Fast Ion Losses in JET Hybrid Scenarios ­ MHD Sources Overview

Plasmas in hybrid scenario tend to exhibit a complex mix of low frequency MHD activity (notably fishbone oscillations, occasional sawteeth, continuous n = 1 modes, and often several pressure driven tearing modes with toroidal mode number 1 n 7), whose impact on the fast ion confinement may differ significantly from the impact on the thermal confinement. The main aim of this work is to document and characterise the main MHD sources of fast ion losses and quantify their relative importance in hybrid operating scenarios with view to their future use in a JET DT campaign. The main tool for these studies are a fast ion losses detector (FILD) probe yielding localised time-resolved velocity space information about the escaping energetic ions (Fig.1a), and a set of activation-foil calibrated Si diodes for volume-integrated 14MeV neutron rates. A total of 92 NBI-heated hybrid pulses from the 2013 experiment campaigns were analysed. It is important to note that the FILD setup allows for the measurement of lost fusion products and ICRH accelerated ions (E > 0.25MeV), whereas neutral beam ions (E 125keV) cannot be currently measured.
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