Enhanced production of runaway electrons during electron cyclotron resonance heating and in the presence of supersonic molecular beam injection in the HL-2A tokamak

Abstract

In the present paper, it is reported that a large production of runaway electrons has been observed during the flattop phase of electron cyclotron resonance heating ͑ECRH͒ discharges and in the presence of supersonic molecular beam injection ͑SMBI͒ in the HuanLiuqi-2A ͑commonly referred to as HL-2A͒ ͓Q. W. Yang, Nucl. Fusion 47, S635 ͑2007͔͒ tokamak. For the set of discharges carried out in the present experiment, the ranges of ECRH power and plasma electron density are 0.8-1.0 MW and ͑3.0-4.0͒ ϫ 10 19 m −3 , respectively. A large number of superthermal electrons are produced through the avalanche effect ͓A. Lazaros, Phys. Plasmas 8, 1263 ͑2001͔͒ during ECRH. The loop voltage increase due to SMBI gives rise to a decline in the critical runaway energy, which leads to that many superthermal electrons could be converted into runaway region. Therefore, this phenomenon may come from the synergetic effects of ECRH and SMBI. That is, the superthermal electrons created by ECRH are accelerated into runaway regime via the Dreicer process which is triggered by SMBI. The experimental results are in well agreement with the calculational ones based on the superthermal electron avalanche effect and the Dreicer runaway theory.

Investigation of relativistic runaway electrons in electron cyclotron resonance heating discharges on Korea Superconducting Tokamak Advanced Research

“…Recently, an enhancement of the population of the runaway electrons during the flat-top phase of ECRH discharges and in the presence of Supersonic Molecular Beam Injection (SMBI) was reported in the HL-2 A tokamak. 18 The classical theory for runaway generation 3 can be only applied in the case of a steady-state electric field such as during a pure Ohmic discharge. This means that applying the theory to the ECRH discharges is not pertinent due to the existence of the non-inductive fluctuating electric field.…”