Thermo-Elastic Analyses of Ion-Thruster Grids

This paper describes a method for estimating the temperature distributions over ion thruster’s grids and their thermal displacements. A thermal model in the method deals with heat transfer from discharge plasma to the grids and an elastic model provides their thermal displacements. Since the parameters needed for an analysis are currents, voltages and the screen-grid-edge temperature, this method is applicable not only to beam-off mode but also to beam-on mode. Temperature distributions and thermal displacements were estimated at four operating points of JAXA’s 35-cm ion thruster. Thermal input to the screen grid was much larger in beam-off modes than that in a beam-on mode and the thermal displacements of the screen grid were up to 2.2 mm. On the other hand, the displacements of the accel grid were up to 0.14 mm. Both grids would contact with each other in the beam-off modes if their separation were set to be appropriate in the beam-on mode. Nomenclature c A = area of cathode potential surface in discharge chamber excluding screen grid, m 2 dc A = area in discharge chamber, m 2 g A = area of grid in discharge chamber, m 2 1 C , 2 C = constant e = electronic charge, C a I = accel grid current, A b I = beam ion current, A d I = discharge current, A s I = screen grid current, A sat