Avalanche photodiodes for suprathermal and energetic ion detectors in future Heliophysics missions

Developing a single detector capable of measuring space plasmas from a few keV up to a few MeV/nuc is crucial to understanding many fundamental processes, including particle heating and acceleration, by providing complete spectra of energetic particle populations near the sun, the heliosphere, and in geospace (e.g., solar energetic particles, interplanetary shocks, corotating interaction regions, Van Allen radiation belts, plasma sheet, Earth’s bow shock, etc.). However, the current techniques pose serious technical challenges for reasons that the suprathermal (a few keV to 100s keV) region lies between the two most commonly used particle detection techniques that used by thermal or plasma instruments and by Solid-State Detector (SSD)–based energetic particle instruments. This suprathermal range represents the source particle populations which initiate acceleration processes. To reveal the mechanisms hidden in these processes, it is essential that precise and consistent measurements span a wider range and cover suprathermal particles along with energetic particles. Our previous work, funded entirely through SwRI’s internal research program, has already demonstrated that a new type of low-noise, low-threshold, SSD – the reach-through Avalanche PhotoDiode (APD) – has a threshold noise level of 1 keV, and can potentially extend the SSD energy coverage into the suprathermal energy range with 0.8 keV intrinsic resolution. In addition, our recent effort identified that fast APD signals triggered by ions are qualified for timing analysis in the Time-Of-Flight (TOF) mass spectrometry system. In preparation for future in-situ instruments, we propose to establish the method to measure ions using this emerging detector technology, including the largely unexplored suprathermal range. The goal of this project is to develop APDs for ions and test them for specific applications and environments expected in future Heliophysics missions. In this project, we will follow the 4 objectives, namely, (1) Device Development: Develop and test monolithic, multi-pixel APDs for future applications in energetic ion telescopes, (2) Timing capability and electronics: Develop electronics suitable for existing APDs for simultaneous TOF and energy measurement using off-the-shelf pick-off preamplifiers with a FPGA data handling program. Evaluate the timing resolution and pulse shape with a thinner depletion APD, (3) Dynamic range investigation and electronics: Evaluate APDs for >MeV ions. Develop a read-out method to cover a wider energy range, (4) Radiation hardness: Investigate radiation damage effects for 100s-keV and >MeV protons, and hot electrons. The APD technique satisfies the scientific and technical requirements of suprathermal and energetic particle instruments for NASA HPD’s near-term science targets such as the top priority recommendation for Solar Terrestrial Probes (STP) of the Decadal Survey 2012 - STP-5: Interstellar Mapping and Acceleration Probe (IMAP) as well as future science targets that require measurements of plasmas and suprathermal particles. If funded, project would fulfills several of NASA's strategic objectives as outlined in the 2012 Heliophysics Decadal Survey and the 2014 SMD Science Plan.