[Show abstract][Hide abstract] ABSTRACT: We describe the SPIDER flight cryostat, which is designed to cool six
millimeter-wavelength telescopes during an Antarctic long-duration balloon
flight. The cryostat, one of the largest to have flown on a stratospheric
payload, uses liquid helium-4 to deliver cooling power to stages at 4.2 and 1.6
K. Stainless steel capillaries facilitate a high flow impedance connection
between the main liquid helium tank and a smaller superfluid tank, allowing the
latter to operate at 1.6 K as long as there is liquid in the 4.2 K main tank.
Each telescope houses a closed cycle helium-3 adsorption refrigerator that
further cools the focal planes down to 300 mK. Liquid helium vapor from the
main tank is routed through heat exchangers that cool radiation shields,
providing negative thermal feedback. The system performed successfully during a
17 day flight in the 2014-2015 Antarctic summer. The cryostat had a total hold
time of 16.8 days, with 15.9 days occurring during flight.
[Show abstract][Hide abstract] ABSTRACT: The bispectrum of single-field inflationary trajectories in which the speed
of sound of the inflationary trajectories $c_s$ is constant but not equal to
the speed of light $c=1$ is explored. The trajectories are generated as random
realisations of the Hubble Slow-Roll (HSR) hierarchy and the bispectra are
calculated using numerical techniques that extends previous work. This method
allows for out-of-slow-roll models with non-trivial time dependence and
arbitrarily low $c_s$. The ensembles obtained using this method yield
distributions for the shape and scale-dependence of the bispectrum and their
relations with the standard inflationary parameters such as scalar spectral
tilt $n_s$ and tensor-to-scalar ratio $r$. The distributions demonstrate the
squeezed-limit consistency relations for arbitrary single-field inflationary
models.
[Show abstract][Hide abstract] ABSTRACT: The simplest interpretation of the Bicep2 result is that the scalar
primordial power spectrum is slightly suppressed at large scales. These models
result in a large tensor-to-scalar ratio $r$. In this work we show that the
type of inflationary trajectory favoured by Bicep2 also leads to a larger
non-Gaussian signal at large scales, roughly an order of magnitude larger than
a standard slow-roll trajectory.
[Show abstract][Hide abstract] ABSTRACT: The recent BICEP2 detection of, what is claimed to be primordial $B$-modes,
opens up the possibility of constraining not only the energy scale of inflation
but also the detailed acceleration history that occurred during inflation. In
turn this can be used to determine the shape of the inflaton potential
$V(\phi)$ for the first time - if a single, scalar inflaton is assumed to be
driving the acceleration. We carry out a Monte Carlo exploration of
inflationary trajectories given the current data. Using this method we obtain a
posterior distribution of possible acceleration profiles $\epsilon(N)$ as a
function of $e$-fold $N$ and derived posterior distributions of the primordial
power spectrum $P(k)$ and potential $V(\phi)$. We find that the BICEP2 result,
in combination with Planck measurements of total intensity Cosmic Microwave
Background (CMB) anisotropies, induces a significant feature in the scalar
primordial spectrum at scales $k\sim 10^{-3}$ Mpc$^{-1}$. This is in agreement
with a previous detection of a suppression in the scalar power.
Journal of Cosmology and Astroparticle Physics 07/2014; 2014(10). DOI:10.1088/1475-7516/2014/10/072 · 5.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We present the technology and control methods developed for the pointing system of the SPIDER experiment. SPIDER is a balloon-borne polarimeter designed to detect the imprint of primordial gravitational waves in the polarization of the Cosmic Microwave Background radiation. We describe the two main components of the telescope's azimuth drive: the reaction wheel and the motorized pivot. A 13 kHz PI control loop runs on a digital signal processor, with feedback from fibre optic rate gyroscopes. This system can control azimuthal speed with < 0.02 deg/s RMS error. To control elevation, SPIDER uses stepper-motor-driven linear actuators to rotate the cryostat, which houses the optical instruments, relative to the outer frame. With the velocity in each axis controlled in this way, higher-level control loops on the onboard flight computers can implement the pointing and scanning observation modes required for the experiment. We have accomplished the non-trivial task of scanning a 5000 lb payload sinusoidally in azimuth at a peak acceleration of 0.8 deg/s$^2$, and a peak speed of 6 deg/s. We can do so while reliably achieving sub-arcminute pointing control accuracy.
