Mid energy ion detector.
This design is based on the ion HEEPS detector flown on several previous missions (most recently HEEPS-M on SERSIO).
Design Goals:
The high G0 of this design comes mainly from its very large analyzer gap. This means there is a single bounce path to the MCP making it susceptible to UV and high energy electron contamination. The large gap also causes the very wide energy resolution. The only way for major improvement in these areas would be to reduce the gap considerably. This would cause a major decrease in G0.
Some minor improvements can be made without changing the analyzer gap.
The following plots show particle trace simulation results for the baseline analyzer (HM0) and for an improved design (HM1). HM1 has a smaller top cap gap and somewhat tighter input angle collimation.
At low energies the paths exiting the analyzer are focused by a lens formed by the "medallion" screen holder and the mcp field. At high energies this lens has less effect so some paths may miss the outer edge of the anode. The HM1 design has slightly different lens dimensions to improve high energy focus.
In the following plots the left panel shows the angle and energy acceptance. The right panel shows the location distribution of particles reaching the MCP. The blue wedge shows a 5 deg bin. The red line shows the radial extent of the resistive anode.
