Browsing by Subject "VASIMR"
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Item Analysis of multifrequency interferometry in a cylindrical plasma(2006-08) Kraft, Daniela Jutta; Bengtson, Roger D.; Breizman, Boris N.This work was motivated by questions raised from multifrequency microwave interferometer measurements taken in a cylindrical plasma on the Variable Specific Impulse Magnetoplasma Rocket (VASIMR) project. Standard data analysis based on a thin beam model neglecting refraction yields inconsistent electron densities and density profiles for different frequencies. This work focuses on the development of a model for the wave propagation through cylindrical plasmas when the plasma radius is on the order of the beam waist. For the calculations presented a Gaussian beam profile and plasma spatial profile were assumed. Both refraction by density gradients and finite beam sizes are found to play important roles and explain polychromatic differences in the electron densities and profiles. Calculations for the new model are compared to a thin beam model not accounting for refraction and experimental data from VASIMR.Item Numerical modeling of plasma detachment from a magnetic nozzle(2010-12) Tushentsov, Mikhail R.; Breizman, Boris N.; Bengtson, Roger D.; Hazeltine, Richard; Horton, Wendell; Hallock, GaryThe numerical simulation and modeling of plasma detachment from a magnetic nozzle is presented. The detachment problem is of key importance to the plasma-based propulsion concepts that employ a guiding magnetic field to control plasma flow and motivated by the needs of the VASIMR (Variable Specific Impulse Magnetoplasma Rocket) project. The detachment of the plasma exhaust is required to produce directed thrust. In the present scenario plasma can stretch the magnetic field lines to infinity, similar to the solar wind. In order to extend the magnetic nozzle model beyond the limitations of analytic theory, a numerical code is developed to simulate steady-state kinetic plasma flows and to evaluate nozzle efficiency. The direct solution of a steady-state problem, as opposed to an initial value problem, eliminates the need to deal with transient phenomena that are of secondary importance for continuously operated plasma thrusters. The new simulation code is verified against the analytic results and then used to model the plasma behaviour for the conditions of the Detachment Demonstration Experiment (DDEX) at the NASA Marshall Propulsion Research Center, Huntsville, Alabama.Item Prediction of Damage to Structure resulting from Recirculation of Particles from a Magnetoplasma Spacecraft Engine(2014-12-17) Martin, Michael WilliamA magnetoplasma spacecraft engine, such as the Variable Area Specific Inpulse Magnetoplasma Rocket (VASIMR?), uses magnetic fields and a magnetic nozzle to constrict and accelerate plasma to produce thrust. Most of the ejected plasma particles are expected to detach from the magnetic field lines and escape to provide thrust but some particles may not and could impact the spacecraft structure resulting in surface erosion and electrical charging. The plasma plume for a magnetoplasma engine was modeled computationally and scaled to determine what percentage of particles remained in the magnetic field and the kinetic energy of all impacting particles. Factors such as average particle velocity at the engine exit, magnetic field strength, and plume density distribution (i.e. width) were varied in a full factorial experiment to ascertain the effects of each factor and the important inter-relationships. The results are presented for a generic magnetoplasma engine and for the specific VASIMR? case. Detachment was found to be occurring with 99.42% of particles escaping under the worst conditions and only 0.0172% of particles impacting structure. It was determined that three things led to an increase in the number of impacting particles on spacecraft structure: a stronger magnetic field, a lower exit velocity of particles into the plume, and a wider plume. In addition, there was an ?erosion zone? where an increasing particle exit velocity led to more erosion until the number of impacting particles was negligible and erosion dropped significantly. For the specific case under nominal conditions, the erosion rate was 1.386 nm/month of engine operating time on aluminum and 0.611 nm/month on silicon. The electrical charging on spacecraft surfaces was found to be -27.85 V DC, which can be mitigated with current plasma contactor technology or some variant. Therefore, magnetoplasma spacecraft engines can be shown to cause minimal erosion and electrical charging and should be capable of operating safely with current technology by varying the three parameters previously mentioned.Item Thermal phenomena and power balance in a helicon plasma(2009-05) Berisford, Daniel Floyd; Bengtson, Roger D.; Raja, Laxminarayan L.This work is motivated by the Variable Specific Impulse Magnetoplasma Rocket (VASIMR) experiment. This device uses a helicon antenna to generate a plasma inside a dielectric tube, which is radially confined and directed towards the rocket nozzle by an axial magnetic field. An ion cyclotron heating antenna further heats the ions, and a magnetic nozzle accelerates the plasma along the confining magnetic field as it leaves the rocket, ultimately allowing it to detach from the magnetic field and produce thrust. The experimental research presented here provides insight into the physical mechanisms of power flow in a helicon system by providing an overall system power balance in the form of heat flux measurements, and exploring changes in the heat fluxes in different parts of the system in response to varying operational parameters. An infrared (IR) camera measures the total heat flux into the dielectric tube surface, and axially scanned bolometer and UV photodiode probes measure the radial power loss from particles and radiation. Results from IR camera measurements on three different helicon systems are presented: the VASIMR VX-50 experiment, the VASIMR VX-CR experiment, and the University of Texas at Austin (UT) helicon experiment. These results demonstrate the development of the IR camera diagnostic for use on helicon systems of varying scale and geometry, and show reasonable agreement as to the fraction of input power lost to the dielectric tube walls. On the UT experiment, the results presented account for essentially all of the input power, providing a full system power balance. The data from all three experiments indicate that radial transport of ions to the interior wall is the dominant mechanism of power loss, with UV radiation contributing a small percentage. Additional experiments on the UT helicon explore energy and particle transport to the wall due to capacitive coupling of ions near the antenna. These experiments show clear damage to the dielectric tube surface directly under the antenna, due to physical plasma etching of the surface by bombarding ions that are accelerated into the wall by local electric fields from the antenna.