Infrared Thermography in the Tokamak \`a Configuration Variable

TL;DR

This paper discusses the infrared thermography systems used in TCV tokamak, highlighting recent upgrades, measurement techniques, and ongoing challenges in heat flux diagnostics.

Contribution

It presents recent developments in TCV's IR systems, including new hardware, measurement methods, and wavelength filtering to improve heat flux analysis accuracy.

Findings

Enhanced IR system capabilities for fast transient analysis.

Addition of new tiles for improved heat flux measurements.

Implementation of long-pass filter to reduce parasitic IR light.

Abstract

In the Tokamak \`a Configuration Variable (TCV), infrared thermography (IR) is currently composed of the horizontal, vertical, and tangential infrared systems (HIR, VIR, TIR), which all use Equus 81k M cameras. The IR diagnostics obtain the surface temperature of TCV's graphite tiles for post-discharge analysis. Target heat flux profiles are inferred from the tile temperature with the THEODOR (Thermal Energy Onto Divertor) code. Fast transient analysis is possible in reduced frame mode, with acquisition frequencies above 10kHz. The main views are the lower inner wall for HIR, the floor for VIR, and the lower outer wall for TIR. The HIR camera can also be moved to view the midplane inner wall, while TIR can be moved to see the midplane inner wall and the upper outer wall, mainly to measure synchrotron radiation and heat deposition due to runaway electrons. Recent developments in TCV's IR systems include (i) tile diffusivity and conductivity measurements to assure the precision of heat flux estimates; (ii) the addition of one new VIR heated valley tile and two rooftop TIR tiles, for measurements of fast heat flux transients; (iii) the implementation of long-pass wavelength filter of 4095 nm, to diminish the measurement of plasma parasitic infrared light, mainly from deuterium 5-4 emission at 4051 nm. Despite these developments, the main sources of uncertainty for IR in TCV are still parasitic infrared light and the determination of the surface layer heat transmission factor, both of which mainly affect the VIR system.