Proceedings - Society of Photo-Optical Instrumentation Engineers 07/2014; 9145. DOI:10.1117/12.2055166
[Show abstract][Hide abstract] ABSTRACT: We present the results of integration and characterization of the SPIDER
instrument after the 2013 pre-flight campaign. SPIDER is a balloon-borne
polarimeter designed to probe the primordial gravitational wave signal in the
degree-scale $B$-mode polarization of the cosmic microwave background. With six
independent telescopes housing over 2000 detectors in the 94 GHz and 150 GHz
frequency bands, SPIDER will map 7.5% of the sky with a depth of 11 to 14
$\mu$K$\cdot$arcmin at each frequency, which is a factor of $\sim$5 improvement
over Planck. We discuss the integration of the pointing, cryogenic,
electronics, and power sub-systems, as well as pre-flight characterization of
the detectors and optical systems. SPIDER is well prepared for a December 2014
flight from Antarctica, and is expected to be limited by astrophysical
foreground emission, and not instrumental sensitivity, over the survey region.
[Show abstract][Hide abstract] ABSTRACT: We present the second generation BLASTbus electronics. The primary purposes
of this system are detector readout, attitude control, and cryogenic
housekeeping, for balloon-borne telescopes. Readout of neutron transmutation
doped germanium (NTD-Ge) bolometers requires low noise and parallel acquisition
of hundreds of analog signals. Controlling a telescope's attitude requires the
capability to interface to a wide variety of sensors and motors, and to use
them together in a fast, closed loop. To achieve these different goals, the
BLASTbus system employs a flexible motherboard-daughterboard architecture. The
programmable motherboard features a digital signal processor (DSP) and
field-programmable gate array (FPGA), as well as slots for three
daughterboards. The daughterboards provide the interface to the outside world,
with versions for analog to digital conversion, and optoisolated digital
input/output. With the versatility afforded by this design, the BLASTbus also
finds uses in cryogenic, thermometry, and power systems. For accurate timing
control to tie everything together, the system operates in a fully synchronous
manner. BLASTbus electronics have been successfully deployed to the South Pole,
and flown on stratospheric balloons.
[Show abstract][Hide abstract] ABSTRACT: An attitude determination system for balloon-borne experiments is presented.
The system provides pointing information in azimuth and elevation for
instruments flying on stratospheric balloons over Antarctica. In-flight
attitude is given by the real-time combination of readings from star cameras, a
magnetometer, sun sensors, GPS, gyroscopes, tilt sensors and an elevation
encoder. Post-flight attitude reconstruction is determined from star camera
solutions, interpolated by the gyroscopes using an extended Kalman Filter. The
multi-sensor system was employed by the Balloon-borne Large Aperture
Submillimeter Telescope for Polarimetry (BLASTPol), an experiment that measures
polarized thermal emission from interstellar dust clouds. A similar system was
designed for the upcoming flight of SPIDER, a Cosmic Microwave Background
polarization experiment. The pointing requirements for these experiments are
discussed, as well as the challenges in designing attitude reconstruction
systems for high altitude balloon flights. In the 2010 and 2012 BLASTPol
flights from McMurdo Station, Antarctica, the system demonstrated an accuracy
of <5' rms in-flight, and <5" rms post-flight.
[Show abstract][Hide abstract] ABSTRACT: The BICEP2 collaboration has reported a strong B mode signal in the CMB
polarization, which is well fit by a tensor-to-scalar ratio of r ~ 0.2. This is
greater than the upper limit r < 0.11 obtained from the temperature
anisotropies under the assumption of a constant scalar spectral index n_s. This
discrepancy can be reduced once the statistical error and the contamination
from polarized dust are accounted for. If however a large value for r will be
confirmed, it will need to be reconciled with the temperature anisotropies
data. The most advocated explanation involves a variation of n_s with scales
that has a magnitude significantly greater than the generic slow roll
predictions. We instead study the possibility that the large scale temperature
anisotropies are not enhanced because (1) of a suppression of the scalar power
at large scales, or (2) of an anti-correlation between tensor and scalar modes.
The first possibility can be achieved for instance by a sudden change of the
speed of the inflaton; the second possibility requires breaking of Lorentz
invariance, and it also leads to violation of statistical isotropy in the
temperature data, which is (i) of O (10%) or less, and (ii) present only at
large scales. Interestingly, violation of statistical isotropy with these two
properties appears to be present both in the WMAP and Planck data.
Journal of Cosmology and Astroparticle Physics 03/2014; 2014(07). DOI:10.1088/1475-7516/2014/07/014 · 5.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We use the Hamilton--Jacobi formalism to constrain the space of possible
single field, inflationary Hubble flow trajectories when compared to the WMAP
and Planck satellites Cosmic Microwave Background (CMB) results. This method
yields posteriors on the space of Hubble Slow Roll (HSR) parameters that
uniquely determine the history of the Hubble parameter during the inflating
epoch. The trajectories are used to numerically determine the observable
primordial power spectrum and bispectra that can then be compared to
observations. Our analysis is used to infer the most likely shape of the
inflaton potential $V(\phi)$ and also yields a prediction for, $f_{\rm NL}$,
the dimensionless amplitude of the non-Gaussian bispectrum.
