Calorimetry system for heat load in long-pulse discharges on EAST tokamak

Abstract

A calorimetry system has been developed in Experimental Advanced Superconducting Tokamak (EAST). It is employed to evaluate the heat load exhausted by cooling water. Full poloidal coverage is achieved after the upgrade in 2019. The experimental results show that the heat load exhausted by cooling water is 64% - 86% of the injected energy. Moreover, the heat load increases faster in the case with a higher heating power, and this is qualitatively confirmed by the simulation. In addition, a longer time is required for the temperature of the cooling water to achieve its maximum for a higher heating power. And in the decay phase of the water temperature, it shows an exponential characteristic. The averaged time constant of the thermal decay obtained by exponential fitting for the upper and the lower divertor are 12.1 s and 107.9 s, respectively. It indicates that the heat removal capability of the upper tungsten divertor outperforms the lower graphite divertor.

The global energy balance of the ASDEX Upgrade tokamak determined with the revised cooling water calorimetry

“…The results derived with both codes coincide well with results based on bolometric reconstructions (see figure 6) and are suitable for a reasonable calculation of the key contribution for any plasma scenario. In previous studies at AUG [9,10], JET [33] and EAST [34] facing the global energy balance challenge, an appropriate determination of radiative losses realized by means of bolometric measurements have not been realized. So far, simplifications, like constant correction factors, were applied on databases in order to take into account radiative losses.…”

“…As an additional application for long-run pulses, monitoring of heat fluxes at any PFCs can be added, an aspect with respect to the unsolved power exhaust challenge still has its importance. The operation of such calorimetries in long-run pulses, as foreseen in ITER or DEMO cannot be tested in AUG, but rather in devices like EAST [34], WEST [37] and soon in JT60-SA operating with superconducting coils. The monitoring of heat fluxes (the monitoring of α-heating cannot be properly tested in current devices) at any PFCs of a discharge is mandatory for the safe operation of the next generation tokamaks and have to be tested in the currently available tokamaks capable to operate with long-run pulses.…”

Calorimetry measurement for energy balance and energy distribution in WEST for L-mode plasmas

“…From the point of view of plasma physics, the heat load distribution over PFCs is essential to understand the physical processes at play and disentangle their contributions: convected power, radiated power, ripple losses, fast ions or electrons. Energy balance is however challenging to perform with the accuracy required, and in most present day devices, 25%-10% of energy is missing [1][2][3], furthermore, heat loads on the remote areas such as the vessel walls are still scarcely characterized. Recently in ASDEX Upgrade, a global energy balance with 5% of missing energy has been achieved based on calorimetry measurement with bolometric reconstruction and NBI loss calculation codes to close the energy balance in the remote areas [4].…”

Study on the effect of EAST divertor geometric accuracy on heat load distribution

“…A calorimetry system is developed in EAST based on water cooling system, which is employed to evaluate the heat load exhausted by cooling water via the temperature difference between inlet and outlet of water pipe, and the heat load 𝑄 (W) on PFCs transported by the cooling water is expressed as [19]:…”

“…Δ𝑇 is the water temperature difference between the inlet and outlet water tube ( • C). 𝜏 is the plasma duration (s), and 𝑡 0 , 𝑡 0 + Δ𝑡 is the interval of cooling time [19]. Armored thermocouple is employed as thermometers with a range of measurement of 0 • C-500 • C. And the measurement range of flowmeters is 0-150 t/h.…”