Phase resolved optical emission spectroscopy: a non-intrusive diagnostic to study electron dynamics in capacitive radio frequency discharges Phase resolved optical emission spectroscopy: a non-intrusive diagnostic to study electron dynamics in capacitive

Abstract Various types of capacitively coupled radio frequency (CCRF) discharges are frequently used for different applications ranging from chip and solar cell manufacturing to the creation of biocompatible surfaces. In many of these discharges electron heating and electron dynamics are not fully understood. A powerful diagnostic to study electron dynamics in CCRF discharges is phase resolved optical emission spectroscopy (PROES). It is non-intrusive and provides access to the dynamics of highly energetic electrons, which sustain the discharge via ionization, with high spatial and temporal resolution within the RF period. Based on a time dependent model of the excitation dynamics of specifically chosen rare gas levels PROES provides access to plasma parameters such as the electron temperature, electron density and electron energy distribution function (EEDF). In this work the method of PROES is reviewed and some examples of its application are discussed. First, the generation of highly energetic electron beams by the expanding sheath in geometrically symmetric as well as asymmetric discharges and their effect on the EEDF are investigated. Second, the physical nature of the frequency coupling in dual frequency discharges operated at substantially different frequencies is discussed. Third, the generation of electric field reversals during sheath collapse in single and dual frequency discharges is analysed. Then excitation dynamics in an electrically asymmetric novel type of dual frequency discharge is studied. Finally, limitations of PROES are discussed

Thomson scattering of plasma turbulence on PSI-2

The turbulent transport in the edge of fusion reactors can be conveniently simulated by linear plasma devices with long duty cycles. At high input power steady state plasma discharges at PSI-2 exhibit intermittent fluctuations similar to the edge of toroidal plasma devices. As their influence on erosion predictions is obscured by time-averaged measurements a time-resolved Thomson scattering setup is installed and tested at PSI-2. Aided by a fast CMOS camera and conditional averaging a time resolution of 3 µs was achieved for temperature and density profile evolution in Argon and Deuterium discharges. A 40 kHz, m = 1 oscillation with 50 µs coherence time and 1 eV electron temperature amplitude was identified in Argon, while in Deuterium intermittent events were associated with a 4 eV rise in edge temperature and a 10% reduction of bulk density. Keywords: Fusion, Plasma diagnostic, Thomson scattering, Turbulence, Conditional averag