Neutral-beam injection heating experiment on currentless plasma in the heliotron E device

Abstract

Recent results of the neutral-beam heating experiments (NBI) on the Heliotron E plasma are reported. The target plasma for NBI is produced by electron cyclotron resonance heating (ECRH), using two gyrotrons (53.2 GHz, 200 kW × 2). The neutral beams of 2.9 MW_max are injected 20 to 40 ms afterwards in order to produce a high-energy currentless plasma. At a magnetic field of 1.9 T, a maximum ion temperature of 1.0 keV is obtained at a density of 1.9 × 10¹³ cm⁻³. The maximum _eτ_E is 2.4 × 10¹² cm ⁻³⋅s. By reducing the magnetic field to 0.94 T and using the second-harmonic resonance of microwaves to produce a target plasma, a high-beta plasma is produced by NBI. The maximum central-beta and volume-average beta values are 3.6% and 2%, respectively. The paper describes the results of NBI heating experiments and the confinement and MHD activity properties of the plasmas in question.