20, rather than 1.5e30
Attempt: Retry and get RF working well. Also increasing Ar puff for the Hirex
team.
Result: EDA H-mode, triggered Ohmically at 0.56s. Good boronization, apparently.
Starting density is still too high. RF is conditioning up.
Shape looks a good match to the target.
Matt says Ar pulse is appropriate.
Attempt. Continue boronization recovery.
Result: EDA H-mode, injection at 1s, followed by faults on J-port.
Density is still high. J-port is still conditioning up.
H-mode power threshold is nice and low.
Attempt. Continue recovering J-port.
Result: Similar, with bigger injection at 1s. Looks like another J-port spew.
Attempt: Modify shape to be more "JFT-2M-like." Trying to match the shape
on 1101214013. The hope is that the change in shape will help get the density
down early. . . .
Result: No big injections that time. Looks like EDA H-mode still.
Lots of J-port restrikes after 1s.
Shape looks good. Density still too high.
Attempt: Clean up RF pulse.
Result: Reasonably good RF program, with some heating in evidence. Prad still
fairly low.
Density is stubbornly high, still.
Next: Go to 8T.
Attempt: Raise field and run it again.
Result: Steady H-mode, with <1.5MW ICRF. Heating is underwhelming.
Injection at 0.9s.
H-mode density clamps at nebar of 2.6e20. neped~2.5e20.
Attempt: Increasing He3 puff.
Result: Target density is way down now. We must have outgassed the walls
with the last disruption.
H-mode is late, and extends into ramp-down. There appear to be ELMs.
Edge Temp is pretty substantial, ~700eV around 1.2s.
Next: adjust nl04 target to a more reasonable level.
There seems to be a dramatic rise in the pedestal pressure around 1.14s that corresponds roughly to the appearance of ELM-like events. During this phase, pedestal temperature (very roughly 700ev) and density (~2e20) both rise, and then seem to saturate. Looks promising for ELMy H-mode at 8T.
Attempt: Try again.
Result: Still a late H-mode: t=1.14s. Nice and hot, but degrading
in quality as the RF faults increase.
No big injection that time.
Next: Ramp to 3MW by 0.9s.
After RF power rises to ~3MW at ~1.1s, get H-mode transition and high pedestal pressure phase from ~1.15-1.25s with some ELMs. RF power is uneven, and this likely impacts the dynamics here.
shots 8 and 9. Here are examples:
Long delay for a fuse change.
Attempt: Higher power sooner.
Result: L-H occurs earlier, at 0.98s. but big injections come in shortly after,
and the radiation is too strong to overcome.
Next: Try to shift strike point inboard with a -5mm RXL change.
at ~1.04s ends high performance phase (some secondary rise in pedestal
pressure at ~1.3s but this is already into rampdown)
No plasma.
OH1 failed to fire.
A PLC test.
Results are not good.
PLC test #2.
Still no OH1
Still testing OH1
Still testing OH1
Still testing OH1. Seems to have succeeded.
Dud.
Attempt: Plasma attempt reproducing shot 10 with RXL shifted in slightly.
Result: Something is heating up in the divertor and injecting during the early
part of the H-mode.
Next: Try some Ne.
Attempt: Repeat with Ne from H-bottom enabled: 0.4--0.6s chopped at 30%.
Fill pressure is 3psi, so there may be too much.
Result: Never got to the Ne puff. Disrupts at 0.42s. Density is too low.
Attempt: Retry
Result: Another early disruption.
Attempt: Repeat shot 010, with some early density tweak.
Result: Makes it to the RF heated phase without disrupting. Still have
substantial injections.
Arturo notes a clear WCM from reflectometry prior to the H-mode formation
This is accompanied by a clear Te pedestal and no ne pedestal.
It seems we can't stay out of I-mode these days.
Attempt: Retry with a less aggressive ICRF ramp-rate.
Result: Injection is there at 0.81s, but not as severe. Matt says we have ample
Ne. Probably need more source power to get the H-mode sooner.
Next: Have ICRF start at 0.6s, ramp at same rate up to 4MW. Continue Ne seeding.
Shot 23.
Attempt: Try to get H-mode earlier
Result: Dithers, then full H-mode transition at 0.92s. A couple of substantial
ELMs in the first H-mode.
period with ELMs from ~0.9-1s.
Attempt: Retry with a different Ne puff (1/2 the fill pressure, 30% instead of
20% chop). Similar RF demand.
Result: Beginning of shot looks similar to 023. H-mode with a couple of ELMs.
Instead of multiple back-transitions, this goes solidly EDA after the
first couple of ELMs. Too collisional, I guess.
Next: Try to reduce the Ne seeding.
***Update: H-bottom was stuck open for nearly the whole shot, apparently.
May explain the EDAness of the shot. ***
Attempt: Rerun 024. A Ne leak occurred after 024, which meant that H-bottom
had to be pumped out before this shot.
Result: Lots of injections. I think we need our Ne back.
There is a phase with apparent ELM(s) at ~1.25s.
Attempt: 025 with H-bottom filled to 1.5psi, 20% chop.
Result: Fizzle. The Ne needs to be moved to behind a non-leaking valve.
Attempt: Ne has been moved to B-side lower. 1.5psi, will try a 40% chop.
Result: Dud. EF1U again.
Attempt: Retry
Result: Plasma, with H-mode. Big injection prior to H-mode at 0.89s, and lots
of Prad after that.
Next: Raise Ne fill to 3psi and increase chop to 80%.
Attempt: Retry with more Ne.
Result: Definitely got more Ne (almost 0.3 torr-L). Maybe too much.
No injections. H-mode comes after 1s.
There is a remarkably coherent fluctuation in the H-alpha, Prad and ICRF in
the period before the L-H transition.
H-modes are EDA, with (I think) QCMs. No ELMs
Next: Reduce Ne
Attempt: Retry with Ne chop reduced from 80% to 60%.
Result: It ran. Got some H-modes. There is some ELM activity at about 0.95s,
and maybe elsewhere. RF ran fairly cleanly. No big injections.
Periods of very high pedestal pressure around 1.02s and 1.22s.