Proposed for a late 2031 launch, PRIMA, the Probe far-Infrared Mission for Astrophysics, closes the gap between JWST and ALMA, offering unprecedented sensitivity and spectroscopic mapping capability in the 24-264 μm range for detailed studies of galactic evolution, planetary atmospheres, and dust-metal dynamics. Onboard PRIMA, the PRIMAger camera operates in the 25-80 μm bands utilizing advanced MKID detector modules for hyperspectral imaging enabled by Linear Variable Filters. This paper presents a graded resonant metal-mesh filter technology, demonstrating very promising efficiency in the short wavelength range. Overcoming dielectric loss limitations, an innovative dual-layer LVF design on thin membranes achieves a transmission of 80-90% at 12 THz. Rigorous electromagnetic modeling, optimization, and position-dependent spectral response measurements validate the filter performance. We present a comprehensive set of simulation and experimental results, including environmental pre-qualification tests, strongly supporting the suitability of this technology for future space applications.
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.
Athena is an ESA-led space telescope to be launched in the early 2030s. The X-ray Integral Field Unit (X-IFU) on board of the Athena mission is an X-ray imaging spectrometer, sensitive to 0.2-12 keV X-rays. The main sensor of the X-IFU is an array of ~3200 closely-packed superconducting transition-edge sensor (TES) microcalorimeters with X-ray absorbers. The X-IFU provides a breakthrough spectral resolution of 2.5 eV (full width at half maximum; FWHM) at 6 keV, which enables us to access unrevealed properties of the hot gases that are formed at every level of the hierarchical structure of the universe. At SRON, we are developing Frequency Division Multiplexing (FDM) readout with SQUID amplifiers as a baseline technology for the X-IFU. In the FDM system, the microcalorimeter pixels are AC-biased at different frequencies from 1 to 5 MHz. Therefore, it is crucial to minimize frequency-dependent phenomena because it causes non-linearity effects in the detector response and degrades the spectral resolution. Theoretical analyses have shown that this non-linearity is caused by weak-link behavior, induced by superconducting leads and can be mitigated by increasing the normal resistance of the TES. We are also developing TES arrays based on a superconducting Ti/Au bi-layer with an Au absorber as a sensor backup technology for the X-IFU. We have recently fabricated TES calorimeters with large variation of normal resistance from 25 to 150 mΩ by changing the width and aspect ratio of the bi-layer. The TESes with 117 and 150 mΩ have shown a promising spectral performance of below 2 eV (FWHM) at 6 keV. However, we still see that the detector response is affected by the weak-link behavior, especially at high frequency regime. In this paper, we briefly summarize our results with a focus on the spectral performance and the detector responsivity for each TES design. We also present our recent works on fabrication related to a superconducting wiring process, which would be useful for further reduction of the weak-link effects.
Hot Universe Baryon Surveyor (HUBS), a Chinese space mission, is proposed to find a large fraction of the so-called missing baryons, which would help us to understand more about the structure formation and evolution of the universe. Both theoretical and experimental results show that developing a highly efficient soft X-ray spectrometer over a large field of view and with a high energy resolution is the key to detect the “missing baryons”. X-ray microcalorimeters based on a transition-edge sensor (TES) array is required for HUBS, which aims to have 1 deg2 field of view (FoV) with 1’ angular resolution and 2 eV energy resolution optimized around 0.6 keV. Taking the high throughput X-ray optical focusing system on HUBS into account, the TES array is designed to have 60 x 60 pixels with an area of 1 mm2 for each pixel. The microcalorimeter consists of a TES, a weak thermal link to a heat bath, and a semi-metal or normal metal absorber to increase the X-ray absorption efficiency. When an X-ray photon with a given energy is absorbed, the temperature of the absorber increase, that can be monitored by measuring the resistance change of the TES. A bilayer of a superconductor and a normal metal is used to fabricate a TES with a critical temperature (Tc) of ~100 mK. The latter is set for the required energy resolution. For HUBS, both MoCu and TiAu TES technologies are considered in its development phase. Here we will focus on TiAu TES calorimeters designed and partially fabricated at SRON for HUBS. Recent demonstration of a resolution of 2.5 eV at 5.9 keV in an AC readout at SRON for X-IFU on board of Athena illustrates the promising of this technology. However, the challenging for the HUBS array is the large pixel size. We will report the design and fabrication of prototype HUBS calorimeters.
The Hot Universe Baryon Surveyor (HUBS) mission is proposed to study “missing” baryons in the universe. Unlike dark matter, baryonic matter is made of elements in the periodic table, and can be directly observed through the electromagnetic signals that it produces. Stars contain only a tiny fraction of the baryonic matter known to be present in the universe. Additional baryons are found to be in diffuse (gaseous) form, in or between galaxies, but a significant fraction has not yet been seen. The latter (“missing” baryons) are thought to be hiding in low-density warm-hot ionized medium (WHIM), based on results from theoretical studies and recent observations, and be distributed in the vicinity of galaxies (i.e., circumgalactic medium) and between galaxies (i.e., intergalactic medium). Such gas would radiate mainly in the soft X-ray band and the emission would be very weak, due to its very low density. HUBS is optimized to detect the X-ray emission from the hot baryons in the circumgalactic medium, and thus fill a void in observational astronomy. The goal is not only to detect the “missing” baryons, but to characterize their physical and chemical properties, as well as to measure their spatial distribution. The results would establish the boundary conditions for understanding galaxy evolution. Though highly challenging, detecting “missing” baryons in the intergalactic medium could be attempted, perhaps in the outskirts of galaxy clusters, and could shed significant light on the large-scale structures of the universe. The current design of HUBS will be presented, along with the status of technology development.
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 are developing an x-ray imaging spectrometer for Super DIOS satellite mission, a future x-ray observatory, planned by JAXA, to be launched in 2030’s. Super DIOS will reveal the nature of the missing baryon in the warm-hot intergalactic medium because of its fine energy and angular resolution, large effective area and large field of view. A main detector on-board Super DIOS consists of a transition-edge sensor (TES) microcalorimeter array of over 30,000 pixels working at a temperature below 100 mK and it poses a considerable technical difficulty to the readout. A microwave superconducting quantum interference device (SQUID) multiplexing is promising technique and expected to achieve a large scale readout of more than 30,000 pixels. We describe our development of a 40-channel microwave SQUID multiplexer with low-noise characteristics∗ and a demonstration of simultaneously reading out 40-pixel TESs. Finally, we discuss a future prospect and a feasibility of reading out an array of more than 30,000 pixels.
SRON is developing X-ray transition edge sensor (TES) calorimeters arrays, as a backup technology for X-IFU instrument on the ATHENA space observatory. These detectors are based on a superconducting TiAu bilayer TES with critical temperature of 100 mK on a 1 μm thick SiN membrane with Au or Au/Bi absorbers. Number of devices have been fabricated and measured using a Frequency Division Multiplexing (FDM) readout system with 1-5 MHz bias frequencies. We measured IV curves, critical temperature, thermal conductance, noise and also X-ray energy resolution at number of selected bias points. So far our best calorimeter shows 3.9 eV X-ray resolution at 6 keV. Here we present a summary of our results and the latest status of development of X-ray calorimeters at SRON.
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