Properties of an ECWR Discharge at Low Pressures

We report an experimental study of an electron cyclotron wave resonance (ECWR) plasma source. The dimensions of the source are considerably larger than in similar experiments. The excitation frequency is 27.12 MHz, the working gas is argon at very low pressures below 0.13 Pa. Spectroscopic data connected with a global model yield electron temperature T
_e
, electron number density n
_e
, population of the metastable state n
_m
. The pressure dependencies of these quantities are discussed. Starting from T
_e
~ 5 eV at pressure p = 0.13 Pa the temperature grows as the pressure goes down until the discharge extinguishes at ~0.6 × 10
^-2
Pa. It becomes in the meantime so high that the emission spectra feature strong Ar(II) lines in the region 400-500 nm. At p = 0.13 Pa and power 300 W the electron density on the axis is about 4 × 10
¹⁰
cm
^-3
and falls down due to the increase in T
_e
as the pressure drops. The discharge was also electrically characterized to determine the plasma impedance Z. The impedance and the plasma resistance Re(Z) are presented as functions of the static magnetic field B
₀
. The distribution of power losses are also shown as B
₀
-dependencies.