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Aachen PK 2003 – scientific programme

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P: Plasmaphysik

P 7: Plasma Diagnostics

P 7.5: Talk

Tuesday, March 18, 2003, 16:50–17:10, FO1

Multichannel Two Color Interferometer for W7-X — •Thomas Bindemann, Matthias Hirsch, and Hans-Jürgen Hartfuß — Max-Planck-Institut für Plasmaphysik, EURATOM Ass., D-17491 Greifswald, Germany

Interferometry is the standard diagnostic for line integrated electron density measurements in fusion plasmas.

The interferometer for W7-X has to operate in the IR to avoid refraction of the probing beams due to the high electrons densities (ne≈ 2× 1020 m−3) and the steep density gradients. Because of geometry restrictions the probing beams have to be reflected at the inner wall of the vessel giving rise to a phase shift caused by vibrations which amounts a multiple of the phase shift due to the plasma at the chosen wavelength.

For W7-X a multichannel interferometer is proposed operating simultaneously at a wavelength of 10.6 µm (CO2) and of 0.633 µm (HeNe) (two colors) allowing for the compensation of the mechanical vibrations.

Measuring with a number of probing beams allows to reconstruct the shape of the density profile (Abel inversion). The number of sightlines and its geometry is currently optimized.

A heterodyne interferometer using frequency stabilized CO2 and HeNe lasers and Acusto Optical Modulators is built in the lab to study the vibration compensation in order to provide a reliable interferometer.

We report the present design status of the system proposed and we present the setup of the test interferometer and we discuss first results of the vibration studies.

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