Infrared Thermography in the Tokamak à Configuration Variable

Abstract

In the Tokamak à 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.

Figures (11)

• Figure 2.1: (a) Magnetic reconstruction of a power exhaust reference shot (87222), repeated from time to time to assess the divertor conditions, with all IR camera views except the TIR upper port. (b) HIR view, with inner strike point at the inner wall. Differences in temperature in the strike point are due to the inner wall tiles not being toroidally symmetric Pitts1999 TCV tiles. (c) VIR view with outer strike point (OSP) at the tilted tiles and line of interest (in red) used for the heat flux analysis in Fig. \ref{['fig: heat flux example']}. Red and yellow circles are screws. Difference in temperature in the OSP are due to leading edges and absence of toroidal symmetry.
• Figure 3.1: HIR raw data view during the temperature calibration with TC at $T=89\;\text{ºC}$. Heated tile (HT) in the center, with the pixels $ij$ used for the calibration in red.
• Figure 3.2: (a) Raw HIR data vs TC temperature for $\Delta t_{int}=0.1\;\text{ms}$. (b) Fits of $A_{TC}$ and $B_{TC}$ vs $\Delta t_{int}$. Fitting Eq. (\ref{['eq: Ntc vs Atc Btc']}) in Fig. \ref{['fig:calib N-vs-T']}(a) gives $A_{TC}$ and $B_{TC}$ at $\Delta t_{int}=0.1\;\text{ms}$. Doing the same for different integration times yields the data of Fig. \ref{['fig:calib N-vs-T']}(b), which can then be fitted by Eq. (\ref{['eq: Atc Btc']}) to obtain $a_{TC}$, $b_{TC}$, and $c_{TC}$ (known as 3 parameter fit).
• Figure 3.3: $a_{ij}$, $b_{ij}$, and $c_{ij}$ matrices for the HIR calibration shown in Fig. \ref{['fig:calib N-vs-T']}.
• Figure 6.1: TCV's graphite tile properties measured by NPL. (a) Mass density. (b) Specific heat capacity. (c) Diffusivity. (d) Conductivity. Blue and circles: data from 2023 samples; orange circles: 2025 samples. Black curves: fit using the functional dependency expected by THEODOR ($f(T)=a+b(1+T/T_{0})^{-2}),$ yielding Eq. (\ref{['eq: D fit']}) and (\ref{['eq: k fit']}). Yellow stars and curves: old estimates used in TCV for the tile diffusivity and conductivity (Eq. (\ref{['eq: old diff']}) and (\ref{['eq: old cond']})).