A Little History
In the United States, the use of ion thrusters for electric propulsion in space began with the launch of Space Electric Rocket Test I (SERT I) in 1964. There are now over a hundred ion thrusters, in various forms, operating on geosynchronous communication satellites. In addition, the highly successful Deep Space 1 mission has shown the usefulness and adaptability of ion thrusters on long missions in hostile space environments.
Ion Propulsion Research at CSU began in the mid 1960's when Bill Michelson and Lionel Baldwin came to CSU, and began a period of work with ion thrusters and ion beam neutralization (work they had started at NASA Glenn). With the help of Virgil Sandborn (also from Glenn) they drew up some plans and had a California-based company build a vacuum chamber 1.2 meters in diameter and 6 meters in length; it was pumped by the same Stokes roughing pump, roots blower and CVC diffusion pump that are in operation today.
In fact, Dr. Sandborn, who came to CSU to research boundary layer separation, and other aerodynamic issues using the then brand new meteorological wind tunnel (and who is still studying the phenomena today), was working with Lionel on anomometers to assist in measuring flow. They came up with a novel idea to put a thoriated tungsten wire within the accelerator electrode aperture (at the time, research was being conducted using a single aperture ion source similar to the Von Ardenne type). The wire eliminated space-charge issues, as it readily released electrons.
In 1968 Dr. Paul J. Wilbur, after finishing his Ph.D. at Princeton, came to CSU where, initially, he continued to work on the same subject of his thesis, Pulsed Plasma. Lionel Baldwin had become Dean of Engineering, however, and with the passing of Bill Michelson, Dr. Wilbur suddenly found himself heading up the Ion Propulsion Research Facility (IPRF) and Plasma Engineering Research Laboratory.
Forty years later, the propellants have changed, but the same passion and perseverance are hallmarks of this internationally recognized CSU facility. The Plasma Engineering Research Lab, located in the Engineering Research Center on the foothills campus of Colorado State University, was developed by Dr. Wilbur and his students, and is still in operation today. Research is focused on broad beam ion sources, their materials and geometries, for both space-based and terrestrial applications as well as the performance of surfaces treated using the terrestrial sources.
In 2002, Dr. John Williams, who received his Ph.D. under Dr. Wilbur in 1991, returned to CSU. His goal is to continue the legacy established by Dr. Wilbur, and maintain CSU's status as the premier institute for electric propulsion research. Forging strong relationships with NASA's various facilities and the companies that support them, Dr. Williams is laying the ground work for a renovation of the facility. Mark Buttweiler, previously a Training Manager for Veeco Instruments' ion source product line, was a part of the staff from 2003 to 2005. Dr. Williams and Mr. Buttweiler added 4 vacuum test chambers (for a total of 9) for graduate student research, and added a 300 sq.ft. laboratory where students can develop and test the projects they are working on. Additionally, a 1000 sq. ft. laboratory is being planned to accommodate larger research projects and a small clean room.
Dr. William's research includes modeling of erosion phenomena on ion thruster components such as ion extraction grids and hollow cathodes and experimental evaluation of plasma and ion beam interactions with materials for both aerospace and terrestrial applications. In 2004, Dr. Williams directed the addition of the Advanced Sputtering Facility which incorporates state of the art equipment used to analyze the sputter yields of a variety of spacecraft materials, and the re-evaluation of sputter yields of known refractory metals using low energy (50eV-500eV) xenon ions.
Dr. Wilbur has a strong interest in Ion-Beam Processing (surface treatments and implantation), Tribological Research, and Hollow Cathode Plasma Contactors. A spinoff of the ion thruster, the broad-beam ion implanter utilizes the same basic hardware as the thruster but the ion beam, instead of being used to produce thrust, is directed onto the surfaces of various mechanical engineering components in vacuum chambers. The resulting treatment of these surfaces can increase their resistance to wear and corrosion, as well as reduce the friction between surfaces in components such as bearings. Laboratory facilities include both gaseous and metallic ion beam systems which produce ion beams with energies that range from 1 to 100 keV and beam current densities that are as high as 5 mA/cm2.
Tribological test facilities include a rolling contact fatigue tester, a block-on-ring wear and friction tester and pin-on-disc wear and friction testers that can be operated over a wide range of temperatures and in controlled environments. These environments may involve for example, an atomic oxygen atmosphere that is representative of space and lubricated, ambient-air environments.
Research is aimed at defining and optimizing broad ion beams for rapid and, therefore, low cost processing of a wide range of materials (metals, ceramics and polymers). Some previous work was on the production of boron-, nitrogen- and carbon-implanted layers on steel surfaces that are both thick and wear resistant.
For more information on the ion implantation and ion beam processing that has occurred in this lab see the list of publications.
The picture on the left is the accelerator grids to the high voltage gas implanter. The picture on the right is of a plasma beam impinging on a graphite plate.
Hollow Cathode Plasma Contactor Research at the Plasma Engineering Research Lab
Theory suggests that electrical power can be generated in space by connecting a wire between two orbiting satellites and pulling it through the Earth's magnetic field. This device, called an electrodynamic tether, enables both the conversion of mechanical (orbital) energy into electrical energy and vice versa. In order to assure proper operation of this device, however, it is necessary to establish electrical contact between each end of the tether and the ambient space plasma. The device that will be used to make these connections is called a plasma contactor and research into its performance and operating characteristics is being undertaken.
The plasma contactor can also be utilized to alleviate electrical charge buildup on a spacecraft. Charging and subsequent uncontrolled discharging of a spacecraft can interfere with the spacecraft instrumentation and control systems and thus its mission. Current research is aimed at understanding the physics of the plasma contactor. The work involves measuring the contactor electrical noise production in an effort to assure it will not interfere with other spacecraft systems.
If you wish to know more about hollow cathode plasma contactors see our publications.