Analysis of neutral hydrogenic emission spectra in a tokamak

Abstract

Balmer-α radiation by the excitation of thermal and fast neutral hydrogenic particles has been investigated in a magnetically confined fusion device, or tokamak, from the Korea Superconducting Tokamak Advanced Research (KSTAR). From the diagnostic point of view, the emission from thermal neutrals is associated with passive spectroscopy and that from energetic neutrals that are usually injected from the outside of the tokamak to the active spectroscopy. The passive spectroscopic measurement for the thermal Balmer-α emission from deuterium and hydrogen estimates the relative concentration of hydrogen in a deuterium-fueled plasma and therefore, makes a useful tool to monitor the vacuum wall condition. The ratio of hydrogen to deuterium obtained from this measurement qualitatively correlates with the energy confinement of the plasma. The Doppler-shifted Balmer-α components from the fast neutrals features the spectrum of the motional Stark effect (MSE) which is an essential principle for the measurement of the magnetic pitch angle profile. Characterization of this active MSE spectra, especially with multiple neutral beam lines crossing along the observation line of sight, has been done for the guideline of the multi-ion-source heating beam operation and for the optimization of the narrow bandpass filters that are required for the polarimeter-based MSE diagnostic system under construction at KSTAR.

Measurement of local density and magnetic field of a magnetized plasma using Raman scattering from a focused laser pulse

“…For example, the core density in the KSTAR Tokamak is ∼ × 2 6 10 13 cm −3 , while the magnetic field is ∼ 2 3 T, from which ω ω / c p is of order unity [15]. In the high density plasma with > n 10 e 18 cm −3 , which typically appears in laser-plasma interaction, a strong transient magnetic field is commonly generated by a relativistic electron current [14]. When a pump pulse is assumed to be focused to the diffraction limit, i.e.…”