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SRON is developing Frequency Domain Multiplexing (FDM) for the read-out of transition edge sensor (TES) soft x-ray microcalorimeters for the XMS instrument of the International X-ray Observatory and far-infrared bolometers for the SAFARI instrument on the Japanese mission SPICA. In FDM the TESs are AC voltage biased at frequencies from 0.5 to 6 MHz in a superconducting LC resonant circuit and the signal is read-out by low noise and high dynamic range SQUIDs amplifiers. The TES works as an amplitude modulator. We report on several AC bias experiments performed on different detectors. In particular, we discuss the results on the characterization of Goddard Space Flight Center x-ray pixels and SRON bolometers. The paper focuses on the analysis of different read-out configurations developed to optimize the noise and the impedance matching between the detectors and the SQUID amplifier. A novel feedback network electronics has been developed to keep the SQUID in flux locked loop, when coupled to superconducting high Q circuits, and to optimally tune the resonant bias circuit. The achieved detector performances are discussed in view of the instrument requirement for the two space missions.

5 páginas, 6 figuras, 1 tabla.-- et al., We fabricated and characterized a low thermal conductance (G) transition edge sensor (TES). The device is based on a superconducting Ti/Au bilayer deposited on a suspended SiN membrane. The critical temperature of the device is 155 mK. The low thermal conductance is realized by using narrow SiN ring-like supporting structures. All measurements were performed having the device in a light-tight box, which to a great extent eliminates the loading of the background radiation. We measured the current-voltage (IV) characteristics of the device in different bath temperatures and determine the thermal conductance (G) to be equal to 1.66 pW/K. This value corresponds to a noise equivalent power (NEP) of 1×10-18 W/√Hz. The current noise and complex impedance are also measured at different bias points at 25 mK bath temperature. The measured electrical (dark) NEP is 2×10-18 W/√Hz, which is about a factor of 2 higher than what is expected from the thermal conductance that comes out of the IV curves analysis. We also measured the complex impedance of the same device at several bias points. Fitting a simple first order thermal-electrical model to the measured data, we find an effective time constant of about 62 μs and a thermal capacity of 3 fJ/K., This work was supported in part by ESA TRP under Contract ITT-1-5922/08/NL/EM TES spectrometer.

Complex impedance measurements are widely used to characterize superconducting transition edge sensors (TESs) in bolometers and microcalorimeters. Typically, models are fit to impedance data to find parameters which pertain to the performance of these detectors. After the parameters are determined, the models are then used to compute the response and noise of these devices. In this paper, we present general relationships between the measured impedance, the thermal response to power in the TES, and noise. We describe a method for measuring αI and βI of the superconducting phase transition, which does not require model fitting. We find bolometer response is determined from the impedance provided that the absorber is strongly coupled to the TES electron system. We also demonstrate how to calculate upper and lower limits on the noise directly from the impedance data without modeling. Additionally, the relations can be used to check the validity of the models and to understand what information can and cannot be obtained from measurements of impedance, response, and noise.

Inductor-Capacitor (LC) filter circuits form an essential component for the readout chain of TES detectors, in the case of frequency division multiplexing. They serve the functions of blocking wide band noise from adjacent pixels and separation of bias frequencies. A key requirement is a high quality factor Q (narrow band resonance) to guarantee voltage bias of the TES detectors, implying a full superconducting circuit, low dielectric loss capacitors and low magnetic loss inductors. Typically, Q should be larger than 500*f [MHz]*L [μH]. Here f is the bias frequency and L the inductor value, which is coupled to the detector speed for stable electro thermal feedback response. In our case, Q must be in the range of 1000 to 10000. The astronomical applications for which these filters are being developed are the micro calorimeter read-out of the XMS instrument on the IXO-mission and far infrared bolometers for the SAFARI instrument on the Japanese mission SPICA. For the latter mission the goal is to readout 160 TES pixels with one SQUID in the frequency range 1 to 2 MHz. We describe fabrication procedures for fully superconducting circuits, resulting in a maximum observed Q of 12000 for a-Si based capacitors. We also report on efforts to minimize the required surface area for the filters and to improve the predictability of the center frequency of the filters. We show measurements on filters in a prototype 16 channel FDM readout setup.

SRON is developing an electronic read-out system for an array of Transition-Edge Sensors (TES) which combines the techniques of Frequency Domain Multiplexing (FDM) with Base-Band FeedBack (BBFB). Its potential astronomical applications are in the read-out of soft X-ray microcalorimeters of the XMS instrument on the International X-ray Observatory (IXO) and the far-IR bolometers of the SAFARI instrument on the Japanese-European mission SPICA. In this paper we focus on the experimental verification of the system, demonstrating for 16 pixels that simultaneous read-out does not degrade the noise performance, and that crosstalk between pixels is close to the requirements for IXO. A detailed analysis of the BBFB system is presented, identifying its limitations and routes for improvement to the levels required for implementation on both missions.

