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We are developing transition-edge sensor microcalorimeters for the X-ray integral field unit (X-IFU) on-board ESA's Athena space telescope. These detectors will be read out using time-domain multiplexing. Due to the limitations on bandwidth and dynamic range of the readout, the optimally filtered pulse heights of the measured X-ray signals suffer from a nonlinear variation with the exact photon arrival time relative to the sampling points. The shape and magnitude of this variation depend on the photon energy. We describe a method to characterize this energy-dependent variation with few parameters, which can then be interpolated to correct event energies across the whole spectrum. We implement our method on measurements from 200 pixels in a prototype X-IFU kilo-pixel array readout using 8-column × 32-row TDM. We show that the interpolation errors between calibration points, over the energy range 4–12 keV, can be made sufficiently small that they do not adversely impact the measured energy resolution across the full spectral range. [ABSTRACT FROM AUTHOR]

In many superconducting transition-edge sensor (TES) microcalorimeters, the measured electrical noise exceeds theoretical estimates based on a thermal model of a single body thermally connected to a heat bath. Here, we report on noise and complex impedance measurements of a range of designs of TESs made with a Mo/Au bilayer. We have fitted the measured data using a two-body model, where the x-ray absorber and the TES are connected by an internal thermal conductance Gae. We find that the so-called excess noise measured in these devices is consistent with the noise generated from the internal thermal fluctuations between the x-ray absorber and the TES. Our fitted parameters are consistent with the origin of Gae being from the finite thermal conductance of the TES itself. These results suggest that even in these relatively low resistance Mo/Au TESs, the internal thermal conductance of the TES may add significant additional noise and could account for all the measured excess noise. Furthermore, we find that around regions of the superconducting transition with rapidly changing derivative of resistance with respect to temperature, an additional noise mechanism may dominate. These observations may lead to a greater understanding of TES devices and allow the design of TES microcalorimeters with improved performance. [ABSTRACT FROM AUTHOR]

The measured noise in Mo/Au transition-edge sensor (TES) microcalorimeters produced at NASA has recently been shown to be well described by a two-body electro-thermal model with a finite thermal conductance between the X-ray absorber and the TES. In this article, we present observations of a high-frequency peak in the measured current noise in some of these devices. The peak is associated with an oscillatory component of the TES response that is not predicted in a single-body model but can be qualitatively described by the two-body model. [ABSTRACT FROM AUTHOR]

In this paper, we report on X-ray transition-edge sensor (TES) microcalorimeters optimized to have the best possible energy resolution for a limited energy range for the incoming X-rays, such as an energy resolution of 0.3 eV full width half maximum (FWHM) for energies up to ≈ 0.8 keV as is desirable for one of the Lynx X-ray Microcalorimeter subarrays. The test array we have fabricated has 60 × 60 sensors on a pitch of 50 μ m , and has 46 × 46 μ m 2 absorbers that are one micrometer thick. We have measured a spectral energy resolution of the same device using 3 eV photons delivered through an optical fiber. For the one-photon 3 eV line, we have obtained an energy resolution of 0.25 eV FWHM, which is consistent with the estimated performance based on the signal size and noise. Further measurements will determine how the energy resolution degrades with energy. Based upon measurements of the TES transition characteristics, it appears that this level of energy resolution should be achievable up to 0.5 keV, and the performance will then gradually degrade to the measured energy resolution of around 2.3 eV at 1.5 keV. In this paper, we describe the full design and characterization of this detector, and discuss the performance limits of pixels designs like this. [ABSTRACT FROM AUTHOR]

Frequency-division multiplexing is the baseline read-out system for large arrays of superconducting transition-edge sensors (TES’s) under development for the X-ray and infrared instruments like X-IFU (Athena) and SAFARI, respectively. In this multiplexing scheme, the sensors are ac-biased at different frequencies from 1 to 5 MHz and operate as amplitude modulators. Weak superconductivity is responsible for the complex TES resistive transition, experimentally explored in great detail so far, both with dc- and ac-biased read-out schemes. In this paper, we will review the current status of our understanding of the physics of the TES’s and their interaction with the ac bias circuit. In particular, we will compare the behaviour of the TES nonlinear impedance, across the superconducting transition, for several detector families, namely: high-normal-resistance TiAu TES bolometers, low-normal-resistance MoAu TES microcalorimeters and high-normal-resistance TiAu TES microcalorimeters. [ABSTRACT FROM AUTHOR]

We present the latest update and progress on the future Japanese X-ray satellite mission Diffuse Intergalactic Oxygen Surveyor (DIOS). DIOS is proposed to JAXA as a small satellite mission, and would be launched with an Epsilon rocket. DIOS would carry on the legacy of ASTRO-H, which carries semiconductor-based microcalorimeters and is scheduled to be launched in 2016, in high-resolution X-ray spectroscopy. A 400-pixel array of transition-edge sensors (TESs) would be employed, so DIOS would also provide valuable lessons for the next ESA X-ray mission ATHENA on TES operation and cryogen-free cooling in space. We have been sophisticating the entire design of the satellite to meet the requirement for the Epsilon payload for the next call. The primary goal of the mission is to search for warm-hot intergalactic medium with high-resolution X-ray spectroscopy by detecting redshifted emission lines from OVII and OVIII ions. The results would have significant impacts on our understanding of the nature of 'dark baryons,' their total amount and spatial distribution, as well as their evolution over cosmological timescales. [ABSTRACT FROM AUTHOR]

