Neutron profiles and fuel ratio nT/nD measurements in JET ELMy H-mode plasmas with tritium puff

Abstract

Two-dimensional (2D) spatial profile and the temporal evolution of the 14 and 2.5 MeV neutron emissivities from D–D and D–T fusion reactions were studied using the measurements of the upgraded neutron profile monitor during the last trace tritium experiments in JET. The JET neutron profile monitor provides unique capability for 2.5 and 14 MeV neutrons line-integrated measurements simultaneously. A systematic comparison of D–D and D–T neutron emissivity was performed. The tritium concentration or fuel ratio (nT/nD) was analysed for a set of 34 ELMy-H mode discharges with tritium puff. Tritium concentration is deduced with a method based on the ratio of D–T 14 MeV and D–D 2.5 MeV neutron emissivities in order to exploit the maximum information available from neutron data. With the help of a tomography algorithm recently developed at JET, 2D spatial profiles of the tritium concentration in the plasma were obtained. These profiles can be used to perform transport studies. Tritium core confinement is clearly seen to increase with plasma density for the set of discharges studied. Differences in the shape of these profiles are also found between low and high density plasmas. Shortly after tritium puffing, 2D spatial profiles of the tritium concentration exhibit typical hollow profiles and in some cases transient poloidal asymmetric features have been observed in 2D images.