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P: Fachverband Plasmaphysik

P 9: Poster: Niedertemperaturplasmen

P 9.21: Poster

Tuesday, March 31, 2009, 17:30–19:30, Foyer des IfP

Wave Heating in Neutral Loop Discharges — •Yusuf Celik, Dragos L. Crintea, Christopher Isenberg, Rachel Fainblat, Dirk Luggenhölscher, and Uwe Czarnetzki — Institute for Plasma and Atomic Physics, Ruhr University Bochum, 44780 Bochum

The Neural Loop Discharge (NLD) is believed to be based on a chaotization of electron trajectories around a magnetic X-point. Single particle and PIC simulations predict strong heating by a superimposed RF electric field. In this contribution we demonstrate that the heating mechanism in inductive NLDs is in fact given by the formation of an azimuthally isotropic m = 0 Helicon wave. The current induced in the vicinity of the X-point modifies the Helicon field structure compared to the standard case observed in homogeneous fields. This leads to a beating of different longitudinal modes. In addition, standing wave patterns by reflection from the chamber bottom are observed. The parallel occurrence of different longitudinal modes stabilizes the discharge and operation is less critical to phase and refractive index matching than in a standard Helicon discharge. The above picture is the result of intensive measurements using Langmuir and B-dot probes as well as phase resolved optical emission spectroscopy (RF-MOS). Maximum optical emission is observed outside the neutral loop (X-point) along a hollow hose oriented parallel to the static magnetic field. The emission pattern remains unchanged when the flux lines to the X-point are blocked by quartz ring. The measured wave field structures agree well with a simple model including the diamagnetic current induced close to the X-point. Supported by DFG via GK 1051.