J. P. Nibarger

SPTpol: an instrument for CMB polarization measurements with the South Pole Telescope

SPTpol is a dual-frequency polarization-sensitive camera that was deployed on the 10-meter South Pole Telescope in January 2012. SPTpol will measure the polarization anisotropy of the cosmic microwave background (CMB) on angular scales spanning an arcminute to several degrees. The polarization sensitivity of SPTpol will enable a detection of the CMB “B-mode” polarization from the detection of the gravitational lensing of the CMB by large scale structure, and a detection or improved upper limit on a primordial signal due to inationary gravity waves. The two measurements can be used to constrain the sum of the neutrino masses and the energy scale of ination. These science goals can be achieved through the polarization sensitivity of the SPTpol camera and careful control of systematics. The SPTpol camera consists of 768 pixels, each containing two transition-edge sensor (TES) bolometers coupled to orthogonal polarizations, and a total of 1536 bolometers. The pixels are sensitive to light in one of two frequency bands centered at 90 and 150 GHz, with 180 pixels at 90 GHz and 588 pixels at 150 GHz. The SPTpol design has several features designed to control polarization systematics, including: singlemoded feedhorns with low cross-polarization, bolometer pairs well-matched to dfference atmospheric signals, an improved ground shield design based on far-sidelobe measurements of the SPT, and a small beam to reduce temperature to polarization leakage. We present an overview of the SPTpol instrument design, project status, and science projections.

Different dynamic and static magnetic anisotropy in thin Permalloy films

The values of uniaxial anisotropy Hk in thin polycrystalline Permalloy™ films measured by static and dynamic methods differ by as much as a factor of 1.5. The anisotropy obtained with a pulsed inductive microwave magnetometer in 2.5 to 100 nm thick Permalloy films exhibits an additional isotropic component of 120 to 240 A/m not observed in static measurements. The static value of anisotropy was obtained with an inductive magnetic hysteresis loop tracer. The time-resolved precessional response was measured as a function of in-plane applied magnetic bias field and the angle between the easy axis and that of the applied bias field. We interpret the constant-offset field as a transient component of the magnetic susceptibility that affects only dynamical response at time scales below 10 ns.

Variation of magnetization and the Landé g factor with thickness in Ni–Fe films

We have measured the Lande g factor, the effective magnetization Meff, the uniaxial anisotropy Hk, and the Gilbert damping parameter α, as a function of Permalloy film thickness from 2.5 to 50 nm. We used a pulsed inductive microwave magnetometer capable of generating dc bias fields of 35.2 kA/m (440 Oe). A significant decrease in g is observed with decreasing thickness below 10 nm. Also, Meff decreases with decreasing thickness consistent with a surface anisotropy constant of 0.196±0.025 mJ/m2. The decrease in g can arise from the orbital motion of the electrons at the interface not being quenched by the crystal field. We also compare our data to a model of an effective g factor suggesting that the decrease in g factor might also stem from the Ni–Fe interface with a Ta underlayer.

A MEASUREMENT OF THE COSMIC MICROWAVE BACKGROUND GRAVITATIONAL LENSING POTENTIAL FROM 100 SQUARE DEGREES OF SPTPOL DATA

We present a measurement of the cosmic microwave background (CMB) gravitational lensing potential using data from the first two seasons of observations with SPTpol, the polarization-sensitive receiver currently installed on the South Pole Telescope. The observations used in this work cover 100 deg^2 of sky with arcminute resolution at 150 GHz. Using a quadratic estimator, we make maps of the CMB lensing potential from combinations of CMB temperature and polarization maps. We combine these lensing potential maps to form a minimum-variance (MV) map. The lensing potential is measured with a signal-to-noise ratio of greater than one for angular multipoles between 100 < L < 250. This is the highest signal-to-noise mass map made from the CMB to date and will be powerful in cross-correlation with other tracers of large-scale structure. We calculate the power spectrum of the lensing potential for each estimator, and we report the value of the MV power spectrum between 100 < L < 2000 as our primary result. We constrain the ratio of the spectrum to a fiducial ΛCDM model to be A_(MV) = 0.92 ± 0.14 (Stat.) ± 0.08 (Sys.). Restricting ourselves to polarized data only, we find A_(POL) = 0.92 ± 0.24 (Stat.) ± 0.11 (Sys.). This measurement rejects the hypothesis of no lensing at 5.9σ using polarization data alone, and at 14σ using both temperature and polarization data.

