An ion mass spectrometer was developed (IMS) that can operate in the high radiation environment of Jupiter’s magnetosphere and its icy moons. If successful, this instrument will provide the first plasma composition measurements within Jupiter’s magnetosphere. This entails development of GEANT (GEometry And Tracking) simulation of a relatively lightweight IMS shielding design, performing measurement of microchannel plate response to energetic electrons and rays, building a radiation test chamber (RTC), and testing IMS with shielding design included using RTC at a high-energy particle accelerator.

The purpose of the shielding for the IMS is to keep background events to a manageable level such as <1 to 10kHz at Europa. Under these circumstances, the background levels can be reduced to a few Hz or less, and allow minor ion detection. The innovated IMS shielding design is based on a tapered stack of stainless steel rings and ceramic spacers. The ceramics spacers may have tantalum rings brazed into them using a baffle design. The novelty of the design is the ASTID-IMS’s Wien Filter, which allows one to preselect mass species so that scattering from major ions cannot hide the minor species, and allows one to establish narrow TOF (time-of-flight) windows, which further reduces the background from penetrating radiation.

The two other important features are to make the shielding part of the IMS construction by using a tapered column of stainless steel rings and ceramic spacers to shield the LEF (linear electric field) region of the IMS, and to replace the LEFMCP with a series of CFs, aluminum foils, and chevron MCP near ground potential. The instrument’s front-end electronics are composed of low-profile, compact, rad-hard preamplifiers; pulse-height analysis; and time-to-digital converter electronics.

This work was done by Edward Sittler of Goddard Space Flight Center. GSC-16437-1