Kiel 2004 – scientific programme

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P: Plasmaphysik

P 3: Postersitzung: Niedertemperaturplasmen Plasmatechnologie I, Diagnostische Methoden I

P 3.11: Poster

Monday, March 8, 2004, 17:45–19:30, Foyer

Enhanced microwave scattering diagnostics on a helicon discharge — •K. D. Lee, R. Madani, T Klinger, M. Hirsch, and H. -J. Hartfuß — Max-Planck-Institut für Plasmaphysik, EURATOM Ass., D-17491 Greifswald, Germany

A helicon discharge can offer superior conditions for enhanced-scattering diagnostics because of the electron plasma frequency being higher than the cyclotron frequency. This method using microwave technique is the best alternative to observe small-scale fluctuations.

The principle is based on the scattering of an extraordinary electromagnetic wave in the vicinity of the upper hybrid resonance. When fluctuations are present in the resonance zone, an incident wave is back-scattered if the Bragg condition is satisfied. The scattered wave has a much shorter characteristic scale-length than the wavelength in vacuum. As a result it becomes sensitive to small-scale fluctuations and has an enhanced intensity as well as a large time delay. Thus the fluctuations near the resonance layer can be detected with a high sensitivity and spatial resolution.

The VINETA device can produce a linearly magnetized helicon discharge and has been dedicated to experiments on nonlinear plasma dynamics. In this work, a swept frequency microwave scattering system is employed in this device, which allows the effective spatial scan of the resonance surface in the helicon plasma. The measured wave number and frequency spectra are shown and discussed. This information reveals ion wave dynamics and implies its relation with intrinsic instabilities in a helicon discharge.