Figure - available from: Journal of Low Temperature Physics
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Left, photograph of a 25-pixel hydra with 25 μm pitch absorbers for the LXM EMA. This image was before absorbers have been deposited to show the hierarchical link layout. The outline of where the absorbers are later deposited is indicated. Each group of 5 pixels is indicated in a different color. Pixels labeled 1–5 are group 1 (black), pixels 6–10 are group 2 (purple), pixels 11–15 are group 3 (green), pixels 16–20 are group 4 (red), and pixels 21–25 are group 5 (blue). Right, simplified thermal model showing part of the hydra ‘tree’ design. Groups of pixels are connected together by link ‘branches’, and these groups then connect to the TES via link ‘trunks’. Only group 5 is shown in full (Color figure online)
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We report on the development of multi-absorber transition-edge sensors (TESs), referred to as ‘hydras’. A hydra consists of multiple X-ray absorbers each with a different thermal conductance to a TES. Position information is encoded in the pulse shape. With some trade-off in performance, hydras enable very large format arrays without the prohibitiv...
Citations
... Thus, the position discrimination can be determined through analysis of the x-ray pulse-shape. 2,3 The development of single-pixel and hydra TES microcalorimeters has been an area of intense study over the last several decades, 4,5 and in particular it has been developed for potential space-based astrophysics applications, such as Lynx, 3,6 Constellation-X, 7,8 and ATHENA. [9][10][11][12][13] LEM places a unique combination of constraints on the TES microcalorimeter design but draws upon knowledge from the designs and prototype arrays of each of these missions. ...
... Thus, the position discrimination can be determined through analysis of the x-ray pulse-shape. 2,3 The development of single-pixel and hydra TES microcalorimeters has been an area of intense study over the last several decades, 4,5 and in particular it has been developed for potential space-based astrophysics applications, such as Lynx, 3,6 Constellation-X, 7,8 and ATHENA. [9][10][11][12][13] LEM places a unique combination of constraints on the TES microcalorimeter design but draws upon knowledge from the designs and prototype arrays of each of these missions. ...
... The integrated noise equivalent power (NEP) for a TES microcalorimeter is an estimate of the achievable energy resolution of the device based on the measured detector responsivity and the measured noise at the equilibrium bias point before an x-ray event. 3,35,36 Figure 9(a) shows the integrated NEP of the single-pixel and hydra as a function of R∕R n for the Al K α x-rays. This shows that the integrated NEP increases as the bias point resistance increases. ...
... Hydras are "thermally multiplexed" TESs consisting of multiple distinct x-ray absorbers, each with a different thermal link to a single TES. [5][6][7] The conductance of each link is tuned to produce a unique pulse shape for x-rays absorbed in each of the 4 pixels. The pulse rise-time is used to determine the pixel that absorbed the photon (see Fig. 2). ...
... We have successfully demonstrated hydras with up to 25 absorbers for mission concepts such as NASA's Lynx. 6 Because of the large number of absorbers, the Lynx hydra design necessitated a complex thermal network, where the pixels are arranged in hierarchical "tree" geometry. The 4-pixel design we are pursuing for LEM, however, is arranged in a "star" geometry where all pixels connect directly to the TES. ...
... The detector design is based on the small, 50 × 50 µm 2 , Mo/Au bare TES described above. A combined energy resolution of 2.16 ± 0.01 eV at 5.9 keV, obtained with more than 200 pixels, in a 8 × 32 multiplexing configuration, has been reported [115]. ...
... The information of which pixel received the photon can be retrieved from the pulse shape recorded by the electronics. The Hydras concept and implementation has been pioneered by the NASA-GSFC team and the most up-to-date theoretical and experimental results have been reported by Smith et al. [115,159]. An intrinsic trade-off between energy resolution and position sensitivity does exist for hydras detectors. ...
... The detector consists of an array of 50 × 50 µm 2 , low resistance TESs with a single pixel resolution of <2 eV at 6 keV. The system has demonstrated a combined exquisite energy resolution, with more than 200 pixels, of: 1.95 eV for Ti-K α (4.5 keV), 1.97 eV for Mn-Kα (5.9 keV), 2.16 eV for Co-K α (6.9 keV), 2.33 eV for Cu-K α (8 keV), 3.26 eV for Br-K α (11.9 keV) [115]. The focus of the team will soon move on demonstrating the performance of a full scale > 3000 pixels array. ...