We present the latest results of the performance of micro-calorimeters based on transition edge sensors (TESs) for space applications. Sensors based on TiAu superconductive layers with Cu/Bi absorbers are discussed and have been characterized. Different coupling schemes between absorber and TES have been tested leading to an optimal (preferred) design for a new batch of arrays. We discuss the progress on array development for the International X-ray Observatory (IXO) in terms of pixel uniformity and filling factor. Inter-pixel cross-talk is discussed as well.

We characterised a TES-based X-ray microcalorimeter in an adiabatic demagnetisation refrigerator (ADR) using synchrotron radiation. The detector response and energy resolution was measured at the beam-line in the PTB radiometry laboratory at the electron storage ring BESSY II in the range from 200 to 1800 eV. We present and discuss the results of the energy resolution measurements as a function of energy, beam intensity and detector working point. The measured energy resolution ranges between 1.5 to 2.1 eV in the investigated energy range and is weakly dependent on the detector set point. A first analysis shows a count-rate capability, without considerable loss of performance, of about 500 counts per second., Comment: 6 pages, 5 figures, Proceedings of the 12th International Workshop on Low Temperature Detectors (LTD12)

Seven microcalorimeters with different geometries have been tested and their performance is compared. The study, for TiAu TESs with a Cu absorber, indicates the presence of so-called constant voltage noise and internal thermal fluctuation noise. The constant voltage noise is not changed by a normal metal pattern on the TES, or by a magnetic field. The energy resolution of the detectors, having different heat capacities, is 2.5 and 5.0 eV (at 5.9 keV).

We are developing X-ray microcalorimeters based on Ti/Au transition-edge sensors (TES). Among sensors we have fabricated, one with a Cu absorber at the center of the TES shows a particularly good X-ray energy resolution: 1.56 eV at 250 eV and 2.5 eV at 5.9 keV. In this paper, a detailed study of its impedance and noise is presented. The noise is not explained by a sum of known sources. The magnitude of unexplained noise is largest when the sensitivity of the TES on temperature (α) and on current (β) are the highest. The observed relation between the noise level and sensitivity suggests a source of thermal fluctuations inside the TES or between the TES and the absorber. We also found that β is linearly correlated to the product of α and current, which limits the effective sensitivity that is expressed as α/(1+β).

TES-based bolometer and microcalorimeter arrays with thousands of pixels are under development for several space-based and ground-based applications. A linear detector response and low levels of cross talk facilitate the calibration of the instruments. In an effort to improve the properties of TES-based detectors, fixing the TES resistance in a resistance-locked loop (RLL) under optical loading has recently been proposed. Earlier theoretical work on this mode of operation has shown that the detector speed, linearity and dynamic range should improve with respect to voltage biased operation. This paper presents an experimental demonstration of multiplexed readout in this mode of operation in a TES-based detector array with noise equivalent power values (NEP) of $3.5\cdot 10^{-19} $W/$\sqrt{\mathrm{Hz}}$. The measured noise and dynamic properties of the detector in the RLL will be compared with the earlier modelling work. Furthermore, the practical implementation routes for future FDM systems for the readout of bolometer and microcalorimeter arrays will be discussed., Comment: 4 pages, 4 figures, ASC14

We are developing nearly quantum limited two-stage SQUID systems for the readout of the MiniGRAIL, the first spherical gravitational wave detector with a diameter of 65 cm and a mass of 1150 kg. The two-stage SQUID systems are based on a conventional dc SQUID as the sensor and a double relaxation oscillation SQUID (DROS) as the second stage. The SQUID systems will be coupled to the detector via a multi-mode inductive transducer. The large flux-to-voltage transfer of the two-stage SQUID system allows a direct voltage readout scheme, i.e. without (ac flux) modulation. At T = 4.2 K, the energy resolution in flux-locked loop was measured to be e = 27 h, and at a temperature around 20 mK, the energy resolution is expected to reach the quantum limit.

An overview is given on the possibilities of building low cost omni-directional gravitational wave detectors using resonant spheres. Sensitivity curves of arrays and xylophones of spheres fabricated from different materials show that spherical detectors can be competitive with the large interferometers at frequencies above 1 kHz, with the additional advantage of being omni-directional and being able to determine the direction and polarization of the gravitational wave. MiniGRAIL is the first spherical resonant detector, being built at the Kamerlingh Onnes Laboratory of Leiden University in the Netherlands. The detector is planned to operate at a temperature of about 20 mK and will have a quantum limited strain sensitivity for a burst signal of the order of 4 × 10−21. We present the progress concerning cryogenics and transducer development.

