This announcement describes a post-doctoral fellowship opportunity to join the Variable Specific Impulse Magnetoplasma Rocket (VASIMR) team at Johnson Space Center’s (JSC) Advanced Space Propulsion Laboratory. The post-doctoral fellow will be responsible for two major tasks. First, he or she will begin the process of making force measurements with the recently installed Marshall Space Flight Center (MSFC) momentum flux probe. In this process it is expected that the plasma and facility effects on the momentum flux probe will be characterized and understood. Second, the fellow will be expected to take the lead in designing and conducting a series of experiments designed to demonstrate the occurrence of plasma detachment in the VASIMR prototype.

A fundamental problem in human and robotic planetary exploration is the intrinsic limitation of today’s chemical rocket. Developing a high power electric propulsion system suitable for use as the sustainer engines for manned missions beyond Earth orbit is directly relevant to JSC’s mission on enabling human space flight. One candidate system, the plasma rocket, opens up new and exciting possibilities for fast space transportation. Utilizing ionized gases accelerated by electric and magnetic fields, these devices expand the performance envelope of rocket propulsion far beyond the limits of the chemical rocket. With a properly shaped magnetic duct, the internal energy of plasma could be extracted in the form of rocket thrust. The duct becomes a magnetic nozzle, the magnetic equivalent of a conventional nozzle.

At the present time, the VX-10 experimental device at the NASA Johnson Space Center in Houston is exploring the physics and engineering of the VASIMR. The VASIMR consists of three main sections: a helicon plasma source, a radio frequency (RF) power booster, and a magnetic nozzle. One key aspect of this concept is its electrode-less design, which makes it suitable for high power density and long component life by reducing plasma erosion and other materials complications. The magnetic field ties the three stages together and, through the magnet assemblies, transmits the exhaust reaction forces that ultimately propel the ship.

In many respects the magnetic nozzle is the most controversial and speculative aspect of the VASIMR concept. If one considers only first order plasma physics, one naively expects the plasma produced in a magnetic bottle configuration to remain in a magnetic flux tube attached to the rocket, thus producing no thrust. In fact, detailed consideration of the expected plasma dynamics indicates that one should expect the exhaust plasma to detach from the engine magnetic field and become a true exhaust plume when one reaches an axial distance where the plasma pressure exceeds the effective pressure of the magnetic field. The principal goal of this project is to demonstrate that plasma detachment is occurring in the VASIMR engine.

The next two years will provide an ideal opportunity to show that plasma detachment occurs. Three recent or planned improvements to the laboratory version of the VASIMR engine will facilitate this research. The power level in the system is being increased from the present 10 kW to 50 kW. This increase will be completed by the end of the summer of 2004. Second, a powered axial translation stage for diagnostic instruments has been built and installed in the large exhaust chamber. This translation stage will enable VASIMR experimenters to scan along the axis of the exhaust plume with a variety of diagnostic instruments designed to measure the properties of the exhaust plasma. The first instrument intended for use on this translation stage is a momentum flux probe developed by Dr. Greg Chavers of NASA Marshall Space Flight Center. Third, a substantial increase in the pumping capacity of the exhaust chamber is being designed. At present, the build up of neutral backpressure owing to recombination of the exhaust plume outrunning the capacity of the available vacuum pumps limits the ability of the system to simulate plasma detachment meaningfully. The increased pumping capacity will significantly reduce this problem.

The project will entail two complementary sets of activities. First, the existing set of diagnostic that are or can be installed on the translation stage in the exhaust bell will be operated during all appropriate VASIMR runs to investigate the plasma dynamics of the extended exhaust plume. These diagnostics include a momentum flux probe, plasma probes, and gridded energy analyzers, also known as retarding potential analyzers (RPAs). There is considerable controversy regarding the validity of momentum flux probe data in electric propulsion applications. Careful and detailed study of the validity of the data is central to the success of the project. Much attention will be paid to identifying and characterizing plasma and facility effects on the momentum flux probe. These instruments will allow us to determine if the exhaust plume is expanding entirely along the lines of the vacuum field or if, as expected, it is pulling the field out into an extended configuration. The most critical data will be the radial profiles of plasma density and directed ion energy as a function of axial distance. This activity will dominate year 1 with routine operations continuing throughout the fellowship.

Second, additional instruments will be procured or developed for use on the translation stage (UH and other VASIMR collaborators have already been awarded funding for this purpose.) These additional instruments include dc magnetometers for mapping the magnetic field configuration to look for evidence of stretching and induction magnetometers (B-dot) probes to look for evidence of reconnection. Further, an additional transverse degree of freedom will be added to the translation stage to facilitate taking radial profiles. This horizontal profile bar will be developed so as to mount multiple probes, including Langmuir probes to determine electron temperature and assess energy balance, a steerable collimated RPA, neutral pressure gauges, and induction magnetometers (B-dot) probes to look for impulsive, time varying reconnection. All the magnetic probes are meant for dynamic measurements of reconnecting structures. At this point we cannot say if the detachment will occur as a single coherent "blob" or rather as a collection of scattered, smaller "islands." Design, procurement and fabrication will take place during year 1, with detailed exhaust studies commencing as the new instruments come on line. Major study with the new instruments is expected during year 2.

