2006 JINST TH 001
Ph.D. degree thesis
accepted by
University of Leicester, UK, in 2006
Stephen James Smith
Supervisor: George W. Fraser
Development of Transition Edge Sensor Distributed Read-Out Imaging Devices for
Applications in X-ray Astronomy
Keywords:
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X-ray detectors
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Cryogenic detectors
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Superconductive detectors (bolometers, tunnel junctions etc)
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X-ray detectors and telescopes
Abstract:
This thesis is concerned with the development of, position-sensitive,
Transition Edge Sensors (TESs) operating at cryogenic temperatures (~
0.1 K). The Distributed Read-Out Imaging Device (DROID) uses TES
read-out at both ends of a linear X-ray absorber, to derive, through
heat diffusion, both spectral and spatial information. Potentially,
DROIDs offer a simpler technological alternative to the development of
large area pixel arrays for future X-ray space observatories. We have
established a finite-element model to numerically calculate the
response of the DROID to an X-ray photon. The model estimates the
noise spectral density at the detector outputs, including the
frequency dependent correlations between the two TESs. This model is
used to implement pre-existing signal processing algorithms, based on
the digital optimal filter, to calculate the position and energy
resolution along the length of experimental DROID designs. We show
that these algorithms do not lead to optimum performance under all
conditions and derive the true optimal filters, based on least-squares
minimisation of the total noise power in the DROID. By numerical
simulation, we show that improvements in the energy and in particular,
in the position resolution, are theoretically possible. We
investigate the trade-offs resulting from changing key detector design
parameters, such as the thermal conductances of the different detector
elements. These simulations enable the DROID design to be optimised
for specific detector applications. The design and experimental
characterisation of prototype DROIDs are described. The first X-ray
results from a prototype DROID, using single TES read-out, are
reported. The data shows different populations of signal
corresponding to X-ray absorption in different parts of the DROID.
These results demonstrate proof of concept, confirming spatial
sensitivity along the length of the DROID absorber, though the actual
spectral and spatial resolutions are limited by the availability of
only a single read-out channel.
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