We are developing a two-mode inductive resonant transducer for MiniGrail. We report several quality factor measurements, down to 4.2 K, performed on a scaled size resonator in different conditions: when suspended from a wire and when clamped, by thermal contraction techniques, into a hole of a sphere of 150 mm diameter and 14 kg mass. Q-factor measurements of a first resonator prototype at 4.2 K for MiniGrail are also presented. Finally, a fabrication process for a Nb film pick-up coil is described.

The results of the first cooldown of MiniGRAIL are presented. MiniGRAIL is a 65 cm diameter spherical gravitational wave detector made of CuAl6%, having a mass of 1150 kg. The sphere is suspended from a seven-stage vibration isolation system with a total weight of about 950 kg. The sphere should be cooled to below 20 mK. During the first run the sphere was cooled down to 1.8 K. A forced helium flow was used to cool the sphere down to 4 K, which took only two days. Further cooling to 1.8 K was done using a 1 K pot. We measured the temperature dependence of the mechanical quality factor and made an evaluation of the heat leaks (for more details see www.minigrail.nl).

The X-ray spectroscopy telescope Athena has been designed to implement the science theme "the hot and energetic universe", selected by the European Space Agency as the second large mission of its Cosmic Vision program. X-IFU, one of the two interchangeable focal plane instruments of Athena, is a high resolution X-ray spectrometer made of a large array of Transition Edge Sensors. Two options are under consideration for the X-IFU microcalorimeters: Ti/Au bilayers or Mo/Au bilayers. Here we report on our efforts to develop Mo/Au-based TES. The TES are made of high quality superconducting Mo/Au bilayers fabricated at room temperature on low stress Si 3 N 4 membranes; Mo is deposited by RF magnetron sputtering and in-situ covered by a thin (15nm) Au layer deposited by DC sputtering; in a second step, the Au layer thickness is increased ex-situ by e-beam deposition, to obtain suitable resistance Rn and operation temperature values. Very sharp transitions (~few mK transition width) are obtained, with typically R n ~25mΩ and T c ~ 100-120mK for 65/215 bilayers. First simple TES designs are being tested. Also, Bi films several μm thick, intended to constitute the X-ray absorber, are fabricated by electrochemical deposition.

We are developing transition-edge sensor (TES)-based microcalorimeters for the X-ray Integral Field Unit (XIFU) of the future European X-Ray Observatory Athena. The microcalorimeters are based on TiAu TESs coupled to 250{\mu}m squared, AuBi absorbers. We designed and fabricated devices with different contact geometries between the absorber and the TES to optimise the detector performance and with different wiring topology to mitigate the self-magnetic field. The design is tailored to optimise the performance under Frequency Domain Multiplexing. In this paper we review the main design feature of the pixels array and we report on the performance of the 18 channels, 2-5MHz frequency domain multiplexer that will be used to characterised the detector array., Comment: 9 pages, 8 figures

The detector system of the X-Ray Integral Field Unit (X-IFU), one of the two ATHENA focal plane instruments will be an ambitious step forward in the field of astronomical X-ray detection. We describe its baseline configuration, consisting of 3840 Transition Edge Sensors (TES) microcalorimeters with an energy resolution of 2.5 eV FWHM, spanning a 5 arcminute field-of-view and allowing an imaging resolution of 5 arcsec. The detectors are read out in 96 channels of 40 pixels each, using frequency domain multiplexing (FDM). Each channel contains a dual-stage SQUID pre-amplifier and a low-noise amplifier (LNA). In order to enhance the dynamic range of the SQUIDs a specific technique, baseband feedback (BBFB), is applied. The generation of the carrier and feedback signals, and the signal processing are done in the digital domain. We review the requirements for the main elements of this system, needed to ensure the high performance of the detector system. From the resolution requirements for the detectors follows a budget for contributions to the energy resolution on top of the intrinsic detector resolution. This budget forms the basis for the assessment of the dynamic range requirements for the SQUID and the LNA and the DACs and the ADC. Requirements are also derived for the levels of crosstalk and non-linearity in the readout chain.

Operation of TES-based bolometers in a resistance locked loop (RLL), i.e. keeping the operating resistance constant by means of feedback on the bias voltage, provides a number of attractive properties for applications. In combination with frequency domain multiplexing, the technique reduces electrical cross talk, and provides a more detector load independent behaviour with respect to operation under standard voltage bias. This paper shows a quantitative estimation of the large signal properties under the RLL, and shows a comparison with the situation under voltage bias. Furthermore, an unorthodox, low-bandwidth mode of operation will be discussed, from the perspective of the electro-thermal stability in the RLL.

