Measurement of limiter heating due to alpha particle losses during high fusion power deuterium-tritium operation of the TFTR tokamak

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Abstract
Measurements and preliminary analysis have been completed on limiter heating during high fusion power deuterium-tritium (D-T) operation of the Tokamak Fusion Test Reactor (TFTR) in an attempt to identify heating from first orbit and ripple losses of fast alpha particles. Recent operation of TFTR with a 50-50 mix of D-T has resulted in fusion power output (≊6.2 MW) orders of magnitude above what was previously achieved on TFTR. A significantly larger absolute number of particles and energy from fusion products, compared to D-D operation, are expected to be lost to the limiters. Power and energy estimates of total alpha losses were as high as 0.13 MW and 64 kJ. Measurements were made in the vicinity of the outer midplane, where most of the losses are expected, with thermocouples mounted on the tiles of a limiter. With an increasingly more reactive mixture of D and T at constant beam power, there was a measurable increase in the limiter tile temperature as the fusion power and alpha yield increased. The measured temperature increases due to heating from alpha losses corresponded to heat loads of ≤5.9 kJ/m2, which are within a factor of 2 of estimates for alpha heating based on simulations assuming a loss rate of fast alphas of 12%. Estimates are made of heating from the various heating sources using simulations from a number of codes. The observed level of alpha heating indicates that there was probably neither an unexpectedly large fraction of lost alphas nor unexpected localization of the losses. Limits on the stochastic ripple loss contribution from alphas can be deduced.