この博士論文は内容の要約のみの公開（または一部非公開）になっています筑波大学 (University of Tsukuba)201

ISLAM MD. SHAHINUL

Tsukuba Repository

Study of Plasma Behavior Based on Particle and
Heat Flux Measurements and Numerical
Simulation in the GAMMA 10/PDX End-cell
著者 ISLAM MD. SHAHINUL
内容記述 この博士論文は内容の要約のみの公開（または一部
非公開）になっています
year 2018
その他のタイトル GAMMA 10/PDXエンドセルにおける粒子・熱流束計測
および数値シミュレーションに基づくプラズマ挙動
に関する研究
学位授与大学 筑波大学 (University of Tsukuba)
学位授与年度 2017
報告番号 12102甲第8462号
URL http://hdl.handle.net/2241/00152421
数理物質科学研究科 博士論文の要約 
 
Study of Plasma Behavior Based on Particle and Heat Flux Measurements and Numerical 
Simulation in the GAMMA 10/PDX End-cell 
(GAMMA 10/PDXエンドセルにおける粒子・熱流束計測および数値シミュレーションに基づくプラズマ
挙動に関する研究) 
ISLAM MD SHAHINUL 
Doctoral Program in Physics 
Student ID Number  201530078 
Doctor of Philosophy in  
Science 
Advised by  Y. Nakashima 
 
 
 
Abstract 
 
1. Background and objectives of the research 
The divertor simulation research is a very much important research topic to explore the physical 
mechanism of plasma detachment for the sustainment of the future fusion devices such as ITER and 
DEMO. The divertor simulation research has been done in the few tokamak and linear devices. These 
devices have been performed experiments by seeding a few neutral species into the divertor region. 
However, the effects of impurity species on the plasma detachment have not yet clarified since the fusion 
devices have shown plasma detachment results for only a few species so far. The radiation cooling rate 
of the radiator gases is different. Therefore, it is very much important to explore the detailed comparison 
of the radiator gases for the formation of detached plasma. The main motivation of the study is to make 
a detailed comparison of the radiator gases in order to clarify the radiation cooling effect of the gas by 
using the best use of simple configuration linear fusion device GAMMA 10/PDX. The effects of Ar, Kr and 
Xe injection into the divertor region of GAMMA 10/PDX have been done in the study. Impurity injection 
experiments have been done in order to understand the radiation cooling effect of the impurity particles 
on the plasma detachment and make an extrapolatable database for the future fusion devices.   
The objective of the research is to understand the effects of radiator gas seeding on the plasma 
parameters toward the plasma detachment in the end-cell of GAMMA 10/PDX based on the experimental 
and numerical simulation study.  
 
2. Experimental studies  
  GAMMA 10/PDX is the world’s largest tandem mirror device which consists of multiple-cells. The 
divertor simulation research (D-module) has been effectively conducted by using the end-loss flux and 
the divertor simulation experimental module (D-module) at the GAMMA 10/PDX end-cell. It has been 
aimed to investigate the physical mechanism of plasma detachment such as radiation cooling, impurity 
transport, etc. A V-shape target made of tungsten has been installed in the D-module. A set of 
calorimeters and Langmuir probes has been installed on the upper and lower plate, respectively, of the 
V-shape target. In addition, a calorimeter and a directional probe have also been installed behind the 
small gad of the V-shape target. In the research, the effects of radiator gases injection into the D-module 
have been investigated based on the Langmuir probe and Calorimeter measurements. 
 
  2.1 Evaluation of various radiator gases 
  Gas injection experiments into the D-module using various radiator gases were carried out for 
evaluation of radiation cooling. Plasma parameters in the D-module have shown a clear dependence on 
the gas species and gas pressure. The heat flux reduces toward the plasma downstream (Z-axis). 
Reduction of the heat flux distribution along the Z-axis of the D-module has been observed according to 
the increment of gas plenum pressure. In the Y-axis, the peak of heat flux distribution has been obtained 
at 0.0 cm and reduced toward both the Y-directions. The distribution of heat flux along ±Y directions 
become uniform with the increasing impurity injection. Xe shows good performance on the reduction of 
the electron temperature, heat and ion fluxes. Particularly, a remarkable reduction in the ion flux has been 
observed for Xe injection. The electron temperature on the target plate has been reduced to nearly 87%, 
90% and 93% by injecting Ar, Kr and Xe, respectively. In the initial stage of the gas injection, the electron 
density increases due to Ar, Kr and Xe injection. Then, however, it reduces according to the increment of 
Ar, Kr and Xe injection. These results indicate that detached plasma has been generated. It has also 
been observed that Xe is the most effective radiator gas than that of Ar and Kr for generating detached 
plasma. 
 
  2.2 Transition of detached to attached plasma using additional plasma heating 
  The transition of a detached to attached plasma experiment has also been performed by using 
additional plasma heating. A short pulse (25 ms) of electron cyclotron heating (ECH) was applied in the 
east plug-cell to examine effects of electron heating on the plasma parameters in the D-module. It has 
been found that the ion flux at the west end-cell increases significantly during ECH injection. In the ECH 
injection period, the ion flux increases with the increasing Xe injection which indicates the Xe ion 
components enhances by ionization in the D-module due to the application of ECH.  
 
