Public reporting burden for this collection ol Infomiatlon Is estimated to average 1 hour per response, Including the time for reviewing Instructions, searching easting data sources, gathering and maintaining the data needed, and completing and reviewing this collection of infomiatlon. Send comments regarding this burden estimate or any other aspect of this oolleotlon of information, Including suggestions for reducing this burden to Department of Defense, Washington Headquarters Serwoes, Directorate for Infomiatlon Operations and Reports (0704-0188), 1215 Jefferson Davis Highway, Suite 1204 Ariington VA 22202-4302. Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for falling to comply v»ith a collection of information If It does not displav a currently valid 0MB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS. REPORT DATE (DD-MM-YYYY) 19 ABSTRACTIn recent teste the plume current density profile, plume ion energy, and radiated EMI were characterized for Pratt & Whita^'s T-220HT Hall Effect thruster. The T-220HT is a high power (6-20 kW) thruster designed for maximum peak thrust. Tests covered a power range jfrom 8-10 kW and discharge voltages of 300 and 600 V. Plume measurements at Air Force Research Laboratoiy (AFRL) facilities demonstrated plume widths narrower than typical Hall thrusters. Halfangles containmg 90% of the integrated plume flux were in the range of 27-29°. Radiated electromagnetic emissions were measured over a frequency range from 200 MHz to 60 GHz at The Aerospace Corporation. For discharge voltages at or below 300 V, EMI was below MIL-STD 461E limits except at a single peak below 1.4 GHz, v^ere the limit was exceeded by only about 5 dB. Increasing flie discharge voltage ID 600 V noticeably increased emissions in this frequency range, but these were still generally below MIL-STD 461B. Plume ion ener^ spectra were also characterized at The Aerospace Corporation's facility.An RPA (Retarding Potential Analyzer) was mounted at a downstream distance of 1 meter and was varied in position from 20° to 100° from tiie thruster centerline. Measuremente generally confirmed tiie plimie profile data taken at AFRL. Energy spectra confirm fliat the flux at high angles is dominated by low eneigy chargeexchange ions.

Thermionic conversion is unique amongst power conversion approaches in its ability to generate power efficiently with high temperature heat rejection. This feature has made thermionics an attractive choice for space power systems; and it has substantial potential for terrestrial advanced energy conversion, if certain recently identified technological developments are realized in a low cost manner. Thermionic energy converters are well suited to a modular approach. Thermionics is a passive system without moving pa&. Thermionic energy conversion is able to use heat at the highest temperatures available, and to reject waste heat at temperatures high enough to be efficiently used by other energy conversion systems. For example, a thermionic converter can utilize heat at a high temperature from a flame or other heat source, convert some of it to electricity, and deliver its waste heat at a temperature high enough to run a steam generator. The combination of the thermionic converter and steam generator could produce as much as 40% more electricity from the fuel than the steam generator alone. Other terrestrial applications include cogeneration and a possible power source for a hybrid, low-emission electric vehicle. These terrestrial applications require advances in efficiency and power density in order to operate with lower emitter temperatures than space power thermionic systems.Recently it has been shown that close spaced thermionic converters can achieve the performance goals necessary to meet these attractive new applications. The paper addresses the progress in this regard and describes approaches for engineering practical closed spaced converters for large scale applications. Clearly the potential for thermionic energy conversion is great. Every effort must now be made to use this technology to help solve the world's energy problems.Investments in the manufacturing infrastructure necessary to make thermionic energy conversion cost effective are needed to reach this goal.

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