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Frequency-domain multiplexing (FDM) is the baseline readout system for the X-ray Integral Field Unit on board the Athena mission. Under the FDM scheme, TESs are coupled to a passive LC flter and biased with alternating current (AC bias) at MHz frequencies. Using high-quality-factor LC flters and room-temperature electronics developed at SRON and low-noise two-stage SQUID amplifers provided by VTT, we have recently demonstrated good performance with the FDM readout of Mo/Au TES calorimeters with Au/Bi absorbers. We have achieved a performance requested for the demonstration model with the single-pixel AC bias (��E = 1.8 eV) and nine-pixel multiplexing (��E = 2.6 eV) modes. We have also demonstrated 14-pixel multiplexing with an average energy resolution of 3.3 eV, which is limited by nonfundamental issues related to FDM readout in our laboratory setup.

Accepted: 2015-11-30, 資料番号: SA1160043000

We report on the eighth cryogenic run of MiniGRAIL, which is planned to be the first science run. Three new capacitive transducers were mounted on the sphere, all coupled to superconducting transformers and a double-stage SQUID amplifier. All SQUID modules had a noise level between 1 and 2 μΦ0 Hz−1/2 at 4 K in separate test runs. The detector was upgraded with a complete data acquisition and data storage system, and a data analysis program for millisecond burst signals was written using a matched filter. Two cosmic-ray detectors were built and installed on the roof above MiniGRAIL as a veto for cosmic rays. A test run was done, but failed because of bad electrical isolation of the transducer electrode at low temperatures. A new cool-down is currently going on. With an already obtained sphere temperature of 65 mK and a SQUID noise of 100, the expected sensitivity should be 4 × 10−22 Hz−1/2.

The MiniGRAIL is one of the three similar spherical gravitational wave detectors that are currently being developed. The detector has a resonant frequency of about 3 kHz and will be operated at 20 mK. The ultimate goal is to use a readout system consisting of six transducers coupled to nearly quantum limited two-stage SQUIDs. The two-stage SQUIDs are based on double relaxation oscillation SQUIDs, which enables a direct voltage readout scheme. We have developed nonintegrated two-stage SQUIDs and experimentally verified the proper operation of the system coupled to a capacitive transducer. Based on the results that were achieved, integrated two-stage SQUIDs were designed. Special attention has been paid to the sensor SQUID, the back action of the SQUID and the feedback scheme that is used for linearizing the SQUID output.

The MiniGRAIL detector was improved. The sphere was replaced by a slightly larger one, having a diameter of 68 cm (instead of 65 cm), reducing the resonant frequency by about 200 Hz to around 2.9 kHz. The last four masses of the attenuation system were machined to increase their resonant frequency and improve the attenuation around the resonant frequency of the sphere. In the new sphere, six holes were machined on the TIGA positions for easy mounting of the transducers. During the last cryogenic run, two capacitive transducers and a calibrator were mounted on the sphere. The first transducer was coupled to a double-stage SQUID amplifier having a commercial quantum design SQUID as a first stage and a DROS as a second stage. The second transducer was read by a single-stage quantum design SQUID. During the cryogenic run, the sphere was cooled down to 4 K. The two-stage SQUID had a flux noise of about 1.6 μ0 Hz−1/2. The detector was calibrated and the sensitivity curve of MiniGRAIL was determined.

Astronomical Data Analysis Software and Systems XXII., The current and forthcoming research lines in X-ray astronomy will require unprecedented spectral resolution with imaging capabilities. The most promising detectors able to provide these capabilities are the calorimeters based on Transition Edge Sensor (TES) technologies, like the one that has been under development for the proposed ATHENA x-ray space mission. We present here the Data Flow designed for one of such instruments covering the detection algorithms to extract the x-ray events (photons) from the noisy signal (as well as to cope with a possible pile-up), the event qualification (event grade) according to the event arrival time and proximity to other events, and finally the filtering process applied to these pulses to get their energy content, and thus the astronomical source spectrum. This development is currently part of a collaboration between IFCA (Spain) and SRON (NL) institutes, as part of a larger project initiated in 2005 and named EURECA (de Korte et al. 2009) involving many other institutes in Europe and the USA. This project was created to design the TES prototype proposed for the XEUS/IXO/ATHENA ESA missions., We acknowledge financial support by the Spanish Ministry of Science and Innovation (MICINN) under projects ESP2006-13608-C02-01, AYA2009-08059 and AYA2010-21490-C02-01.

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.

The Po River (Northern Italy) is the longest watercourse in Italy and over half of its length is safeguarded by major river embankments. Their stability is crucial for the local communities, being the Po River plain densely populated. Among all possible failure mechanisms, backward erosion piping at the interface between the bottom sandy aquifer and the overlying fine-grained soils has proved to be one of the most threatened phenomena. This paper describes the reactivation of a sand boil in a river embankment section in the Province of Ferrara, during the 2014 major high-water event. Detailed stratigraphic soil profiling as well as careful geotechnical characterization of the embankment and of the subsoil have been carried out on the basis of in-situ tests. Then, safety assessment of the backward erosion piping has been performed using simplified prediction tools and a preliminary 2D numerical model. Results are compared and discussed with the aim of providing some insight into the mechanism under investigation.

This paper summarizes a preliminary design concept for the focal plane assembly of the X-ray Integral Field Unit on the Athena spacecraft, an imaging microcalorimeter that will enable high spectral resolution imaging and point-source spectroscopy. The instrument's sensor array will be a ~ 3840-pixel transition edge sensor (TES) microcalorimeter array, with a frequency domain multiplexed SQUID readout system allowing this large-format sensor array to be operated within the thermal constraints of the instrument's cryogenic system. A second TES detector will be operated in close proximity to the sensor array to detect cosmic rays and secondary particles passing through the sensor array for off-line coincidence detection to identify and reject events caused by the in-orbit high-energy particle background. The detectors, operating at 55 mK, or less, will be thermally isolated from the instrument cryostat's 2 K stage, while shielding and filtering within the FPA will allow the instrument's sensitive sensor array to be operated in the expected environment during both on-ground testing and in-flight operation, including straylight from the cryostat environment, low-energy photons entering through the X-ray aperture, low-frequency magnetic fields, and high-frequency electric fields.