(SG3) Instability & Anisotropy group report
Apr. 23, 2024 (T. Kawate)
Date: Apr. 19, 2024
Time: 10:50 – 14:30
Shot#: 189901 – 189969 (69 shots)
Prior wall conditioning: Yes (He)Divertor pump: No
Gas puff: H2, Ar, He, Ne
NBI#(1, 2, 3, 4, 5)=gas(H, H, H, H, H)=P(4.4, -, -, 3.1, 5.4)MWECH(77GHz)=ant(5.5-U, 2-OUR)=P(0.70, 0.71)MWECH(154GHz)=ant(2-OLL, 2-OUL, 2-OLR)=P(0.71, 0.89, 0.98)MWICH(3.5U, 3.5L, 4.5U, 4.5L)=P(0.60, -, 0.62, 0.70)MWTopics
1. Interplay of fast ions and impurities in LHD in helium (D. Moseev (IPP), K. Tanaka)
2. Impurity exhaust by 3-ion heating at LHD (D. Moseev (IPP), K. Tanaka)Interaction of fast ions and impurities with sawteeth in He plasmas

No sawtooth

Experimental conditions:(Rax, Polarity, Bt, γ, Bq) = (3.6 m, CW, 2.75 T, 1.254, 100.0%)

Objective and method:Ø Fast ion transport and impurity
transport due to sawtooth crashes
Ø FI sources: NBI1,4,5. Impurity sources(F, Fe, W) - TESPELResults:
Ø In comparison with H plasma, it isdifficult to produce sawteethØ The appearance of sawteeth is not
reproducible in seemingly similar
experimental conditions
Ø No clear sign of F redistribution due tothe crash – evacuated too quicklyØ Awaiting for Fe data
Ø More analysis needed

Similar plasma params
sawtooth3-ion ICRF heating scheme on impurity
Experimental conditions:

F intensity

F intensity(Rax, Polarity, Bt, γ, Bq) = (3.6 m, CW, 2.68 T, 1.254, 100.0%)

Objective and method:Ø Impurity pump-out by 3-ion heating
scheme ICRF (2nd harmonic)Ø Needs low density of H

Results:
Ø There is a visible effectØ Has to be checked for other possible
explanations before reaching positive
conclusions
Ø Plasma had too large H density
Ø Was difficult to vary H/He ratio

F Tespel
Min in H/He ratio(SG2) Turbulence & Confinement group report
Apr. 23, 2024 (T. Kobayashi)
Date: Apr. 19, 2024
Time: 14:30 – 16:45
Shot#: 189970 – 190006 (37 shots)
Prior wall conditioning: Yes (He)Divertor pump: No
Gas puff: Ar, He
NBI#(1, 2, 3, 4, 5)=gas(H, H, H, H, H)=P(4.4, -, -, 3.1, -)MWECH(77GHz)=ant(5.5-U, 2-OUR)=P(0.70, 0.71)MWECH(154GHz)=ant(2-OLL, 2-OUL, 2-OLR)=P(0.71, 0.89, 0.98)MWICH(3.5U, 3.5L, 4.5U, 4.5L)=P(0.60, -, 0.62, 0.70)MWTopics
1. Investigation of electron-scale turbulence characteristics and its influence to transport (T.
Nasu)
2. Comparison of turbulence driven transport between LHD and W7-X (H. Sakai)

Investigation of electron-scale turbulence and its influence to transport
Proponent: Tatsuhiro Nasu, Tokihiko Tokuzawa, Motoki Nakata
Background: We have investigated electron-scale turbulence characteristics
because its influence to transport is not ignorable in high Te plasma. Especially, weobserved their intensity dependence on Rax/LTe in D plasma with constant Te/Ti in
24th LHD experimental campaign. To investigate the difference in thecharacteristics when Zeff is changed, we tried to observe intensity dependence onRax/LTe in He plasma.
Experimental conditions:• (Rax, Bt, polarity, gamma, Bq) = (3.6, 2.75, CW, 1.2538, 100), gas: HeResults:• On-/off-axis ECHs were used to control Te profile
with control of power and deposition location.
• He/(H+He) ~ 0.6 should be sufficient purity to observe
any difference in electro-scale turbulence intensity.
• We successfully observed wide variety of Te profiles,
which have different ∇Te with constant Te
at reff/a99~0.5.

ex) #189981– Ti and ne profiles are almost unchanged then.

•We could observe electron-scale turbulence by BSmeasurement at reff/a99~0.5.

ECHComparison of turbulence driven transport between LHD and W7-X (He-case)
H. Sakai (Kyushu Univ.), K. Tanaka
Shot No: #189983~190006 (24 shots)Experimental conditions: (Rax, Polarity, Bt, γ, Bq) = (3.6 m, CW, 2.75 T, 1.2538, 100 %)Gas-puff: He※Experimental sequence was set to 3min +30sec
Approach
To clarify more detail difference in the picture of turbulence driven transport
in LHD and W7-X, electron density scan was performed as flat-top with ECH(#4,5,7, ~2MW). Experimental sequence was changed from 3min to
3min+30sec in order to perform discharge cleaning using ICH for high He
purity in same shot, because H plasma discharge was conducted all day oneday earlier. To sustain ICH plasma, ECH (#1,2,4) was used as long pulse.
ECH (#4,5,7)Density scan
0.5-4.5x
3.3 3.6

NBI (#1)

5.6

ICH+ECH (#1,2,4)

7.0 7.6

40.0

Result✓ Unfortunately, ECH#4,5 was very unstable in my time (probably due to using commercial power supply for long pulse ECH).
We requested 18 shot combination of short (2sec) and long (40sec) pulse operation. Only four shots were successful.
Considering He purity, only one shot (ne~1.5x, He purity~75%) will be useful for comparison between the devices.
✓ Same line-averaged density plasma was generated at W7-X, so the comparison of turbulence profile will be performed.