Conceptual design of reciprocating probes and material-testing manipulator for tokamak COMPASS Upgrade

Abstract

Three new in-vessel manipulators are designed and built for the new COMPASS Upgrade tokamak with uniquely high vessel temperature (250–500 °C) and heat flux density (perpendicular to divertor surface q ⊥ ∼ 80 MW/m2 and q ∥ ∼ GW/m2 at separatrix), which challenges the edge plasma diagnostics. Here we show their detailed engineering designs supported by heat conduction and mechanical models. Deep reciprocation of electrostatic probes near the separatrix should be possible by optimizing older concepts in (a) the head and probe geometry, (b) strongly increasing the deceleration up to 100× gravity by springs and strengthening the manipulator mechanical structure. One reciprocates close to the region of edge plasma influx (the outer midplane), the other at the plasma sink (between the outer divertor strike point and X-point), for studying the plasma divertor (impurity-seeded) detachment and liquid metal vapor transport. Both probe heads are equipped with a set of ball-pen and Langmuir probes, measuring reliably and extremely fast (10−6 s) local (1 mm resolution) plasma potential, density, electron temperature and heat flux and even ion temperature with 10−5 s resolution. The divertor manipulator (without reciprocation) will place various material test targets at the outer divertor. Unique will be its capability to increase 15× the surface heat flux with respect to the surrounding tungsten tiles just by controllable surface inclination of the test targets. We plan to test liquid metal targets where such inclined surface was found critical to achieve the desired mode with lithium vapor shielding. Even in the conservative expected performance of COMPASS Upgrade, we predict to reach and survive the EU DEMO relevant heat fluxes.

COMPASS Upgrade: a high-field tokamak for ITER- and DEMO-relevant research

“…Future refining of this model, by including additional physics mechanisms using codes such as SOLPS-ITER, BIT1 and ERO 2.0, is planned to verify this prediction. COMPASS Upgrade will be equipped with a divertor manipulator, mainly for material testing purposes [81], where different concepts of an LM divertor tile will be tested (different capillary porous materials and structure shapes, and different LMs). The pre-conceptual design of the LM divertor module is currently under development with the objective to contribute to the alternative DEMO divertor solution based on LM technology.…”

Embedded-probes diagnostics for the COMPASS upgrade tokamak: a concept

“…The divertor system will be presented separately in future publication. The concept of the reciprocating manipulators observing the X-point and the mid-plane SOL plasma are published in [9].…”