COMPARATIVE-STUDY OF LOW-ENERGY NEUTRAL ATOM IMAGING TECHNIQUES

Low-energy neutral atom (LENA) imaging promises to be a revolutionary tool for global imaging of space plasmas. The technical challenges of LENA detection include separating them from the intense ambient UV wit hout losing information about their incident trajectories, quantifying their trajectories, and obtaining high-sensitivity measurements. Two techniques that have been proposed for this purpose are based on funda mentally different atomic interaction mechanisms between LENAs and a s olid: LENA transmission through an ultrathin foil and LENA reflection from a solid surface. Both of these methods provide LENA ionization (f or subsequent removal from the UV by electrostatic deflection) and sec ondary electron emission (for time-of-flight start pulse generation an d/or coincidence). We present a comparative study of the transmission and reflection techniques based on differences in atomic interactions with solids and surfaces. Transmission methods are shown to be superio r for secondary electron emission rather than reflection methods. Furt hermore, transmission methods are shown to be sufficient for LENA imag ing at LENA energies of approximately 1 keV to greater than 30 keV. A hybrid instrument using reflection from a tow work function surface fo r LENA ionization and transmission for secondary electron emission is optimal for imaging of LENAs with energies less than approximately 1 k eV.