At SRON we are developing Frequency Domain Multiplexing for the read-out of superconducting transition edge sensor microcalorimeters for future X-ray astrophysical missions. We will report on the performance of Goddard Space Flight Center pixels under AC bias in the MHz frequency range. Superconducting flux transformers are used to improve the impedance matching between the low ohmic TESs and the SQUID. We connected 5 pixels to the LC filters with resonant frequencies ranging between 1 and 5 MHz. For X-ray photons of 6 keV we measured a best X-ray energy resolution of 3.6 eV at 1.4 MHz, consistent with the integrated Noise Equivalent Power. In addition, we improved the electrical circuit by optimizing the coupling ratio of the impedance matching transformer. In addition, we improved electrical circuit for impedance matching; modified transformer coupling ratio. As a result, we got the integrated noise equivalent power resolution of 2.7 eV at 2.5 MHz. A characterization of the detector response as a function of the AC bias voltage, bias frequency and the applied magnetic field is presented.

SRON is developing the electronic read-out for arrays of transition edge sensors using frequency domain multiplexing in combination with base-band feedback. The astronomical applications of this system are the read-out of soft X-ray micro-calorimeters in a potential instrument on the European X-ray mission-under-study Athena+ and far-IR bolometers for the Safari instrument on the Japanese mission SPICA. In this paper we demonstrate the simultaneous read-out of 38 bolometer pixels at a 1 $$-$$ 2 aW/ $$\surd $$ Hz dark NEP level. The stability of the read-out is assessed over 400 s. time spans. Although some 1/f noise is present, there are several bolometers for which 1/f-free read-out can be demonstrated.

Athena is designed to implement the Hot and Energetic Universe science theme selected by the European Space Agency for the second large mission of its Cosmic Vision program. The Athena science payload consists of a large aperture high angular resolution X-ray optics (2 m2 at 1 keV) and twelve meters away, two interchangeable focal plane instruments: the X-ray Integral Field Unit (X-IFU) and the Wide Field Imager. The X-IFU is a cryogenic X-ray spectrometer, based on a large array of Transition Edge Sensors (TES), oering 2.5 eV spectral resolution, with approximately 5" pixels, over a field of view of 5' in diameter. In this paper, we present the X-IFU detector and readout electronics principles, some elements of the current design for the focal plane assembly and the cooling chain. We describe the current performance estimates, in terms of spectral resolution, effective area, particle background rejection and count rate capability. Finally, we emphasize on the technology developments necessary to meet the demanding requirements of the X-IFU, both for the sensor, readout electronics and cooling chain.

Following earlier presentations of arrays of high quality factor (Q $$>$$ 10.000) superconducting resonators in the MHz regime, we report on improvement of the packing density of resonance frequencies to 160 in the 1–3 MHz band. Spread in the spacing of resonances is found to be limited to 1 kHz (1 $$-$$ $$\sigma )$$ with the present fabrication procedure. The present packing density of frequencies and chip area approaches the requirements for the SAFARI instrument on the SPICA mission (in preparation). The a-Si:H dielectric layer in the planar S-I-S capacitors shows a presently unexplained apparent negative effective series resistance, depending on operating temperature and applied testing voltage.

The performance of a single-pixel microcalorimeter is described and analyzed. The microcalorimeter has a Cu absorber which is isolated from the heat bath by means of a Si x N y membrane and is connected to a voltage-biased Ti/Au proximity bilayer thermometer with a transition temperature of about 150 mK. The measured FWHM energy resolution for 5.9 keV X-ray photons is 12.4 eV for this sensor while 2.36( k B T 2 C ) 1/2 equals 9.1 eV. The detector time constant is about 1 ms. The measured current–voltage characteristic and current noise spectra are analyzed in detail in the context of the energy resolution. High frequency excess noise is measured in the superconducting transition and is briefly discussed.

A two-dimensional polyacrylamide gel electrophoresis map of bull seminal plasma proteins has been established. About 250 spots were detected after silver staining and polypeptides from 24 spots have been N-terminally sequenced. Major proteins already described in bull seminal plasma, like PDC-109 and aSFP, have been located on the map; proteins not yet reported in male reproductive tracts have been evidenced; for some polypeptides showing a previously unknown N-terminal sequence, structural similarities with proteins described in other organisms have been found. A reference map of seminal plasma proteins could be useful in relating protein pattern changes to physiopathological events influencing the reproductive sphere.

