DENSEPACK: An array of Langmuir probes in the limiter shadow plasma of the Alcator C tokamak fusion experiment

Abstract

The boundary plasma of the Alcator C tokamak exhibits poloidal asymmetries in plasma parameters. In order to investigate this phenomenon, an array of 80 closely spaced Langmuir probes has been built to directly sample this plasma region. This specially developed, densely packed probe array (DENSEPACK) is unique in that it provides a simultaneous, time-dependent, two-dimensional mapping (minor radius r, poloidal angle θ) of plasma density, electron temperature, and floating potential over nearly the full 360° poloidal extent of the boundary plasma in this circular cross-section tokamak. The construction and operation of the DENSEPACK probe array, as well as support hardware and software systems needed to handle the large volume of data generated by this array, are described in this paper.