Threefold Increase of the Bulk Electron Temperature of Plasma Discharges in a Magnetic Mirror Device

This Letter describes plasma discharges with a high temperature of bulk electrons in the axially symmetric high-mirror-ratio (R = 35) open magnetic system gas dynamic trap (GDT) in the Budker Institute (Novosibirsk). According to Thomson scattering measurements, the on-axis electron temperature averaged over a number of sequential shots is 660 +/- 50 eV with the plasma density being 0.7 x 10(19) m(-3); in few shots, electron temperature exceeds 900 eV. This corresponds to at least a threefold increase with respect to previous experiments both at GDT and at other comparable machines, thus, demonstrating the highest quasistationary (about 1 ms) electron temperature achieved in open traps. The breakthrough is made possible by application of a new 0.7 MW /54.5 GHz electron cyclotron resonance heating system in addition to standard 5 MW heating by neutral beams, and application of a radial electric field to mitigate the flute instability.