Comparison of runaway dynamics in LH and ECRH heated discharges in the Frascati Tokamak Upgrade

The behaviour of high energy runaway electrons during the flat-top phase of lower hybrid (LH) heated discharges has been investigated in the Frascati Tokamak Upgrade. It is found that, as in electron cyclotron (EC) heated discharges, the fall of the electric field during the wave injection phase yields a reduction of the runaway energy (frequently leading to runaway quenching). However, in contrast to EC heated discharges, after the heating phase, in LH discharges the acceleration of the wave-resonant suprathermal tail allows the runaway population to be restored.