At SRON we are developing the Frequency Domain Multiplexing (FDM) for the read-out of the TES-based detector array for the future infrared and X-ray space mission. We describe the performances of a multiplexer designed to increase the experimental throughput in the characterisation of ultra-low noise equivalent power (NEP) TES bolometers and high energy resolving power X-ray microcalorimeters arrays under ac and dc bias. We discuss the results obtained using the TiAu TES bolometers array fabricated at SRON with measured dark NEP below $5\cdot 10^{-19}W/Hz^{1/2}$ and saturation power of several fW, Comment: 7 pages, 6 figures, Proc. SPIE 8453, High Energy, Optical, and Infrared Detectors for Astronomy V, 845333 (25 September 2012). arXiv admin note: text overlap with arXiv:1604.02593

SRON is developing an electronic system for the multiplexed read-out of an array of transition edge sensors (TES) by combining the techniques of frequency domain multiplexing (FDM) with base-band feedback (BBFB). The astronomical applications are the read-out of soft X-ray microcalorimeters and the far-infrared bolometers for the SAFARI instrument on the Japanese mission SPICA. In this paper we derive the requirements for the read-out system regarding noise and dynamic range in the context of the SAFARI instrument, and demonstrate that the current experimental prototype is capable of simultaneously locking 57 channels and complies with these requirements.

Transition-edge-sensor (TES) bolometers are the chosen detector technology for the SAFARI Imaging Spectrometer on the SPICA telescope. For this mission, SRON is developing bolometers, each consisting of a TiAu TES that is weakly coupled to the thermal bath through thin legs of silicon nitride. In order to understand and optimize the bolometer and to verify our detector models, we characterize the devices using a series of complex impedance measurements. We apply equivalent bolometer analysis (EBA) in combination with model fitting to these data. From this analysis, we obtain important parameters that give us confidence in our understating of the response and noise of these sensitive detectors.

At the Netherlands Institute for Space Research (SRON) we are developing Transition Edge Sensors (TES) bolometers for the SAFARI Imaging Spectrometer on the SPICA telescope. With the current design of the SPICA telescope a background magnetic field of about a Gauss with fluctuations of a couple percent is expected. The effect of this external magnetic field on the bolometer needs to be well understood in order to design effective shielding. We present the results of an investigation of magnetic field on the performance of TES bolometers. For this experiment we used a Ti/Au TES bolometer which has a measured NEP of 5.0 × 10?19 W/Hz1/2. The TES is exposed to a parallel and perpendicular magnetic field of varying strength and the baseline and responsivity are determined. We see that the bolometers are sensitive to the perpendicular field but are relative insensitive to the parallel magnetic field. Fluctuations with a period of 30 mG are present as function of perpendicular magnetic field

We present results of the analysis of electrical noise in a transition edge sensor (TES) as a resistively shunted conducting junction (the RSJ model). We derive an expression for the spectral density of voltage fluctuations taking into account weak superconductivity of a TES. We analyse and discuss differences in voltage noise in a TES compared to the familiar situation for the Josephson junction. The spectral density of voltage noise in the RSJ model has a unique analytical structure and cannot be reduced to the expression for the nonlinear Johnson noise near equilibrium

Trabajo presentado a la conferencia: "Space Telescopes and Instrumentation: Ultraviolet to Gamma Ray" celebrada en Amsterdam (Holanda) el 1 de julio de 2012.-- et al., One of the instruments on the Advanced Telescope for High-Energy Astrophysics (Athena) which was one of the three missions under study as one of the L-class missions of ESA, is the X-ray Microcalorimeter Spectrometer (XMS). This instrument, which will provide high-spectral resolution images, is based on X-ray micro-calorimeters with Transition Edge Sensor (TES) and absorbers that consist of metal and semi-metal layers and a multiplexed SQUID readout. The array (32 x 32 pixels) provides an energy resolution of < 3 eV. Due to the large collection area of the Athena optics, the XMS instrument must be capable of processing high counting rates, while maintaining the spectral resolution and a low deadtime. In addition, an anti-coincidence detector is required to suppress the particle-induced background. Compared to the requirements for the same instrument on IXO, the performance requirements have been relaxed to fit into the much more restricted boundary conditions of Athena. In this paper we illustrate some of the science achievable with the instrument. We describe the results of design studies for the focal plane assembly and the cooling systems. Also, the system and its required spacecraft resources will be given. © (2012) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

We have developed a model for the resistive transition in a transition edge sensor (TES) based on the model of a resistively shunted junction, taking into account phase-slips of a superconducting system across the barriers of the tilted washing board potential. We obtained analytical expressions for the resistance of the TES, R(T,I), and its partial logarithmic derivatives α I and β I as functions of temperature and current. We have shown that all the major parameters describing the resistive state of the TES are determined by the dependence on temperature of the Josephson critical current, rather than by intrinsic properties of the S-N transition. The complex impedance of a pristine TES exhibits two-pole behaviour due to its own intrinsic reactance.

