Global ion heating/transport during merging spherical tokamak formation

Abstract

Here we report global ion heating/transport characteristics of magnetic reconnection during merging spherical tokamak formation experiment on TS-6 (TS-3U). Using the 96CH/320CH ultra high resolution ion Doppler tomography diagnostics, the full-2D imaging measurement clearly revealed that magnetic reconnection initially forms localized hot spots in the downstream region of outflow jet with inboard/outboard asymmetry (more deposition in the high field side) but the continuous accumulation of the heating coupled with transport process expands the high temperature region globally and forms characteristic poloidally ring-like structure aligned with field lines. The dynamic ion heating/transport process is also affected by the polarity of toroidal field and poloidally tilted/rotating global structure has experimentally been found both during and after merging. The characteristic poloidal asymmetry gets flipped when toroidal field direction is reversed and it was found that higher temperature appears in the positive potential side, which is opposite to the conventional understanding/prediction of guide field reconnection. Through the parallel acceleration process coupled with global heat transport, poloidally asymmetric non-classical feature has experimentally been found for the first time.

Control of Transient Static Electric Field in the Magnetic Reconnection Experiment with Large Guide Field

“…The University of Tokyo Spherical Tokamak (UTST) [8] is the device designed to generate a high-beta spherical tokamak (ST) plasmas by merging start-up scheme. This scheme utilizes MR as a plasma heating method and is employed on several devices, such as TS-6 (The University of Tokyo) [9], MAST (UKAEA) [10], and ST-40 (Tokamak Energy Ltd.) [11].…”

Pseudo-Maxwellian Velocity Distribution Formed by the Pickup-like Process in Magnetic Reconnection

“…Magnetic reconnection is a fundamental process in a plasma through which stored magnetic energy is rapidly released to plasma kinetic and thermal energies (Yamada, 2007). Magnetic reconnection is thought to be involved with various active phenomena in astrophysical and laboratory plasmas (Yamada et al, 2014;Burch et al, 2016) such as solar flares, substorms in the geomagnetosphere, and tokamak disruptions, and it is utilized as one of the initial heating methods in spherical tokamaks (Tanabe et al, 2017;Inomoto et al, 2019;Ono et al, 2019;Tanabe et al, 2021). In addition, magnetic reconnection has attracted the extensive attention and has been explored by many researchers for long periods of history, mainly because it contains a wide variety of research topics, such as topology change on global scale, acceleration, heating, and chaotic motions (Zenitani et al, 2017;Yoon and Bellan, 2021).…”