An initial measurement of a fast neutral spectrum for ion cyclotron range of frequency heated plasma using two-channel compact neutral particle analyzers in KSTAR

Abstract

The accurate measurement of fast neutral particles from high energy ion tails is very important since it is a measure of ion cyclotron range of frequency (ICRF) or neutral beam (NB) ion heating. In KSTAR, fast neutral measurements have been carried out using a compact neutral particle analyzer based on the silicon photo diode since 2010. As a result, the fast neutral spectrum was observed consistent with the ion temperature, diamagnetic energy, and neutron flux in 2011. However, there was fast neutral count beyond the injected neutral beam energy in NB-only heating. Since it is difficult to expect the count unless the temperature is high enough to diffuse the fast ions beyond the beam energy it was required to identify what it is. During the 2012 campaign, the two-channel diode detectors with and without a particle stopper were used to distinguish fast neutral counts and other counts by a hard X-ray or neutrons. As a result, it was confirmed that the high energy component beyond the beam energy originated from a hard X-ray or neutrons. Finally, it was observed that faster neutrals are generated by ICRF heating and enhanced by electron cyclotron heating compared to NB-only heating.

Overview and recent progress of KSTAR diagnostics

“…In particular, local changes in the fast-ion loss intensity and its phase-space pattern have been observed with various 3D field configurations for the ELM control. A solid-state neutral particle analyzer (SSNPA) [38] successfully measured the fast-ion energy distribution in the initial development phase of the fast-ion charge-exchange diagnostics. Later it was replaced by the fast-ion D α (FIDA) spectroscopy.…”

Measurement of the fast ion distribution using active NPA diagnostics at the Globus-M2 spherical tokamak

“…In these approaches diagnostics weight functions [2][3][4][5] are usually used in order to simplify forward or inverse calculations as well as for the analysis of the diagnostics capabilities. Neutral particle analyzers (NPAs) are widely used in fast ion studies at magnetic fusion devices [5][6][7][8][9][10][11][12][13][14][15][16][17][18] along with other diagnostics of the confined energetic particles, such as fastion D α spectroscopy [19][20][21][22], collective Thomson scattering (TS) [23][24][25][26], neutron [27][28][29][30] and γ-ray [31][32][33] counters and spectrometers. Interpretation of the experimental NPA data is straightforward, since atoms detected by the NPA are former plasma ions, having the same velocity vector as ions at the point of neutralization.…”