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

A detailed description of the construction and commissioning of the fast-moving reciprocating divertor Langmuir probe array on the Tokamak a 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 approximate to 30 MW/m(2) 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 approximate to 200 plasma discharges and has been hit by approximate to 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.

Automated summary

This study presents the construction and commissioning of a fast-moving reciprocating divertor Langmuir probe array on the TCV, which provides unprecedented two-dimensional measurements of plasma properties. The probe design is compact and resilient, withstanding high temperatures and accelerations, and has successfully conducted measurements in numerous plasma discharges.