Bulletin of the American Physical Society
68th Annual Gaseous Electronics Conference/9th International Conference on Reactive Plasmas/33rd Symposium on Plasma Processing
Volume 60, Number 9
Monday–Friday, October 12–16, 2015; Honolulu, Hawaii
Session DT1: Plasma Thrusters |
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Chair: Tatsuo Ishijima, Kanazawa University Room: 301 B |
Tuesday, October 13, 2015 8:00AM - 8:15AM |
DT1.00001: Phase-resolved emission spectroscopy of a neutraliser-free gridded ion thruster James Dedrick, Andrew Gibson, Dmytro Rafalskyi, Ane Aanesland Power-efficient electric propulsion systems that operate without an external neutraliser have the potential to increase the longevity of traditional concepts. The Neptune gridded-ion thruster prototype, which uses a single radio-requency (rf) power source for plasma generation, ion acceleration and beam neutralisation, is under development. Previous research has suggested that the time-resolved electron dynamics in the plume are important for maintaining charge neutrality and overall performance. In this study, the electron dynamics in the exhaust beam are investigated within the rf cycle using phase-resolved emission spectroscopy. The results are compared with time-resolved and time-integrated electrical diagnostics to investigate the mechanisms behind beam neutralisation. [Preview Abstract] |
Tuesday, October 13, 2015 8:15AM - 8:30AM |
DT1.00002: Increasing Extracted Beam Current Density in Ion Thrusters through Plasma Potential Modification Neil Arthur, John Foster A gridded ion thruster's maximum extractable beam current is determined by the space charge limit. The classical formulation does not take into account finite ion drift into the acceleration gap. It can be shown that extractable beam current can be increased beyond the conventional Child-Langmuir law if the ions enter the gap at a finite drift speed. In this work, ion drift in a 10 cm thruster is varied by adjusting the plasma potential relative to the potential at the extraction plane. Internal plasma potential variations are achieved using a novel approach involving biasing the magnetic cusps. Ion flow variations are assessed using simulated beam extraction in conjunction with a retarding potential analyzer. Ion beam current density changes at a given total beam voltage in full beam extraction tests are characterized as a function of induced ion drift velocity as well. [Preview Abstract] |
Tuesday, October 13, 2015 8:30AM - 8:45AM |
DT1.00003: Cathode-less gridded ion thrusters for small satellites Ane Aanesland, Dmytro Rafalskyi We present here a new gridded ion thruster, called Neptune, that operates with only one Radio Frequency (RF) power source for ionization, ion acceleration and beam neutralization in addition to solid iodine as propellant. Thus significant simplifications, over excising gridded thrusters, might allow downscaling to satellites as small as 6 kg. The combined acceleration and neutralization is achieved by applying an RF voltage to the grid system via a blocking capacitor. As for similar RF capacitive systems, a self-bias is formed such that ions are continuously accelerated while electrons are emitted in brief instants within the RF sheath collapse. Moreover, the RF nature of the acceleration system leads to a higher space charge limited current extracted across the grids compared to classical DC operated systems. Measurements of the ion and electron energy distribution functions in the plasma plume show that in addition to the directed beam of ions, the electrons are also anisotropic resulting in a flowing plasma, rather than a beam of positive ions. Experimental characterization of this RF accelerated plume is detailed. [Preview Abstract] |
Tuesday, October 13, 2015 8:45AM - 9:00AM |
DT1.00004: Particle-in-Cell Simulation of a Micro ECR Plasma Thruster Keisuke Ueno, Daisuke Mori, Yoshinori Takao, Koji Eriguchi, Kouichi Ono Downsizing spacecrafts has recently been focused on to decrease mission costs and to increase launch rates, and missions with small satellites would bring a great advantage of reducing their risks. Such a concept supports a new approach to developing precise, reliable, and low-cost micropropulsion systems. We have developed a new type of electromagnetic micro plasma thruster using electron cyclotron resonance (ECR) discharges. The microthruster consists of a microwave antenna and a quartz microplasma chamber 4.15 mm in inner diameter surrounded by two permanent magnet rings. The plasma is generated by 4-GHz microwaves of \textless\ 10 W with a propellant gas of Xe, where the ions are accelerated through divergent magnetic fields and the resulting ambipolar electric fields generated. To investigate plasma characteristics of the thruster, we simulated the plasma density, electrostatic potential, and ion velocity in the exhaust area by the particle-in-cell (PIC) method with a Monte Carlo calculation for particle collisions, where the electrostatic field and the ion velocity were obtained by solving the Poisson equation and the equation of motion, respectively. The numerical results showed that the ions generated in the plasma are well confined by the applied magnetic fields and diffuse out of the discharge tube, then being accelerated by a potential drop of $\sim$7 V through divergent magnetic fields from \textless\ 1000 to \textgreater\ 3000 m/s (\textless\ 0.7 to \textgreater\ 6 eV) in the axial direction. [Preview Abstract] |
Tuesday, October 13, 2015 9:00AM - 9:15AM |
DT1.00005: Energetic ion production in high current hollow cathodes John Foster, Yao Kovach, Neil Arthur, Eric Viges, Chris Davis High power Hall and gridded ion thrusters are being considered as a propulsion option supporting human operations (cargo or tug) to Mars. These engines utilize hollow cathodes for plasma production and beam neutralization. It has now been well documented that these cathodes produce energetic ions when operated at high current densities. Such ions are observed with peak energies approaching 100 eV. Because these ions can drive erosion of the cathode assembly, they represent a credible failure mode. An understanding of energetic ion production and approaches to mitigation is therefore desired. Presented here are data documenting the presence of energetic ions for both a barium oxide and a lanthanum hexaboride cathode as measured using a retarding potential analyzer. Also presented are energetic ion mitigation approaches, which are designed to eliminate the ion energy transfer mechanism. [Preview Abstract] |
Tuesday, October 13, 2015 9:15AM - 9:30AM |
DT1.00006: Simulation of Magnetic Field Guided Plasma Expansion Frans Ebersohn, J.P. Sheehan, Alec Gallimore, John Shebalin Magnetic field guided expansion of a radio-frequency plasma was simulated with a quasi-one-dimensional particle-in-cell code. Two-dimensional effects were included in a one-dimensional particle-in-cell code by varying the cross-sectional area of the one dimensional domain and including forces due to the magnetic field. Acceleration of electrons by the magnetic field forces leads to the formation of potential structures which then accelerate the ions into a beam. Density changes due to the plasma expansion only weakly affect the ion acceleration. Rapidly diverging magnetic fields lead to more rapid acceleration and the electrons cool as they expand. [Preview Abstract] |
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