Magnetic Reconnection Experiments by Use of Merging Tokamak and Spheromak Plasmas

Summary

This paper presents an overview of closed-type toroidal magnetic reconnection experiments utilizing merging tokamak and spheromak plasmas across devices such as TS-3, TS-4, UTST, and MAST. It highlights key findings regarding ion and electron reconnection heating, particle acceleration, and fast reconnection mechanisms. Additionally, it discusses application studies including Field-Reversed Configuration (FRC) formation and high-power plasma heating verified through experiments and particle-in-cell (PIC) simulations.

Magnetic Reconnection Experiments by Use of Merging Tokamak and Spheromak Plasmas

Y. Ono1, M. Akimitsu1, H. Tanabe1, Q. Cao1, A. Sawada1, H. Hatano1, X. Guo1, S. Inoue2, R. Horiuchi3, S. Usami3, C. Z. Cheng4,1

1 Graduate School of Frontier Sciences, University of Tokyo, Japan 2 National Institutes for Quantum and Radiological Science and Technology, Jp 3 National Institute of Fusion Science, Japan 4 National Cheng Kung University, Taiwan

Since initiation of TS-3 merging experiment (1986), a series of closed-type (toroidal) reconnection experiments TS-3, TS-4, UTST, MAST, TS-U and ST-40 have been studying a number of new reconnection physics mostly for space-, solar-, astro- and fusion plasmas. Those physics, particularly the reconnection heating physics lead us to new types of fusion plasma heating and current drive. I will focus my presentation on this recent tokamak and spheromak merging experiments both for physics and application of magnetic reconnection [1], Our findings and applications of reconnection are as follows:

reconnection heating by reconnection electric field and electrostatic potential: a) global outflow heating of ions in the downstream [1-4] b) local X-point and separatrix heating of electrons [1].
particle acceleration for high energy particle formation
fast reconnection mechanisms: [1] a) anomalous resistivity, b) plasmoid ejection and c) 3D reconnection
application studies of reconnection/ merging [1,2]: a) FRC formation by two merging spheromaks with counterhelicity b) high-power heating of tokamak plasmas by their axial merging.

A significant reconnection heating over 1keV was documented by the world-largest merging experiment: MAST [2] after 2D elucidation of ion and electron heating characteristics by TS-3 and TS-4 merging experiments [3]. Their detailed mechanisms have been further investigated in collaboration with particle (PIC) simulations made by Horiuchi etc. [4] and with solar/ space observations [1]. This talk reviews major progresses in those international and interdisciplinary reconnection studies for physics and applications of toroidal plasma merging and reconnection.

[1] Y. Ono, H. Tanabe et al., Phys. Plasmas 22, 055708 (2015) [2] Y. Ono, H. Tanabe et al., Plasma Phys. Control. Fusion 54, 124039, (2012) [3] Y. Ono, H. Tanabe et al., Phys. Rev. Lett. 107, 185001, (2011). [4] S. Inoue et al., Nucl. Fusion 55, 083014, (2015).