138 research outputs found
Magnetic field dependence of the internal quality factor and noise performance of lumped-element kinetic inductance detectors
We present a technique for increasing the internal quality factor of kinetic
inductance detectors (KIDs) by nulling ambient magnetic fields with a properly
applied magnetic field. The KIDs used in this study are made from thin-film
aluminum, they are mounted inside a light-tight package made from bulk
aluminum, and they are operated near . Since the thin-film
aluminum has a slightly elevated critical temperature (), it therefore transitions before the package (), which also serves as a magnetic shield. On cooldown, ambient
magnetic fields as small as approximately can produce
vortices in the thin-film aluminum as it transitions because the bulk aluminum
package has not yet transitioned and therefore is not yet shielding. These
vortices become trapped inside the aluminum package below
and ultimately produce low internal quality factors in the thin-film
superconducting resonators. We show that by controlling the strength of the
magnetic field present when the thin film transitions, we can control the
internal quality factor of the resonators. We also compare the noise
performance with and without vortices present, and find no evidence for excess
noise beyond the increase in amplifier noise, which is expected with increasing
loss.Comment: 5 pages, 4 figure
A Titanium Nitride Absorber for Controlling Optical Crosstalk in Horn-Coupled Aluminum LEKID Arrays for Millimeter Wavelengths
We discuss the design and measured performance of a titanium nitride (TiN)
mesh absorber we are developing for controlling optical crosstalk in
horn-coupled lumped-element kinetic inductance detector arrays for
millimeter-wavelengths. This absorber was added to the fused silica
anti-reflection coating attached to previously-characterized, 20-element
prototype arrays of LEKIDs fabricated from thin-film aluminum on silicon
substrates. To test the TiN crosstalk absorber, we compared the measured
response and noise properties of LEKID arrays with and without the TiN mesh.
For this test, the LEKIDs were illuminated with an adjustable, incoherent
electronic millimeter-wave source. Our measurements show that the optical
crosstalk in the LEKID array with the TiN absorber is reduced by 66\% on
average, so the approach is effective and a viable candidate for future
kilo-pixel arrays.Comment: 7 pages, 5 figures, accepted for publication in the Journal of Low
Temperature Physic
Horn-Coupled, Commercially-Fabricated Aluminum Lumped-Element Kinetic Inductance Detectors for Millimeter Wavelengths
We discuss the design, fabrication, and testing of prototype horn-coupled,
lumped-element kinetic inductance detectors (LEKIDs) designed for cosmic
microwave background (CMB) studies. The LEKIDs are made from a thin aluminum
film deposited on a silicon wafer and patterned using standard
photolithographic techniques at STAR Cryoelectronics, a commercial device
foundry. We fabricated twenty-element arrays, optimized for a spectral band
centered on 150 GHz, to test the sensitivity and yield of the devices as well
as the multiplexing scheme. We characterized the detectors in two
configurations. First, the detectors were tested in a dark environment with the
horn apertures covered, and second, the horn apertures were pointed towards a
beam-filling cryogenic blackbody load. These tests show that the multiplexing
scheme is robust and scalable, the yield across multiple LEKID arrays is 91%,
and the noise-equivalent temperatures (NET) for a 4 K optical load are in the
range 26\thinspace\pm6 \thinspace \mu \mbox{K} \sqrt{\mbox{s}}
The Detector System for the Stratospheric Kinetic Inductance Polarimeter (SKIP)
The Stratospheric Kinetic Inductance Polarimeter (SKIP) is a proposed
balloon-borne experiment designed to study the cosmic microwave background, the
cosmic infrared background and Galactic dust emission by observing 1133 square
degrees of sky in the Northern Hemisphere with launches from Kiruna, Sweden.
The instrument contains 2317 single-polarization, horn-coupled, aluminum
lumped-element kinetic inductance detectors (LEKID). The LEKIDs will be
maintained at 100 mK with an adiabatic demagnetization refrigerator. The
polarimeter operates in two configurations, one sensitive to a spectral band
centered on 150 GHz and the other sensitive to 260 and 350 GHz bands. The
detector readout system is based on the ROACH-1 board, and the detectors will
be biased below 300 MHz. The detector array is fed by an F/2.4 crossed-Dragone
telescope with a 500 mm aperture yielding a 15 arcmin FWHM beam at 150 GHz. To
minimize detector loading and maximize sensitivity, the entire optical system
will be cooled to 1 K. Linearly polarized sky signals will be modulated with a
metal-mesh half-wave plate that is mounted at the telescope aperture and
rotated by a superconducting magnetic bearing. The observation program consists
of at least two, five-day flights beginning with the 150 GHz observations.Comment: J Low Temp Phys DOI 10.1007/s10909-013-1014-3 The final publication
is available at link.springer.co
A LEKID-based CMB instrument design for large-scale observations in Greenland
We present the results of a feasibility study, which examined deployment of a
ground-based millimeter-wave polarimeter, tailored for observing the cosmic
microwave background (CMB), to Isi Station in Greenland. The instrument for
this study is based on lumped-element kinetic inductance detectors (LEKIDs) and
an F/2.4 catoptric, crossed-Dragone telescope with a 500 mm aperture. The
telescope is mounted inside the receiver and cooled to K by a
closed-cycle He refrigerator to reduce background loading on the detectors.
