Measurement of Ion Energy Distribution Function of Fast Plasma Flow Driven by Plasma Focus Device Using Retarding Field Energy Analyzer

Abstract

To understand the mechanism of particle acceleration in collisionless shocks, generating a collisionless plasma flowing through dilute gas is required. We have proposed a compact plasma focus (CPF) device to generate collisionless plasma by using pulsed-power discharge. To discuss a particle acceleration process in collisionless shocks, it is necessary to evaluate an ion energy distribution function (IEDF) of the plasma. In this study, we measured the IEDF of the plasma flow using a retarding field energy analyzer (RFA). The experimental results measured by the RFA showed that ions with a few eV are dominant in the plasma flow generated by the CPF device. The IEDF could be fitted with the shifted Maxwellian distribution. The plasma parameters were estimated to be the ion number density n_i = 4.6⁺₋⁰₀^._.²₈ × 10¹⁹ m⁻³, the ion temperature T_i = 0.8⁺₋⁰₀^._.⁶₄ eV, and the drift velocity v_d = 11⁺₋⁰₃^._.⁵₅ km/s. The estimated velocity approximately agreed with the result of a time-of-flight method calculated by the ion current waveform.