A fast-reciprocating probe array for two-dimensional measurements in the divertor region of the Tokamak à configuration variable

Abstract

A detailed description of the construction and commissioning of the fast-moving reciprocating divertor Langmuir probe array on the Tokamak à Configuration Variable (TCV) is presented. A horizontal array of 24 Langmuir probes (12 Mach probes) combined with a fast vertical movement provides unprecedented two-dimensional measurements of the plasma properties across the entire divertor outer leg volume and up to the X-point. The L-shape probe arm has to be very compact to minimize plasma perturbations and, at the same time, has to house 24 coaxial transmission lines, withstand time-averaged heat fluxes of up to ≈30 MW/m2 and accelerations of up to 8 g, and be resilient to violent plasma disruptions. For the fast vertical motion of the probe arm, extending up to 38 cm into the TCV vacuum vessel, an assembly with a precise and powerful linear electric motor (up to 4000 N of force) was mounted in a 4 m high structure within the limited space below the TCV. The diagnostic has already performed measurements in ≈200 plasma discharges and has been hit by ≈20 disruptions without suffering any critical damage. The measurements are qualitatively and quantitatively consistent with other reference diagnostics, such as upstream electron Thomson scattering and downstream wall-embedded Langmuir probes, and are used extensively on the TCV for experimental divertor studies and for comparisons with edge transport and turbulence code results.