Technology Development of High Speed CMOS Detectors and Multilayer Mirrors for Dynamic Solar Soft X-ray Spectral Imaging

We propose to the H-TiDS ITDS 2019 call to further enhance capabilities for soft X-ray and EUV dynamic imaging. We will develop high speed readout back-illuminated CMOS soft X-ray (sxr) detectors to 1) mitigate saturation and blooming of solar flare images, 2) study high time cadence (0.05 second variations) phenomena, and 3) generate spectral images of active regions (ARs), coronal bright points (CBPs), small flares (A - B GOES class) and aspects of the quiet Sun (QS). The high speed read out detectors alone can provide course low time cadence (minutes) moderate spectral resolution (resolving powers, E/dE of 10 – 40) spectra. To enable narrowband (resolving powers, E/dE of 50 – 100) spectral images, we will also design, deposit, and measure reflectivity of sxr narrowband multi-layer mirrors (MLM) as a proof of concept. This work will setup a future proposal for spaceflight demonstrations on future sounding rocket launches, CubeSats, and large satellite missions. Our proposed work directly addresses the NASA Heliophysics DIvision and NRC decadal survey fundamental science question "What causes the Sun to vary?", and addresses the NASA Heliophysics Science Goal of "Explore the physical processes in the space environment from the Sun to the Earth and throughout the solar system". Question 1 is, do solar flares vary on sub-second timescales and if so what does this tell us about the magnetic field? Sxr filters can be used to modify the spectral bandpass and intensity range of high speed readout (40 Hz - 1,000 Hz, speed varies as a function of readout region size) CMOS detectors, which can be used to study the brightness evolution of solar flares on sub-second timescales. Furthermore, charge blooming, which commonly occurs with CCDs and has hindered Hinode X-ray Telescope large flare images, can be minimized with CMOS detectors. Each CMOS pixel is uniquely addressable with separate preamplifier and readout capabilities, and architecture to prevent charge from "spilling" to adjacent pixels. This can greatly increase sxr flare image quality. Intensity variations of ARs, CBPs and the QS can also be determined on sub-second timescales depending on the instrumentation that is coupled to the detector. Question 2 is, how are heating processes and plasma transport different for ARs, CBPs, small flares and the QS? Fast readout rates allow the detection of single photon events in the CMOS detector. The number of electron-hole pairs liberated is directly proportional to the energy of the incident photon. Thus, low resolving power spectroscopy can be performed on timescales of minutes for ARs, CBPs, small flares and longer timescales for the QS. These spectrally separated images can be used to investigate the temperature structure, which is vital for constraining heating processes and variations in the elemental abundances of Mg, Si, O and Fe which are enhanced in the corona, to constrain plasma transport. The narrowband multilayer mirrors can be tuned to sxr energies below 2.0 keV for spectral line and/or continuum measurements at high time cadence during solar flares. We will expand the initial testing in Kenter et al. 2014 on new 16 micrometer (um) pitch 1k x 1k CMOS detectors that are already at SAO. The current architecture allows for 10 - 20 us readout time per column. We will characterize the actual readout rates vs. number of columns, readout noise, dark noise, fixed pattern noise, and other noise along the data chain as a function of operating temperature. We will determine and model the spectral resolution and charge splitting as a function of energy using the onsite Chandra High Resolution Camera (HRC) calibration facility with manson and Fe 55 sources from 0.5 - 6.4 keV. We will also test linearity, which is vital for the integrating mode (dynamic range). We will use MLM resources from Marshall et al. 2018 for deposition and reflectivity measurements.

Support NASA's Heliophysics strategic science objectives to understand the Sun and its interactions with Earth and the solar system, including space weather. This will be achieved by developing/demonstrating instrumentation technology necessary to address the following science goals: Explore the physical processes in the space environment from the Sun to the Earth and throughout the solar system; Advance our understanding of the connections that link the Sun, the Earth, planetary space environments, and the outer reaches of our solar system; Develop the knowledge and capability to detect and predict extreme conditions in space to protect life and society and to safeguard human and robotic explorers beyond Earth.

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