Deceleration mechanism of spheromak-like compact toroid penetrating into magnetized plasmas

Abstract

To understand the fueling process in a fusion device by a spheromak-like compact toroid (SCT) injection method, magnetohydrodynamic numerical simulations, where a SCT is injected into magnetized target plasmas, have been carried out so far. As a result, it has been found that the SCT penetration into magnetized target plasmas is accompanied by complex physical dynamics, which is not adequately described by the conventional simple theoretical model. In this study, based on the previous simulation results, a new theoretical model to determine the penetration depth of the SCT is represented. Here, the SCT is considered to be decelerated not only by the magnetic pressure force but also by the magnetic tension force, which is generated by the bending of the target magnetic field as a result of the SCT penetration. Furthermore, by comparing the penetration depth of the SCT estimated from the theoretical model with that in the simulation, the accuracy of the model is examined. Finally, the effect of magnetic reconnection on the SCT penetration is discussed.

Ideal magnetohydrodynamic simulations of low beta compact toroid injection into a hot strongly magnetized plasma

“…In this regime, the CT tilts while reconnection occurs between the CT and background plasma magnetic fields. Suzuki et al proposed the non-slipping conducting sphere (NS) model [5][6][7], which matches their simulation results of vertical injection without a magnetic field gradient pretty well [7]. Our simulation results in this regime verify their conclusions.…”

“…After the CT has fully entered the background plasma region (after t ∼ 4), the background field lines, some of which have reconnected with the CT magnetic field at the CT's leading edge, are reconnected again with the CT magnetic field at the CT's trailing edge, as seen in figure 6(c). As pointed out by Suzuki et al [5], via this process the CT is separated from the background fields lines, through which the magnetic tension force decelerating the CT is relaxed. At t = 4.375, a magnetic configuration schematically shown in figure 7 is formed.…”

“…As stated above, this does not favour controlled plasma fuelling. In the regime 1 < S r 10, which is the regime Suzuki et al have discussed extensively [5][6][7], the CT is decelerated by both the magnetic pressure and magnetic tension forces. In this regime, the CT tilts while reconnection occurs between the CT and background plasma magnetic fields.…”

“…Among them, CT fuelling is considered to be the most promising method for core fuelling because the injection speed via this method is far higher than those of the other methods. Although extensive worldwide efforts have been devoted to studying CT fuelling theoretically [1,3,4], numerically [5][6][7][8] and experimentally [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27], the dynamics of core CT fuelling of large devices such as the International Thermonuclear Experimental Reactor (ITER) [28] is not well understood. CT injection has the potential to deposit fuel in a controlled manner at any point in the machine, from the edge to the core.…”

Ideal magnetohydrodynamic simulations of unmagnetized dense plasma jet injection into a hot strongly magnetized plasma

“…2(b). This enables magnetic reconnection [22] which as pointed out by Suzuki et al [16] allows the jet to be "detached" from the background field lines and by which the magnetic tension force decelerating the jet is relaxed. Clearly, any reconnection observed in our results is due to numerical resistivity (see further discussion in Sec.…”