University of Maryland
Computer & Space Science Building, Room 2400
4:30 PM Monday, February 25, 2008
Coffee, Tea & Cookies 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 Debbie Jenkins at (301) 405-4780 or go to the UMD Space Physics group seminar web site.
For free parking please park in lot DD or anywhere on levels 1-2 in lot B (the big parking garage) after 4:00 pm.
Make sure that you park in a spot WITHOUT a parking meter. More parking information is at the seminar website.