Ion Distribution Function Evaluation Using Escaping Neutral Atom Kinetic Energy Samples

概要

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A reliable method to evaluate the probability density function of escaping atom kinetic energies is required for analyzing neutral particle diagnostic data used to study the fast ion distribution function in fusion plasmas. In this paper, digital processing of solid state detector signals is proposed as an improvement of the simple histogram approach. Probability density function of kinetic energies of neutral particles escaping from plasma has been derived in a general form, taking into consideration the plasma ion energy distribution, electron capture and loss rates, superposition along the diagnostic sight line, and the magnetic surface geometry. A pseudorandom number generator has been realized to simulate a sample of escaping neutral particle energies for given plasma parameters and experimental conditions. Empirical probability density estimation code has been developed and tested to reconstruct the probability density function from simulated samples assuming Maxwellian ion energy distribution shapes for different temperatures and classical slowing down distributions with different slowing down times. The application of the developed probability density estimation code to the analysis of experimental data obtained by the novel Angular-Resolved Multi-Sightline Neutral Particle Analyzer has been studied to obtain the suprathermal particle distributions. The optimum bandwidth parameter selection algorithm has also been realized.