Laser-induced fluorescence measurements of ion fluctuations in electron and ion presheaths

摘要: Electrostatic flow-driven instabilities have been predicted in the presheath region of low-temperature plasmas for both ion and electron rich sheaths. The ion-acoustic fluctuations that arise from these can influence transport through an enhanced collision rate. In this work, fluctuation spectra were measured using laser-induced fluorescence (LIF) sheath polarities. non-invasive nature LIF compared to probes is particularly valuable measurements because around a probe may generate their own instabilities, which obscure measurement. Measurements made recently implemented field programmable gate array-based system able measure up 1 MHz two-point correlation function technique. Narrow bandwidth observed near 0.46 f pi (460 kHz) polarities, where plasma frequency. significantly stronger case over larger volume plasma. Fluctuations at locations far enough linear theory predicts stability, suggesting generated relatively small unstable boundary reflect perturb much This expected affect with sheaths, meaning any dc biased effectively act as wave antenna. These are consistent recent particle-in-cell results.