No abstract

Stable plasma production in a radio-frequency plasma source and steady-state high-neutral-pressure environment in a test region has been achieved simultaneously with backflow suppression components such as orifices and a differential pumping system. Neutral pressure in the test region is changed by two orders, resulting in changes in the electron temperature and density in the test region. Conversely, neutral pressure, electron temperature, and electron density near a plasma production region showed little change. The result indicates that the experimental device provides us independent control knobs of source plasma and neutral pressure in the test region.

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A directional Langmuir probe was designed and fabricated for measurement of ion flow in the RF plasma source, DT-ALPHA, in order to understand plasma structure in divertor study. Radial distribution and circumferential distribution of ion saturation current for He plasma were measured using the directional Langmuir probe. Ion flow velocity was obtained. A calibration factor was determined by comparing the radial profile of the azimuthal ion flow with E × B drift velocity and diamagnetic drift velocity.