3. Numerical simulation studies 
  3.1 Multi-fluid code “LINDA” 
  A numerical simulation study by using a multi-fluid code “LINDA” (LINear Divertor Analysis with fluid 
model) has also been performed in the end-cell of GAMMA 10/PDX to understand the energy loss 
processes during impurity injection. The LINDA code is a 2D multi-fluid code, which has been developed 
based on the same fluid model as the B2 code. The B2 code has been developed by B.J. Braams for the 
numerical simulation of tokamak Scrape-Off Layer (SOL) and divertor plasma. The LINDA code consists 
of five fluid equations. The fluid equations are discretized and numerically solve in the same way as the 
B2 code. The standard finite volume method has been applied to solve the fluid equations. The mesh 
structure of the simulation space has been designed according to the magnetic field configuration of the 
GAMMA 10/PDX. A tungsten target plate has been designed at the end of the mesh. The atomic 
processes of hydrogen (CX, ionization, and recombination) are included in the present code. In addition 
to the hydrogen atomic processes, atomic processes of the radiator gases (radiative power loss, 
ionization, and recombination) have also been considered in the present code. The recycling hydrogen 
neutral near the target plate is also considered.  
  From the simulation results with the LINDA code, it is found that hydrogen (H) seeding into the plasma 
significantly reduces the ion temperature by enhancing the charge-exchange (CX) loss. The ion 
temperature also reduces according to the increasing H injection. However, a moderate reduction in the 
electron temperature has also been observed for H injection. On the contrary, a remarkable reduction in 
the electron temperature has been observed during simultaneous injection of Ar and H, which indicates 
the radiation cooling effects of Ar. Under this condition, the energy loss terms for both the electron and 
ion enhances significantly via the CX, Ionization and radiation loss. It is also found that the CX loss and 
ionization loss increases with the increasing H injection. On the other hand, the radiation power loss of 
Ar increases with the increasing Ar injection. 
  Radiation cooling effect was investigated by using the LINDA code. A comparison among Ar, Kr and 
Xe shows that Xe is the most effective gas on the reduction of electron and ion temperature. Xe injection 
leads to a strong reduction in the temperature of electron and ion. The energy loss terms for both the 
electron and the ion are enhanced signiﬁcantly during Xe injection. Especially, the radiative power loss 
increases significantly for Xe injection, which induces a strong reduction in the electron temperature. It is 
found that the major energy loss channels for ion and electron are charge-exchange loss and radiative 
power loss of the radiator gas, respectively. These outcomes indicate that Xe injection in the plasma edge 
region is effective for reducing plasma energy and generating detached plasma in linear device GAMMA 
10/PDX.  
 
 
  3.2 Development of kinetic neutral code 
  Transport of hydrogen neutral particles toward the upstream region has also been studied in the end-
cell of GAMMA 10/PDX by developing a kinetic neutral transport code. As a first step, a series of initial 
test calculations have been performed by injecting hydrogen gas puffing molecules from the target plate 
with fixed plasma background. The hydrogen neutral particles are introduced into the background plasma 
with cosine distribution. In the present study, recycling hydrogen neutrals are considered as hydrogen 
atoms. On the other hand, gas puffing neutrals are considered as hydrogen molecules. It has been shown 
that neutral particles concentrate near the target plate and reduce toward the upstream region. The 
hydrogen molecules are dissociated into atoms. As a result, the hydrogen atoms density is increased 
with the increasing gas puffing molecules. The hydrogen atoms also concentrate near the target plate 
and reduce toward the upstream region. The kinetic neutral code will be a robust basis in the future to 
study the effects of molecular processes (especially MAR) on the plasma detachment.  
 
4. Conclusion 
  In this study, effects of radiator gas seeding into the D-module has been studied based on the 
calorimeter and Langmuir probe. The radiator gas injection into the D-module reduces both the heat and 
particle flux. Especially, for the Xe injection, the ion flux reduces drastically. Kr shows intermediate 
performance between Ar and Kr. The electron density shows a roll-over phenomenon for the Ar, Kr and 
Xe injection.  
  From the numerical simulation study by using a multi-fluid code “LINDA”, the following results are 
clarified: (1) Hydrogen injection reduces the ion temperature significantly by enhancing the CX loss. (2) 
The electron temperature reduces remarkably during radiator gases (Ar, Kr and Xe) by enhancing the 
radiation power loss. (3) The radiation power loss for Xe injection is higher than that of Ar and Kr. 
 


GAMMA 10/PDXエンドセルにおける粒子・熱流束計測および数値シミュレーションに基づくプラズマ挙動に関する研究

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GAMMA 10/PDXエンドセルにおける粒子・熱流束計測および数値シミュレーションに基づくプラズマ挙動に関する研究

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