ABSTRACT
When incorporated into a top-hat electrostatic analyzer, a gate electrode enables the separation of ions by their mass-per-charge with modest mass resolution (M/∆M â¼ 10). Gated-time-of-flight (TOF) instruments avoid the energy straggling and angular scattering effects prevalent in foil-based detection systems, providing more pristine measurements of three-dimensional distribution functions of incident ions. Gated-TOF implementations are ideal for measuring the properties of low-energy (i.e., <100 eV) thermal ions in various space environments. We present an instrument prototype capable of separating H+, He+, O+, and O2+ in Earth's ionosphere and demonstrate that in addition to providing species determination, precise operation of the gate electrode provides an electronically adjustable geometric factor that can extend a single instrument's dynamic range by several orders of magnitude.
ABSTRACT
Microchannel plate (MCP) detectors provide a mechanism to produce a measureable current pulse (â¼0.1 mA over several nanoseconds) when stimulated by a single incident particle or photon. Reductions of the device's amplification factor (i.e., gain) due to high incident particle flux can lead to significant degradation of detection system performance. Here we develop a parameterized model for the variation of MCP gain with incident flux. This model provides a framework with which to quantify the limits of high-flux MCP operation. We then compare the predictions of this model to laboratory measurements of an MCP's response to a pulsed charged particle beam. Finally, we demonstrate that through integration of the MCP output current in pulsed operation, effective count rates up to â¼1 GHz can be achieved, more than an order of magnitude increase over conventional counting techniques used for spaceflight applications.
