Plasma pressure and particle loss studies in the Pilot-PSI high flux linear plasma generator

Abstract

Plasma detachment in tokamak divertors reduces the particle and power fluxes to the plasma facing components and is essential for successful operation of ITER. The linear plasma generator Pilot-PSI can produce a high density (∼1021 m−3), low temperature (∼1eV) plasma which is similar to that expected at the ITER divertor strike-points during the partially detached regime [1]. Given the simple geometry of the device, Pilot-PSI allows to diagnose the plasma beam at multiple axial positions. In this study, the incoherent Thomson scattering (TS) diagnostic [2] is exploited to measure the radial plasma Te and ne profiles at two locations of the hydrogen plasma beam: near the plasma source (upstream) and 2cm from the target plate. At the target, the TS measurements are supported by an embedded Langmuir probe. These measurements prove the existence of parallel plasma pressure loss as well as particle loss, confirming that physical processes believed to cause detachment in tokamak divertors also hold in Pilot-PSI (ion-neutral friction, volume recombination). It is found that the fractional reduction of the plasma pressure varies between ∼4 and ∼5000, depending strongly on the pressure of the background neutrals. The importance of individual loss channels is discussed. Keywords: Detachment, Pilot-PSI, Langmuir probe, Thomson scattering, Divertor, Volume recombination