Superconducting Transition Edge Sensor Using Dilute AlMn Alloys

We have fabricated a bolometer using a transition-edge sensor (TES) made of Al doped with Mn to suppress the superconducting critical temperature (Tc) of Al from ∼1Kto∼100mK. The resulting detector exhibits low-frequency noise consistent with theory, with a noise-equivalent power of 7.5×10−18W/√Hz. The addition of Mn impurities did not significantly increase the heat capacity of the TES. In addition, the detector is surprisingly insensitive to applied magnetic fields. The use of AlMn alloy films in arrays of TES detectors has advantages in simplicity of fabrication when compared to traditional bilayer fabrication techniques

Science Objectives for an X-Ray Microcalorimeter Observing the Sun

We present the science case for a broadband X-ray imager with high-resolution spectroscopy, including simulations of X-ray spectral diagnostics of both active regions and solar flares. This is part of a trilogy of white papers discussing science, instrument (Bandler et al. 2010), and missions (Bookbinder et al. 2010) to exploit major advances recently made in transition-edge sensor (TES) detector technology that enable resolution better than 2 eV in an array that can handle high count rates. Combined with a modest X-ray mirror, this instrument would combine arcsecondscale imaging with high-resolution spectra over a field of view sufficiently large for the study of active regions and flares, enabling a wide range of studies such as the detection of microheating in active regions, ion-resolved velocity flows, and the presence of non-thermal electrons in hot plasmas. It would also enable more direct comparisons between solar and stellar soft X-ray spectra, a waveband in which (unusually) we currently have much better stellar data than we do of the Sun

Science with Micro-X: the TES Microcalorimeter X-ray Imaging Rocket

Micro-X is a proposed sounding rocket experiment that will combine a transition-edge-sensor X-ray-microcalorimeter array with a conical imaging mirror to obtain high-spectral-resolution images of extended and point X-ray sources. We describe the payload and the science targeted by this mission including the discussion of three possible Micro-X targets: the Puppis A supernova remnant, the Virgo Cluster, and Circinus X-1. For example, a Micro-X observation of the bright eastern knot of Puppis A will obtain a line-dominated spectrum with 90,000 counts collected in 300 seconds at 2 eV resolution across the 0.3-2.5 keV band. Micro-X will utilize plasma diagnostics to determine the thermodynamic and ionization state of the plasma, to search for line shifts and broadening associated with dynamical processes, and seek evidence of ejecta enhancement. For clusters of galaxies, Micro-X can uniquely study turbulence and the temperature distribution function. For binaries, Micro-X's high resolution spectra will separate the different processes contributing to the Fe K lines at 6 keV and give a clear view of the geometry of the gas flows and circumstellar gas

Using ion implantation to adjust the transition temperature of superconducting films

We summarize a continuing investigation into using ion implantation to alter the transition temperature of superconducting thin films. The primary motivation for the work presented here was to study the feasibility of using magnetic ion doping to replace the bi-layer Tc control process currently used for certain cryogenic detector applications at National Institute for Standards and Technology. The results from work with various ion species implanted into aluminum, molybdenum, titanium and tungsten host films are presented

Dilute Al–Mn alloys for superconductor device applications

We discuss results on the superconducting and electron-transport properties of Mn-doped Al produced by sputter deposition. The critical temperature of Al has been systematically reduced to below 50 mK by doping with 1000–3000 ppm Mn. Values of the α parameter are in the range of 450–500, indicating sharp normal-to-superconductor transitions. This material is thus of significant interest for both transition-edge sensors operating in the 100 mK regime and superconductor/insulator/superconductor and superconductor/insulator/normal devices, in the latter case where appropriately doped Al–Mn replaces the normal metal

High-resolution calorimetry: limitations of doped semiconductor thermometers

Small thermal calorimeters operating at cryogenic temperatures have achieved an energy resolution for single X-ray photons that is a factor of 20 better than the theoretical limit for a silicon ionization detector. To determine the potential for further improvements and decide on likely routes for achieving them, we discuss detector design optimization, first for an ideal calorimeter, and then for the case where components exhibit non-ideal behavior. Two serious non-ideal properties of doped semiconductor thermometers are electron–phonon decoupling and excess noise. These have been characterized over a range of sensitivity and operating temperature, and their effects on design optimization and ultimate performance can be evaluated

TES Detector Noise Limited Readout Using SQUID Multiplexers

The availability of superconducting Transition Edge Sensors (TES) with large numbers of individual detector pixels requires multiplexers for efficient readout. The use of multiplexers reduces the number of wires needed between the cryogenic electronics and the room temperature electronics and cuts the number of required cryogenic amplifiers. We are using an 8 channel SQUID multiplexer to read out one-dimensional TES arrays which are used for submillimeter astronomical observations. We present results from test measurements which show that the low noise level of the SQUID multiplexers allows accurate measurements of the TES Johnson noise, and that in operation, the readout noise is dominated by the detector noise. Multiplexers for large number of channels require a large bandwidth for the multiplexed readout signal. We discuss the resulting implications for the noise performance of these multiplexers which will be used for the readout of two dimensional TES arrays in next generation instruments