Computer Science – Sound
Scientific paper
Jan 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002iaf..confe.798s&link_type=abstract
IAF abstracts, 34th COSPAR Scientific Assembly, The Second World Space Congress, held 10-19 October, 2002 in Houston, TX, USA.,
Computer Science
Sound
Scientific paper
The Advanced Space Propulsion Laboratory (ASPL) of NASA's Johnson Space Center is performing research on a Variable Specific Impulse MagnetoPlasma Rocket (VASIMR). The VASIMR is a high power, radio frequency (RF) driven magnetoplasma rocket, capable of very high exhaust velocities, > 100 km/s. In addition, its unique architecture allows in- flight mission-optimization of thrust and specific impulse to enhance performance and reduce trip time. A NASA-led research team involving industry, academia and government facilities is pursuing the development of this concept in the United States. The ASPL's experimental research focuses on three major areas: helicon plasma production, ion cyclotron resonant acceleration (ICRA) and plasma expansion in a magnetic nozzle. The VASIMR experiment (VX-10) performs experimental research that demonstrates the thruster concept at a total RF power on the order of 10 kW. A flexible four- magnet system, with a 1.3 Tesla maximum magnetic field strength, is computer controlled to study axial magnetic field profile shape effects. Power generated at 10 - 50 MHz with about 5 kW is used to perform helicon plasma source development. A 3 MHz RF transmitter capable of 100 kW is available for ICRA experiments. The primary diagnostics are: gas mass flow controllers, RF input power, Langmuir probes, Mach probe, retarding potential analyzers (RPA), microwave interferometer, neutral pressure measurements and plasma light emission. In addition, many thermocouples are attached inside the vacuum chamber to measure heat loads around the plasma discharge. Helicon research so far has been done with hydrogen, deuterium, helium, nitrogen, argon, xenon and mixtures of these gases. Optimization studies have been performed with the magnetic field axial profile shape, gas flow rate, gas tube geometry and RF frequency. The highest performing discharges are found with a high magnetic field choke downstream of the helicon antenna. Upwards of a 40% gas utilization is measured. We measure high flow velocities (> ion sound speed) in the exhaust section after the magnetic choke and the velocity increases with the choke field strength. A strong interaction between the neutral gas and the plasma is observed with measurements in the source region, indicating the possible and desirable acceleration of neutrals by the charge exchange process. Heating profiles on the helicon gas tube indicate plasma production profiles. Highlights of the helicon optimization and measurements will be presented and discussed. ICRA experiments have begun, primarily using a helium helicon discharge as a target. Over 4 kW of power has been applied using a simple antenna array. We observe significant effects, plasma density and energy increase, when applying the power near the second harmonic of the helium ion in the magnetic field. These experiments are recent, so further studies and measurements are in progress. The latest results will be highlighted. Plasma flow measurements in the expanding magnetic field of the exhaust are in progress. Some highlights will be discussed, but more of the recent data are presented in another paper in this session.1 REFERENCES 1. Bering, III, EA, et al. "Ion Dynamics and ICRH Heating in the Exhaust Plasma of The VASIMR Engine", 53rd IAC, this session.
Díaz R. Chang F.
Jacobson V. T.
McCaskill G. E.
Squire J. P.
Winter D. S.
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