Journal of Cosmology and Astroparticle Physics 12/2013; 2014(08). DOI:10.1088/1475-7516/2014/08/050 · 5.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We carry out a numerical calculation of the bispectrum in generalised
trajectories of canonical, single--field inflation. The trajectories are
generated in the Hamilton-Jacobi (HJ) formalism based on Hubble Slow Roll (HSR)
parameters. The calculation allows generally shape and scale dependent
bispectra, or dimensionless $f_{NL}$, in the out-of-slow-roll regime. The
distributions of $f_{NL}$ for various shapes and HSR proposals are shown as an
example of how this procedure can be used within the context of Monte Carlo
exploration of inflationary trajectories. We also show how allowing
out-of-slow-roll behaviour can lead to a bispectrum that is relatively large
for equilateral shapes.
Journal of Cosmology and Astroparticle Physics 11/2013; 2014(09). DOI:10.1088/1475-7516/2014/09/001 · 5.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The Hamilton-Jacobi (HJ) approach for exploring inflationary trajectories is
employed in the generation of generalised inflationary non-Gaussian signals
arising from single field inflation. Scale dependent solutions for $f_{NL}$ are
determined via the numerical integration of the three--point function in the
curvature perturbation. This allows the full exploration of single field
inflationary dynamics in the out-of-slow-roll regime and opens up the
possibility of using future observations of non-Gaussianity to constraint the
inflationary potential using model-independent methods. The distribution of
`equilateral' $f_{NL}$ arising from single field inflation with both canonical
and non-canonical kinetic terms are show as an example of the application of
this procedure.
[Show abstract][Hide abstract] ABSTRACT: Templates for polarised emission from Galactic foregrounds at frequencies
relevant to Cosmic Microwave Background (CMB) polarisation experiments are
obtained by modelling the Galactic Magnetic Field (GMF) on large scales. This
work extends the results of O'Dea et al. by including polarised synchrotron
radiation as a source of foreground emission. The polarisation direction and
fraction in this calculation are based solely on the underlying choice of GMF
model and therefore provide an independent prediction for the polarisation
signal on large scales. Templates of polarised foregrounds may be of use when
forecasting effective experimental sensitivity. In turn, as measurements of the
CMB polarisation over large fractions of the sky become routine, this model
will allow for the data to constrain parameters in the, as yet, not well
understood form of the GMF.
[Show abstract][Hide abstract] ABSTRACT: The upcoming generation of cosmic microwave background experiments face a major challenge in detecting the weak cosmic B-mode signature predicted as a product of primordial gravitational waves. To achieve the required sensitivity these experiments must have impressive control of systematic effects and detailed understanding of the foreground emission that will influence the signal. In this paper, we present templates of the intensity and polarization of emission from one of the main Galactic foregrounds, interstellar dust. These are produced using a model which includes a three-dimensional description of the Galactic magnetic field, examining both large and small scales. We also include in the model the details of the dust density, grain alignment and the intrinsic polarization of the emission from an individual grain. We present here Stokes parameter template maps at 150 GHz and provide an online repository () for these and additional maps at frequencies that will be targeted by upcoming experiments such as EBEX, Spider and SPTpol.
Monthly Notices of the Royal Astronomical Society 01/2012; 419(2):1795-1803. DOI:10.1111/j.1365-2966.2011.19851.x · 5.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Model-independent parametrisations for examining departures from General
Relativity have been increasingly studied over the past few years. Various
observables have been used to constrain the parameters and forecasts for future
surveys have been carried out. In one such forecast, galaxy cluster counts were
used to constrain the parameters. Here, we carry out a limited set of $N$-body
simulations, with a modified Poisson equation, to examine the accuracy of
existing mass functions for modified gravity cosmologies. As well as altering
the gravitational calculation, we include the effect of a screening scale to
ensure consistency of the theory with solar system tests. Our results suggest
that if a screening scale exists its effect can be taken into account in the
cluster count calculation through its effect on the linear matter power
spectrum. If this is done, the accuracy of the standard mass function formalism
in modified gravity theories with reasonably small departures from General
Relativity, as tested in this work, is comparable to the standard case.
[Show abstract][Hide abstract] ABSTRACT: SPIDER is a balloon-borne instrument designed to map the polarization of the cosmic microwave background (CMB) with degree-scale resolution over a large fraction of the sky. SPIDER's main goal is to measure the amplitude of primordial gravitational waves through their imprint on the polarization of the CMB if the tensor-to-scalar ratio, r, is greater than 0.03. To achieve this goal, instrumental systematic errors must be controlled with unprecedented accuracy. Here, we build on previous work to use simulations of SPIDER observations to examine the impact of several systematic effects that have been characterized through testing and modeling of various instrument components. In particular, we investigate the impact of the non-ideal spectral response of the half-wave plates, coupling between focal-plane components and Earth's magnetic field, and beam mismatches and asymmetries. We also present a model of diffuse polarized foreground emission based on a three-dimensional model of the Galactic magnetic field and dust, and study the interaction of this foreground emission with our observation strategy and instrumental effects. We find that the expected level of foreground and systematic contamination is sufficiently low for SPIDER to achieve its science goals.
