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poster_presentation_summary.pdf2011-08-05 03:06:23Takayuki Watanabe
icc_poster.pdf2011-08-02 21:08:17Takayuki Watanabe

Computation of Neutral Gas Flow Generation from a CT Neutralization Fuel-Injector

Author: Takayuki Watanabe
Requested Type: Poster Only
Submitted: 2011-06-07 01:39:06

Co-authors: T.Ohshima, T,Takahashi, N.Fukumoto, M.Nagata

Contact Info:
Gunma University
1-5-1 Tenjin-cho
Kiryu, Gunma   376-851

Abstract Text:
"CT Neutralization Fuel Injection" is an expansion of the "CT Injection” method. The "CT Injection" method was proposed as a fuel-injection method for large-scale power generation plasmas such as the ITER. However, feasibility is still unclear because of the difficulty concerning the translation process of a plasmoid across the vertical magnetic field of the fuel injection target. To resolve this problem, the "CT Neutralization Fuel Injection" method utilizes a neutralization cell which transforms the injection plasmoid into an ultra-fast neutral gas flow. It is expected to be faster than conventional methods such as the "Gas-Puff" or "Pellet Injection". Therefore, there is a high possibility of reaching the core of the fuel injection target.
In this study, we will check if the neutral gas generation is enough to meet above quotas. We run a computer simulation on the neutralization cell of the "CT Neutralization Fuel Injection" device. In our calculations, we focus on the plasmoid itself moving through the cell. The plasmoid is treated as a stationary target upon which the neutral gas particles of the cell collide and charge exchange with. Therefore only gas pressure inside the cell and injection speed of the plasmoid is changed. The collision processes are reproduced by the Monte Carlo calculation. The calculation determines the plasmoid's degree of neutralization, and as a result optimum cell length is found.
When the central ion temperature is 100 [eV] and the injection speed of CT at 50-300 [km/s], it was determined that 0.4 [m] is the optimum cell length due to thermal diffusion of the generated gas flow. Any cell longer will be not efficient, owing to the increased chance of the neutral gas particles colliding with the cell and translation tube walls. This will likely cause a reduction of the gas injection speed. Furthermore, it was calculated that the gas pressure inside the neutralization cell and the plasmoid's injection speed does not largely affect the neutralization level and process. Also, on the subject of interactions with the cell wall, we have determined that the incident angle for most of the impacts is 30 to 60 degrees.
We also show preliminary results of a hybrid simulation on CT plasma. The hybrid simulation model under development will take into account the neutralization process to investigate an electromagnetic behavior inside the neutralization cell. In particular, it should be clarified that magnetic flux decay occurs by reducing the plasma current and associated radial expansion of the plasma caused by imbalance of the radial force. We will also study the influence of the axial electric field generated by the friction force between electrons in the moving plasmoid and cold ions.

Characterization: A3,A7


University of Washington

Workshop on Innovation in Fusion Science (ICC2011) and
US-Japan Workshop on Compact Torus Plasma
August 16-19, 2011
Seattle, Washington

ICC 2011