The Primordial Inflation Polarization Explorer (Piper) is a balloon-borne cosmic microwave background (CMB) polarimeter designed to search for evidence of inflation by measuring the large-angular scale CMB polarization signal. Bicep2 recently reported a detection of B-mode power corresponding to the tensor-to-scalar ratio r = 0:2 on 2 degree scales. If the Bicep2 signal is caused by inflationary gravitational waves (IGWs), then there should be a corresponding increase in B-mode power on angular scales larger than 18 degrees. Piper is currently the only suborbital instrument capable of fully testing and extending the Bicep2 results by measuring the B-mode power spectrum on angular scales ϴ =~0:6° to 90°, covering both the reionization bump and recombination peak, with sensitivity to measure the tensor-to-scalar ratio down to r = 0:007, and four frequency bands to distinguish foregrounds. Piper will accomplish this by mapping 85% of the sky in four frequency bands (200, 270, 350, 600 GHz) over a series of 8 conventional balloon flights from the northern and southern hemispheres. The instrument has background-limited sensitivity provided by fully cryogenic (1.5 K) optics focusing the sky signal onto four 32x40-pixel arrays of time-domain multiplexed Transition-Edge Sensor (TES) bolometers held at 140 mK. Polarization sensitivity and systematic control are provided by front-end Variable- delay Polarization Modulators (VPMs), which rapidly modulate only the polarized sky signal at 3 Hz and allow Piper to instantaneously measure the full Stokes vector (I; Q;U; V ) for each pointing. We describe the Piper instrument and progress towards its first flight.
The Primordial Inflation Polarization Explorer (PIPER) is a balloon-borne instrument to measure the gravitational wave signature of primordial inflation through its distinctive imprint on the polarization of the cosmic microwave background. PIPER combines cold (1.5 K) optics, 5120 bolometric detectors, and rapid polarization modulation using VPM grids to achieve both high sensitivity and excellent control of systematic errors. A series of flights alternating between northern and southern hemisphere launch sites will produce maps in Stokes I, Q, U, and V parameters at frequencies 200, 270, 350, and 600 GHz (wavelengths 1500, 1100, 850, and 500 μm) covering 85% of the sky. The high sky coverage allows measurement of the primordial B-mode signal in the `reionization bump" at multipole moments l < 10 where the primordial signal may best be distinguished from the cosmological lensing foreground. We describe the PIPER instrument and discuss the current status and expected science returns from the mission.
The Primordial Inflation Polarization Explorer (PIPER) is a balloon-borne instrument designed to search for
the faint signature of inflation in the polarized component of the cosmic microwave background (CMB). Each
flight will be configured for a single frequency, but in order to aid in the removal of the polarized foreground
signal due to Galactic dust, the filters will be changed between flights. In this way, the CMB polarization at a
total of four different frequencies (200, 270, 350, and 600 GHz) will be measured on large angular scales. PIPER
consists of a pair of cryogenic telescopes, one for measuring each of Stokes Q and U in the instrument frame.
Each telescope receives both linear orthogonal polarizations in two 32 × 40 element planar arrays that utilize
Transition-Edge Sensors (TES). The first element in each telescope is a variable-delay polarization modulator
(VPM) that fully modulates the linear Stokes parameter to which the telescope is sensitive. There are several
advantages to this architecture. First, by modulating at the front of the optics, instrumental polarization is
unmodulated and is therefore cleanly separated from source polarization. Second, by implementing this system
with the appropriate symmetry, systematic effects can be further mitigated. In the PIPER design, many of the
systematics are manifest in the unmeasured linear Stokes parameter for each telescope and thus can be separated
from the desired signal. Finally, the modulation cycle never mixes the Q and U linear Stokes parameters, and
thus residuals in the modulation do not twist the observed polarization vector. This is advantageous because
measuring the angle of linear polarization is critical for separating the inflationary signal from other polarized
Adiabatic demagnetization refrigerators (ADRs) can provide very low temperatures (< 100mK), making them
an attractive option for cooling millimeter and submillimeter detectors. One drawback to their use has been
the bulky electronic equipment that was often needed to operate them. In this paper, we present a compact,
ADR controller that is designed for applications such as scientific ballooning and spaceflight where weight and
reliability are primary concerns. The complete controller is contained on a 160mm by 100mm circuit card. A
prototype has been tested with a single-stage ADR system. A minimum temperature of 180mK was achieved
and stable control was demonstrated with an RMS temperature noise of 4.4 uK and a 1/f knee of order 1mHz.
The dominant source of noise is digitization noise in the thermometer readout. Three cards on a backplane
are currently being set up to control a three-stage ADR that is designed for continuous operation at 100mK.
Additionally, a lower noise control card is under development.
QUaD is a ground-based high-resolution (up to l ≈ 2500) instrument designed to map the polarisation of the Cosmic Microwave Background and to measure its E-mode and B-mode polarisation power spectra. QUaD comprises a bolometric array receiver (100 and 150 GHz) and re-imaging optics on a 2.6-m Cassegrain telescope 2. It will operate for two years and begin observations in 2005. CMB polarisation measurements will require not only a significant increase in sensitivity over earlier experiments but also a better understanding and control of systematic effects particularly those that contribute to the polarised signal. To this end we have undertaken a comprehensive quasi-optical analysis of the QUaD telescope. In particular we have modelled the effects of diffraction on beam propagation through the system. The corrugated feeds that couple radiation from the telescope to phase-sensitive bolometers need to have good beam symmetry and low sidelobe levels over the required bandwidth. It is especially important that the feed horns preserve the polarisation orientation of the incoming fields. We have used an accurate mode-matching model to design such feed horns. In this paper we present the diffraction analysis of the QUaD front-end optics as well as the electromagnetic design and testing of the QUaD corrugated feeds.
We look at anticipated science results achievable with QUaD, a ground-based experiment to measure the polarization of the CMB from the South Pole, and describe the features that will enable it to measure this weak polarized signal. We show that QUaD can make a high resolution measurement of the polarization signals on small angular scales. This will lead to tighter constraints on the key cosmological parameters and could also put new limits on the inflationary model.