Excitation and Propagation of Electrostatic Ion Cyclotron Waves in rf-Sustained Plasmas of Interest to Propulsion Research

Abstract

Excitation and propagation of Electrostatic Ion Cyclotron (EIC) waves in an rf-sustained argon plasma are reported along with measurement of dispersion relation. Such waves can be used to energize the plasmas of a number of promising propulsion concepts. The waves are excited by an antenna consisting of two parallel metal plates inserted at the edge of a plasma column with their surface normal perpendicular to magnetic field. The plates can be driven in or out of phase. The in-phase configuration couples better to plasma. It is shown that EIC waves launched at frequencies between ω ci and 10ω ci propagate with little damping at an angle between 82 • and 86 • with respect to the magnetic field. The amplitude of the excited waves can be optimized by properly matching the impedance of the driving circuit to the plasma and choosing the right plasma conditions. The dispersion relation was measured using a phase-delay technique and was found to be in good agreement with the theoretical EIC dispersion relation over a wide range of frequencies.

Evolution of the parallel and perpendicular ion velocity distribution functions in pulsed helicon plasma sources obtained by time resolved laser induced fluorescence

“…The only modification to the experimental apparatus that we typically use for LIF measurements in steady-state plasmas is the addition of a digital oscilloscope on which the LIF emission versus time is averaged over many tens of pulses [29]. A time resolution of 1 ms is sufficient to investigate ion heating by pulsed electrostatic ioncyclotron beat-waves [10,30,31], in helicon sources and the formation of ion beams in pulsed expanding helicon source plasmas [32]. We note that other researchers have used similar techniques to investigate externally imposed, repetitive, transient phenomena in a steady-state background plasma, e.g.…”