Thomson scattering measurements on a low pressure surface wave sustained plasma in argon

Abstract

Thomson scattering (TS) experiments have been made on a low pressure surfatron induced plasma. TS is an active diagnostic method and the experimental results are directly related to important plasma properties such as the electron density, ne, and the electron temperature, Te. Therefore, the TS results for ne and Te can be used to calibrate passive diagnostic methods which are often based on plasma models. However, to apply TS on a surfatron induced plasma inside a quartz tube is experimentally demanding because of the large amount of stray light and a low intensity of the TS signal. To achieve low detection limits and high stray light rejection, a triple grating spectrograph was used in the detection branch and an iCCD was used to record the TS spectrum. For a typical plasma condition with an argon pressure of 10 mbar and an absorbed power of 50 W, the measured electron density was found to be equal to ne 4 × 1019 m-3 and the electron temperature Te 1.2 eV. In addition, frame-averaged results for 6, 10, 15 and 20 mbar argon plasmas for absorbed microwave powers in between 25 = Pab = 60 W are presented. The trends found in the dependence of the pressure and power density are according to theory.