ABSTRACT
In the power-off phase, plasmas generated by repetitive short-pulse microwaves in a multicusp (MC) magnetic field show a transitive nature from interpulse to afterglow as a function of pulse duration tw = 20-200 μs. The ionized medium can be driven from a highly nonequilibrium to an equilibrium state inside the pulses, thereby dictating the behavior of the plasma in the power-off phase. Compared to afterglows, interpulse plasmas observed for tw < 50 μs are characterized by a quasi-steady-state in electron density that persists for ~20-40 μs even after the end of the pulse, and has a relatively slower decay rate (~4.3 × 104 s−1) of the electron temperature, as corroborated by optical measurements. The associated electron energy probability function (EEPF) indicates depletion in low-energy electrons, which appear at higher energies just after the end of the pulse. The transition occurs at tw ~ 50 μs, as confirmed by time evolution of integrated electron number densities obtained from the distribution function.
