INCA - Inductively Coupled Array Discharge

TL;DR

This paper introduces the INCA discharge, a novel plasma generation method using structured vortex fields produced by an array of coils, demonstrating stable operation, efficient power coupling, and potential for large-scale applications.

Contribution

First experimental realization of the INCA plasma source, demonstrating scalable vortex field arrays, stable low-pressure operation, and characteristic plasma behaviors including super energetic electrons.

Findings

Stable operation at pressures below 1 Pa

Linear scaling of plasma density with power and pressure

Presence of super energetic electrons indicating stochastic heating

Abstract

Recently a novel concept for collisionless electron heating and plasma generation at low pressures was proposed theoretically (U Czarnetzki and Kh Tarnev, Phys. Plasmas 21 (2014) 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 (U Czarnetzki, submitted to PSST (2018), arXiv:1806.00505). Here, the new concept is experimentally realized for the first time by the INCA (INductively Coupled Array) 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 behaviour 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 for the presence of super energetic 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.