Design of an interplanetary ultralow-noise three-dimensional energetic particle spectrometer

The origin and acceleration of solar and heliospheric energetic particles have been prevalent research frontiers in space physics. Solar and heliospheric energetic particles measured in the interplanetary medium (IPM) can be classified into two major groups: continuous "solar wind suprathermal particles" and transient "solar energetic particles". Due to the limited sensitivity of instruments used to investigate energetic particles in the IPM, the origin/acceleration processes of heliospheric energetic particles remain poorly understood. In this study, we designed a new-generation interplanetary ultralow-noise three-dimensional energetic particle spectrometer meeting leading world-class specifications. The spectrometer utilizes a double-ended telescope structure and multi-layer, multi-pixel semiconductor detectors to assess the complete three-dimensional distribution of 20-1000 keV electrons and 25-12000 keV protons in the IPM. The spectrometer integrates the following cutting-edge technologies: (1) utilizing anti-coincidence correlations between adjacent detectors with narrow interlayer spacing to minimize the noise generated by cosmic rays and other high-energy penetrating particles in the semiconductor detectors; (2) a double-ended open telescope structure design, with thin foil covering to stop protons for high-sensitivity electron detection in one direction, magnets to sweep away electrons for high-sensitivity proton detection in the opposite direction, multi-layer detectors for dE/dX analysis, and high-precision discrimination of electron, proton, and helium ion types; (3) a large-area silicon semiconductor detector, combined with a large field of view covering nearly 4π solid angles, to improve the geometric factor and temporal resolution of the spectrometer; (4) four layers of a 5-pixel silicon semiconductor detector array to achieve high angular resolution; and (5) low-noise multi-channel Application Specific Integrated Circuit (ASIC) technology to achieve precise energy level observation and high energy resolution. The spectrometer will provide key measurements that reveal the physical nature of the origin/acceleration processes of solar and heliospheric energetic particles, which will prove beneficial for the upcoming interplanetary and deep space explorations by China.