Search

Neutralization of ion beams in electric propulsion applications is a well-known phenomenon. The physics behind the robust matching of ion and electron currents and densities, are not. As electric propulsion devices move into micro and macro regimes with colloids, FEEPs, and thruster arrays, thruster-neutralizer interactions are under increasing scrutiny. A series of 2D simulations using PIC codes are presented, detailing starting and steady state interactions. It is shown that the expectations of full current coupling of electrons to the beam is not seen, but there is similar coupling behavior exhibited. Numerical mechanisms for coupling the current to the beam are examined for effect on coupling behavior., JAXA Special Publication, 宇宙航空研究開発機構特別資料

It can be shown that ion beams in electric propulsion devices create a potential well which acts to retain neutralizing electrons to a degree. To be trapped in the well, however, it is necessary for the energy and momentum that got the electrons to the well to "bounce" off the other side of the well to bring their dwell time up to a point where they can be trapped. We demonstrate that conditions exist in normal electric propulsion plumes where a collisional scattering mechanism can be sufficient to scatter a neutralizing electron beam into the ion beam. Furthermore, once in the well for a sufficiently long period, collective instabilities such as the Buneman instability thermalize the electrons, dropping the bulk electron velocity to match that of the ions. While normally this would mean that electron temperature should be equal to the well depth, we show by means of a simple flux model that electrons thermalize only to a point where the flux of "hot" electrons out of the well is matched by the ambient "cold" electrons moving into the well., Presented at the AIAA/ASME/SAE/ASEE Joint Propulsion Conference (44th), held in Hartford, CT, 2008. Prepared in cooperation with Worcester Polytechnic Institute, Worcester, MA.

The Ion Proportional Surface Emission Cathode (IProSEC) is a low-brightness cathode technology under development for applications where large areas are available for emission and it is advantageous to avoid the space charge effects associated with bright or intense sources. Space applications include spacecraft charge control and electrodynamic tethers. Surface Emission Cathodes emit electrons by concentrating an electric field between a p-doped insulating substrate and an adjacent metal cathode element. The substrate potential is held positive of the cathode with gate elements. In plasma, the gate is eliminated due to ambient ion flux which maintains the substrate potential near plasma ground. Prototype devices have been tested using a laboratory plasma source achieving sustained and stable operation over a wide bias voltage for a given ion flux. Chip-based sources are compared to carbon nanotube mats. The principle of operation, ion flux proportionality, and prototype performance is discussed., Presented at the AIAA/ASME/SAE/ASEE Joint Propulsion Conference (44th), held in Hartford, CN, paper AIAA-2008-4640, 2008. Prepared in collaboration with Massachusetts Institute of Technology, Lexington, MA.

This report describes R&D to measure and model the near-Earth space environment and its effects on spacecraft in orbit. A Compact Environmental Anomaly Sensor (CEASE) was developed, and two versions of the instrument were flown in two different orbital domains. Other space environment instruments are being developed for flight on the Demonstration and Science Experiment (DSX) satellite. Data from CEASE and other sensors were used to develop new models of the space environment, which have been incorporated into AF-GEOSpace, a software program that includes many space environment models, applications, and data visualization products. Spacecraft charging technology includes development of the NASA-Air Force Spacecraft Charging Analyzer Program (NASCAP-2K) to model interactions between spacecraft surfaces and plasma environments and a Satellite Charge/Discharge Product (Char/D) to create tailored system-impact decision aids related to both surface and deep charging of satellites. NASCAP-2K has been used in the design of spacecraft components and in the analysis of on-orbit anomalies. We developed a second-generation Charge Control System (CCS-II), which is designed to emit xenon plasma to neutralize electrostatic charge on a spacecraft, and explored alternative charge mitigation techniques., The original document contains color images.

While it is common knowledge that ion beams are easily neutralized for both current and charge density using a variety of means, the precise process of neutralization remains unknown. With the increasing importance of electric propulsion, and in particular micropropulsion systems, this question is of significant importance. Additionally, it has bearing on thruster design, space instrument calibration, electrodynamic tethers, and ionospheric research. A review of the present state of knowledge on this topic is presented as well as results from ion beam simulations using 2D and 3D Particle-in-Cell (PlC) codes. We investigate both the early "filing" problem of the beam starting to move away from the spacecraft and the steady state problem where the beam encounters a wall at an infinite distance from the spacecraft., Prepared in collaboration with Mechanical Engineering Department, Worcester Polytechnic Inst, Worcester, MA.

The fact that ion beams readily neutralize given a source of electrons is well known, but the physics behind that process is not. As electric propulsion devices move into the micro and macro regions with colloids, FEEPs, and large arrays of thrusters, the interactions between the neutralizer and the thruster are under examination. Simulations using 2D and 3D Particle-in-Cell (PIC) codes are presented, detailing starting and steady state interactions between an ion beam and an electron beam. It is shown that the starting conditions require detailed current coupling to propagate normally. Steady state simulations show robust behavior regardless of ion or electron currents. Further investigation of steady state reveals no mechanism for imparting ion beam bulk velocity to electrons., Presented at the AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit (40th), held in Ft. Lauderdale, FL, 11-14 Jul 2004. Prepared in collaboration with Worcester Polytechnic Institute, Worcester, MA.

While it is common knowledge that ion beams are easily neutralized using a variety of means, the precise process of neutralization remains unknown. With the increasing popularity of electric propulsion, and in particular micropropulsion systems, this question is of significant importance. Additionally, it has a bearing on thruster design, space instrument calibration, electrodynamic tethers, and ionospheric research. A review of the present state of knowledge on this topic is presented as well as results from ion beam simulations using 2D and 3D Particle-in-Cell codes. The grid generation methodology, adaptation, charged-particle transport, and field solver methodologies of the 3D code are reviewed. The simulations show electrons moving to neutralize the ion beam from background and neutralizer sources. The simulations show the dependence of neutralization on beam energy and the electron/ion velocity ratio. The results are compared favorably with previous computations and experimental observations., Presented at the AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit (39th), held in Huntsville, AL, 20-23 Jul 2003. Prepared in collaboration with Worcester Polytechnic Institute, Worcester, MA.