A sketch of the SRIM/TRIM coordinate system in the (a) and (b) planes. is the angle between the surface normal and the incoming particle’s trajectory (large arrowhead). are the direction cosines of the reflected particle’s trajectory (small arrowhead) relative to the axes, respectively. See Eqs. (1) and (2) for the definitions of and .
The efficiency of reflection as calculated by SRIM/TRIM, , of 1, 2, and 3 keV (black, blue, and red, respectively) from a target of (plus symbols) and Al (triangles) vs , the angle from the normal of the surface, in degrees.
The PDF of (a) , (b) , and (c) for an incoming beam with , 2, and 3 keV (black, blue, and red) reflected from an (solid) or Al (dashed) surface at and .
The means, (a) , (b) , and (c) , for each PDF vs , calculated as in Eq. (3). Symbol colors and styles have the same meaning as in Fig. 2.
A cut through the plane of the SWAP SIMION model and the trajectories (black) of a beam of 1 keV protons confined to the same plane. A −600 V potential is applied to the inner ESA dome. The green trajectories are those of ions reflected from where the beam strikes closest to the detector. Some of the reflected particles strike the carbon foil, which counts as detected in our simulations.
Normalized coincidence counts (red triangles) from SWAP II for a 1 keV beam near a central plane of the instrument (any plane through the -axis) with Poisson statistics drawn as error bars. We also show the simulated ideal ESA response, i.e., the directly detected beam (solid black line), the simulated reflected response from each surface of the instrument available for reflection ( dome, dome, dashed- cone, and dashed-triple- cone), and the sum of all these simulated responses (squares), also normalized. Note that the reflected response has been scaled by a factor of relative to the peak of the ideal simulated response in order to match the data.
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