SRON is developing an electronic read-out system for an array of transition edge sensors (TES) based on the techniques of frequency domain multiplexing (FDM) and base-band feedback (BBFB). The astronomical applications of our system are the read-out of soft X-ray micro-calorimeters in a potential instrument on the European X-ray mission-under-study Athena and far-IR bolometers for the SAFARI instrument on the Japanese mission SPICA. In this paper we demonstrate the simultaneous locking of up to 51 BBFB loops. While locked, the in-band read-out noise of the loops is shown to reach the \(\mbox{10~pA/}\sqrt{\mathrm{Hz}}\) level required for these missions.

Frequency domain multiplexing (FDM) is one of the candidates for the SQUID based readout of TES-based imaging microcalorimeter arrays for applications such as IXO, and imaging bolometer arrays for the SAFARI instrument on the Japanese SPICA space telescope. Usage of the TES as modulating element by applying an AC bias is an essential part of FDM. Within this framework the small signal characteristics of array pixels under both AC and DC bias have been measured. We will present a small signal model of the TES under AC bias, and apply the results to the measurements on an X-ray microcalorimeter.

Transition edge sensor (TES) is the selected detector for the SAFARI FIR imaging spectrometer (focal plane arrays covering a wavelength range from 30 to 210 μm) on the Japanese SPICA telescope. Since the telescope is cooled to 50 mK. Also the time constant should be below 8 ms. We fabricated and characterized low thermal conductance transition edge sensors (TES) for SAFARI instrument on SPICA. The device is based on a superconducting Ti/Au bilayer deposited on suspended SiN membrane. The critical temperature of the device is 155 mK. The low thermal conductance is realized by using narrow SiN ring-like supporting structures. All measurements were performed having the device in a light-tight box, which to a great extent eliminates the loading of the background radiation. We measured the current-voltage (IV) characteristics of the device in different bath temperatures and determine the thermal conductance (G) to be equal to 1.66 pW/K. This value corresponds to a noise equivalent power (NEP) of 1E-18 W/√Hz. The current noise and complex impedance is also measured at different bias points at 25 mK bath temperature. The measured electrical (dark) NEP is 2E-18 W/√Hz, which is about a factor of 2 higher than what we expect from the thermal conductance that comes out of the IV curves. Despite using a light-tight box, the photon noise might still be the source of this excess noise. We also measured the complex impedance of the same device at several bias points. Fitting a simple first order thermal-electrical model to the measured data, we find an effective time constant of about 65 μs and a thermal capacity of 3-4 fJ/K in the middle of the transition

One of the instruments on the International X-ray Observatory (IXO), under study with NASA, ESA and JAXA, is the X-ray Microcalorimeter Spectrometer (XMS). This instrument, which will provide high spectral resolution images, is based on X-ray micro-calorimeters with Transition Edge Sensor thermometers. The pixels have metallic X-ray absorbers and are read-out by multiplexed SQUID electronics. The requirements for this instrument are demanding. In the central array (40 x 40 pixels) an energy resolution of < 2.5 eV is required, whereas the energy resolution of the outer array is more relaxed (≈ 10 eV) but the detection elements have to be a factor 16 larger in order to keep the number of read-out channels acceptable for a cryogenic instrument. Due to the large collection area of the IXO optics, the XMS instrument must be capable of processing high counting rates, while maintaining the spectral resolution and a low deadtime. In addition, an anti-coincidence detector is required to suppress the particle-induced background. In this paper we will summarize the instrument status and performance. We will describe the results of design studies for the focal plane assembly and the cooling systems. Also the system and its required spacecraft resources will be given.

The current noise at the output of a microcalorimeter with a voltage biased superconducting transition edge thermometer is studied in detail. In addition to the two well-known noise sources: thermal fluctuation noise from the heat link to the bath and Johnson noise from the resistive thermometer, a third noise source strongly correlated with the steepness of the thermometer is required to fit the measured noise spectra. Thermal fluctuation noise, originating in the thermometer itself, fully explains the additional noise. A simple model provides quantitative agreement between the observed and calculated noise spectra for all bias points in the superconducting transition.

We report the results of a detailed numerical analysis of a real resonant spherical gravitational wave antenna operating with six resonant two-mode capacitive transducers read out by superconducting quantum interference devices (SQUID) amplifiers. We derive a set of equations to describe the electro-mechanical dynamics of the detector. The model takes into account the effect of all the noise sources present in each transducer chain: the thermal noise associated with the mechanical resonators, the thermal noise from the superconducting impedance matching transformer, the back-action noise and the additive current noise of the SQUID amplifier. Asymmetries in the detector signal-to-noise ratio and bandwidth, coming from considering the transducers not as point-like objects but as sensor with physically defined geometry and dimension, are also investigated. We calculate the sensitivity for an ultracryogenic, 30 ton, 2 meter in diameter, spherical detector with optimal and non-optimal impedance matching of the electrical read-out scheme to the mechanical modes. The results of the analysis is useful not only to optimize existing smaller mass spherical detector like MiniGrail, in Leiden, but also as a technological guideline for future massive detectors. Furthermore we calculate the antenna patterns when the sphere operates with one, three and six resonators. The sky coverage for two detectors based in The Netherlands and Brasil and operating in coincidence is also estimated. Finally, we describe and numerically verify a calibration and filtering procedure useful for diagnostic and detection purposes in analogy with existing resonant bar detectors., 23 pages, 20 figures, codes of the simulations are available on request by contacting the author

