Gundestrup is a Langmuir/Mach probe array which measures the flow velocity in the scrape-off layer of Tokamak de Varennes (TdeV). It is based on the concept of a Mach probe where presheaths extending upstream and downstream from the probe, parallel to the magnetic field, attract charge to a circular array of collecting pins. The polar distribution of ion saturation currents to the circular array is used to compute the components of flow velocity in the plasma. With Gundestrup, there is an assumed flow perpendicular to the magnetic field as well as parallel to it. Equations representing the collection of charge by individual pins on the probe are presented and sample flow patterns from the scrape-off layer are shown.

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