Mitigation of ELMs by Electrostatic Field in Tokamaks

Zhongtian Wang,Na Wu,Lin Nie,Xiaochang Chen,Huidong Li,Qian Liu,Zhanhui Wang,Ming Xu,Yingkun Yan ,M L Mou ,Rui Ke

doi:10.4236/jhepgc.2019.51007

Abstract

Mitigation of ELMs by electrostatic field is studied. The perpendicular heating in cyclotron waves tends to pile up the resonant particles toward the low magnetic field side in which a electrostatic field may result [J. Y. Hsu, V. S. Chan, R. W. Harvey, R. Prater, and S. K. Wong, Phys. Rev. Lett. 53, 564 (1984)]. The electrostatic field can make circulating particles trapped or make trapped particles circulating depending on the field direction. The trapped- particle population and bootstrap current change accordantly. Modulating bootstrap current, mitigation of type-1 ELM by the electrostatic field is possible. The electrostatic potential needed for the mitigation is quantitatively estimated. Experiments by either ECRH or biasing are being prepared to verify the theory.

Highlights

In present tokamaks operating in high-confinement regimes (H-modes), the steep pressure gradients at edge are often observed to relax through frequent intermittent discharges of energy, known as ELMs
The perpendicular heating in cyclotron waves tends to pile up the resonant particles toward the low magnetic field side in which a electrostatic field may result [J
The electrostatic field can make circulating particles trapped or make trapped particles circulating depending on the field direction

Summary

Introduction

In present tokamaks operating in high-confinement regimes (H-modes), the steep pressure gradients at edge are often observed to relax through frequent intermittent discharges of energy, known as ELMs. The physics of ELMs is a key issue for ITER operation. The onset of ELMs constrains the pressure at top of edge transport barrier (pedestal height). A predictive understanding of the onset of type-I ELMs has been gained via the development of peeling-ballooning modes [1] in which EL Ms are triggered by instabilities driven by the large pressure gradient and bootstrap current in the edge. Variations of the electrostatic potential at plasma edge are observed in HL-2A [3]. With the assumption neoclassical transport the population of the trapped particles and bootstrap current change accordantly. Modulating bootstrao current by changing the electrostatic field, mitigation of type-1 ELM is possible. Experiments by either ECRH or biasing [5] are being prepared to verify the theory

Full Particle Orbit Simulation in Tokamaks

Bootstrap Current

Peeling-Ballooning Modes

Summary