Studies of energetic particle transport induced by multiple Alfvén eigenmodes using neutron and escaping energetic particle diagnostics in Large Helical Device deuterium plasmas

Abstract

Studies of energetic particle transport due to energetic-particle-driven Alfvénic instability have progressed using neutron and energetic particle diagnostics in Large Helical Device deuterium plasmas. Alfvénic instability excited by injecting an intensive neutral beam was observed by a magnetic probe and a far-infrared laser interferometer. The interferometer showed Alfvénic instability composed of three modes that existed from the core to the edge of the plasma. A comparison between the observed frequency and shear Alfvén spectra suggested that the mode activity was most likely classified as an Alfvénic avalanche. A neutron fluctuation detector and a fast ion loss detector indicated that Alfvénic instability induced transport and loss of co-going transit energetic ions. The dependence of the drop rate of the neutron signal on the Alfvénic instability amplitude showed that significant transport occurred. Significant transport might be induced by the large amplitude and radially extended multiple modes, as well as a large deviation of the energetic ion orbit from the flux surface.

Application of Digital Phase Analysis to Far-Infrared Laser Interferometer for the Large Helical Device

“…As 10 -11 channels in the plasma were available, the integratedfluctuation signal provided essential information about the spatial structure of the MHD mode. The results were compared with theoretical model [15].…”

“…The intermittent signal of the magnetic probe shown in Fig. 3 (b) is an indication of a fast-ion driven instability [15]. When the NBI power was stepped down, the spectral peak of the intermittent signal changed.…”

Fusion product diagnostics based on commercially available chemical vapor deposition diamond detector in large helical device

“…Therefore, advances in energetic particle confinement were expected [38][39][40] through the neutron diagnostics [41][42][43][44][45][46][47][48][49] because neutrons are mainly created by so-called beam-thermal reactions [50]. Energetic particle confinement research, e.g., energetic particle confinement in magnetohydrodynamic quiescent plasmas [51][52][53], visualization of energetic particle transport [54][55][56][57][58][59], and demonstration of MeV ion confinement [60,61], has progressed [62,63]. Recently the beam ion energy spectrum has been studied using D-D neutron energy spectrometers [64][65][66][67][68].…”

Gamma ray diagnostics for high time resolution measurement in large helical device

“…Because the deuterium experiment is the first deuterium experiment in large stellarators/helical devices, one of the targets of the experiment was to enhance the energetic ion confinement study in helical systems toward helical-type fusion reactors [17][18][19]. The classical confinement of energetic ions [20][21][22][23] as well as energetic ion transport due to magnetohydrodynamics [24][25][26][27][28][29] have been studied using comprehensive neutron diagnostics [30][31][32][33][34][35][36][37][38]. The installation of gamma ray systems was planned [39] to understand the MeV ion confinement created by the ion cyclotron range of frequency wave heating experiments [40].…”