Damping as a function of pulsed field amplitude and bias field in thin film Permalloy

We have measured the step response in thin film Permalloy as a function of both a hard-axis pulsed field amplitude and an easy-axis longitudinal magnetic bias field using a pulsed inductive microwave magnetometer. The bias field ranged from 0 to 8000 A/m (0 to 100 Oe) and the pulsed field varied from 0.32 to 320 A/m (0.004 to 4 Oe). The rotation angle of the equilibrium magnetization direction varied from 0.002° to 40° for this range of field values. Data were analyzed to extract the Gilbert damping parameter, α. The damping parameter decreased monotonically with an increase in longitudinal bias field. However, there is no observed dependence of α on the pulse amplitude, indicating that the damping is independent of the angle of rotation. We conclude that there is no significant nonlinear generation of spin waves that affects the damping in the case of free induction decay for the range of field pulses employed.

The Atacama Cosmology Telescope: Two-Season ACTPol Spectra and Parameters

Author(s): Louis, T; Grace, E; Hasselfield, M; Lungu, M; Maurin, L; Addison, GE; Ade, PAR; Aiola, S; Allison, R; Amiri, M; Angile, E; Battaglia, N; Beall, JA; De Bernardis, F; Bond, JR; Britton, J; Calabrese, E; Cho, HM; Choi, SK; Coughlin, K; Crichton, D; Crowley, K; Datta, R; Devlin, MJ; Dicker, SR; Dunkley, J; Dunner, R; Ferraro, S; Fox, AE; Gallardo, P; Gralla, M; Halpern, M; Henderson, S; Hill, JC; Hilton, GC; Hilton, M; Hincks, AD; Hlozek, R; Patty Ho, SP; Huang, Z; Hubmayr, J; Huffenberger, KM; Hughes, JP; Infante, L; Irwin, K; Kasanda, SM; Klein, J; Koopman, B; Kosowsky, A; Li, D; Madhavacheril, M; Marriage, TA; McMahon, J; Menanteau, F; Moodley, K; Munson, C; Naess, S; Nati, F; Newburgh, L; Nibarger, J; Niemack, MD; Nolta, MR; Nunez, C; Page, LA; Pappas, C; Partridge, B; Rojas, F; Schaan, E; Schmitt, BL; Sehgal, N; Sherwin, BD; Sievers, J; Simon, S; Spergel, DN; Staggs, ST; Switzer, ER; Thornton, R; Trac, H; Treu, J; Tucker, C; Engelen, AV; Ward, JT; Wollack, EJ | Abstract:

Measurements of E-mode polarization and temperature-E-mode correlation in the cosmic microwave background from 100 square degrees of SPTPOL data

We present measurements of E-mode polarization and temperature-E-mode correlation in the cosmic microwave background using data from the first season of observations with SPTpol, the polarization-sensitive receiver currently installed on the South Pole Telescope (SPT). The observations used in this work cover 100 deg^2 of sky with arcminute resolution at 150 GHz. We report the E-mode angular auto-power spectrum (EE) and the temperature-E-mode angular cross-power spectrum (TE) over the multipole range 500 < l ≤ 5000. These power spectra improve on previous measurements in the high-l (small-scale) regime. We fit the combination of the SPTpol power spectra, data from Planck, and previous SPT measurements with a six-parameter ΛCDM cosmological model. We find that the best-fit parameters are consistent with previous results. The improvement in high-l sensitivity over previous measurements leads to a significant improvement in the limit on polarized point-source power: after masking sources brighter than 50 mJy in unpolarized flux at 150 GHz, we find a 95% confidence upper limit on unclustered point-source power in the EE spectrum of D_l = l(l + 1) C_l/2π < 0.40 µK^2 at l = 3000, indicating that future EE measurements will not be limited by power from unclustered point sources in the multipole range l < 3600, and possibly much higher in l.

Corrugated silicon platelet feed horn array for CMB polarimetry at 150 GHz

Next generation cosmic microwave background (CMB) polarization anisotropy measurements will feature focal plane arrays with more than 600 millimeter-wave detectors. We make use of high-resolution photolithography and wafer-scale etch tools to build planar arrays of corrugated platelet feeds in silicon with highly symmetric beams, low cross-polarization and low side lobes. A compact Au-plated corrugated Si feed designed for 150 GHz operation exhibited performance equivalent to that of electroformed feeds: ~ -0.2 dB insertion loss, < -20 dB return loss from 120 GHz to 170 GHz, < -25 dB side lobes and < -23 dB cross-polarization. We are currently fabricating a 50mm diameter array with 84 horns consisting of 33 Si platelets as a prototype for the SPTpol and ACTpol telescopes. Our fabrication facilities permit arrays up to 150mm in diameter.

Measurements of the Temperature and E-mode Polarization of the CMB from 500 Square Degrees of SPTpol Data

We present measurements of the

Performance and on-sky optical characterization of the SPTpol instrument

E