Fast ion D-alpha measurements using a bandpass-filtered system on EAST

Based on the charge exchange reaction between fast ions and a neutral beam, fast ion features can be inferred from the spectrum of Doppler-shifted Balmer-alpha light from energetic hydrogenic atoms. In order to study the interaction between instabilities and fast-ion transport, recently we extended the fast ion D-alpha (FIDA) measurements by using a combination of a bandpass filter and a photomultiplier tube (PMT) (f-FIDA).

A bandpass filter selects the desired spectral band from 651 nm to 654 nm before detection by the PMT. Preliminary data from the EAST tokamak show that the active signals have been detected from reneutralized beam ions along the vertical and tangential viewing geometries. The details will be presented in this paper to primarily address the specifications and performance of f-FIDA hardware components and preliminary FIDA measurements.