Abstract
The mechanism of plasma heating through magnetic reconnection with a guide magnetic field is investigated by means of two-dimensional electromagnetic particle simulations. These simulations mimic the dynamics of two torus plasmas merging through magnetic reconnection in a spherical tokamak (ST) device. It is found that a large part of protons, which behave as nonadiabatic, are effectively heated in the downstream because a ring-like structure of proton velocity distribution is observed at a local point in the downstream. The characteristic features of the velocity distribution can be explained as the following proton motion. Upon entering the downstream across the separatrix, nonadiabatic protons suddenly feel the strong electromagnetic field in the downstream and move in the outflow direction while rotating mainly around the guide magnetic field. The protons gain kinetic energy not only on the separatrix but also in the downstream. This effective heating process can be interpreted as the “pickup,” which,...
Highlights
The spherical tokamak (ST) attracts attention as a candidate for future fusion reactors, because STs enable the confinement of a higher-beta plasma compared with standard tokamaks [1]
Magnetic reconnection is driven by plasma inflows supplied from the upstream and the reconnection point lies almost at the center
By means of electromagnetic particle simulations, we have studied the proton effective heating in the downstream of magnetic reconnection with a guide field
Summary
The spherical tokamak (ST) attracts attention as a candidate for future fusion reactors, because STs enable the confinement of a higher-beta plasma compared with standard tokamaks [1]. In plasma merging experiments of STs, two torus plasmas are merged together to form a single torus plasma under magnetic compression. In plasma merging experiments it is observed that electrons are heated significantly in the vicinity of the contact point, namely, the reconnection point, whereas ions are heated mainly in the downstream of reconnection [2,3,4]. The mechanism of such plasma heating is considered to be crucial for a complete understanding of high-beta plasma formation. As the ion heating mechanism, for example, shock or viscosity heating [4], thermalization via remagnetization, collisions, and scattering by wave-particle interactions [5], and phase mixing due to the finite
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