The state-of-the-art technology of X-ray microcalorimeters based on superconducting transition edge sensors (TESs), for applications in astrophysics and particle physics, is reviewed. We will show the advance in understanding the detector physics and describe the recent breakthroughs in the TES design that are opening the way towards the fabrication and the read-out of very large arrays of pixels with unprecedented energy resolution. The most challenging low temperature instruments for space- and ground-base experiments will be described.
... This can be detrimental to device performance, particularly reproducibility and uniformity in large format arrays [133,139,159,173]. Thus, these types of features are not universally adopted on all TES devices [106,142]. Understanding all these geometry dependent effects on TES performance has been an a very active area of research and has enabled better control of the device properties and ever improving energy resolution. ...
... The more complex thermal network of the tree-hydras means that more sophisticated position-discrimination algorithms may be required to determine the event position. Prototype tree-hydras have been developed with up to 25 pixels per TES (5 trunks each with 5 branches) for NASA's Lynx mission concept [142]. The authors were able to demonstrate position discrimination using a simple approach to parameterize the rising-edges with two metrics that extracts a fast and slow component to the rise-time. ...
... This allowed unique identification of every branch and trunk pixel. These treehydras demonstrated ∆ E FW HM = 1.66 eV and ∆ E FW HM = 3.24 eV for hydras with a 25 µm and 50 µm absorber pitch, respectively, for Al-Kα X-rays [142]. ...
Large arrays of superconducting transition-edge sensor (TES) microcalorimeters are becoming the key technology for future space-based X-ray observatories and ground-based experiments in the fields of astrophysics, laboratory astrophysics, plasma physics, particle physics and material analysis. Thanks to their sharp superconducting-to-normal transition, TESs can achieve very high sensitivity in detecting small temperature changes at very low temperature. TES based X-ray detectors are non-dispersive spectrometers bringing together high resolving power, imaging capability and high-quantum efficiency simultaneously. In this chapter, we highlight the basic principles behind the operation and design of TESs, and their fundamental noise limits. We will further elaborate on the key fundamental physics processes that guide the design and optimization of the detector. We will then describe pulse-processing and important calibration considerations for space flight instruments, before introducing novel multi-pixel TES designs and discussing applications in future X-ray space missions over the coming decades.
... As such, they are a potential candidate for a range of applications, including XPS. Large arrays of TESs can be fabricated lithographically and operated simultaneously, increasing the available measurement rate without compromising energy resolution; multiplexed arrays numbering thousands of TESs are currently being developed for spacebased astronomical X-ray measurements [1,2]. TESs are also being developed for infrared, optical and UV spectroscopy in the context of emerging quantum experiments and technologies [3]. ...
Transition-edge sensors (TESs) are capable of highly accurate single particle energy measurement. TESs have been used for a wide range of photon detection applications, particularly in astronomy, but very little consideration has been given to their capabilities as electron calorimeters. Existing electron spectrometers require electron filtering optics to achieve energy discrimination, but this step discards the vast majority of electrons entering the instrument. TESs require no such energy filtering, meaning they could provide orders of magnitude improvement in measurement rate. To investigate the capabilities of TESs in electron spectroscopy, a simulation pipeline has been devised. The pipeline allows the results of a simulated experiment to be compared with the actual spectrum of the incident beam, thereby allowing measurement accuracy and efficiency to be studied. Using Fisher information, the energy resolution of the simulated detectors was also calculated, allowing the intrinsic limitations of the detector to be separated from the specific data analysis method used. The simulation platform has been used to compare the performance of TESs with existing x-ray photoelectron spectroscopy (XPS) analysers. TESs cannot match the energy resolution of XPS analysers for high-precision measurements but have comparable or better resolutions for high count rate applications. The measurement rate of a typical XPS analyser can be matched by an array of ten TESs with 120 μ s response times and there is significant scope for improvement, without compromising energy resolution, by increasing array size.
