At SRON we are studying the performance of a Goddard Space Flight Center single pixel TES microcalorimeter operated in an AC bias configuration. For x-ray photons at 6 keV the pixel shows an x-ray ...energy resolution Δ
E
FWHM
=3.7 eV, which is about a factor 2 worse than the energy resolution observed in an identical DC-biased pixel. In order to better understand the reasons for this discrepancy we characterised the detector as a function of temperature, bias working point and applied perpendicular magnetic field. A strong periodic dependency of the detector noise on the TES AC bias voltage is measured. We discuss the results in the framework of the recently observed weak-link behaviour of a TES microcalorimeter.
Controlling the critical temperature (
T
C
) of Ti/Au bilayers is vital in the development of practical TES detectors. Previously empirical studies have been done on aging effects in Ti/Au and other ...superconducting bilayers but no link with theory has been made. Here we attempt to explain the change in
T
C
with a diffusion mechanism. The change in
T
C
has been measured for a set of Ti/Au bilayer samples that have been given a variety of bake-out treatments, where we found a trend that can be partly explained by an inter-diffusion mechanism. With an empirical model based on diffusion a safe zone can be defined as a region of bake-out treatments, where the
T
C
is not affected beyond the requirements. This will shine light on the bake-out and the storage condition boundaries of these detectors.
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.
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.
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.
The high sensitivity of cryogenic TES-based detectors opens new windows for astrophysical observations ranging from (far) infrared to X-rays. A number of operational and future space and ground-based ...instruments rely on cryogenic detectors to improve their performance with respect to the capabilities of earlier technologies. To reach the required sensitivities, base temperatures as low as 50 mK are necessary, and stringent requirements on magnetic shielding, microvibrations, and temperature stability are applicable. To minimize the heat load and complexity of the instruments, efficient multiplexing schemes and low-power amplifiers are needed. In addition, for space-based cryogenic instruments, mechanical launch loads and power consumption limitations constrain the available parameter space for engineering further. This paper discusses the system design considerations which are applicable to optimize the multiplex factor within the boundary conditions as set by the space craft for the X-IFU instrument on the Athena observatory. More specifically, the interplay between the science requirements such as pixel dynamic range, pixel speed, and cross talk, and the space craft requirements such as the power dissipation budget, and available bandwidth will be discussed.
SAFARI is an imaging Fourier Transform Spectrometer for 35–200 μm under development for flight on the Japanese IR-satellite SPICA (2018). The 3.25 m diameter actively cooled telescope (<6K) will ...provide a sky background limited signal, which implies that detectors will need to have an NEP of
in order not to be limiting the sensitivity. The instrument will utilize three TES-based detector arrays, covering the 2×2 arcmin field-of-view in three octaves of wave length. This contribution will present an overview of the detector sub-system, i.e.: the detector arrays and radiation coupling, the focal plane assembly, the amplification chain and the frequency-domain- multiplexed electronics. The focus will be on the implications on the system design of the readout under the stringent power dissipation, heat load, and weight limitations.
Transition edge sensors (TES) are the chosen detector technology for the SAFARI imaging spectrometer on the SPICA telescope. The TES are required to have an NEP of
to take full advantage of the ...cooled mirror. SRON has developed TiAu TES bolometers for the short wavelength band (30–60 μm). The TES are on SiN membranes, in which long and narrow legs act as thermal links between the TES and the bath. We present a distributed model that accounts for the heat conductance and the heat capacity in the long legs that provides a guideline for designing low noise detectors. We report our latest results that include a measured dark NEP of
and a saturation power of about 10 fW.
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