Post-Doctoral Fellow’s Role

All of the instruments mentioned above are in plan or on order. Some have been procured by out-of-town collaborators or "belong" to students not yet able to spend full-time at ASPL. The most important of these is the MSFC momentum flux probe. The critical functions that the post-doc will fulfill including operating and validating the momentum flux probe and making sure that none of the instruments from our external collaborators become "orphans." They also include design and construction of the horizontal profile bar, and welding all of the available downstream diagnostics together into a coherent, focused investigation of detachment.

JSC Resources to be made available

The post-doctoral fellow will have access to the VX-50 prototype, associated diagnostic equipment, the new axial diagnostic translation stage, the MSFC momentum flux probe, UH and UT diagnostic probes installed on the VX-50, digital data acquisition system and the rest of the panoply of associated hardware as needed.

Desired Background of Fellowship Applicants

An applicant should have a recent Ph.D. or equivalent degree in physics, electrical engineering or aerospace engineering, with a thesis topic and area of specialization appropriate to the project. Appropriate thesis topics include electric propulsion, lab plasma physics, controlled fusion, or space plasma physics. Preference will be given to applicants with prior work experience on electric spacecraft propulsion projects.

Professional Biographies of Investigators

Edgar Andrew Bering, III

Education
B.A., cum laude in Physics, Harvard College, Cambridge, Mass., June 1967.
Ph.D. in Physics, University of California, Berkeley, June 1974.

Professional Experience
University of Houston, Houston, Texas
1998-present  Professor of Physics and Electrical and Computer Engineering
1989-1998  Professor of Physics
1981-1989  Associate Professor of Physics
1975-1981  Assistant Professor of Physics
1974  Research Scientist

Participated in experiments to measure electron bremsstrahlung beneath auroras, electron bremsstrahlung accompanying both natural and triggered VLF events, auroral zone electric fields, plasmapause electric fields, electric fields at high altitude due to thunderstorms and sprites, and the electromagnetic radiation spectrum of lightning and sprites at high altitude, VLF magnetic fields accompanying active experiments in the ionosphere, dc plasma properties in the ionosphere near pulsating aurora, and electric fields near the magnetospheric cusp. Presently involved in the development of the Variable Specific Impulse Magnetoplasma Rocket (VASIMR) at the Advanced Space Propulsion Laboratory, NASA - Johnson Space Center.

79 Refereed Publications, 36 Technical Reports, 55 Invited Talks, 217 Abstracts

John V. Shebalin

Education
Ph.D., Physics, College of William & Mary, 1982
M.S., Physics, Old Dominion University, 1976
B.S., Physics, Old Dominion University, 1972

Professional Experience
2000-present  Adjunct Faculty, University of Houston-Clear Lake, Houston, TX 77058
1997-present  Astrophysicist, NASA Johnson Space Center, Houston, TX 77058
1987-1997  Senior Scientist, NASA Langley Research Center, Hampton, VA 23681
1987 Research Associate, Dept. of Physics, Dartmouth College, Hanover, NH 03755
1984-1986  Assistant Professor, Electrical Eng., Old Dominion U., Norfolk, VA 23529
1982-1984  Engineering Specialist, Kentron International, Inc., Hampton, VA 23666
1981-1982  Senior Engineer, Westinghouse Electric Corporation, Annapolis, MD 21404
1980-1981  Scientist, Science Applications, Inc, McLean, VA 22102
1977-1980  Physicist/Mathematician, Naval Surface Weapons Center, Dahlgren, VA 22446

Recent Publications
Shebalin, J. V. "Størmer regions for axisymmetric magnetic multipole fields," to appear in Phys. Plasmas.
Shebalin, J. V. "Theory and simulation of real and ideal magnetohydrodynamic turbulence," to appear in Discrete & Continuous Dynamical Systems B.
Shebalin, J. V. "A spectral algorithm for solving the relativistic Vlasov-Maxwell equations," Computer Physics Communications 156 (2003): 86-94.

Caveat

Appointment is contingent on full funding of FY 2005 and 2006 of an existing grant.

Points of Contact

Professor Edgar A. Bering, III
UH Phone, Fax, E-mail
Phone: 713-743-3543
Fax: 713-743-3589
E-mail: ebering@mail.uh.edu
JSC Phone, Fax, E-mail
Phone: 281-792-5991
Fax: 281-792-5661
E-mail: edgar.a.bering1@jsc.nasa.gov

Dr. John V. Shebalin
Phone: 281-792-5390
Fax: 281-792-5661
E-mail: john.v.shebalin@nasa.gov