Next-Generation Plasma Particle Measurements in the Medium Energy Range: Development of Cusp Type Electrostatic Analyser and Ion Mass Spectrometer.

In regions such as the reconnection sites and the ring current, plasmas are highly accelerated and their energies sometimes exceed the uppermost energy level of low-energy plasma sensors (typically ∼40 keV). In order to study acceleration mechanisms in such key regions, in-situ observations with continuous energy coverage from low (∼ eV) to medium (∼10–∼200 keV) or to even higher energies are necessary. In fact, ERG and Cross scale missions are planned to explore the above regions with plasma instrument packages that require covering the majority of the energy range. We, therefore, develop a medium energy ion mass spectrometer, which consists of an Electrostatic Analyser (ESA), a Time-of-Flight mass spectrometer (ToF), and solid-state detectors (SSDs). It can simultaneously and independently measure energy-per-charge (E/q), velocity (v), and energy (E) of incoming ions, thus deducing E, m, and q. In addition, the coincidence method via the combination of ToF start-stop signals and SSD signals is useful to reject background noise that is caused by radiation belt electrons and/or solar energetic protons. In order to enable electrostatic analyses with a practical sensor size, we have developed a novel “cusp type” electrostatic analyser. This design provides us a relatively small instrument that has an energy range up to ∼200 keV/q with a full solid angle coverage (using the spacecraft spin motion). This kind of electrostatic analyser may also be used for electron measurements. [ABSTRACT FROM AUTHOR]