Solar flares are some of the most energetic events in the solar system and can be studied to investigate the physics of plasmas and stellar processes. One interesting aspect of solar flares is the presence of accelerated (nonthermal) particles, whose signatures appear in solar flare hard x-ray emissions. Debate has been ongoing since the early days of the space age as to how these particles are accelerated, and one way to probe relevant acceleration mechanisms is by investigating short-timescale (tens of milliseconds) variations in solar flare hard x-ray flux. The impulsive phase rapid energetic solar spectrometer (IMPRESS) CubeSat mission aims to measure these fast hard x-ray variations. In order to produce the best possible science data from this mission, we characterize the IMPRESS scintillator detectors using Geant4 Monte Carlo models. We show that the Geant4 Monte Carlo detector model is consistent with an analytical model. We find that Geant4 simulations of x-ray and optical interactions explain observed features in experimental data, but do not completely account for our measured energy resolution. We further show that nonuniform light collection leads to double-peak behavior at the 662 keV 137Cs photopeak and can be corrected in Geant4 models and likely in the lab.
KEYWORDS: Spectroscopy, Hard x-rays, Particles, Time metrology, Space operations, Solar radiation models, Solar processes, Silicon, Sensors, Scintillators
In the past two decades, great advances have been made in investigating hard X-rays from accelerated electrons in solar flares. This emission is of interest because the means by which flares so efficiently accelerate particles are still not understood. Observations from the RHESSI spacecraft led to better understanding in the imaging and spectral domains, but presented difficulty for time domain analysis at scales less than ~2 seconds. This leaves the behavior of flare emission at small timescales poorly explored. The NSF-funded IMpulsive Phase Rapid Energetic Solar Spectrometer (IMPRESS) CubeSat is designed specifically to measure hard X-ray emission up to 100 keV from flares at a tens-of-ms cadence. This will provide novel constraints for flare particle acceleration models. IMPRESS is a student-centered collaboration between UMN, MSU, SwRI, and UCSC. This presentation will describe the science, mission concept, and some design specifics for IMPRESS.
NASA Goddard Space Flight Center (GSFC) has successfully developed and tested a custom-designed low-noise multi-channel digitizer (MCD) application specific integrated circuit (ASIC) for operation in harsh radiation environments. The MCD-ASIC is optimized for low-frequency and low-voltage signal measurements from sensors and transducers. It has 20 input channels where each channel is comprised of auto-zeroed chopper variable-gain amplifier, post amplifier, and a second order ΣΔ modulator. ΣΔ analog-to-digital converter (ADC) relies on oversampling and noise shaping to achieve high-resolution conversion. However, the MCD-ASIC requires digital filtering and decimation to convert the output single bit streams from the ADC to useful data words. A parallel digital platform such as a field-programmable-gate-array (FPGA) is highly suitable to fully leverage the capabilities of the MCD-ASIC. The FPGA controls the MCD-ASIC via serial peripheral interface (SPI) protocol and acquires data from it. A Python-script communicates with the FPGA board through a USB interface on a cross operating platform. Using this architecture, the system is capable of monitoring up to 20 voltage readout channels simultaneously in a real-time manner. Each channel’s parameters can be programmed independently allowing maximum user versatility. In this paper, we present analysis of the analog front-end, the implementation of the digital processing unit on the FPGA, and provide noise performance results from the MCD-ASIC readout.
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