Inductively coupled array (INCA) discharge

Abstract

Recently a novel concept for collisionless electron heating and plasma generation at low pressures was theoretically proposed (Czarnetzki and Tarnev 2014, Phys. Plasmas 21 123508). It is based on periodically structured vortex fields, which produce certain electron resonances in velocity space. A more detailed investigation of the underlying theory is presented in a companion paper (Czarnetzki 2018, Plasma Sources Sci. Technol. 27 105011). Here, a new concept is experimentally realized for the first time by the inductively coupled array (INCA) discharge. The periodic vortex fields are produced by an array of small planar coils. It is shown that the array can be scaled up to arbitrary dimensions while keeping its electrical characteristics. Stable operation at pressures around and below 1 Pa is demonstrated. The power coupling efficiency is characterized, and an increase in the efficiency is observed with decreasing pressure. The spatial homogeneity of the discharge is investigated, and the behavior of the plasma parameters with power and pressure are presented. Linear scaling of the plasma density with power and pressure, typical for conventional inductive discharges, is observed. Most notably, the plasma potential and the corresponding mean ion energy show clear evidence of the presence of superenergetic electrons, attributed to stochastic heating. In the stochastic heating mode, the electron distribution function becomes approximately Maxwellian, but with increasing pressure it turns to the characteristic local distribution function known from classical inductive discharges. Large-area processing or thrusters are possible applications for this new plasma source.