Speaker
Mr
Md. Maidul Islam
(Plasma research center, University of Tsukuba Tsukuba, Ibaraki 305-8577, Japan)
Description
In magnetically confined plasmas, optimization of particle fueling is a critical issue to obtain high performance plasmas. In large fusion devices, most of the particles supplied by gas puffing are ionized in the peripheral region. Pellet injection can reduce the edge recycling and help to obtain a peak density profile. However, this system is complicated and it is not easy to make a pellet small enough for density control in medium or small devices. Supersonic molecular beam injection (SMBI) system is a new fueling method [1], which can combine both advantage of the conventional gas puffer and the pellet injection. The SMBI system consists of a high-speed valve and a nozzle in order to produce a supersonic flow with low divergence. GAMMA 10 is the world largest tandem mirror and an open magnetic plasma confining device [2]. SMBI experiment in GAMMA 10 has been carried out by three conditions; without any nozzle, with straight nozzle and Laval nozzle. The first experimental results of SMBI achieved higher density plasmas at the core region than the conventional gas puffing [3]. A Laval nozzle has been newly mounted on the high-speed valve in order to improve the effectiveness of fueling by SMBI. We investigate the neutral particles behavior during SMBI by using the Laval nozzle. Comparison between the straight and the Laval nozzle is also discussed from the view of neutral transport.$\\$
Monte-Carlo simulation code (DEGAS) [4] was performed in order to analyze the behavior of neutral particle in GAMMA 10. Three-dimensional mesh-model for DEGAS has been applied to the central-cell [5]. In this mesh model, the limiters and ICRF antennae are precisely implemented in a realistic configuration. Furthermore, this mesh model was improved for modeling SMBI experiments; it was expanded around the SMBI injection port and new mesh was added to simulate the valve and the Laval nozzle. The background plasma parameters (*T$_e$,T$_i$, n$_e$=n$_i$*, etc) were given based on the experimental data. The neutral gas from the SMBI nozzle was modeled by introducing a $\sigma_{div}$ parameter as an index of divergence angle of the initial particles. In the case that the angular profile of launched particle has a cosine distribution, $\sigma_{div}$ =1. It was observed that the plenum pressure correlates with the divergence angle index. By changing the value of $\sigma_{div}$ the experimental results was fairly reproduced by the Monte-Carlo simulation code. This result will enable us to discuss the spatial structure for investigating the penetration depth. Above results contribute to the optimization of fueling. In the paper, detail results of experimental and simulation will be presented. $\\$
1. L. Yao *et al*., Nucl. Fusion **47**, 1399 (2007).$\\$
2. M. Inutake *et al*., Phys. Rev. Lett. **55**, 939 (1985).$\\$
3. K. Hosoi *et al*., Plasma Fusion Res. **7**, 2402126 (2012).$\\$
4. D. Heifetz, *et al*., J. Comput. Phys. **46**, 309 (1982).$\\$
5. Y. Nakashima, *et al*., J. Plasma Fusion Res. SERIES **6**, 546 (2004).
Primary author
Mr
Md. Maidul Islam
(Plasma research center, University of Tsukuba Tsukuba, Ibaraki 305-8577, Japan)
Co-authors
Dr
Junko Kohagura
(Plasma research center, University of Tsukuba Tsukuba, Ibaraki 305-8577, Japan)
Dr
Katsuhiro Hosoi
(Plasma research center, University of Tsukuba Tsukuba, Ibaraki 305-8577, Japan)
Mr
Kazuma Fukui
(Plasma research center, University of Tsukuba Tsukuba, Ibaraki 305-8577, Japan)
Dr
Kazuya Ichimura
(Plasma research center, University of Tsukuba Tsukuba, Ibaraki 305-8577, Japan)
Mr
Keita Shimizu
(Plasma research center, University of Tsukuba Tsukuba, Ibaraki 305-8577, Japan)
Dr
Mafumi Hirata
(Plasma research center, University of Tsukuba Tsukuba, Ibaraki 305-8577, Japan)
Dr
Makoto Ichimura
(Plasma research center, University of Tsukuba Tsukuba, Ibaraki 305-8577, Japan)
Mr
Masato Ohuchi
(Plasma research center, University of Tsukuba Tsukuba, Ibaraki 305-8577, Japan)
Dr
Masayuki Yoshikawa
(Plasma research center, University of Tsukuba Tsukuba, Ibaraki 305-8577, Japan)
Mr
Md. Shahinul Islam
(Plasma research center, University of Tsukuba Tsukuba, Ibaraki 305-8577, Japan)
Mr
Mizuho Arai
(Plasma research center, University of Tsukuba Tsukuba, Ibaraki 305-8577, Japan)
Prof.
Mizuki Sakamoto
(Plasma research center, University of Tsukuba Tsukuba, Ibaraki 305-8577, Japan)
Dr
Nobuhiro Nishino
(Graudate school of Engineering, Hiroshima University, Hiroshima 739-8527, Japan)
Dr
Ryuya Ikezoe
(Plasma research center, University of Tsukuba Tsukuba, Ibaraki 305-8577, Japan)
Dr
Shinji Kobayashi
(Institute of Advanced Energy, Kyoto University, Gokasyo, Uji 611-0011, Japan)
Mr
Takayuki Yokodo
(Plasma research center, University of Tsukuba Tsukuba, Ibaraki 305-8577, Japan)
Prof.
Tsuyoshi Imai
(Plasma research center, University of Tsukuba Tsukuba, Ibaraki 305-8577, Japan)
Prof.
Yousuke Nakashima
(Plasma research center, University of Tsukuba Tsukuba, Ibaraki 305-8577, Japan)
