Development of the Thomson scattering measurement system for cascade arc device with indirectly heated hollow cathode

TL;DR

This paper reports the development of a Thomson scattering measurement system to analyze electron density and temperature in a cascade arc device, aiding the understanding of plasma behavior for pressure separation applications.

Contribution

The paper introduces a novel Thomson scattering system specifically designed for cascade arc plasma, enabling detailed electron parameter measurements in a plasma window device.

Findings

Electron density increased from 2×10^19 to 7×10^19 m^-3 with discharge power.

Electron temperature remained nearly constant at about 2 eV.

Successfully measured plasma parameters to support plasma window research.

Abstract

We have developed a Thomson scattering measurement system for the cascade arc discharge device designed for the plasma window (PW) application study. The PW is one of the plasma application techniques that sustain the steep pressure gradient between high pressure (10-100 kPa) and a vacuum environment due to the thermal energy of the plasma. Since the plasma thermal energy is the essential parameter for the pressure separation capability of PW, we installed the Thomson scattering measurement system to observe the electron density and temperature within the anode and cathode of the PW for the detailed analysis of the pressure separation capability. The frequency-doubled Nd:YAG laser (532 nm, 200 mJ, 8 ns) was employed for the probe laser. The scattered light was fed to the triple grating spectrometer. The notch filter between the first and second grating eliminated the stray light, realizing a sufficiently high signal-to-noise ratio. The Thomson scattering measurement system successfully obtained the electron density and temperature of the cascade arc plasma at 20 mm downstream from the tip of the cathode. The installed system successfully obtained the Thomson scattering spectrum and showed that the electron density increased from $2\times10^{19} {\rm m}^{-3}$ to $7\times10^{19} {\rm m}^{-3}$ with the discharge power, while the electron temperature was almost constant at about 2 eV. The obtained data successfully contributed to the study of the pressure separation capability of the PW.