Thomson scattering on argon surfatron plasmas at intermediate pressures: Axial profiles of the electron temperature and electron density

The axial profiles of the electron density n_e and electron temperature T_e of argon surfatron plasmas in the pressure range of 6–20 mbar and microwave power between 32 and 82 W have been determined using Thomson Scattering of laser irradiation at 532 nm. For the electron density and temperature we found values in the ranges 5 × 10¹⁸ < n_e < 8 × 10¹⁹ m^− 3 and 1.1 < T_e < 2.0 eV. Due to several improvements of the setup we could reduce the errors of n_e and T_e down to 8% and 3%, respectively. It is found that n_e decreases in the direction of the wave propagation with a slope that is nearly constant. The slope depends on the pressure but not on the power. Just as predicted by theories we see that increasing the power leads to longer plasma columns. However, the plasmas are shorter than what is predicted by theories based on the assumption that for the plasma-wave interaction electron–atom collisions are of minor importance (the so-called collisionless regime). The plasma vanishes long before the critical value of the electron density is reached. In contrast to what is predicted by the positive column model it is found that T_e does not stay constant along the column, but monotonically increases with the distance from the microwave launcher. Increases of more than 50% over 30 cm were found.