A transition edge sensor (TES) microcalorimeter array as an X-ray sensor for a scanning transmission electron microscope system is being developed. The technical challenge of this system is a high count rate of $$\sim $$ 5000 counts/second/array. We adopted a 64 pixel array with a parallel readout. Common SQUID bias, and common TES bias are planned to reduce the number of wires and the resources of a room temperature circuit. The reduction rate of wires is 44 % when a 64 pixel array is read out by a common bias of 8 channels. The possible degradation of the energy resolution has been investigated by simulations and experiments. The bias fluctuation effects of a series connection are less than those of a parallel connection. Simple calculations expect that the fluctuations of the common SQUID bias and common TES bias in a series connection are $$10^{-7}$$ and $$10^{-3}$$ , respectively. We constructed 8 SQUIDs which are connected to 8 TES outputs and a room temperature circuit for common bias readout and evaluated experimentally. Our simulation of crosstalk indicates that at an X-ray event rate of 500 cps/pixel, crosstalk will broaden a monochromatic line by about 0.01 %, or about 1.5 eV at 15 keV. Thus, our design goal of 10 eV energy resolution across the 0.5-15 keV band should be achievable. [ABSTRACT FROM AUTHOR]

We are developing the frequency-division multiplexing (FDM) readout system aimed to realize the 400-pixel transition edge sensor (TES) microcalorimeter array for the DIOS mission as well as large-format arrays with more than a thousand of TES for future space missions such as the ATHENA mission. The developed system consists of the low-power superconducting quantum interference device (SQUID), the digital FDM electronics, and the analog front-end to bridge the SQUID and the digital electronics. Using the developed readout system, we performed a TES readout experiment and succeeded to multiplex four TES signals with the single-staged cryogenic setup. We have experienced two issues during the experiment: an excess noise and crosstalk. The brief overview of the developed system and the details, results, and issues of the TES multiplexing readout experiment is discussed. [ABSTRACT FROM AUTHOR]

We discuss the design and performance of a transition edge sensor (TES) X-ray microcalorimeter array for scanning transmission electron microscope (STEM)-energy dispersive X-ray spectroscopy (EDS). The TES X-ray microcalorimeter has better energy resolution compared to conventional silicon drift detector and STEM-EDS utilizing a TES detector makes it possible to map the distribution of elements on a specimen in addition to analyze the composition. The requirement for a TES detector is a high counting rate ( $$>$$ 20 kcps), wide energy band (0.5-15 keV) and good energy resolution ( $$<$$ 10 eV) full width at half maximum. The major improvement of this development is to increase the maximum counting rate. In order to accommodate the high counting rate, we adopted an $$8 \times 8$$ format, 64-pixel array and common biasing scheme for the readout method. We did all design and fabrication of the device in house. With the device we have fabricated most recently, the pulse decay time is 40 $$\upmu $$ s which is expected to achieve 50 kcps. For a single pixel, the measured energy resolution was 7.8 eV at 5.9 keV. This device satisfies the requirements of counting rate and energy resolution, although several issues remain where the performance must be confirmed. [ABSTRACT FROM AUTHOR]

We are developing frequency-division multiplexing (FDM) systems with baseband feedback for TES X-ray microcalorimeter arrays for use with the DIOS mission. To meet the requirement of limited cooling capacity at cryogenic temperatures, we developed low-power and FDM-optmized dc-SQUIDs. To make maximum use of the SQUIDs, we also developed digital electronics using FPGA evaluation boards and ADC/DAC FMC daughter cards, and evaluated signal-to-noise ratios and gain-bandwidth products. [ABSTRACT FROM AUTHOR]

We have been improving our TEM-EDS for elemental microanalysis after a successful achievement of a high energy resolution (7.8 eV at 1.7 keV) using a TES microcalorimeter. The improvements fall into a 3D superconductive wiring and a high-speed processing (∼3,000 cps). We are implementing a 10-ch TES array for higher count rate and a broader dynamic range. The shape of a probe needs to be a small polygonal rod with an approximate size of 1 cm×1 cm×10 cm, and hence the placing and wiring of the TES array and read-out circuits at the cryogenic stage were very demanding. We overcame those difficulties by 3D photolithography and electrodeposition. With these new technologies, we developed the OFC probe with solder-plated 3D wiring, and successfully observed a superconductivity at the temperature of liquid helium. As a required count rate per channel is ∼300 cps, the overall system count rate is ∼3,000 cps, which is incomparably higher than before. In the last model, we used an embedded system to process waveforms from a 4-ch 14-bit 1 MS/s ADC due to a small signal bandwidth, but this time we parallelized three identical ADCs and transfer raw waveforms by Ethernet lines to a host to achieve the required system count rate. [ABSTRACT FROM AUTHOR]

For future X-ray astronomy, a microcalorimeter array that has both mega-pixel imaging capability and eV-level high energy-resolution is desirable. In order to realize it, thermometers with negligible self-heating, multiplexing readout and close packing are essential components. We propose a novel detector concept, a dielectric microcalorimeter (DMC) and present current design studies. The DMC uses dielectric pixels as thermometers which form LC resonators in GHz band. The signals from many pixels can be easily multiplexed in a similar way to kinetic inductance detectors. The dielectric pixels are easy to be integrated into large and dense arrays. However, dielectrics with temperature-dependent permittivity below 2 K were not known. We evaluated quantum ferroelectric strontium titanate (STO) used in a capacitive thermometer higher than 2 K as a suitable dielectric for the DMC pixels. We fabricated STO capacitors and measured their capacitance from 2 K down to 80 mK. As a result, we found that their capacitive thermometer sensitivity at 100 mK are dlog C/ dlog T∼10, and they can be sensitive enough to detect X-ray with a resonator. We report the concepts, the measurement details, expected response to X-ray irradiation and our designs of the DMC. [ABSTRACT FROM AUTHOR]