Investigation of beam– and wave–plasma interactions in spherical tokamak Globus-M

Abstract

The experimental and theoretical results obtained in the last two years on the interaction of neutral particle beams and high-frequency waves with a plasma using the spherical tokamak Globus-M are discussed. The experiments on the injection of low-energy proton beam of ∼300 eV directed particle energy are performed with a plasma gun that produces a hydrogen plasma jet of density up to 3 × 1022 m−3 and a high velocity up to 250 km s−1. A moderate density rise (up to 30%) is achieved in the central plasma region without plasma disruption. Experiments on high-energy (up to 30 keV) neutral beam injection into the D-plasma are analysed. Modelling results on confinement of fast particles inside the plasma column that follows the neutral beam injection are discussed. The influence of the magnetic field on the fast particle losses is argued. A neutral beam injection regime with primary ion heating is obtained and discussed. The new regime with fast current ramp-up and early neutral beam injection shows electron temperature rise and formation of broad Te profiles until the q = 1 flux surface enters the plasma column. An energetic particle mode in the range of frequencies 5–30 kHz and toroidal Alfvén eigenmodes in the range 50–300 kHz are recorded in that regime simultaneously with the Te rise. The energetic particle mode and toroidal Alfvén eigenmodes behaviour are discussed. The toroidal Alfvén eigenmode spectrum appears in Globus-M as a narrow band corresponding to n = 1. The first experimental results on plasma start-up and noninductive current drive generation are presented. The experiments are carried out with antennae providing mostly poloidal slowing down of waves with a frequency of 920 MHz, which is higher than a lower hybrid one existing under the experimental conditions. The high current drive efficiency is shown to be high (of about 0.25 A W−1), and its mechanism is proposed. Some near future plans of the experiments are also discussed.

Overview of physics results from the conclusive operation of the National Spherical Torus Experiment

“…In addition, NSTX-U plasmas operating at up to twice the toroidal field of normal NSTX operation (B t = 1 T) will allow an expanded investigation of the effect of decreasing the ratio of fast-particle velocity to Alfvén velocity on Alfvén eigenmodes. A decrease in this ratio led to a decrease in unstable Alfvénic modes in Globus-M experiments [94].…”

Effect of toroidal Alfvén eigenmodes on fast particle confinement in the spherical tokamak Globus-M

“…On the spherical tokamak Globus-M, owing to the smaller dimensions compared to NSTX and MAST, a regime of TAE generation is realized with strongly developed single modes (Gusev et al. 2011; Petrov et al. 2011).…”

Two-point kinetics model for hybrid cascade subcritical reactor

“…Thermonuclear source is based on the tokamak, so it could be designed on the basis of research conducted for ITER [1]- [4]. In electronuclear source neutrons comes from the interaction of high energy proton beam with a heavy atom nucleus (spallation) [5].…”