Design and implementation of a space qualified DAQ system for the HEPD-02 silicon tracker

The Low Earth Orbit (LEO) is an interesting location to observe gamma rays and charged particles either of cosmic origin or generated in the atmosphere and trapped in the Earth Magnetic field. Detectors placed in the Earth's orbits range from 200 to 800 kilometers above sea level can perform measurements avoiding the atmosphere screening effect and are still close enough to relay a considerable amount of data to the ground. Depending on the orbit inclination and the observed energy range, detectors flying in the Low Earth Orbits are currently performing a large set of measurement in the fields of the Astroparticle physics and the Space Weather, and more ambitious and specialized mission are constantly planned. This possibility to perform interesting measurement in the LEO, generates a demand for lightweight detectors suitable for space missions hosted on satellites, with their tight limits in term of mass, power and data budgets and no possibility of servicing the hardware once deployed. To this days a large number of such instruments have been built and they are successfully producing a large amount of valuable data on a wide range of phenomena, including cosmic rays, solar physics, magnetosphere dynamics. The China Seismo-Electromagnetic Satellite (CSES) is a Chinese-Italian space mission aiming to deploy a small constellation of satellites providing correlated measurement of electromagnetic fields and particle fluxes in the Earth's magnetosphere. The main purpose of this mission is to help investigating the relatively new field of ``seismo-electromagnetics'', which consist in the study of electromagnetic phenomena possibly correlated with seismic events. In particular it is posited that perturbations of the Earth's Magnetic field can be detected directly by Electric and Magnetic field measurements and indirectly by observing variations in the trapped particles fluxes. The existence and nature of correlations between seismic activity and EM perturbations is at this moment matter of discussion, but supposedly involves interactions in the lithosphere-atmosphere-ionosphere-magnetosphere system. The CSES program with its satellites performing a simultaneous and accurate measurements of particle fluxes and the E and B fields, it is supposed to study and clarify this possible correlation. It is also important to mention that CSES detectors are also capable of producing relevant data for space weather and cosmic rays research. In the first chapter of this work the CSES mission is discussed, its goals are presented and a particular proposed seismo-EM interaction mechanism is introduced in qualitative terms. A review of the previous studies and measurements that claims a possible observation of correlation signals closes the chapter. The second chapter discuss the High Energy Particle Detector (HEPD-02) of CSES-02, the second satellite in the constellation, that is scheduled to be launched in early 2023. HEPD-02 is a compact particle detector, which measures the single particle arrival direction by means of a pixel silicon tracker and its total energy by means of a calorimetric system. HEPD-02 is designed primarily to detect particles in the energy range from few MeV to several hundreds of MeV@; mostly electrons and protons trapped in the magnetosphere, but also particles and nuclei of the cosmic radiation. The plastic scintillators segmented calorimeter is completed at the bottom by two layers of LYSO crystals allowing for an excellent energy resolution and particle identification. As mentioned, the HEPD-02 accurate measurements of the trapped particle fluxes versus time is relevant since a magnetosphere electromagnetic perturbation should also produce large perturbations of these particle populations. One of the HEPD-02 distinct features is the use of digital pixel silicon sensors for the tracking system. HEPD-02 will be the first spaceborne instruments where Monolithic Active Pixels (MAPS) are used in place of the more traditional micro-strips detector technology. The spatialisation of a detector designed for use on ground is a major task. It involves taking care of the survival to the stresses and vibrations of the launch on a rocket, the operation in an hostile environment (vacuum, electro-magnetic interferences, radiation), the thermal management where there is only direct conduction and radiation, the optimisation for operating with limited resources in terms of power and bandwidth of produced data. The third chapter, which covers the main topic of this thesis work,discuss the design and implementation of a custom readout system, tailored to fit the HEPD-02 needs and constraints in terms of power, and makes extensive use of clock gating and employs a sparsified readout scheme to reduce the power consumption. A series of software procedures for calibration and testing have been developed to allow the test and characterisation of the tracker. Those procedures were then adapted to be executed entirely on a soft-processor implemented in the tracker readout FPGA, allowing their use after the deployment of the instrument. The fourth chapter finally presents results from the test and characterisation of the tracker modules are reported, together with an overview of the stress testing activity for the space qualification of the produced hardware.