Electron energy distribution in a divertor simulating device with an RF source

Electron energy distribution measurement with oscillating plasma potential compensation was performed in the radio-frequency plasma device, DT-ALPHA. Electrons near the plasma production region are confirmed to have Maxwellian distribution. The radial profile of the electron energy distribution in the high neutral pressure region, which is maintained by secondary helium gas puffing, was also investigated. Whereas the electrons still have Maxwellian distribution, the electron temperature in the outer region of the plasma column is lower compared with the inner region. This indicates that the volumetric recombination is enhanced at the periphery of the gas target experiment in the DT-ALPHA device.