Development of a large-bore plasma window with an indirectly heated hollow cathode

Abstract

For plasma window (PW) applications, we developed the cascade arc discharge device with an indirectly heated hollow cathode. The 8-mm channel diameter hollow cathode made of a lanthanum hexaboride (LaB6) was heated by the C/C composite heater surrounding the cathode to increase the thermionic electron emission. The PW developed successfully separated 2.4 kPa and 16 Pa, and the pressure separation capability was sustained for over 1 h. H-β Stark broadening measurement and the Thomson scattering measurement showed that the electron density and temperature inside the channel reached 1019–1020m−3 and 2.0 eV, respectively. The power balance analysis on the electron thermal energy revealed that the neutral density and temperature inside the channel were as high as 1023m−3 and 4000 K, respectively. The relation between the pressure separation capability and the neutral temperature showed that the flow inside the channel of the PW had the molecular flow feature. The SEM-EDX analysis on the LaB6 cathode showed that boron diffused to the molybdenum (Mo) shaft during plasma operation, which supported the LaB6 cathode. Mo shaft became brittle after more than 50 h of operation, exhibiting the necessity of buffer material between the LaB6 cathode and Mo shaft for long-duration operation.

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

“…The other power supply sustained the discharge, which supplied the voltage and current up to 200 V and 100 A, respectively. The further details of the discharge device can be found in another publication [13].…”

“…On the other hand, the error of the estimation, especially the electron temperature, increased to about 50% for the cases with discharge power of less than 12 kW, suggesting that signal-to-noise ratio must be improved for the detailed analysis of the data with lower discharge power conditions. The detailed analysis on the performance of the PW, using the obtained 𝑛 e and 𝑇 e , is described in other publication [13].…”