Plasma parameters measured inside and outside a microwave-discharge-based plasma cathode using laser-induced fluorescence spectroscopy

Abstract

An understanding of the plasma physics inside a microwave discharge cathode is key to extending the lifetime of microwave ion thruster systems. However, probes can only measure the plume region due to their low spatial resolution and electromagnetic disturbance. In this study, we develop a microwave discharge-based cathode with a small optical window in the discharge chamber that provides visual access to the cathode interior. The cathode has the same anode currents as those of a flight model in the diode mode (anode voltage error is within 7%). Laser-induced fluorescence spectroscopy is applied to the cathode. The axial and radial ion velocity distribution functions (IVDFs) in the plume region and the axial IVDFs inside the cathode are measured. The measured functions, which represent the number density of Xe II (3P2)6p[3]5/2, are compared to a previously reported number density of Xe II measured by an electrostatic probe in the plume region. The functions exhibit multimodal characteristics. Theoretical models based on the measured current oscillation support these characteristics.

Time-resolved laser-induced fluorescence spectroscopy using CW diode laser for diagnostics of argon-ion velocity distribution near AC-biased electrode

“…[27][28][29] To investigate the behavior of rare-gas ions in lowtemperature plasmas in the steady state, the LIF method has been utilized to diagnose bulk plasmas, [30][31][32][33] pre-sheaths, [34][35][36][37][38] ion sheaths formed on floated, 39,40 and DC-biased electrodes, [41][42][43][44][45] and plumes of electric propulsion devices. [46][47][48][49][50][51][52] To understand the dynamic behaviors of ions in plasmas, time-resolved LIF systems have been developed and applied to diagnose spatiotemporal fluctuations in plasma thrusters, [53][54][55][56][57] the temporal evolution of discharge and afterglow phases in pulsed plasmas, 58,59 and ion sheaths formed on AC-biased electrodes. [60][61][62][63][64][65] Time-resolved LIF measurements of ion sheaths were achieved by using pulsed dye lasers as the excitation-laser source and controlling the laser-pulse timing synchronized with the AC bias voltage applied to the electrode.…”

Influence of applied magnetic field in an air-breathing microwave plasma cathode

“…Another ECR microwave cathode with significant research maturity is the µ10 neutralizer developed by JAXA and flown on the Hayabusa-1 and 2 asteroid sample return missions. Studies include those in [13,14] and, more recently, [15]. The µ10 operates at a nominal current of 0.18 A with 0.07 mg s −1 of xenon flow rate, at an input 4.2 GHz microwave power of 8 W and total bias of 32 V between the neutralizer and anode in standalone testing [15].…”

“…Studies include those in [13,14] and, more recently, [15]. The µ10 operates at a nominal current of 0.18 A with 0.07 mg s −1 of xenon flow rate, at an input 4.2 GHz microwave power of 8 W and total bias of 32 V between the neutralizer and anode in standalone testing [15]. An updated neutralizer design for the µ20 configuration demonstrates a maximum current of 0.5 A with xenon at 20 W microwave power [16].…”