(IA) Instability & Anisotropy Session report
June 19, 2024 (Y. Takemura)
Date: June 18, 2024
Time: 10:30 - 16:45
Shot#: 193394-193476 (83 shots)
Prior wall conditioning: None, Divertor pump: Off
Gas puff: H2, Pellet: None
NBI#(1, 2, 3, 4, 5)=gas(H, H, H, H, H)=P(4.1, 2.5, 3.1, 3.8, 3.6)MWECH(56GHz)=ant(1.5-U)=P(-)MW
ECH(77GHz)=ant(5.5-U, 2-OUR)=P(0.337, 0.380)MWECH(116GHz)=P(-)MW
ECH(154GHz)=ant(2-OLL, 2-OUL, 2O-LR)=P(-, -, 0.982)MWICH(3.5U, 3.5L, 4.5U, 4.5L) = P(0.20, -, -, -)MWTopics
1. Development operational scenarios of stochastic acceleration in LHD (S. Kobayashi(Kyoto-U), K. Nagaoka)
2. Construction of exp. scaling law of Ext.-RMP penetration threshold (K.Y.Watanabe,S.Shimode(Nagoya-U))
3. Plasma shape effect on BSC in high collisional regime (O.Mitarai, K.Y.Watanabe)1Development operational scenarios of stochastic acceleration in LHD
Experimental conditions:(Rax, Polarity, Bt, γ, Bq) = (3.55 m, CW, 0.5 T, 1.2538, 100.0%)(#193440 - #193459) w/ flux swing (Rax = 3.55-3.75 m)
Objective:
To develop operation scenarios of stochastic acceleration in LHD(1) Production of initial electrons w/ IC initiation and flux swing(2) Electron acceleration by non-resonant ECH

ICEC(77G+156G)(S. Kobayashi (Kyoto-U), K. Nagaoka)
Results:✓ Obtained a sustainment of initial electrons
during flux swing (closed GVs of NBI)
✓ No significant response in scintillator signals✓ Observed a clear high frequency (~70 x ci)
signals → due to WPI of high energy
electrons?

ECtime(s)Construction of exp. scaling law of Ext.-RMP penetration threshold(K.Y.Watanabe, S.Shimode)
Rax=3.6m

Background and motivation:
In early LHD researches, the RMP penetration threshold on the collisionality isinvestigated for magnetic configurations with various plasma aspect ratio. In order
to compare the RMP penetration behavior in tokamaks, the scaling with the beta,
the collisionality and the normalized gyro-radius is effective. However, the data set
is not enough to extract the beta and the normalized gyro-radius independently.
Then, we try to get the additional experiments to construct the scaling with thebeta, the collisionality and the normalized gyro-radius.

Experimental conditions:(Rax, Polarity, Bt, γ, Bq) = (3.60m, CW, 1.8T/1T, 1.2538, 100%);#193397-418(1.8T), 193422-38(1T)# RMP calibration; #193394 #7O enlarged@3.6m, ramp up rate 300A/s@B2 coil

Results:

We can extend the dataset of the Ext.-RMP penetration threshold in the (, ei/b)
diagram as shown in the right-bottom figure. Now we are analyzing the Ext.-RMPpenetration threshold, and try to construct the the scaling law scaling with the beta,
the collisionality and the normalized gyro-radius.

Ext.-RMP threshold dependence
on the collisionality in the LHD[K.Y.Watanabe et al., NF (2019)]
r360g125__beta-nu3.qpc

Additional
Dataset101previous
data
1

1.8T
1T

10
< > (%)
av3

Plasma shape effect on BSC in high collisional regime (O.Mitarai[, K.Y.Watanabe])
Te0
Te02024June18-byOM_ne-Te0.qpc

Background and motivation:
results(tentative)
According to a helical fusion reactor design, there is a possibility the BSC(BootStrapCurrent) affect the MHD equilibrium and instability. We already investigated the BSC
2dependence on the magnetic axis location and the collisionality, and found that it isreduced in more torus-inward magnetic axis and in more collisional regime. Now, we
Ip/Bt@Bq0%
1
2024June18-byOM_ne-Ip.qpc
focus on the magnetic surface shape effect on the BSC. According to a theoretical
Ip/Bt
prediction, elongated deformation of the magnetic surface vertically(Bq0%) reduces
0the BSC comparing with quasi-circular shape(Bq100%) in a low collisional regime [N.
1234 3.60m/B
567q0%
860
19 -3
Nakajima et al., NF 29 (1989) 605, and K.C.Shaing et al., POF B1, (8) (1989) 1663].
n[10 3.75m/Bm ]q0%e-bar
Now we would like to confirm the plasma shape effect in the relatively high4collisional plateau regime in LHD.
Experimental conditions:(Rax, Polarity, Bt, γ, Bq) = (3.60m, CW, 2.64T, 1.2538, 0%); #193460-75# Balanced NB(BL2+BL3) is injected for 3 second.

200123ne-bar

Results:
We compare Ip(around the end of discharge) and central elec. temp. dependence inbetween Rax3.6m/Bq0% and Rax3.75m/Bq0% with almost same NBI power. Ip
decreases with density in both cases. In the same density, Ip in Rax3.6m/Bq0% issmaller than that in Rax3.75m/Bq0%, which is consistent with those in theconfiguration with Bq100%. However, the central temperature of Rax3.6m/Bq0% islower than that of Rax3.75m/Bq0%, and we have not compared the BSC of betweenRax3.6m/Bq0% and Rax3.6m/Bq100%. They are our future subjects.

4519 -3[10 m ]

678

Te0 and Ip at the end of discharge
dependence on density in balanceinjected NB discharges.

4