We present the performances and the strain sensitivity of the first spherical gravitational wave detector equipped with a capacitive transducer and read out by a low noise two-stage SQUID amplifier and operated at a temperature of 5 K. We characterized the detector performance in terms of thermal and electrical noise in the system output sygnal. We measured a peak strain sensitivity of $1.5\cdot 10^{-20} Hz^{-1/2}$ at 2942.9 Hz. A strain sensitivity of better than $5\cdot 10{-20}Hz{-1/2}$ has been obtained over a bandwidth of 30 Hz. We expect an improvement of more than one order of magnitude when the detector will operate at 50 mK. Our results represent the first step towards the development of an ultracryogenic omnidirectional detector sensitive to gravitational radiation in the 3kHz range., 8 pages, 5 figures, submitted to Physical Review D

We present a numerical analysis to simulate the response of a spherical resonant gravitational wave detector and to compute its sensitivity. Under the assump- tion of optimal filtering, we work out the sensitivity curve for a sphere first taking into account only a single transducer, and then using a coherent analysis of the whole set of transducers., 24 pages, 11 figures, published version

Trabajo presentado como comunicación a la Conferencia "Space Telescopes and Instrumentation 2008: Ultraviolet to Gamma Ray" celebrada en Francia el 23 de Junio del 2008., The EURECA (EURopean-JapanEse Calorimeter Array) project aims to demonstrate the science performance and technological readiness of an imaging X-ray spectrometer based on a micro-calorimeter array for application in future X-ray astronomy missions, like Constellation-X and XEUS. The prototype instrument consists of a 5 x 5 pixel array of TES-based micro-calorimeters read out by by two SQUID-amplifier channels using frequency-domain-multiplexing (FDM). The SQUID-amplifiers are linearized by digital base-band feedback. The detector array is cooled in a cryogenfree cryostat consisting of a pulse tube cooler and a two stage ADR. A European-Japanese consortium designs, fabricates, and tests this prototype instrument. This paper describes the instrument concept, and shows the design and status of the various sub-units, like the TES detector array, LC-filters, SQUID-amplifiers, AC-bias sources, digital electronics, etc. Initial tests of the system at the PTB beam line of the BESSY synchrotron showed stable performance and an X-ray energy resolution of 1.58 eV at 250 eV and 2.5 eV @ 5.9 keV for the read-out of one TES-pixel only. Next step is deployment of FDM to read-out the full array. Full performance demonstration is expected mid 2009., The authors acknowledge an ESA Technological Research Program contract for the development of TES-arrays and SQUIDs, being a significant support to the EURECA program. Also the recent ESA TRP contract for the development of SQUID-based electronics is of crucial importance for this work.

The latest results of the measurements on the vibration isolation system of MiniGRAIL at room temperature as well as an overview of the results of the ultra-cryogenic tests with the dilution refrigerator are presented. Two types of capacitive transducers have been developed and tested separately in a cryogenic set-up. The rosette-design transducers have been mounted on the sphere and tested at low temperature. We also report the progress in developing a two-mode inductive transducer with an Al5056 resonator as a second resonating mass and a Nb film coil as superconducting pick-up loop. Furthermore, we developed and tested two double-SQUID systems based on two types of dc SQUIDs as sensors and a DROS as the preamplifier stage.

EURECA (EURopEan Calorimeter Array) is a European-Japanese project that aims to demonstrate technical readiness for a Transition-Edge-Sensor based X-ray imaging spectrometer on ESA's XEUS observatory. EURECA comprises a 5 x 5 pixel TES micro-calorimeter array with an energy resolution aim of 1 - 2 eV for the 0.1 - 3 keV energy range. The small array will be read out by four SQUID channels using frequency domain multiplexing (FDM).

In the process to develop the transition edge sensor (TES) bolometer technology for the SAFARI FIR Imaging Spectrometer on the SPICA telescope and for future FIR space telescopes, we have recently demonstrated a TiAu TES with a Ta thin film absorber on a thin SiN membrane, which has a dark NEP as low as 4.2 × 10-19 W/√Hz. It is known that superconductors are sensitive to magnetic fields. Therefore, it is important to know how these extremely sensitive TES detectors are affected by external magnetic fields. This is desirable from an application point of view since the design of the SAFARI instrument demands such knowledge and interesting from a fundamental point of view. In this paper, we will describe a detailed experimental study of the effects of magnetic fields, both parallel and perpendicular to the TiAu plane, on the performance of a TES. We investigated the effect on the current, responsivity, speed, and TES parameters of α (dependence of temperature) and β (dependence of current), around the operating points. In order to achieve this highly sensitive measurement, the temperature stability has been improved and a new coil assembly has been designed. The latter allows accurately applying a parallel magnetic field.

