A fast scanning probe for DIII–D

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Abstract
A fast reciprocating probe has been developed for DIII–D which can penetrate the separatrix during H mode with up to 5 MW of NBI heating. The probe has been designed to carry various sensor tips into the scrape‐off layer at a velocity of 3 m/s and dwell motionless for a programmed period of time. The driving force is provided by a pneumatic cylinder charged with helium to facilitate greater mass flow. The first series of experiments have been done using a Langmuir probe head with five graphite tips to measure radial profiles of ne, Te, φf, ñe, and φ̃f. The amplitude and phase of the fluctuating quantities are measured by using specially constructed vacuum compatible 5‐kV coaxial transmission lines which allow us to extend the measurements into the MHz range. TTZ ceramic bearings and fast stroke bellows were also specially designed for the DIII–D probe. Initial measurements will be presented.

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