6 research outputs found
Heat transfer coefficient saturation in superconducting Nb tunnel junctions contacted to a NbTiN circuit and an Au energy relaxation layer
In this paper we present the experimental realization of a Nb tunnel junction
connected to a high-gap superconducting NbTiN embedding circuit. We investigate
relaxation of nonequilibrium quasiparticles in a small volume Au layer between
the Nb tunnel junction and the NbTiN circuit. We find a saturation in the
effective heat-transfer coefficient consistent with a simple theoretical model.
This saturation is determined by the thickness of the Au layer. Our findings
are important for the design of the ideal Au energy relaxation layer for
practical SIS heterodyne mixers and we suggest two geometries, one, using a
circular Au layer and, two, using a half-circular Au layer. Our work is
concluded with an outlook of our future experiments.Comment: Applied Superconductivity Conference 201
A 490 GHz planar circuit balanced Nb-AlO-Nb quasiparticle mixer for radio astronomy: Application to quantitative local oscillator noise determination
This article presents a heterodyne experiment which uses a 380-520 GHz planar
circuit balanced Nb--Nb
superconductor-insulator-superconductor (SIS) quasiparticle mixer with 4-8 GHz
instantaneous intermediate frequency (IF) bandwidth to quantitatively determine
local oscillator (LO) noise. A balanced mixer is a unique tool to separate
noise at the mixer's LO port from other noise sources. This is not possible in
single-ended mixers. The antisymmetric IV characteristic of a SIS mixer further
helps to simplify the measurements. The double-sideband receiver sensitivity of
the balanced mixer is 2-4 times the quantum noise limit over the
measured frequencies with a maximum LO noise rejection of 15 dB. This work
presents independent measurements with three different LO sources that produce
the reference frequency but also an amount of near-carrier noise power which is
quantified in the experiment as a function of the LO and IF frequency in terms
of an equivalent noise temperature . In a second experiment we use only
one of two SIS mixers of the balanced mixer chip, in order to verify the
influence of near-carrier LO noise power on a single-ended heterodyne mixer
measurement. We find an IF frequency dependence of near-carrier LO noise power.
The frequency-resolved IF noise temperature slope is flat or slightly negative
for the single-ended mixer. This is in contrast to the IF slope of the balanced
mixer itself which is positive due to the expected IF roll-off of the mixer.
This indicates a higher noise level closer to the LO's carrier frequency. Our
findings imply that near-carrier LO noise has the largest impact on the
sensitivity of a receiver system which uses mixers with a low IF band, for
example superconducting hot-electron bolometer (HEB) mixers.Comment: 13 pages, 8 figures, 2 tables, see manuscript for complete abstrac
SOFIA FEEDBACK Survey: The Pillars of Creation in [C II] and Molecular Lines
We investigate the physical structure and conditions of photodissociation
regions (PDRs) and molecular gas within the Pillars of Creation in the Eagle
Nebula using SOFIA FEEDBACK observations of the [C II] 158 micron line. These
observations are velocity resolved to 0.5 km s and are analyzed
alongside a collection of complimentary data with similar spatial and spectral
resolution: the [O I] 63 micron line, also observed with SOFIA, and rotational
lines of CO, HCN, HCO, CS, and NH. Using the superb spectral
resolution of SOFIA, APEX, CARMA, and BIMA, we reveal the relationships between
the warm PDR and cool molecular gas layers in context of the Pillars' kinematic
structure. We assemble a geometric picture of the Pillars and their
surroundings informed by illumination patterns and kinematic relationships and
derive physical conditions in the PDRs associated with the Pillars. We estimate
an average molecular gas density cm
and an average atomic gas density cm
and infer that the ionized, atomic, and molecular phases are in pressure
equilibrium if the atomic gas is magnetically supported. We find pillar masses
of 103, 78, 103, and 18 solar masses for P1a, P1b, P2, and P3 respectively, and
evaporation times of 1-2 Myr. The dense clumps at the tops of the pillars
are currently supported by the magnetic field. Our analysis suggests that
ambipolar diffusion is rapid and these clumps are likely to collapse within
their photoevaporation timescales.Comment: 42 pages, 16 figures. Accepted for publication in The Astronomical
Journa
The Herschel-Heterodyne Instrument for the Far-Infrared (HIFI): instrument and pre-launch testing
This paper describes the Heterodyne Instrument for the Far-Infrared (HIFI), to be launched onboard of ESA's Herschel Space Observatory, by 2008. It includes the first results from the instrument level tests. The instrument is designed to be electronically tuneable over a wide and continuous frequency range in the Far Infrared, with velocity resolutions better than 0.1 km/s with a high sensitivity. This will enable detailed investigations of a wide variety of astronomical sources, ranging from solar system objects, star formation regions to nuclei of galaxies. The instrument comprises 5 frequency bands covering 480-1150 GHz with SIS mixers and a sixth dual frequency band, for the 1410-1910 GHz range, with Hot Electron Bolometer Mixers (HEB). The Local Oscillator (LO) subsystem consists of a dedicated Ka-band synthesizer followed by 7 times 2 chains of frequency multipliers, 2 chains for each frequency band. A pair of Auto-Correlators and a pair of Acousto-Optic spectrometers process the two IF signals from the dual-polarization front-ends to provide instantaneous frequency coverage of 4 GHz, with a set of resolutions (140 kHz to 1 MHz), better than < 0.1 km/s. After a successful qualification program, the flight instrument was delivered and entered the testing phase at satellite level. We will also report on the pre-flight test and calibration results together with the expected in-flight performance
SOFIA FEEDBACK Survey: The Pillars of Creation in [C ii] and Molecular Lines
We investigate the physical structure and conditions of photodissociation regions (PDRs) and molecular gas within the Pillars of Creation in the Eagle Nebula using SOFIA FEEDBACK observations of the [C ii ] 158 μ m line. These observations are velocity resolved to 0.5 km s ^−1 and are analyzed alongside a collection of complimentary data with similar spatial and spectral resolution: the [O i ] 63 μ m line, also observed with SOFIA, and rotational lines of CO, HCN, HCO ^+ , CS, and N _2 H ^+ . Using the superb spectral resolution of SOFIA, APEX, CARMA, and BIMA, we reveal the relationships between the warm PDR and cool molecular gas layers in context of the Pillars’ kinematic structure. We assemble a geometric picture of the Pillars and their surroundings informed by illumination patterns and kinematic relationships and derive physical conditions in the PDRs associated with the Pillars. We estimate an average molecular gas density cm ^−3 and an average atomic gas density n _H ∼ 1.8 × 10 ^4 cm ^−3 and infer that the ionized, atomic, and molecular phases are in pressure equilibrium if the atomic gas is magnetically supported. We find pillar masses of 103, 78, 103, and 18 M _⊙ for P1a, P1b, P2, and P3, respectively, and evaporation times of ∼1–2 Myr. The dense clumps at the tops of the pillars are currently supported by the magnetic field. Our analysis suggests that ambipolar diffusion is rapid and these clumps are likely to collapse within their photoevaporation timescales