In this paper, we present the progress made at SRON in the read-out of X-ray Transition Edge Sensor (TES) microcalorimeters under AC bias. The experiments reported so far, whose aim was to demonstrate an energy resolution of 2 eV at 6 keV with a TES acting as a modulator, were carried out at frequencies below 700 kHz using a standard flux locked loop SQUID read-out scheme. The TES read-out suffered from the use of suboptimal circuit components, large parasitic inductances, low quality factor resonators, and poor magnetic field shielding. We have developed a novel experimental set-up that allows us to test several read-out schemes in a single cryogenic run. In this set-up, the TES pixels from a GSFC array are coupled via superconducting transformers to 18 high-Q lithographic LC filters with resonant frequencies ranging between 2 and 5 MHz. The signal is amplified by a two-stage SQUID current sensor and baseband feedback is used to overcome the limited SQUID dynamic range. We measured an X-ray energy resolution of 3.6 eV at 1.4 MHz, which is consistent with the measured integrated Noise Equivalent Power.

We present multitone harmonic-balance (MTHB) simulations of a Ti–Au x-ray transition-edge sensor (TES) microcalorimeter in a 5×5 pixel spectrometer array. The dynamic response of the TES microcalorimeter under simulation has been extremely well characterized at the BESSY II Synchrotron Radiation Facility in Berlin. We compare our simulated results directly with these measurements, and show that the MTHB algorithm is able to simulate to great accuracy the dynamic behavior of the TES, even when saturated by 6 keV photons. In this paper, we provide a detailed account of the MTHB simulations, and discuss the impact of this work on future missions such as the International X-ray Observatory.

Frequency-division multiplexing (FDM) is the current baseline read-out system for the large array of superconducting transition edge sensors (TES's) under development for the X-ray instrument XIFU ( Athena ). In this multiplexing scheme the sensor operates as amplitude modulator of a MHz carrier. To achieve the best performance with these and similar instruments the detector physics and its interaction with the read-out circuit needs to be better understood. In particular we need an explanation for the dependence of the TES microcalorimeter nonlinear impedance on the bias point, because it directly affects the choice of the detector optimal working point. With the TES microcalorimeters fabricated at NASA-Goddard we observe current steps in the amplitude of the uncalibrated IV characteristics when the detectors are read-out in the frequency domain and are biased in the low-resistance part of the superconducting transition. In this paper, we report on the characterization under FDM of NASA-Goddard TES microcalorimeters under development for the XIFU instrument. We have measured several pixels with different size and geometry in the bias frequency range from 1 to 4 MHz and at different bath temperatures. The results will be discussed within the recently developed weak-link theoretical framework.

Efficient use of the available frequency space for frequency domain multiplexing is essential for space-based TES detector applications such as the X-IFU instrument on the Athena X-ray telescope. For cross talk reasons, there exists a lower limit on the distance between neighbouring pixels in frequency space, so that accurate control of the resonance frequency helps to use the available frequency space. Independently, from the point of view of efficient sinusoidal bias voltage generation, placing the frequencies on a grid with a fixed spacing helps to avoid the effects of nonlinearity on the detector performance. Inevitable tolerances in the lithographic production of LC bandpass filters and margins in the design of stray inductances limit the relative accuracy of the resonance frequencies to a few times $$10^{-3}$$ . In this paper we will propose a new method which uses the active SQUID readout electronics at room temperature to further fine-tune the resonance frequencies of the LC filters beyond the manufacturing limitations.

EURECA (EURopean-JapanEse Calorimeter Array) comprises a 5 x 5 pixel imaging TES-based micro-calorimeter array read-out by SQUID-based frequency-domain-multiplexed electronics and cooled down by an adiabatic demagnetization refrigerator. A European-Japanese consortium designs, fabricates, and tests this prototype instrument with the aim to show within about 2 years technology readiness of a TES-based X-ray imaging micro-calorimeter array in anticipation of future X-ray astronomy missions, like XEUS (ESA), Constellation-X (NASA), NEXT (JAXA), DIOS (JAXA), ESTREMO (ASI), and NEW (Dutch-multinational). This paper describes the instrument concept, and shows the design of the various sub-units, like the TES detector array, LC-filters, SQUID-amplifiers, flux-locked-loop electronics, AC-bias sources, etc.