Electro-thermal coupling in semiconductor bolometers is known to create nonlinearities in transient detector response, particularly when such detectors are biased outside of their ideal regions (i.e. ...past the turnover point in their IV curves). This effect is further compounded in the case where a stray capacitance in the bias circuit is present, for example in long cryogenic cabling. We present a physical model of the influence of such electro-thermal coupling and stray capacitance in a composite NTD germanium bolometer, in which previous experimental data at high
V
bias
resulted in oscillations of the impulse response of the detector to irradiation by alpha particles. The model reproduces the transient oscillations seen in the experimental data, depending both on electro-thermal coupling and stray capacitance. This is intended as an experimental and simulated example of such oscillations, demonstrated for the specific case of this bolometric detector.
Systematic effects arising from cosmic rays have been shown to be a significant threat to space telescopes using high-sensitivity bolometers. The LiteBIRD space mission aims to measure the polarised ...Cosmic Microwave Background with unprecedented sensitivity, but its positioning in space will also render it susceptible to cosmic ray effects. We present an end-to-end simulator for evaluating the expected scale of cosmic ray effects on the LiteBIRD space mission, which we demonstrate on a subset of detectors on the 166 GHz band of the Low Frequency Telescope. The simulator couples the expected proton flux at L2 with a model of the thermal response of the LFT focal plane and the electrothermal response of its superconducting detectors, producing time-ordered data which is projected into simulated sky maps and subsequent angular power spectra.
The data from the Planck and Herschel space observatories revealed that the cosmic rays at L2 orbit can have a significant impact on the performance of scientific instruments. In this paper, we ...present our simulation results of such impacts on SAFARI/SPICA, a far-infrared spectrometer equipped with transition-edge sensors (TESs). These TESs are fabricated on SiN membranes and suspended by long and thin SiN legs that thermally isolate them from the surrounding silicon structure (wafer). Cosmic rays that pass through this surrounding structure deposit a portion of their energy, leading to temperature fluctuations in the wafer. These temperature fluctuations are sensed by the TES detectors as an effective bath temperature and result in additional noise. To simulate the impact, we generate a 2D model of the wafer and the suspended TESs in COMSOL 5.4. This 2D model is bombarded with 128 randomly generated cosmic rays according to the observed energy distributions at L2. Subsequently, the temperature fluctuations at different points on the wafer are estimated. Our results show that these thermal fluctuations, as well as the calculated additional TES noise caused by them, depend strongly on the heat-sink design of the wafer. We study the impact of the different heat sink designs on the noise profile of the system. Later, these results are compared to the SAFARI instrument noise requirements.
We introduce the ‘Joule stepping’ technique, whereupon a constantly biased bolometer has its bias voltage modified by a small additional step. We demonstrate this technique using a composite NTD ...semiconductor bolometer and a pulsing device that sends an extra step in voltage. We demonstrate the results of the technique over a range of bias voltages at 100, 200 and 300 mK. Joule stepping allows us to directly measure long thermal tails with low amplitudes in the response of the global thermal architecture of bolometers and could be a useful tool to quickly and easily calibrate the thermal time response of individual bolometric detectors or channels. We also show that the derivative of the Joule step is equivalent to the bolometer response to a
δ
-pulse (or Joule pulse), which allows for greater understanding of transient behaviour with a better signal-to-noise ratio than pulsing alone can provide. Finally, we compare Joule step pulses with pulses produced by
α
particles, finding a good agreement between their fast decay constants, but a discrepancy between their thermal decay constants.