The Astrophysical Journal 08/2011; 738(1):63. DOI:10.1088/0004-637X/738/1/63 · 5.99 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Model-independent parametrisations of modified gravity have attracted a lot
of attention over the past few years and numerous combinations of experiments
and observables have been suggested to constrain the parameters used in these
models. Galaxy clusters have been mentioned, but not looked at as extensively
in the literature as some other probes. Here we look at adding galaxy clusters
into the mix of observables and examine how they could improve the constraints
on the modified gravity parameters. In particular, we forecast the constraints
from combining Planck satellite Cosmic Microwave Background (CMB) measurements
and Sunyaev-Zeldovich (SZ) cluster catalogue with a DES-like weak lensing
survey. We find that cluster counts significantly improve the constraints over
those derived using CMB and WL. We then look at surveys further into the
future, to see how much better it may be feasible to make the constraints.
Journal of Cosmology and Astroparticle Physics 07/2011; 12(12). DOI:10.1088/1475-7516/2011/12/013 · 5.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We evaluate the ability of SPIDER, a balloon-borne polarimeter, to detect a
divergence-free polarization pattern ("B-modes") in the Cosmic Microwave
Background (CMB). In the inflationary scenario, the amplitude of this signal is
proportional to that of the primordial scalar perturbations through the
tensor-to-scalar ratio r. We show that the expected level of systematic error
in the SPIDER instrument is significantly below the amplitude of an interesting
cosmological signal with r=0.03. We present a scanning strategy that enables us
to minimize uncertainty in the reconstruction of the Stokes parameters used to
characterize the CMB, while accessing a relatively wide range of angular
scales. Evaluating the amplitude of the polarized Galactic emission in the
SPIDER field, we conclude that the polarized emission from interstellar dust is
as bright or brighter than the cosmological signal at all SPIDER frequencies
(90 GHz, 150 GHz, and 280 GHz), a situation similar to that found in the
"Southern Hole." We show that two ~20-day flights of the SPIDER instrument can
constrain the amplitude of the B-mode signal to r<0.03 (99% CL) even when
foreground contamination is taken into account. In the absence of foregrounds,
the same limit can be reached after one 20-day flight.
Journal of Cosmology and Astroparticle Physics 06/2011; 2013(4). DOI:10.1088/1475-7516/2013/04/047 · 5.81 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We describe the cryogenic system for SPIDER, a balloon-borne microwave
polarimeter that will map 8% of the sky with degree-scale angular resolution.
The system consists of a 1284 L liquid helium cryostat and a 16 L
capillary-filled superfluid helium tank, which provide base operating
temperatures of 4 K and 1.5 K, respectively. Closed-cycle helium-3 adsorption
refrigerators supply sub-Kelvin cooling power to multiple focal planes, which
are housed in monochromatic telescope inserts. The main helium tank is
suspended inside the vacuum vessel with thermally insulating fiberglass
flexures, and shielded from thermal radiation by a combination of two vapor
cooled shields and multi-layer insulation. This system allows for an extremely
low instrumental background and a hold time in excess of 25 days. The total
mass of the cryogenic system, including cryogens, is approximately 1000 kg.
This enables conventional long duration balloon flights. We will discuss the
design, thermal analysis, and qualification of the cryogenic system.
Proceedings of SPIE - The International Society for Optical Engineering 06/2011; 7741. DOI:10.1117/12.857925 · 0.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We describe SPIDER, a balloon-borne instrument to map the polarization of the
millimeter-wave sky with degree angular resolution. Spider consists of six
monochromatic refracting telescopes, each illuminating a focal plane of
large-format antenna-coupled bolometer arrays. A total of 2,624 superconducting
transition-edge sensors are distributed among three observing bands centered at
90, 150, and 280 GHz. A cold half-wave plate at the aperture of each telescope
modulates the polarization of incoming light to control systematics. Spider's
first flight will be a 20-30-day Antarctic balloon campaign in December 2011.
This flight will map \sim8% of the sky to achieve unprecedented sensitivity to
the polarization signature of the gravitational wave background predicted by
inflationary cosmology. The Spider mission will also serve as a proving ground
for these detector technologies in preparation for a future satellite mission.
Proceedings of SPIE - The International Society for Optical Engineering 06/2011; DOI:10.1117/12.857720 · 0.20 Impact Factor