  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.