Linearly polarized signals from the sky are modulated with a metal-mesh
half-wave plate that is rotated at the aperture stop of the telescope with a
hollow-shaft motor based on a superconducting magnetic bearing. The modular
detector array design includes at least 2300 LEKIDs, and it can be configured
for spectral bands centered on 150~GHz or greater. Our study considered
configurations for observing in spectral bands centered on 150, 210 and
267~GHz. The entire polarimeter is mounted on a commercial precision rotary air
bearing, which allows fast azimuth scan speeds with negligible vibration and
mechanical wear over time. A slip ring provides power to the instrument,
enabling circular scans (360 degrees of continuous rotation). This mount, when
combined with sky rotation and the latitude of the observation site, produces a
hypotrochoid scan pattern, which yields excellent cross-linking and enables
34\% of the sky to be observed using a range of constant elevation scans. This
scan pattern and sky coverage combined with the beam size (15~arcmin at
150~GHz) makes the instrument sensitive to in the angular
power spectra
Welding fume nanoparticles from solid and flux-cored wires: Solubility, toxicity, and role of fluorides
Welding fume particles are hazardous. Their toxicity likely depends on their composition and reactivity. This study aimed at exploring the role of sodium or other fluorides (NaF), which are intentionally added to flux-cored wire electrodes for stainless steel welding, on the solubility (in phosphate buffered saline) and toxicity of the generated welding fume particles. A multi-analytical particle characterization approach along with in-vitro cell assays was undertaken. The release of Cr(VI) and Mn from the particles was tested as a function of fluoride solution concentration. The welding fume particles containing NaF released significantly higher amounts of Cr(VI) compared with solid wire reference fumes, which was associated with increased cytotoxicity and genotoxicity in-vitro. No crystalline Na or potassium (K) containing chromates were observed. Cr(VI) was incorporated in an amorphous mixed oxide. Solution-added fluorides did not increase the solubility of Cr(VI), but contributed to a reduced Mn release from both solid and flux-cored wire fume particles and the reduction of Cr(VI) release from solid wire fume particles. Chemical speciation modeling suggested that metal fluoride complexes were not formed. The presence of NaF in the welding electrodes did not have any direct, but possibly an indirect, role in the Cr(VI) solubility of welding fumes
High quality factor manganese-doped aluminum lumped-element kinetic inductance detectors sensitive to frequencies below 100 GHz
Aluminum lumped-element kinetic inductance detectors (LEKIDs) sensitive to millimeter-wave photons have
been shown to exhibit high quality factors, making them highly sensitive and multiplexable. The superconducting
gap of aluminum limits aluminum LEKIDs to photon frequencies above 100 GHz. Manganese-doped
aluminum (Al-Mn) has a tunable critical temperature and could therefore be an attractive material for
LEKIDs sensitive to frequencies below 100 GHz if the internal quality factor remains sufficiently high when
manganese is added to the film. To investigate, we measured some of the key properties of Al-Mn LEKIDs.
A prototype eight-element LEKID array was fabricated using a 40 nm thick film of Al-Mn deposited on a
500 µm thick high-resistivity, float-zone silicon substrate. The manganese content was 900 ppm, the measured
Tc = 694 ± 1mK, and the resonance frequencies were near 150 MHz. Using measurements of the forward
scattering parameter S21 at various bath temperatures between 65 and 250 mK, we determined that the
Al-Mn LEKIDs we fabricated have internal quality factors greater than 2 × 105
, which is high enough for
millimeter-wave astrophysical observations. In the dark conditions under which these devices were measured,
the fractional frequency noise spectrum shows a shallow slope that depends on bath temperature and probe
tone amplitude, which could be two-level system noise. The anticipated white photon noise should dominate
this level of low-frequency noise when the detectors are illuminated with millimeter-waves in future measurements.
The LEKIDs responded to light pulses from a 1550 nm light-emitting diode, and we used these light
pulses to determine that the quasiparticle lifetime is 60 µs
Photon noise from chaotic and coherent millimeter-wave sources measured with horn-coupled, aluminum lumped-element kinetic inductance detectors
We report photon-noise limited performance of horn-coupled, aluminum lumped-element kinetic inductance detectors at millimeter wavelengths. The detectors are illuminated by a millimeter-wave source that uses an active multiplier chain to produce radiation between 140 and 160 GHz. We feed the multiplier with either amplified broadband noise or a continuous-wave tone from a microwave signal generator. We demonstrate that the detector response over a 40 dB range of source power is well-described by a simple model that considers the number of quasiparticles. The detector noise-equivalent power (NEP) is dominated by photonnoise when the absorbed power is greater than approximately 1 pW, which corresponds to NEP ≈ 2×10^(−17) W Hz^(−1/2), referenced to absorbed power. At higher source power levels, we observe the relationships between noise and power expected from the photon statistics of the source signal: NEP∝P for broadband (chaotic) illumination and NEP∝P^(1/2) for continuous-wave (coherent) illumination
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