(SG1) Multi-phase and Atomic/Molecular physics group report
June 14, 2024 (M. Kobayashi)
Date: June 13, 2024
Time: 10:30 -16:45
Shot#: 193158 – 193271 (114 shots)
Prior wall conditioning: No
Divertor pump: On
Gas puff: H2, Ne, Ar, N2 IPD: Yes
LID: Yes
NBI#(1, 2, 3, 4, 5)=gas(H, H, H, H, H)=P(2.3, 2.3, 2.3, 3.3, 2.8) MW
ECH(77GHz)=ant(5.5-U, 2-OUR)=P(698, 380)kW
ECH(154GHz)=ant(2-OLL, 2-OUL, 2O-LR)=P(705, 889, 982) kW
ECH(116GHz)=ant(2O-LR)=P(-)kW
ECH(56GHz)=ant(1.5-U)=P(-)kW
ICH(3.5U, 3.5L, 4.5U, 4.5L) = P(-, -, -, -) MWTopics
1. The relation between plasma confinement and edge neutral particle (G. Motojima)
2. Sustainment of divertor detachment by using feedback control impurity seeding (S. Masuzaki)
3. Plasma modification and supplemental wall conditioning through lithium granule introduction (R. Lunsford)
1

The relation between plasma confinement and edge neutral particle(G. Motojima) Experimental conditions:
Rax=3.55m, CCW, B=2.78T, γ=1.254, Bq=100%#193158-193179: Divertor Cryo OFF (Panel > 80 K)#192968-192974: Divertor Cryo ON (Panel <20K)

Motivation

Div. Cryo ON (#192969)

 In the 24th LHD campaign, very high neutral pressures were measured in
the sub-divertor region in Rax=3.55m (Wenzel et al., Nuclear Fusion 2024).
 In such kind of high neutral compression state, it is tried to control therecycling under the divertor pump condition.

Div. Cryo OFF(#192964)

Div. Cryo ON

 Experiments
Density steady state (8-11x1019 m-3)
Density modulation

 Results
Divertor pressures of around 50-100 times higher than mid planepressures have been achieved.
In gas puff modulation, density decay after gas puff off is faster with Div.
On (effective confinement time is lower). Mid. plane pressure is also lower
with Div. On, confirming low recycling.

Div. Cryo OFF

Te0Div. Cryo ON

Div. Cryo OFF
Div. Pressure

ne0 Mid. Plane PressureSustainment of divertor detachment by using feedback-controlled
impurity seeding

S. Masuzaki

Shot #: 193180 – 193209(Rax, Bt, γ, Bq) = (3.65 m, 2.7123 T, 1.2538, 100.0%) ,Working gas: H2, Impurity gas: N2, Ne
PECH～0.4 MW, Pt-NBI~ 2.3MW/injector (pulse length:4s),
Pp-NBI~3 MW/injector (modulated)

Wpne,barPt-NBI

PradPp-NBI

Background and Purpose•In the Rax=3.65m configuration, the stabledetachment without impurity seeding was(SURPENS mode).

completeobtained•

However, the density in the operation is near the density limit.

•To conduct a more flexible detachment operation, impurity
seeding has been examined in the Rax=3.65m configuration.

Result•Using feedback-controlled Ne gas puffing (pulse puffing), astable “mild” detachment state was obtained.

•The expected deeper detachment state, in which ion
saturation current to divertor tiles less than 50% of theattached case, could not be obtained for radiative collapse.

Typical time evolutions of w/ and w/o Ne seeding :#193214(w/ Ne), 193185 (w/o Ne)

4

LHD Lithium Granule Injection Experiments (193217 – 193248)
32 Pulses ( 16 with 850 µm Li granules, 16 without Li)••••

Large granules are much more perturbative
This limited applicable IPD voltages and Li quantities•
Modifications to the plasma were substantial•
Conditioning effect was minimal when compared
to what was achieved with B powder injection.
Critical information for ITER as it considers
pellet vs powder injection
Possible next steps : Smaller Li powder or larger B powder
to confirm size effects

B Injection Comparison
169616 – Pre B
169618 – During B
169625 – After B
R. Lunsford et al.,2022 Nucl. Fusion 62 086021

Li Injection
193233 – Pre Li
193243 – During Li
193246 – After Li