Browsing by Author "Spanswick, Emma L."

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    The Development of a Modern Correlator for the DRAO Synthesis Telescope
    (2019-12-17) Freeman, Pamela; Brown, Jo C.; Landecker, T. L.; Spanswick, Emma L.; Belostotski, Leonid
    The development of computationally powerful and efficient instrumentation is a necessity in radio astronomy, and is possible thanks to recent commercial technological advances. In this thesis project, I built and characterized a modern correlator to be used by the Synthesis Telescope (ST) at the Dominion Radio Astrophysical Observatory (DRAO). The current ST correlator is a decades-old, highly specified system that cannot be upgraded, and must be replaced, in order for the ST to have greater observational capability. The new ST correlator I constructed is based on the design implemented at the Canadian Hydrogen Intensity Mapping Experiment telescope at the DRAO. The system uses an FPGA-based digitizer and a liquid-cooled GPU-based correlator. I characterized the system’s performance and radio frequency emissions, then deployed the correlator to the DRAO and interfaced it with the ST. I first tested the correlator with artificial and telescope signals. Then, two observations of known calibrator sources were completed, with the old and new correlator systems in parallel, to compare data output and investigate the performance of the new correlator. The raw data output and the resulting images match quite closely, demonstrating the success of the system and the capability to proceed with further ST upgrades.
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    Static and Alfvénic Electrodynamics in the Auroral Region
    (2020-07-21) Wu, Jiashu; Knudsen, David J.; Brown, Jo C.; Spanswick, Emma L.; Davidsen, Jörn; Lynch, Kristina A.; Potter, Mike E.
    Auroral arcs, a type of aurora with curtain-like structure, can remain quasi-static for tens of minutes, and can also appear with rapid motions and changing brightness. One of the main challenges in constructing a self-consistent theory to explain the generation and morphology of auroral arcs is an adequate description of the arc circuit, meaning the electric field and currents that span the region from the magnetospheric generator to the ionospheric footprint. The ionospheric electrodynamics plays a critical role in formation of auroral arcs and in the whole magnetosphere-ionosphere coupling system. The high-precision magnetic and electric field data collected by the Swarm satellites are well suited to study both quasi-static auroral electrodynamics and waves in the low-frequency range. With the aid of ground-based optical data, I performed three studies about field-aligned currents (FACs) and Alfvén waves in the auroral region. The first study presents two types of FACs associated with quasi-static multiple arc systems. The comparison between ``unipolar'' and ``multipolar'' FAC systems provides insights in understanding the multiplicity of auroral arcs. The second study presents the statistical relation between Alfvén waves and large-scale FACs. It is found that Alfvénic fluctuations occur over a much wider range of locations and conditions than previously reported. The third study presents the first statistical survey of suprathermal electron bursts (STEBs) in the ionospheric Alfvén resonator. The case event presented in this study demonstrates both normal and inverse dispersion in energy and pitch angle spectrograms of adjacent suprathermal electron bursts. Observations presented in these studies provide important constraints in testing models of electron acceleration and theories of auroral arc generation.