Role of Recycling in JET Trace Tritium Transport Experiments

JET experiments with transient puffed injection of low tritium levels (<1%) were carried out with the goal of using measured time- and space-dependent neutron emission to determine the r*, n* and b scaling of particle transport in the core (normalized radius r<0.8) for ITB, ELMy H -mode and hybrid scenario [1]. Although the diagnostics were well suited to this task, several attempts to find core tp scaling based on the same dataset have reached contradictory conclusions. For example a scaling of core particle diffusivity inversely proportional to density was found using an interpretive-predictive approach, a scaling proportional to density in using predictive modeling, and a scaling independent of collisionality (density independence) in by fitting the neutron emission data. The analyses cited have also varied the assumed boundary conditions. In a three reservoir model was used for the region exterior to the core, with model parameters varied as needed to fit the time behavior of the outermost neutron channel. In, the boundary value of the tritium density was assumed small enough not to influence the core simulations, with a value of core tritium recycling from 3-7% of the total deuterium and tritium flux. Finally, it was assumed that 0<RT <1. The core tritium recycling coefficient RT is defined as the ratio of T influx to the core to the T efflux from the core. In all three cases, ELM-averaged transport was analyzed.
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