Laser Induced Fluorescence Characterization of Cusped Field Plasma Thrusters

Laser Induced Fluorescence Characterization of Cusped Field Plasma Thrusters
Author: Natalia Adrienne MacDonald
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Total Pages:
Release: 2012
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Cusped field plasma thrusters are a recent development in electrostatic propulsion, aimed at improving operation in the low power regime. Several diagnostic techniques have been employed to characterize these discharges. The present study focuses on the use of laser induced fluorescence to map ion velocities throughout the plumes of several cusped field thruster variants. Laser induced fluorescence provides the opportunity to probe small plasma sources with high spatial resolution, and is particularly useful for studying plasma propulsion devices where hot, energetic and highly non-uniform environments can adversely affect intrusive probes. The first half of this thesis focuses on time-averaged laser induced fluorescence velocimetry for three cusped-field thrusters. While a time-averaged velocity diagnostic is adequate in determining overall performance, it cannot resolve the dynamics seen in oscillatory modes of thruster operation. The second half of this research focuses on the development of an advanced CW laser induced fluorescence diagnostic technique, capable of correlating high frequency current fluctuations to the resulting fluorescence excitation lineshapes. This method is validated using simulations and a 60 Hz xenon spectral lamp. It is then applied to an oscillatory mode of the diverging cusped field thruster. Results show that the positions of the ionization and peak acceleration regions in the thruster vary over the course of a discharge current oscillation, causing the ion velocities to fluctuate in time. This new method of time-synchronized CW laser-induced fluorescence will be invaluable for better understanding the dynamics of thruster operation as well as other quasi-periodic oscillatory discharges, in fields from combustion to materials processing, among others.

Establishing a Facility for Making Non-Intrusive, Near-Real-Time Electric Propulsion Thruster Erosion Measurements Via Simultaneous Two-Frequency Laser Induced Fluorescence

Establishing a Facility for Making Non-Intrusive, Near-Real-Time Electric Propulsion Thruster Erosion Measurements Via Simultaneous Two-Frequency Laser Induced Fluorescence
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Total Pages: 15
Release: 2002
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ISBN:

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DURIP funds were used to purchase three cryopumps, a state-of-the-art tunable-diode laser, a dye-to-Ti:sapphire conversion kit for a ring laser (for enhanced IR capability), and a commercial ion-sputtering source. The new cryopumps increased the xenon pumping speed of the Large Vacuum Test Facility (LVTF) at the University of Michigan's Plasmadynamics and Electric Propulsion Laboratory (PEPL) from 140,000 to 240,000 1/s. The new lasers will be used in conjunction with our tunable ring laser to make Two-Wavelength Simultaneous Laser Induced Fluorescence (TWSLIF) measurements for Hall thruster discharge channel erosion characterization. TWSLIF will first be demonstrated in a smaller vacuum facility with a commercial ion source and a boron nitride substrate. Once perfected in the smaller chamber, TWSLIF will be used in the LVTF to characterize discharge channel erosion of the P5 Hall thruster. This capability will not only enhance PEPL, but will establish a national facility where thruster erosion and spacecraft integration issues are investigated.

Development and Simulation of a Cylindrical Cusped-field Thruster and a Diagnostics Tool for Plasma-materials Interactions

Development and Simulation of a Cylindrical Cusped-field Thruster and a Diagnostics Tool for Plasma-materials Interactions
Author: Anthony Pang
Publisher:
Total Pages: 125
Release: 2013
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ISBN:

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A low power, Hall-effect type plasma thruster known as the MIT-Cylindrical Cusped- Field Thruster (MIT-CCFT) has been developed and simulated using a fully-kinetic plasma model, the Plasma Thruster particle-in-cell (PTpic) model. Similar to the Diverging Cusped-Field Thruster (DCFT) previously developed in the Massachusetts Institute of Technology Space Propulsion Laboratory, this thruster uses cusped magnetic fields aligned in alternating polarity in order to confine electrons, thus slowing their flow to the anode and readily ionizing neutral gas, which is then electrostatically accelerated by the anode. The design methodology for the CCFT will be discussed, with significant emphasis on the effects of magnetic topology on thruster performance. In particular, while the topology is similar to that of the DCFT in that it also confines the discharge plasma away from the channel walls to limit wall erosion, the CCFT was also designed to minimize plume divergence. To predict the CCFTs performance and plasma dynamics, the design has been modeled and simulated with PTpic. From multiple simulations of the CCFT under different operating conditions, the thruster performance and plume characteristics were found and compared to past simulations of the DCFT. Specifically, the predicted nominal total efficiency ranged from 25 to 35 percent, providing 4-9 mN of thrust at a fixed xenon mass flow rate of 4.0 sccm, whilst consuming 90-400 W of power and with a corresponding nominal specific impulse of 1050 to 1800 s. Preliminary observations of the particle moments suggest that the magnetic confinement of the plasma isolates erosion of the channel walls of the discharge chamber to the ring cusps locations. In addition, in contrast to the DCFT, the CCFT does not have a hollow conic plume; instead, its beam profile is similar to that of traditional Hall-effect thrusters. To supplement the efforts for optimizing longevity of the cusped-field thruster, a new diagnostic tool for erosion studies, novel to the electric propulsion community, has been implemented and has undergone preliminary validation. Ion beam analysis (IBA) allows for in-situ measurements of both composition and profile of the surfaces of the discharge region of a plasma thruster during operation. The technique has been independently tested on individual coupons with the use of the Cambridge Laboratory for Accelerator Study of Surfaces (CLASS) tandem ion accelerator. The coupons, which are composed of materials with known sputtering rates and/or are commonly used as insulator material, are exposed to helicon-generated plasma to simulate the sputtering/re-deposition found in thruster discharge region. Through comparison of ion beam analysis traces taken before and after plasma exposure, the effective erosion rates were found and validated against simulated results.

Experimental Investigations with a 5-kW-Class Laboratory Model Closed-Drifted Hall Thruster

Experimental Investigations with a 5-kW-Class Laboratory Model Closed-Drifted Hall Thruster
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Total Pages: 0
Release: 2001
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ISBN:

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This final technical report summarizes research conducted at the Plasmadynamics and Electric Propulsion Laboratory (PEPL) to characterize the internal and plume plasma of a closed-drift Hall thruster (CDT). The project was composed of the following segments: 1) a 5-kW-class CDT (P5) was built and characterized in terms of performance and plume divergence; 2) the molecular-beam mass spectrometer (MBMS) was used to measure the ion energy distribution finction and charge state throughout the PS plume; 3) laser-induced fluorescence was used to measure the ion velocity and temperature in the near-field plume; 4) a 35 GHz microwave interferometer was developed to measure plasma oscillations and electron density in the plume; and 5) the near-field and internal plasma of the PS were characterized using the High-speed Axial Reciprocating Probe (HARP) system developed for this effort. The HARP system enabled, for the first time, the insertion and removal of probes from a CDT discharge channel while minimizing perturbation to thruster operation. The magnetic field, electron temperature, ion number density, plasma and floating potential, and Hall current were mapped throughout the PS discharge chamber at two operating conditions. Thruster perturbation, determined by monitoring discharge current, was less than 10% for the majority of measurements.