Observation of a novel reduced-turbulence regime with boron powder injection in a stellarator

Abstract

We report the first observation of a novel confinement regime in a stellarator plasma, characterized by increased confinement and reduced turbulent fluctuations. The transition to this new regime is driven by the injection of sub-millimetric boron powder grains into the plasma. With the line averaged electron density being kept constant, substantial increase of stored energy, electron and ion temperature have been observed. At the same time, the amplitude of the plasma turbulent fluctuations is halved. While lower frequency fluctuations are damped, higher frequency modes in the range 100 ≤ f [kHz] ≤ 200 are excited. The access to this regime has been observed for different heating schemes, namely with both electron and ion cyclotron resonant radio frequency, and neutral beams, for both directions of the magnetic field, and for both hydrogen and deuterium plasmas.

Particle control in long-pulse discharge using divertor pumping in LHD

“…dytrans_ts is available in AutoAna [28], a tool that automatically calculates the physical data for the LHD server. This module is starting to be utilized for transport analysis [29]. In the analysis, ECH power deposition (P ECH ) profiles calculated using the ray-tracing code LHDGauss [30] and neutral beam injection (NBI) deposition power profiles that consider slowdown calculated using CONV_FIT3D code [31] are utilized.…”