In this letter, we present the performance of a 100 μm × 400 μm × 40 nm W Transition-Edge Sensor with a critical temperature of 40 mK. This device has a noise equivalent power of 1.5×10-18 W/Hz, in a ...bandwidth of 2.6 kHz, indicating a resolution for Dirac delta energy depositions of 40 ± 5 meV (rms). The performance demonstrated by this device is a critical step toward developing a O(100) meV threshold athermal phonon detector for low-mass dark matter searches.
•We present sub-kelvin thermal conductivity data for an artificial graphite, polyimides (3), titanium alloys (3), a shape memory alloy and a bulk metallic glass.•The heat flow along the length of a ...laminated flat cable can be predicted by composing the thermal conductivities of its constituent materials, but heat flow across its thickness cannot be predicted in this way.•Titanium alloys are useful as low thermal conductivity superconducting structural and flat cabling materials.•SCP-5050 VESPEL is a useful insulating structural material due to its very low thermal conductivity, and high strength and dimensional stability.•Structural parts made from bulk metallic glass would have thermal conductivity on par with stainless steel and could be manufactured via injection molding.
We present measurements of the low temperature thermal conductivity for materials useful in the construction of cryogenic supports for scientific instrumentation and in the fabrication of flat flexible cryogenic cabling. The materials we measure have relatively low thermal conductivity. We present a method for measuring the heat transfer coefficient of flat cabling and show, using an example, that the thermal conductivity of a flex cable is reasonably well predicted by composing the thermal conductivities of its constituent material layers. Room temperature physical and mechanical data is given for the materials studied, as well as an overview of relevant materials science and manufacturing details. Materials include Timet Ti 15-3 and Ti 21S, Materion alloy vit105 (LM105) in amorphous state, ATI Metals Nb-47Ti, Johnson Matthey nitinol (NiTi), Mersen graphite grade 2020, DuPont Pyralux coverlay and Vespel SCP-5050, and Fralock Cirlex polyimide sheets. All data is in the temperature range 0.05–2 K, and up to 5 K for SCP-5050.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
We propose disk resonators for use as kinetic inductance detectors. Benefits and drawbacks of this design are discussed with consideration for potential detector applications. We have conducted ...electromagnetic simulations of the resonator geometry and will use them to examine the disk resonator properties. We will compare several schemes for coupling these resonators to feed lines and review the effect of a large kinetic inductance on the design equations for the resonant frequency. Additionally, a strategy to reduce the resonator metal volume by meshing is considered, and its effects on the resonator’s current distribution are shown. We find that meshing can significantly alter the resonant frequency of the disk. We conclude by discussing an example disk resonator, gamma-ray microcalorimeter detector design.
A model for charge trapping and impact ionization and an experiment to measure these parameters are presented for the SuperCDMS HVeV detector. A procedure to isolate and quantify the main sources of ...noise (bulk and surface charge leakage) in the measurements is also described. This sets the stage to precisely measure the charge trapping and impact ionization probabilities in order to incorporate this model into future dark matter searches.
A portable monoenergetic 24 keV neutron source based on the 124Sb-9Be photoneutron reaction and an iron filter has been constructed and characterized. The coincidence of the neutron energy from SbBe ...and the low interaction cross-section with iron (mean free path up to 29 cm) makes pure iron specially suited to shield against gamma rays from 124Sb decays while letting through the neutrons. To increase the 124Sb activity and thus the neutron flux, a >1 GBq 124Sb source was produced by irradiating a natural Sb metal pellet with a high flux of thermal neutrons in a nuclear reactor. The design of the source shielding structure makes for easy transportation and deployment. A hydrogen gas proportional counter is used to characterize the neutrons emitted by the source and a NaI detector is used for gamma background characterization. At the exit opening of the neutron beam, the characterization determined the neutron flux in the energy range 20–25 keV to be 6.00±0.30 neutrons per cm2 per second and the total gamma flux to be 245±8 gammas per cm2 per second (numbers scaled to 1 GBq activity of the 124Sb source). A liquid scintillator detector is demonstrated to be sensitive to neutrons with incident kinetic energies from 8 to 17 keV, so it can be paired with the source as a backing detector for neutron scattering calibration experiments. This photoneutron source provides a good tool for in-situ low energy nuclear recoil calibration for dark matter experiments and coherent elastic neutrino-nucleus scattering experiments.
We have measured the ionization performance of a CDMS II detector using CNRS/LPN HEMTs as opposed to Si JFETs in the front end electronics. We find no significant difference in ionization resolution ...when using HEMTs compared to Si JFETs indicating the CNRS/LPN HEMTs can act as a low power, low noise replacement for Si JFETs in cryogenic applications. We present the HEMT DC/AC properties, measured noise in both low impedance and high impedance closed-loop configurations using CDMS electronics, and performance with a CDMS detector exposed to a
241
Am source.
We present measurements of the thermal conductivity between 0.05 and 1 K, and radioactive contamination levels, for some thermally isolating materials. TIMET Ti 15-3-3-3, Mersen grade 2020 graphite, ...Vespel SP-1, Vespel SP-22, Vespel SCP-5000, Vespel SCP-5050, Graphlite CFRP, and a Kapton/epoxy composite are all investigated. Thermal conductivities were measured using a single-heater longitudinal heat flow method. Material radioactivity was determined for the materials at a low background counting facility using a high-purity gamma detector and GEANT4 Monte Carlo simulations.
This work describes the transport and capture processes of electrons and holes in ultrapure germanium
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at low temperature and low electric field. Dynamic space-charge effects are responsible ...for the most significant systematics of the Cryogenic Dark Matter Search. To understand the relationship of transport dynamics to space charge evolution, it is important that we understand charge carrier transport under these nonequilibrium operating conditions. Here, we present measured data and a consistent model of electron and hole dynamics and capture. A charged and a neutral capture probability for both electrons and holes appears to explain the multiple, field-dependent power laws observed in data. This offers a quantitative understanding why germanium crystals operating under these conditions should “neutralize” when grounded, but accrue space charge while under bias.
A common challenge in low temperature instrumentation is adequately heat sinking signal wires between room temperature and devices at base temperature. Using cryostat space for adequate heat sinking ...typically comes at the cost of complexity or experimental space. As such, it is useful to know how much heat sinking is adequate given the materials, heat sources and cooling capacities involved. We present a differential equation for modeling the heat flowing out of a flat cable along an interval over which it is adhered to an insulating interface which is bound to a metallic heat sinking surface and numerical results for realistic heat sinks in the Kelvin range. We also present a computational method for solving this differential equation.
We present the measured baseline ionization resolution of a HEMT-based cryogenic charge amplifier coupled to a CDMS-II detector. The amplifier has been developed to allow massive semiconductor dark ...matter detectors to retain background discrimination at the low recoil energies produced by low-mass WIMPs. We find a calibrated baseline ionization resolution of σE=91eVee. To our knowledge, this is the best direct ionization resolution achieved with such massive (≈150 pF capacitance) radiation detectors.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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