... The detector design is based on the small, 50 × 50 µm 2 , Mo/Au bare TES described above. A combined energy resolution of 2.16 ± 0.01 eV at 5.9 keV, obtained with more than 200 pixels, in a 8 × 32 multiplexing configuration, has been reported [115]. ...
... The information of which pixel received the photon can be retrieved from the pulse shape recorded by the electronics. The Hydras concept and implementation has been pioneered by the NASA-GSFC team and the most up-to-date theoretical and experimental results have been reported by Smith et al. [115,159]. An intrinsic trade-off between energy resolution and position sensitivity does exist for hydras detectors. ...
... The detector consists of an array of 50 × 50 µm 2 , low resistance TESs with a single pixel resolution of <2 eV at 6 keV. The system has demonstrated a combined exquisite energy resolution, with more than 200 pixels, of: 1.95 eV for Ti-K α (4.5 keV), 1.97 eV for Mn-Kα (5.9 keV), 2.16 eV for Co-K α (6.9 keV), 2.33 eV for Cu-K α (8 keV), 3.26 eV for Br-K α (11.9 keV) [115]. The focus of the team will soon move on demonstrating the performance of a full scale > 3000 pixels array. ...
The state-of-the-art technology of X-ray microcalorimeters based on superconducting transition-edge sensors (TESs), for applications in astrophysics and particle physics, is reviewed. We will show the advance in understanding the detector physics and describe the recent breakthroughs in the TES design that are opening the way towards the fabrication and the read-out of very large arrays of pixels with unprecedented energy resolution. The most challenging low temperature instruments for space-and ground-base experiments will be described.
... Today, several unique concepts exist how this temperature increase is determined in modern cryogenic micro-calorimeters. Often used are semiconductor thermistors [Mos84,McC05,Kra17], transition edge sensors [Irw05,Smi12,Smi20] and metallic magnetic calorimeters [Ens00,Fle09,Kem18]. The latter are at the center of discussion in this thesis. ...
This thesis describes the development of a high-resolution soft X-ray detector based on metallic magnetic calorimeters (MMCs). MMCs are cryogenic, energy dispersive particle detectors which consist of a particle absorber that is thermally coupled to a paramagnetic temperature sensor. The latter is placed in a weak magnetic field, hence exhibiting a temperature dependent magnetization M(T). Upon X-ray photon absorption, the rise of detector temperature causes a change of sensor magnetization, which is usually read out with a current-sensing dc-SQUID via a superconducting flux transformer. Here, an imperfect transformer matching, as well as a transformer intrinsic energy coupling losses, limit the achievable energy resolution. To challenge this limit, a novel integrated detector was developed, in which the temperature sensor is integrated into a custom-designed dc-SQUID to maximize signal coupling. A major challenge of this configuration is the Joule heating of the SQUID, since heating effects prevent cooling of the detector and thus limit its performance. For this reason, the developed 32 pixel detector makes use of a newly developed thermalization scheme for the SQUID’s shunt resistors, resulting in operation temperatures below 20 mK for the detector. With this kind of detector, a baseline energy resolution of dE = 1.3 eV, and dE = 1.8 eV at 5.9 keV was achieved.
Transition-edge sensors (TESs) have the potential to perform electron spectroscopic measurements with far greater measurement rates and efficiencies than can be achieved using existing electron spectrometers. Existing spectrometers filter electrons by energy before detecting a narrow energy band at a time, discarding the vast majority of electrons available for measurement. In contrast, TESs have intrinsic energy sensitivity and so do not require prior filtering to perform energy-resolved measurements. Despite this fundamental advantage, TES electron spectroscopy has not, to our knowledge, previously been reported in the literature. We present the results of a set of proof-of-principle experiments demonstrating TES electron spectroscopy experiments using Mo/Au TESs repurposed for electron calorimetry. Using these detectors, we successfully measured the electron spectrum generated by an electron beam striking a graphite target with energies between 750 and 2000 eV, at a noise-limited energy resolution of 4 eV. Based on the findings of these experiments, we suggest improvements that could be made to TES design to enhance their electron detection capabilities through the use of a dedicated electron absorber in the device with integrated electron optics.