We present the design and implementation of a thermal model, developed in COMSOL, aiming to probe the wafer-scale thermal response arising from realistic rates and energies of cosmic rays at L2 ...impacting the detector wafer of Athena X-IFU. The wafer thermal model is a four-layer 2D model, where two layers represent the constituent materials (Si bulk and Si
3
N
4
membrane) and two layers represent the Au metallization layer’s phonon and electron temperatures. We base the simulation geometry on the current specifications for the X-IFU detector wafer and simulate cosmic ray impacts using a simple power injection into the Si bulk. We measure the temperature at the point of the instrument’s most central TES detector. By probing the response of the system and pulse characteristics as a function of the thermal input energy and location, we reconstruct cosmic ray pulses in Python. By utilizing this code, along with the results of the GEANT4 simulations produced for X-IFU, we produce realistic time-ordered data (TOD) of the temperature seen by the central TES, which we use to simulate the degradation of the energy resolution of the instrument in space-like conditions on this wafer. We find a degradation to the energy resolution of 7 keV X-rays of
≈
0.04 eV. By modifying wafer parameters and comparing the simulated TOD, this study is a valuable tool for probing design changes on the thermal background seen by the detectors.
Cosmology space missions have been known to be particularly sensitive to systematic effects arising from the interaction between cosmic rays and highly sensitive detectors below 200 mK. To remove ...this signal, one must first understand the deposition and dissipation of energy into these detectors. Using a well-known NTD germanium composite bolometer, we simulate the effect of cosmic rays using a radioactive source in the laboratory. Through analysis of experimental data, we find that the glitch signal shape is a function of incoming particle position, as well as the incoming particle energy. We report also on nonlinear effects in the fit, in order to lay the groundwork towards a new physical model for this energy propagation in the bolometer.
LiteBIRD is a proposed JAXA satellite mission to measure the CMB B-mode polarization with unprecedented sensitivity (
σ
r
∼
0.001
). To achieve this goal, 4676 state-of-the-art TES bolometers will ...observe the whole sky for 3 years from L2. These detectors, as well as the SQUID readout, are extremely susceptible to EMI and other instrumental disturbances, e.g., static magnetic field and vibration. As a result, careful analysis of the interference between the detector system and the rest of the telescope instruments is essential. This study is particularly important during the early phase of the project, in order to address potential problems before the final assembly of the whole instrument. We report our plan for the preparation of a cryogenic testbed to study the interaction between the detectors and other subsystems, especially a polarization modulator unit consisting of a magnetically rotating half-wave plate. We also present the requirements, current status and preliminary results.
For the future satellite mission at the second sun–earth Lagrangian point (L2), we need to mitigate phonon propagation created by cosmic rays to superconducting detectors. We simulate phonon ...propagation in silicon substrate and show that putting a metal layer on the substrate or making hole in the substrate reduces the propagation. We also show a function which shows the response of a TES bolometer on a substrate. To validate these theoretical expectations, we make irradiation tests using two types of superconducting detectors: transition edge sensor bolometers and kinetic inductance detectors. From the tests, we show that putting metal can reduce correlations between detectors and number of hit events from charged particles.
Attention-deficit hyperactivity disorder (ADHD) affects ∼3%–5% of children in the United States. In the current psychiatric nomenclature, ADHD comprises three subtypes: inattentive, ...hyperactive-impulsive, and combined. In this study, we used four analytic strategies to examine the association and linkage of the dopamine transporter gene (DAT1) and ADHD. Our sample included 122 children referred to psychiatric clinics for behavioral and learning problems that included but were not limited to ADHD, as well as their parents and siblings. Within-family analyses of linkage disequilibrium, using the transmission disequilibrium test (TDT), confirmed the 480-bp allele as the high-risk allele. In between-family association analyses, levels of hyperactive-impulsive symptoms but not inattentive symptoms were related to the number of DAT1 high-risk alleles. Siblings discordant for the number of DAT1 high-risk alleles differed markedly in their levels of both hyperactive-impulsive and inattentive symptoms, such that the sibling with the higher number of high-risk alleles had much higher symptom levels. Within-family analyses of linkage disequilibrium, using the TDT, suggested association and linkage of ADHD with DAT1 and that this relation was especially strong with the combined but not the inattentive subtype. The relation of DAT1 to ADHD increased monotonically, from low to medium to high levels of symptom severity. Our results replicate and extend previous findings of the association between the DAT1 gene and childhood ADHD. This represents one of the first replicated relations of a candidate gene and a psychiatric disorder in children.
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