Thomson scattering diagnostic systems in ITER

TLDR

Thomson scattering is a proven diagnostic used on most fusion machines, and ITER will deploy three independent TS systems, but the harsh environment demands new subsystem designs. The paper presents the challenges and proposed solutions for all three TS systems. The design comprises an Edge TS measuring high‑resolution Te and ne profiles for r/a > 0.8, a Core TS covering r/a < 0.85 up to 40 keV, and a Divertor TS observing a >700 mm divertor segment down to 0.3 eV, with Edge and Core positioned closely (toroidal separation <600 mm) to enable profile matching while meeting ITER’s radiation, temperature, and reliability constraints.

Abstract

Thomson scattering (TS) is a proven diagnostic technique that will be implemented in ITER in three independent systems. The Edge TS will measure electron temperature Te and electron density ne profiles at high resolution in the region with r/a>0.8 (with a the minor radius). The Core TS will cover the region r/a<0.85 and shall be able to measure electron temperatures up to 40 keV . The Divertor TS will observe a segment of the divertor plasma more than 700 mm long and is designed to detect Te as low as 0.3 eV . The Edge and Core systems are primary contributors to Te and ne profiles. Both are installed in equatorial port 10 and very close together with the toroidal distance between the two laser beams of less than 600 mm at the first wall (∼ 6° toroidal separation), a characteristic that should allow to reliably match the two profiles in the region 0.8<r/a<0.85. Today almost every existing fusion machine has one or more TS systems installed, therefore substantial experience has been accumulated worldwide on practical methods for the optimization of the technique. However the ITER environment is imposing specific loads (e.g. gamma and neutron radiation, temperatures, disruption-induced stresses) and also access and reliability constraints that require new designs for many of the sub-systems. The challenges and the proposed solutions for all three TS systems are presented.