(SG2, TC) Session Report

June 18, 2024 (T. Kobayashi)

Date: June 14, 2024
Time: 10:30 – 16:45
Shot#: 193272 – 193391 (120 shots)
Prior wall conditioning: HeDivertor pump: On
Gas puff: H2, Ne, Ar
Pellet: NBI#(1, 2, 3, 4, 5) = gas(H, H, H, H, H)=P(2,1.9,1.9,4.3,2.8) MW
ECH(77GHz) = ant(1.5-Uo, 5.5-U, 2-OUR)=P(0.337,0.38,0.389) MW
ECH(154GHz) = ant(2-OLL, 2-OUL, 2-OLR)=P(0.58, 0.606, -) MWICH(3.5U, 3.5L, 4.5U, 4.5L) = P(-, -, -, -) MW
Topics
1. Study of MHD equilibrium, global stability and transport phenomena in an LHD plasma with zero rotationaltransform layer (K. Toi)
2. Real-time plasma control using turbulence level signal (H. Sakai)
3. Real-time plasma control under low-turbulence conditions focusing on turbulent transition (T. Kinoshita)
4. Effect of boron powder injection on density limit (F. Nespoli, K. Tanaka)

Study of MHD equilibrium, global stability and transport phenomenain an LHD plasma with zero rotational transform layer

K. Toi (Professor emeritus, NIFS),
K. Ogawa

LHD experiment summary on 16 June 2024
Shot#: 193276-193310 (35 shots incl. NBI calibration shots)Experimental conditions:(Rax, Polarity, Bt, γ, Bq) = (3.60 m, CW, 1.3 T, 1.2538, 100.0%)

Purpose: To study the characteristics of MHD equilibria, global
stability and plasma transport in LHD plasmas with zero-rotationaltransform generated by strong counter NBCD and compare themwith the current clamping phenomena in the tokamak “current hole”.

n=0 mode

n=0 GAE ?

Results (see Figs.1 and 2):••••The achieved maximum current is ~125 kA, which is appreciably
lower than the required target value of 150kA. Because of thelimitations of PNB and Ebeam in 5-second operation, plasmas withzero-rotational transform were not produced in the experiments.
n=0 mode is excited as same as the past experiment. It is thought
to be the global Alfven eigen mode(GAE). Time evolution of 𝜄!"#can be estimated from the mode frequency. The mode frequency
reaches the lowest value (~20 kHz) during the forced current rampdown by co-NBCD. The mode is also detected by HIBP.
Characteristic evolutions of Te and ne profiles are observed during
the plasma current evolution.
CXRS diagnostics yielded profiles of Ti, Vt, Vp and neon ion
densities under limited plasma conditions of Ip ~ 75 kA, because of
the electron density rises due to #4 and #5 NBI.

Time= 3.0 s

4.0 s

5.0 s

6.0 s

7.0 s

8.0 s

9.0 s

Fig.1 (upper)discharge waveform, (lower) toroidal mode number

Fig.2 Te (red) & ne (blue) profiles at 6 time slices indicated bygreen arrows in Fig.1 (from the top-left to the right-bottom).

Real-time plasma control using turbulence level signal 2

H. Sakai (Kyushu Univ.), K. Tanaka, T. Kinoshita
K. Nagahara, Y. Ito

Shot No: #193322-193331, 193339-193341, 193347-193360 (total=27shots)Experimental conditions: (Rax, Polarity, Bt, γ, Bq) = (3.6 m, CW, 2.75 T, 1.2538, 100 %)Gas-puff: H2
Motivation
In 6/12, turbulence control experiment had been performed and the control for constant heating had been succeeded.
Therefore, a new method was tried to control the lowest turbulence level (TL) under different heating conditions during control.

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ECH#4,7

Resultü Unfortunately, the control did not converge in blue phase, but in red phase, the control
converged and the turbulence level was maintained at a minimum value.
→ The minimum value could be found even if the heating changed during the process of control.
ü In the control using gas puffing, overshoot in TL was noticeable because the TL varied greatly
depending on the strength of the gas. However, on the electron density, the overshoot wassuppressed to a small level.

NB#1,2

NB#2

gas fuelingtime [s]NB#2
TL [a.u.]32

gas𝑛! [×10"# /𝑚$]𝑛(1Logic

NB#1,2
gray: ramp-up
colored: w/ control

𝑛! [×10"# /m$ ]Real-time plasma control under low-turbulence conditions focusing on turbulent transition
T. Kinoshita(Kyushu Univ.), Y. Morishita(Kyoto Univ.),
Shot No: #193311~193346 (36shots)
N. Kenmochi, H. Funaba, K. Tanaka, H. Sakai (Kyushu Univ.)
Gas-puff: H
Experimental conditions: (Rax, Polarity, Bt, γ, Bq) = (3.6 m, CW, 2.75 T, 1.2538, 100 %)Motivation
A turbulence and its driven anomalous transport are minimized when the dominate turbulence mode changes in LHD. The
condition of turbulence transition is expressed by ne=4.20Te-5.28 (TT condition). The aim of this study is to control theplasma to satisfy TT conditions and to realize low-turbulence plasma.
Results• We successfully controlled the plasma along the TT.
• Approach 1 is ne control under constant heating conditions. By
following the TT conditions, ne increase and Te increase wereobserved simultaneously.
• Approach 2 is Te control under constant ne. The TT condition
could be satisfied by ON/OFF control of ECRH, but theturbulence did not change.
Approach1
NO ECRH

w/ control #193320 Base heating: #1#2

Approach2
w/ control #193346

Base heating: half power of #1#2

w/o control #193313Base heating: half power of #1#2

NO ECRH

Effect of boron powder on density limit and role of turbulence
LHD experiment summary on June 12th 2024

Shot#: #193362-193391 (3 0shots)Experimental conditions:(Rax, Polarity, Bt, γ, Bq) = (3.60 m, CW, 2.75 T, 1.2538, 100.0%)

Purpose:: Study effect of B powder injection on density limit, possibly to be
increased since B injection decreases both
intrinsic impurities, radiated powerTurbulence

Result1:••~3.6 MW NB heating~3.6 MW NB heating + 1.5 MW ECH•

Density ramps without and with B powder injection•No clear effect of powder observed in the lower power scenario,
plasma terminated earlier if too much powder injected
Higher density reached with powder injection with respect toreference case in the higher power scenario
Higher density increases with amount of injected power, collapsed
earlier if too much powder injected
Slight increase of Te during powder injection.

•••

F. Nespoli K. Tanaka S. Masuzaki M. Shojiü Role of turbulence are investigated.

ü Turbulence expands from reff/a99~0.9 toward inner and outerin both shot, however, the expansion is stopped when density
ü Time evolution of electron density was control to have flat top
reach to flat top in 193381.
after ramp up phase. This is in order to find controllable density
limit.
ü ne max of flat top was scanned. At ne max =8.5x1019m-3, flat top
density was controlled, while at ne max =9.25x1019m-3, plasma
collapsed.
ü Boron powder did not help to improve the density controllability.

Fig.2 Expanded trace of ne bar and turbulence amplitude
Fig.1 Time trace of density control experiments