L. Ferreira

Characterization and reduction of unexplained noise in superconducting transition-edge sensors

The noise in superconducting transition-edge sensors (TESs) commonly exceeds simple theoretical predictions. The reason for this discrepancy is presently unexplained. We have measured the amplitude and frequency dependence of the noise in TES sensors with eight different geometries. In addition, we have measured the dependence of the noise on operating resistance, perpendicular magnetic field, and bath temperature. We find that the unexplained noise contribution is inversely correlated with the temperature width of the superconducting-to-normal transition and is reduced by a perpendicular field and in certain geometries. These results suggest paths to improved sensor performance.

14-pixel, multiplexed array of gamma-ray microcalorimeters with 47eV energy resolution at 103keV

The authors present a prototype for a high-energy-resolution, high-count-rate, gamma-ray spectrometer intended for nuclear forensics and international nuclear safeguards. The prototype spectrometer is an array of 14 transition-edge-sensor microcalorimeters with an average energy resolution of 47eV (full width at half maximum) at 103keV. The resolution of the best pixel is 25eV. A cryogenic, time-division multiplexer reads out the array. Several important topics related to microcalorimeter arrays are discussed, including cross-talk, the uniformity of detector bias conditions, fabrication of the arrays, and the multiplexed readout. The measurements and calculations demonstrate that a kilopixel array of high-resolution microcalorimeters is feasible.

Optimized transition-edge x-ray microcalorimeter with 2.4eV energy resolution at 5.9keV

We present measurements from a series of transition-edge x-ray microcalorimeters designed for optimal energy resolution. We used the geometry of the sensors to control their heat capacity and employed additional normal metal features and a perpendicular magnetic field to control the sharpness of the superconducting-to-normal transition. These degrees of control allow an optimal selection of sensor saturation energy and noise. Successive design changes improved the measured energy resolution of the sensors from 4.5eV full width at half maximum at 5.9keVto2.4eV at 5.9keV. Sensors with this energy resolution are well matched to applications in x-ray astrophysics and terrestrial materials analysis.

Array-compatible transition-edge sensor microcalorimeter γ-ray detector with 42eV energy resolution at 103keV

The authors describe a microcalorimeter γ-ray detector with measured energy resolution of 42eV full width at half maximum for 103keV photons. This detector consists of a thermally isolated superconducting transition-edge thermometer and a superconducting bulk tin photon absorber. The absorber is attached with a technique compatible with producing arrays of high-resolution γ-ray detectors. The results of a detailed characterization of the detector, which includes measurements of the complex impedance, detector noise, and time-domain pulse response, suggest that a deeper understanding and optimization of the thermal transport between the absorber and thermometer could significantly improve the energy resolution of future detectors.

Time-division multiplexing of high-resolution x-ray microcalorimeters: Four pixels and beyond

We present experimental results from a four-pixel array of transition-edge-sensor, x-ray microcalorimeters read out through a single amplifier channel via a time-division superconducting quantum interference device multiplexer. We map the dependence of the x-ray energy resolution of the microcalorimeters on multiplexer timing parameters. We achieve multiplexed, four-pixel resolution of 6.94±0.05eV full width at half maximum of the MnKα complex near 5.9keV, which is a degradation of only 0.44eV from nonmultiplexed operation. An analysis of straightforward upgrades to the multiplexer predicts that a linear array of 32 of these pixels could be multiplexed with a degradation in resolution of only 0.1eV. These results, the first demonstration of a time-division multiplexer for x-ray detectors, establish a clear path to the instrumentation of a kilopixel microcalorimeter array.