reciprocating probe measurements of l-h transition in lhcd h-mode on east east
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ASIPPASIPPReciprocating probe measurements of L-H transition in LHCD H-mode on EAST
EASTPeng LiuPeng Liu
Institute of Plasma PhysicsInstitute of Plasma PhysicsChinese Academy of SciencesChinese Academy of Sciences
11stst APTWG meeting June 2011 NIFS Toki APTWG meeting June 2011 NIFS Toki
ASIPPASIPPOutline
I. Introduction
II. L-H transition measured by RCP
First H-mode on EAST
Experiment setup
L-H transition
III. Summary
ASIPPASIPPOutline
I. Introduction
II. L-H transition measured by RCP
First H-mode on EAST
Experiment setup
L-H transition
III. Summary
ASIPPASIPPMotivation
• H-modes have rarely been obtained in Lower Hybrid Current Drive
(LHCD) alone.
• LHCD has produced dithering ELMy H-modes on JET in single null
divertor plasmas and ELM-free H-modes on JT-60 in limiter
plasmas.
• In the recent experimental campaign of EAST the first H-mode was
produced by lower-hybrid wave (LHW) as the only auxiliary power
source.
• Two reciprocating probes were mounted at the outer midplane,
toroidally separated by 89°to provide direct measurement of L-H
transition in LHCD H-mode.
ASIPPASIPPI. Introduction
First H mode on 7 Nov. 2010, 23:16 Shot number 32525
EAST missions : 1MA, 20MW high-performance steady-state operation (SSO).
1.Stationary H mode operation > 400 sAchieved : 6.4 s H mode, HIPB98(y,2)~0.92.Long pulse divertor operation >1000 sAchieved : 100 s L mode, Te0~1.2 keV3.Plasma current up to 1.5 MAAchieved : Ip = 1 MA, L mode
EAST parameters :Major radius : R0 = 1.9 mMinor radius : a = 0.5 mToroidal field : Bt = 3.5 TElongation : = 2Triangularity : = 0.65
H mode
100 s
1 MA
ASIPPASIPPOutline
I. Introduction
II. L-H transition measured by RCP
First H-mode on EAST
Experiment setup
L-H transition
III. Summary
ASIPPASIPPOutline
I. Introduction
II. L-H transition measured by RCP
First H-mode on EAST
Experiment setup
L-H transition
III. Summary
ASIPPASIPPFirst H-mode on EAST
490 H mode shots in total
89% : POhm + PLHW including the first H mode discharge
duration 3.6 s, limited by Ip flat top durations
11% : POhm + PLHW + PICRF
duration 6.4 s, limited by discharge durations51% : DN or unbalanced DN 16% : LSN (BB towards lower X-point)33% : during configuration switches from DN to LSN0% : USN 80% : first L-H transition during Ip flat top
16% : first L-H transition during Ip ramp-up
4% : first L-H transition during Ip ramp-down
Parameters at L-H :Bt = 1.4~2 T
Ip = 0.4~0.8 MA
ne = 1.9~3.41019m3
PLHW = 0.5~1.1 MW
PICRF < 0.5 MW
SA = 38~42 m2
= 1.64~1.94low = 0.45~0.58
q95 = 2.7~5.0
ASIPPASIPPKey actions leading to the H mode
1. Wall conditioning by lithium coating : to reduce recycling, suppress impurities and radiation.
2. Outer gap optimization by isoflux control and antenna position adjustment : to improve LHW & ICRF power coupling and minimize impurity generation by the plasma-antenna interaction.
3. Local gas puffing near the LHW launcher : to improve LHW coupling (not routinely applied).
4. Shape the plasma into a divertor configuration early during Ip ramp-up : to reduce impurities and radiation.
5. Increase the gas puffing rate during Ip ramp-up : to suppress runaway electrons.
6. Gas fueling from either the HFS or the domes : higher fueling efficiency than LFS gas fueling.
Typical H-mode discharge on EAST. The ne increased after H-mode started, and returned L-mode because Ploss increased too much.
ASIPPASIPPLHW power coupling problem
Multiple L-H-L transitions : when the applied LHW power was marginal to the threshold.
H-L back transitions : increased power loss by radiation & LHW reflection during ELM-free phases.
ASIPPASIPPWhat triggers the transition?
ASIPPASIPPMean Er in L-H transition
ASIPPASIPPThere are differences between experiments
ASIPPASIPPOutline
I. Introduction
II. L-H transition measured by RCP
First H-mode on EAST
Experiment setup
L-H transition
III. Summary
ASIPPASIPP
Two fast reciprocating probe systems for toroidally long-distance correlation
ASIPPASIPP
Reciprocating probe measurements of L-H transition in LHCD H-mode on EAST
ASIPPASIPPOutline
I. Introduction
II. L-H transition measured by RCP
First H-mode on EAST
Experiment setup
L-H transition
III. Summary
ASIPPASIPPComparison of L and H mode
Two adjacent shots, red line for L-mode(36292) and black line for H-mode(36291); the probes were at the same position
36291 36292
ASIPPASIPPL-H transition
Ploss = Paux+ Poh–Prad–dWp/dt
ASIPPASIPPSOL Profiles
Time history in SOL SOL profiles
Reciprocating Langmuir probe measurements at the outer midplane showed that the ne and Te in the SOL were significantly reduced in the ELM-free phase, resulting in increased LHW reflection.
ASIPPASIPPGAM disappear during H mode
Reciprocating probe data at the plasma edge show GAM oscillation in L mode but it disappeared in H mode.
ASIPPASIPPNegative spike before L-H transition
H-modeL-mode
The negative spike correspond with Ha
ASIPPASIPPDithering just before L-H transition
Dithering
Dithering like
Dithering like was frequently observed just before L-H transition or sometimes in L mode when ne>2
ASIPPASIPPOutline
I. Introduction
II. L-H transition measured by RCP
First H-mode on EAST
Experiment setup
L-H transition
III. Summary
ASIPPASIPPSummary
Stationary ELMy H mode has been achieved with only 1 MW of LHCD on EAST.
Reciprocating Langmuir probe measurements at the outer midplane showed that the ne and Te in the SOL were significantly reduced in the ELM-free phase
Multiple L-H-L transitions were observed during a single shot, when the applied LHW power was marginal to the threshold.
Some typical phenomena were observed by reciprocating probe measurement when L-H transition occurred.
ASIPPASIPP
Thank you very much for your attention!
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