Frans H. Ebersohn

Magnetic Nozzle Plasma Plume: Review of Crucial Physical Phenomena

This paper presents a review of the current understanding of magnetic nozzle physics. The crucial steps necessary for thrust generation in magnetic nozzles are energy conversion, plasma detachment, and momentum transfer. The currently considered mechanisms by which to extract kinetic energy from the plasma include the conservation of the magnetic moment adiabatic invariant, electric eld forces, thermal energy directionalization, and Joule heating. Plasma detachment mechanisms discussed include resistive di usion, recombination, magnetic reconnection, loss of adiabaticity, inertial forces, and selfeld detachment. Momentum transfer from the plasma to the spacecraft occurs due to the interaction between the applied eld currents and induced currents which are formed due to the magnetic pressure. These three physical phenomena are crucial to thrust generation and must be understood to optimize magnetic nozzle design. The operating dimensionless parameter ranges of six prominent experiments are considered and the corresponding mechanisms are discussed.

Initial experiments of a new permanent magnet helicon thruster

Summary form only given. A new design for a permanent magnet helicon thruster is presented. Its small plasma volume (~10 cm3) and low power requirements (<;100 W) make it ideal for propelling nanosatellites (<;10 kg). The magnetic field reached a maximum of 600 G in the throat of a converging-diverging nozzle and decreased to 0.5 G, the strength of earths magnetic field, within 50 cm allowing the entire exhaust plume to develop in the vacuum chamber without being affected by the chamber walls. Low gas flow rates (~10 sccm) and high pumping speeds (~10,000 l/s) were used to more closely approximate the conditions of space. A parametric study of the thruster operational parameters was performed to determine its capabilities as both a thruster and as a plasma source for magnetic nozzle experiments. The plasma density, electron temperature, and plasma potential in the plume were measured with Langmuir probes, double probes, and emissive probes. These measurements characterized the ion acceleration mechanism which produces thrust. Thrust measurements were made with an innovative micronewton thrust stand. Measurements were compared to predictions made with fluid theory and particle-in-cell simulations.

Manned sample return mission to phobos: A technology demonstration for human exploration of Mars

In order to reduce the knowledge gap associated with long-duration human exploration of Mars, a manned precursor mission destined for one of the Martian moons is currently considered a feasible option for testing and demonstrating critical technologies within the Martian system. The 2013 Caltech Space Challenge, a student mission design competition held at the California Institute of Technology, addressed the interest in human precursor missions. Two teams of 16 students, with varying backgrounds and nationalities, were allocated five days to design a mission to land at least one human on a Martian moon and return them, along with a sample, safely to Earth with a launch date no later than January 1, 2041. This paper provides an overview of Technology Advancing Phobos Exploration and Return (TAPER-1), the manned Phobos sample return mission devised by Team Explorer. As the first manned mission to the Martian system, TAPER-1 is designed as an opposition class mission to Phobos, carrying four astronauts, with a launch date in April 2033, and a nominal time of flight of 456 days. In addition, this paper demonstrates the feasibility and value of exposing students to the process of rapid mission design.

Quasi-one-dimensional code for particle-in-cell simulation of magnetic nozzle expansion

The formulation and validation of a novel quasi-one-dimensional particle-in-cell code for the simulation of magnetic nozzles is presented. Quasi-one-dimensional effects are included through virtual displacements of magnetized particles from the axis of symmetry and cross-sectional area variation according to preservation of magnetic flux. A modified, semi-implicit Boris algorithm is developed for capturing the Lorentz force effects in quasi1D. Validation problems are selected to test the components of the code required to model the important physics of magnetic nozzles. Simulations are performed of two stream instabilities, Landau damping, source and collector sheaths, and magnetic mirrors. Results from the validation simulations show that the code produces physically accurate results when compared with both theory and other simulations.

Towards Computation of Resistive Magnetohydrodynamic Magnetic Nozzle Plasma Flow

Plasma ow physics in magnetic nozzles must be clearly understood for optimal design of plasma propulsion devices. An order of magnitude analysis of the governing equations reveal: i) most magnetic nozzles under consideration operate at the edge of the continuum regime rendering continuum-based description and computation valid; ii) in the context of MHD framework, the generalized Ohm’s law must be used to capture all of the relevant physics. Next, we continue the development of the Magneto Gas Kinetic Method (MGKM) computational tool. Validation of the code is performed in shock-tube ows with Hall effects, Hartmann channel ows with Hall e ects, and simple jet con gurations. Comparison with theory and available data is made whenever possible. The preliminary results are encouraging and further challenges are identi ed.

Kinetic simulation technique for plasma flow in strong external magnetic field

Abstract A technique for the kinetic simulation of plasma flow in strong external magnetic fields was developed which captures the compression and expansion of plasma bound to a magnetic flux tube as well as forces on magnetized particles within the flux tube. This quasi-one-dimensional (Q1D) method resolves a single spatial dimension while modeling two-dimensional effects. The implementation of this method in a Particle-In-Cell (PIC) code was verified with newly formulated test cases which include two-particle motion and particle dynamics in a magnetic mirror. Results from the Q1D method and fully two dimensional simulations were compared and error analyses performed verifying that the Q1D model reproduces the fully 2D results in the correct regimes. The Q1D method was found to be valid when the hybrid Larmor radius was less than 10% of the magnetic field scale length for magnetic field guided plasma expansions and less than 1% of the magnetic field scale length for a plasma in a converging–diverging magnetic field. The simple and general Q1D method can readily be incorporated in standard 1D PIC codes to capture multi-dimensional effects for plasma flow along magnetic fields in parameter spaces currently inaccessible by fully kinetic methods.

Magneto-Gas Kinetic Method for Nonideal Magnetohydrodynamics Flows: Verification Protocol and Plasma Jet Simulations

In this work, the gas-kinetic method (GKM) is enhanced with resistive and Hall magnetohydrodynamics (MHD) effects. Known as MGKM (for MHD–GKM), this approach incorporates additional source terms to the momentum and energy conservation equations and solves the magnetic field induction equation. We establish a verification protocol involving numerical solutions to the one-dimensional (1D) shock tube problem and two-dimensional (2D) channel flows. The contributions of ideal, resistive, and Hall effects are examined in isolation and in combination against available analytical and computational results. We also simulate the evolution of a laminar MHD jet subject to an externally applied magnetic field. This configuration is of much importance in the field of plasma propulsion. Results support previous theoretical predictions of jet stretching due to magnetic field influence and azimuthal rotation due to the Hall effect. In summary, MGKM is established as a promising tool for investigating complex plasma flow phenomena.

Quasi-one-dimensional simulations of magnetic nozzles for plasma thruster applications

Novel quasi-one-dimensional, electrostatic particle-in-cell (PIC) simulations of magnetic nozzles were performed to study the energy exchange, particle acceleration, and instabilities in a magnetic nozzle. Field-particle and particle-particle energy exchange were both studied to fully characterize energy exchange in the magnetic nozzle. The effects of instabilities on the thermal behavior of the plasma were also investigated. Research results and design implications will be discussed.