MHD Simulation of Merging Fueling Method Used for ST Plasma

Abstract

Three-dimensional resistive MHD simulation was carried out in order to develop a method to fuel the plasma core by merging two Spherical Torus (ST) plasmas. A relatively small ST plasma was translated into the axial direction by external magnetic field control and made to collide with the larger ST. In this calculation, ballooning instability occurred in both plasmas during translation, while the magnetic surface was observed to collapse from the Poincare plot of the magnetic lines. It was observed that the magnetic lines in the core regions of the two STs were connected to each other and that the merging was completed. Keywords: advanced fusion, spherical torus plasma, fueling, MHD simulation, merging, magnetic reconnection DOI: 10.1585/pfr.13.1203008As ITER construction progresses, the establishment of fueling technology to fusion burning plasmas is still a key unresolved issue. Neutral particles injected as fuel are ionized in the periphery and have difficulty reaching the core under the high temperature conditions of 10 keV or more, such as those of burning plasma. For this reason, it is urgent to develop a method of supplying particles to the burning plasma core. Under these circumstances, the concept of the merging fueling method is proposed [1].Progress in plasma merging experiments via the magnetic reconnection process was taken as the background to this proposal [1]. Historically, merging experiments of spheromak have been carried out at TS-3/4 [2, 3], SSX [4], and others. Additionally, Tri-Alpha Energy Inc. has succeeded in generating field-reversed configuration (FRC), with good confinement performance, by merging two FRC plasmas [5,6]. In recent years, merging experiments of spherical torus (ST) plasmas have also been carried out at UTST, and reports have been submitted on the generation of high energy electrons during the merging process [7].The merging fueling method [1] aims to supply particles to large plasma via the merging of two ST plasmas with different sizes. The purpose of this preliminary research was to analyze the process of axially translating and colliding the small secondary plasma pushed by the magnetic pressure difference to the large plasma by using the three-dimensional (3-D) MHD simulation, and to determine research tasks in the merging fueling method. There are several reports on the reproduction of the plasma merging phenomenon by MHD simulation [8][9][10]. However, the 3-D simulation of two large and small ST collision phenomena has not been carried out so far.In this paper, we clarify the change of the macroscopic author's e-mail: t09306025@gunma-u.ac.jp plasma structure, especially in the translation/collision process in the category of the ordinary MHD model. Additionally, by considering the development of the fueling method, it was necessary to simulate and predict whether the particles in the smaller secondary plasma could reach the larger main plasma core. For this reason, a particle trajectory calculation was performed based on the MHD simulation. Thus, it was clarified...