JINST Instrumentation Theses Archive

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:

• X-ray detectors
• Cryogenic detectors
• Superconductive detectors (bolometers, tunnel junctions etc)
• 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.