Early Departure from Free Acceleration and Turbulent Heating of Electrons in a Toroidal Experiment

Shortly after initiation of a high-voltage toroidal discharge in Ar, departure from free-electron acceleration is observed, together with electron heating such that the total energy input is accounted for. This early behavior is attributed to a high-frequency instability (${\omega }_{\mathrm{pi}}<\omega <{\omega }_{\mathrm{pe}}$) due to interaction between relatively few trapped electrons and the streaming electrons.