University of Maryland
Atlantic Building, Room 2400
4:30 PM Monday, February 25, 2008
Coffee, Tea & Snacks 4:15-4:30 PM

Patrick Hughes
University of Maryland
Efficient Surface Conversion for Neutral Atom Detection

Neutral atom detection is a useful way of studying astrophysical plasma structures such as the heliosphere and planetary magnetospheres. When plasma ions undergo charge exchange with the neutral background gas, energetic neutral atoms (ENAs) are generated. These neutral atoms travel in straight lines from the point of charge exchange because they are not subject to deflection by the electric and magnetic fields in space. As a result ENAs can be used to image the plasma structures from which they originate. ENAs in the energy range from a few eV to a few keV are particularly worth studying and are best detected by conversion to negative ions at a surface, a method that has been successfully used by ENA imagers on the Imager for Magnetosphere-to-Aurora Global Exploration (IMAGE) spacecraft. The function and construction of the imager is dependent upon the efficiency of the conversion surface used. A surface with a high conversion efficiency would allow the imager to be smaller and still collect a measurable signal compared to an imager using a surface with low conversion efficiency. The previously used conversion surface had an efficiency of about 1%. In order to find a more efficient conversion surface, detailed as well as comparative measurements of conversion efficiencies were taken at two facilities. The surfaces studied are polished tungsten, highly ordered pyrolytic graphite, diamond-like carbon, a secondary electron emitting leaded glass, gold, silver and platinum. The work function and smoothness of some of the sample surfaces were measured. These measurements have been compared with measured conversion efficiencies to identify those surface properties that are critical for conversion efficiency. For many surfaces, adsorbates and roughness appear to play an important role in conversion efficiency.

Sponsored by: Department of Physics and the Institute for Physical Science and Technology, University of Maryland. For information call Catha Stewart at (301) 405-4811 or go to the UMD Space Physics group seminar web site.

There is free parking after 4:00 PM in lot B (the big parking garage across the street from the ATL building). There are a limited number of spaces in lot Q next to the new ATL wing with free parking after 4PM even when there is a basketball game on campus.