(SG1, MAP) Session Report
Date: May 21, 2024
Time: 9:42 – 16:43
Shot#: 191511 – 191631 (121 shots)
Prior wall conditioning: He GDCDivertor pump: Off
Gas puff: He, H2Pellet: TESPELMay 22, 2024 (M. Shoji)

NBI#(1, 2, 3, 4, 5) = gas(H, H, H, H, H)=P(4.5, 4.4, 4.3, 3.7, 3.4) MW
ECH(77GHz) = ant(1.5-Uo, 5.5-U, 2-OUR)=P(-, 0.69, 0.38) MW
ECH(154GHz) = ant(2-OLL, 2-OUL, 2-OLR)=P(0.71, 0.89, 0.98) MW
ICH(3.5U, 3.5L, 4.5U, 4.5L) = P(?, ?, ?, ?) MW
Topics
1. RF plasma production at relatively low magnetic fields for wall conditioning（Y. Kovtun(KIPT), T. Seki）
2. Micro-trench measurement of incident ion angles and boron deposition at the divertor surface (S. Abe(PPPL),S. Masuzaki)
3. Mitigation of tungsten-induced plasma termination and identification of transient transport mechanisms (H.
Bouvain(IPP), N. Tamura)RF plasma production at relatively low magnetic fields for wall conditioning(Y. Kovtun, T. Seki, V. Moiseyenko)
Experimental conditions: (Rax, Polarity, Bt, γ, Bq) = (3.6 m, CW, 0.4 T, 1.254, 100.0%) Shots: #191515 - #191565
Goal of this experiment:
 To study the plasma production with only ICRF heating (higher harmonic
cyclotron resonance conditions) on the low magnetic field configuration in He
plasmas for wall conditioning
Results:
 Different scenarios of ICRF plasma production under constant gas flow andadditional gas injection have been make out.
 In all scenarios, stable RF breakdown and plasma creation are observed.
 The plasma density is observed to be 6e18 m-3 at an injected power of 0.9
MW.
 The achieved densities were proportional to the injection power of ICRF.
Checking the neutral pressure and these contents using QMS

Micro-trench measurement of incident ion angles and boron
S. Abe (PPPL), S. Masuzaki
deposition at the divertor surface
Shot #: 191566 – 191586 (sample exposure: 191582-191586)(Rax, Bt, γ, Bq) = (3.6 m, 2.75 T, 1.2538, 100.0%)
Working gas: He
PECH～3 MW, Pt-NBI ~ 12 MW, Pp-NBI ~ 6MW (modulated)
Objectives•

Measurements on the incident ion angle (IIA) for both polar andazimuthal directions of H and He ions at ITER-relevant magneticfield incident angle, α ~ 86° (referenced to the surface normal).

•Measurements on boron gross deposition transported from theimpurity powder dropper (IPD).

Method•The sample holder designed to have the Si crystal surface andAl-coated Si crystal surface at α ~ 86° is installed in LHD using
the 4.5L manipulator. We expose two micro-trench fabricated Sicrystals for each H and He shots.

•Surface analysis using SEM-EDS.

Results•

Samples were exposed to He dominant plasmas with He/(He+H+D)>85%.

•Surface analysis of the samples will be conducted after retrieving themfrom the manipulator.

Positions of micro-trench(35µmx35µmx4or6µm) on
Si / Al coated Si sample

Mitigation of tungsten induced plasma termination and identification of transient transportmechanisms (N. Tamura, H. Bouvain, A. Dinklage et al.)Magnetic configuration: (Rax, Polarity, Bt, γ, Bq) = (3.60 m, CW, 2.750 T, 1.2538, 100.0%)
Shots: #191598 - #191631
Goal of this experiment Investigate difference in electron and ion heating as rescue mechanism for tungsten TESPEL induced plasma termination.
 Investigate dependency of termination mitigation on ECRH deposition position

Background & Motivation

 On-axis ECRH in H-plasma mitigates plasma termination induced by tungsten TESPEL
 It is presumed that off-axis ECRH as mitigation measure changes the time scales of the thermal quench
 It is presumed that pure ion heating changes the dynamics of the thermal quench

Approach & Methodology

 Injection of 3e17 W tungsten TESPEL into ECRH-heated He/H plasmas:
 Scan of delay time of additional ~1MW ECRH at 𝜌𝜌 = 0.3 with delay times Δ𝑡𝑡 = [5,10,15,20,40,80,150,200] ms
 Scan of delay time of additional ~1MW ECRH at 𝜌𝜌 = 0.5 with delay times Δ𝑡𝑡 = [5,10,15,20,40,80,150,200] ms
× Scan of delay time of additional ICRH  trigger failed

Mitigation of tungsten induced plasma termination and identification of transient transportmechanisms (N. Tamura, H. Bouvain, A. Dinklage et al.)Results
 28 3e17 W TESPEL injected (89% successful delivery) Additional ECRH prevents He/H plasma termination induced by tungsten TESPEL Optimal delay time for off-axis ECRH (𝜌𝜌 = 0.3): Δ𝑡𝑡 = 15ms
 Additional ECRH closer to on-axis deposition shows stronger mitigation effect