Charge exchange between xenon ions and xenon atoms is the source of a detrimental low energy plasma in the vicinity of electrostatic spacecraft thrusters. Proper modeling of charge-exchange induced spacecraft interactions requires knowledge of the respective charge-exchange cross sections. Guided-ion beam measurements and semiclassical calculations are presented for xenon atom charge-exchange collisions with Xe+ and Xe2+ at energies per ion charge ranging from 1 to 300 eV. The present measurements for the symmetric Xe++Xe exchange system are in good agreement with several earlier experimental studies and semiclassical calculations based on the most recently computed Xe2+ interaction potentials. The cross sections are ∼30% higher than predictions by the Rapp and Francis model [D. Rapp and W. E. Francis, J. Chem. Phys. 37, 2631 (1962)]. The present Xe2++Xe symmetric charge exchange measurements are the first to cover the ion energy range from 40 to 600 eV. The cross sections are in good agreement with low-e...

Xenon charge exchange cross sections for electrostatic thruster models

Afully three-dimensionalparticle-in-cell simulationmodelwas developed to compute the ionpropulsion induced plasma environment for the Deep Space 1 (DS1) spacecraft. Simulationsare comparedwith in- ightmeasurements of charge-exchange plasma from the ion propulsion diagnostics subsystem on DS1, and the results show good agreement. It is found that the plasma environment of DS1 is dominated by the charge-exchange plasma from the plume. For a typical ion thruster operating condition, the charge exchange plasma near the spacecraft surface has a density ranging from 106 cmi 3 near the thruster to 104 cmi 3 at the opposite end of the spacecraft and a current density ranging from 10i 7 A/cm2 to 10 i 9 A/cm2. It is shown that, for an interplanetary spacecraft with a moderate charging potential, charge-exchange ion back ow is through an expansion process similar to that of the expansion of a mesothermal plasma into a vacuum.

Three-Dimensional Particle Simulations of Ion Propulsion Plasma Environment for Deep Space 1

An axisymmetric model of the plume and backflow contamination from an ion-thruster plume is presented. Components included are primary beam ions, neutral propellant efflux, thermal propellant ions created mainly by charge-exchange collisions between primary beam ions and neutral propellant, nonpropellant efflux sputtered from thruster components, and neutralizing electrons. The plasma hybrid particle-in-cell technique is applied to both propellant charge-exchange ions and nonpropellant efflux ions produced within the beam and to their transport out of the beam to the regions surrounding a model spacecraft. Simulation results for plume properties such as ion density, beam potential, and ion flow angle are compared with experimental data. It is shown that the charge-exchange ions formed in the beam are accelerated outward by strong radial beam electric fields and form two distinct energy populations—one with a significant backstreaming velocity component.

Ion-thruster plume modeling for backflow contamination

The transition from old space to new space along with increasing commercialization has a major impact on space flight, in general, and on electric propulsion (EP) by ion thrusters, in particular Ion thrusters are nowadays used as primary propulsion systems in space This article describes how these changes related to new space affect various aspects that are important for the development of EP systems Starting with a historical overview of the development of space flight and of the technology of EP systems, a number of important missions with EP and the underlying technologies are presented The focus of our discussion is the technology of the radio frequency ion thruster as a prominent member of the gridded ion engine family Based on this discussion, we give an overview of important research topics such as the search for alternative propellants, the development of reliable neutralizer concepts based on novel insert materials, as well as promising neutralizer-free propulsion concepts In addition, aspects of thruster modeling and requirements for test facilities are discussed Furthermore, we address aspects of space electronics with regard to the development of highly efficient electronic components as well as aspects of electromagnetic compatibility and radiation hardness This article concludes with a presentation of the interaction of EP systems with the spacecraft

Ion thrusters for electric propulsion: Scientific issues developing a niche technology into a game changer.

A new model of the plasma plume from Hall Effect Thrusters (HET's) is presented. The model includes the self-expansion of the main beam by density gradient electric fields, lowenergy ions produced by resonant charge exchange between beam ions and neutral atoms (ambient and thruster-induced), and angle-dependent elastic scattering of beam ions off neutral atoms. The variation of radial velocities across the annular thruster beam is also included. The model is an advance over previous plume models in the way it numerically models the self-expansion of the main beam, and in particular, the treatment of elastic scattering using recently calculated differential cross sections. The results are compared with recent measurements of the energy and angledependent plume from the BPT4000 Hall-Effect Thruster. Both the intensity and energy dependence of the scattering peaks are compared. The principal result is that elastic scattering is the source of the majority of ions with energy greater than E/q=50V that are observed at angles greater than 45° with respect to the thrust axis. The model underscores the need for elastic scattering cross sections for multiply charged ions, as well as a better understanding of HET propellant utilization.

/pdf/a-hall-effect-thruster-plume-model-including-large-angle-i4yiyqjeeu.pdf

A Hall effect thruster plume model including large-angle elastic scattering

A two-dimensional axisymmetric model was developed to investigate the plasma environment induced by an ion thruster and to assess plume backflow contamination. Predictions of the propellant charge-exchange plasma and sputtered molybdenum-grid metal effluents from the NASA 30-cm xenon ion thruster over a wide range of operating conditions during space operation are presented and discussed. It is verified that previous scaling relationships for the backflowing contamination, for a given geometry configuration, can be used to scale backflowing currents as a function of thruster operating conditions. The deposition of sputtered molybdenum-grid ions is computed and is found to be less than previous estimates. It is shown that the electron temperature plays an important role in the plume, with the backflow currents increasing with electron temperature. In addition, the effectiveness of a plume shield in reducing backflow contamination is assessed and found to be effective.

N. A. Gastonis

Papers

Ion-thruster plume modeling for backflow contamination

Numerical study of spacecraft contamination and interactions by ion-thruster effluents