On a fusion born triton effect in JET deuterium discharges with H-minority ion cyclotron range of frequencies heating

Abstract

An effect due to fusion born triton production has been observed in JET high-performance deuterium plasma discharges with neutral beam injection (NBI) and H-minority ion cyclotron range of frequencies (ICRF) heating, using DD and deuterium tritium (DT) neutron spectrometry as well as fusion product loss measurements. The observations show that a decrease of the second harmonic omega = 2 omega(cD) enhancement of the DD neutron rate correlates with an increase of the triton burnup rate. An acceleration of tritons due to absorbing ICRH power at the third harmonic omega = 3 omega(cT) has been observed. This effect could indicate a redistribution of ICRH power absorption at omega approximate to omega(cH) = 2 omega(cD) = 3 omega(cT) with increasing triton concentration at the ion cyclotron resonance layer. Also, the reduction of the second harmonic enhancement of the DD neutron rate can be caused by burning of the accelerated deuterium as the tritium concentration grows. This is an extremely non-linear process as both mechanisms intensify with triton concentration. It determines the necessity to consider the ICRH power absorption omega = 3 omega(cT) in modelling of high-performance deuterium discharges with simultaneous NBI and H-minority ICRF heating as well as the assessment of enhanced burnup of ICRF accelerated deuterium for the development of high-performance plasma scenarios and DT fusion rate predictions.