The X-ray Integral Field Unit (X-IFU) instrument is the high-resolution X-ray spectrometer of the ESA Athena X-ray Observatory. X-IFU will deliver spectra from 0.2 to 12 keV with a spectral resolution requirement of 4 eV (3 eV design goal) up to 7 keV from 5" pixels, with a hexagonal field of view of 4' equivalent diameter. The main sensor array and its associated detection chain is one of the major functional chains of the X-IFU instrument, and is the main contributor to XIFU performance. CNES (Centre National d’Études Spatiales) is the prime contractor for the X-IFU and leads the project development and procurement aspects within the X-IFU Consortium; additional major partners of the main detection chain are NASA-GFSC, SRON, VTT, APC, NIST, IRAP, and IAP. The detection chain design for X-IFU has evolved in the past few years in order to secure the performances and development costs, in the frame of the New Athena mission. New TES pixels are implemented with slower time constant and a reduced sensitivity to magnetic field. The slower time constant directly allows an increase of the MUX factor and a reduction of the number of channels, together with the decrease of the number of proximity electronics boxes, or warm front end electronics (WFEE). The cryostat outer vessel temperature is now a 50 K thermal interface, cooled passively thanks to L-shaped thermal shield (L-grooves). This has a direct impact of the cryo-harness between the 4 K core interface and the WFEE interface. In the past years, we have performed early demonstration on the critical components in order to secure the detection chain design and performances. This paper presents the progress done on early demonstrations (warm electronics, cryo-harness breadboarding,...), while providing an update to the detection-chain design description.
In the early 2030s, ESAs new x-ray observatory, Athena, is scheduled to be launched. It will carry two main instruments, one of which is the x-ray integral field unit (X-IFU), an x-ray imaging spectrometer, which will consist of an array of several thousand transition-edge sensors (TESs) with a proposed energy resolution of 2.5 eV for photon energies up to 7 keV. At SRON we develop the backup TES array based on Ti/Au bilayers with a transition temperature just below 100 mK. In this contribution we will give a broad overview of the properties and capabilities of these state-of-the-art detectors. Over the years we have fabricated and studied a large number of detectors with various geometries, providing us with a good understanding of how to precisely control the properties of our detectors. We are able to accurately vary the most important detector properties, such as the normal resistance, thermal conductance and critical temperature. This allows us to finely tune our detectors to meet the demands of various applications. The detectors have demonstrated excellent energy resolutions of below 1.8 eV for 5.9 keV x-rays. By tuning the properties of the devices, they can be optimally matched to various read-out schemes using both AC and DC biasing. The next step is to increase the size of our TES arrays from our current kilo-pixel arrays towards the full-sized array for X-IFU.
We are developing Frequency Domain Multiplexing (FDM) read-out of Transition-Edge Sensors (TESs) for the X-ray Integral Field Unit (X-IFU) on board of the future European X-Ray observatory Athena. The X-IFU Focal-Plane Assembly consists of a $sim$ 3000-pixel array, read out by SQUID-based FDM. The multiplexing readout scheme is a critical technology for the X-IFU instrument because of the cooling and electronic power limits for the satellite. In this contribution, we report on the development of FDM readout technology and on the performance of TESs array under an AC bias at MHz frequencies.
We present the design and experimental demonstration of a 16-channel frequency domain multiplexing (FDM) readout for transition-edge sensor (TES) bolometers. This readout system is going to be implemented on the LSPE/SWIPE balloon-borne experiment, whose goal is to detect the polarization of cosmic microwave background (CMB) at large angular scales and whose launch is scheduled for December 2019.
We describe the fabrication process of the Niobium superconducting inductors and the qualification tests performed in our 300 mK cryogenic facility in INFN Pisa of the boomerang shaped PCBs hosting the LC chains and the gradiometric SQUIDs, which are going to be mounted on the back of the SWIPE focal planes. The development of the warm readout electronics is presented, together with the firmware for the generation and readout of the biasing frequency comb.
We present the design and first tests of a prototype readout for the SWIPE instrument onboard the LSPE balloon-borne experiment. LSPE aims at measuring the linear polarization of the Cosmic Microwave Background (CMB) at large angular scales, to find the imprint of inflation on the B-mode CMB polarization. The SWIPE instrument hosts two focal planes hosting 163 TES Au/Mo spiderweb bolometers each, cooled at 0.3 K for the detection of microwave frequencies of 140, 220 and 240 GHz.
To read all the detectors, a 16 channel frequency domain multiplexing readout system has been devised, consisting of LC resonators composed of custom Nb superconducting inductors and commercial SMD capacitors.
A set-up consisting of 14 LC resonators shows that we can accommodate 16 channels in the frequency range between 200 kHz and 1.6 MHz, since the necessary line-widths can be achieved. A preliminary firmware for the generation and read-out of the biasing frequency comb is also discussed.
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