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!