7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Effect of high-particle flux produced by pellet fueling in the core plasma to thedivertor simulation module plasma in GAMMA 10/PDX

M. Yoshikawa1, J. Kohagura1, Y. Nakashima1, Y. Shima1, S. Kobayashi2, R. Minami1, N. Ezumi1
and M. Sakamoto1
1Plasma Research Center, University of Tsukuba, 2 Institute of Advanced Energy, Kyoto University
e-mail: yosikawa@prc.tsukuba.ac.jp

0.4

Diamagnetism
Line density in CC
Line density in D-modue

10Pellet

80.3

60.240.1217-2m ]Diamagnetism [10-4Wb]

0.5Line density [10The plasma detachment is one of the key issues innuclear fusion plasma experiments. The fomation ofplasma detachment decreases the impact of both heat flux
and particle flux to the divertor plate. In the tandem mirror
GAMMA 10/PDX, a divertor simulation experimental
module (D-module) was installed for plasma detachment
study in high heat flux conditions (> 20 MW/m2). In theprevious studies, we successfully performed the plasma
detachment condition in the D-module [1-3]. However,the plasma density of core plasma in GAMMA 10/PDX
was low compared to the scrape of layer plasma of normal
fusion devises. To study the effect of higher density
particle flux during plasma detachment, as in edge
localized mode (ELM)-like simulations, we preparedpellet fueling to produce a higher density of core plasma
and introduced it to the D-module. In this experiment, werevealed the effect of higher particle flux produced bypellet injection into the detached simulation plasma for thefirst time.
GAMMA 10/PDX is the largest tandem mirror machineconsisting of main confining region of central cell, twoaxisymmetric minimum-B anchor cells, and two plug andbarrier cells. In the west end region, the divertor
simulation experimental module (D-module) was set fordivertor simulation experiments with the use of the endloss plasma from the core plasma. The plasma is produced
and maintained with the application of the ion cyclotron
resonance frequency (ICRF) wave heating after the initialplasma injection by the plasma gun. Typical electron
densities and temperatures are about 2 × 1012 cm−3 and 25eV in the central cell and 1 × 1011 cm−3 and 25 eV in theend cell without additional gas injection into the Dmodule, respectively.
The hydrogen plasma is produced and heated by ion
cyclotron range of frequency wave from t = 51 to 440 msand additional hydrogen gas puffing for radiator gas in theD-module from t = 50 to 450 ms with pressure of 1000
mbar for plasma detachment. The sub-millimeter pellet isinjected in the central cell plasma at approximately t = 350
ms. Time evolutions of diamagnetism (red dotted line) andline densities in the central cell (blue line) and the Dmodule (green line) are shown in Fig. 1 with indication ofpellet injection time. It is clearly confirmed that theelectron line density increase and diamagnetism decrease
with pellet injection in the central cell. In the D-module,
the electron line density increased a little and decreased
with pellet injection. injection. Line density in the Dmodule shows that the pellet was injected during theplasma detachment condition. The electron temperature

0050 100 150 200 250 300 350 400 450

Time [ms]FIG. 1. Time evolutions of diamagnetisms (red dottedline) and line densities of central cell (blue line) andof west end cell (green line).
and density measured by using electrostatic probes on thetarget plate of upstream side in the D-module weredecreased with pellet injection, respectively. The probesof downstream side in the D-module showed no clear
difference with and without pellet injection. Ion fluxes
with pellet injection showed only a little decrease. One of
the reasons of decrease of line density and ion flux in Dmodule with pellet injection is the decrease of electron
temperature which made the plasma ionization ratedegrade in D-module. The higher electron density plasma
condition by pellet injection in core plasma affects toimprove plasma detachment. This is the first result of theeffect of higher particle flux produced by pellet fuelingintroduced to the divertor simulation plasma experiments.
This study was supported by the bilateral collaboration
research program in the University of Tsukuba and Kyoto
University (NIFS20KUGM148, NIFS20KUGM159,
NIFS21KUGM165 and NIFS21KUHL101). The author
sincerely thanks the members of the GAMMA 10 groupfor their collaboration on the experiments.
References[1] Y. Nakashima, et al., Nuclear Fusion, 57 (2017)
116033.
[2] N. Ezumi, et al., Nuclear Fusion, 59 (2019) 066030.
[3] M. Yoshikawa, et al., AIP advances, 11 (2021) 125231.
[4] M. Yoshikawa, et al., Plasma Fusion Res. 17 1202093(2022)