Erosion rate diagnostics in ion thrusters using laser-induced fluorescence

ABSTRACT fio = atomic transition oscillator strength g = linewidth distribution function, sec We have demonstrated the use of laser-induced flu- g = energy-averaged Gaunt factor orescence (LIF) to monitor the charge-exchange ion 9i = degeneracy for atomic level i erosion of the molybdenum accelerator electrode in h = Planck's constant, J sec ion thrusters. This real-time, nonintrusive method h = Planck's constant/2r, J-sec was implemented by operating a 30-cm-diameter I = intensity of optical radiation, W/m 2 ring-cusp thruster using xenon propellant. With the JA = accelerator electrode current, A thruster operating at a total power of 5 kW, laser ra- Jb = extracted beam ion current, A diation at a wavelength of 390 nm (corresponding to JE = cathode emission current, A a ground state atomic transition of molybdenum) was k = Boltzmann's constant, J/°K directed through the extracted ion beam adjacent to M = mass of molybdenum atom, kg the downstream surface of the molybdenum acceler- mass of the electron, kg