Design of 280 GHz feedhorn-coupled TES arrays for the balloon-borne polarimeter SPIDER

Abstract

We describe 280 GHz bolometric detector arrays that instrument the balloon-borne polarimeter spider. A primary science goal of spider is to measure the large-scale B-mode polarization of the cosmic microwave background (cmb) in search of the cosmic-inflation, gravitational-wave signature. 280 GHz channels aid this science goal by constraining the level of B-mode contamination from galactic dust emission. We present the focal plane unit design, which consists of a 16×16 array of conical, corrugated feedhorns coupled to a monolithic detector array fabricated on a 150 mm diameter silicon wafer. Detector arrays are capable of polarimetric sensing via waveguide probe-coupling to a multiplexed array of transition-edge-sensor (TES) bolometers. The spider receiver has three focal plane units at 280 GHz, which in total contains 765 spatial pixels and 1,530 polarization sensitive bolometers. By fabrication and measurement of single feedhorns, we demonstrate 14.7• FHWM Gaussian-shaped beams with <1% ellipticity in a 30% fractional bandwidth centered at 280 GHz. We present electromagnetic simulations of the detection circuit, which show 94% band-averaged, single-polarization coupling efficiency, 3% reflection and 3% radiative loss. Lastly, we demonstrate a low thermal conductance bolometer, which is well-described by a simple TES model and exhibits an electrical noise equivalent power (NEP) = 2.6 × 10 −17 W/ √ Hz, consistent with the phonon noise prediction.

Microwave SQUID multiplexer demonstration for cosmic microwave background imagers

“…To obtain an expression of phonon noise, we assume the radiative transfer model of Boyle and Rogers 20 which we find to be a good match for our devices. 21,22 When recast in terms of the variables defined in Eq. 1, we obtain the following expression for phonon NEP, $${\mathit{\text{NEP}}}_G=\sqrt{2k_b\text{italicTPn}\frac{1+{false(T_b/Tfalse)}^{n+1}}{1-{false(T_b/Tfalse)}^n}}.$$…”

SPIDER: CMB Polarimetry from the Edge of Space

“…The SPIDER collaboration is preparing for a second observing flight in Dec. 2018, also on an Antarctic LDB. This flight will incorporate three new receivers to map the same sky at 280 GHz, using feedhorn-coupled arrays of AlMn TES polarimeters developed at NIST 29,30 . The resulting 280 GHz data will yield maps of galactic dust polarization over a large sky fraction at a frequency in between the existing Planck sky maps, which will have lasting value in the field.…”

280 GHz Focal Plane Unit Design and Characterization for the Spider-2 Suborbital Polarimeter

“…Every TES bolometer island contains two sensors in series with differing superconducting critical temperatures (T c ): a 420 mK T c aluminum-manganese (AlMn) sensor for flight operations and a 1.6 K T c Al sensor for on the ground pixel characterization. 12,[14][15][16][17] In total, the three SPIDER-2 280 GHz focal planes contain 765 spatial pixels and 1,530 polarization sensitive bolometers. These exhibit an electrical noise equivalent power (NEP) = 2.6 × 10 −17 W/ √ Hz, as reported in Hubmayr, et al, 2016.…”

“…Details of the sensor array and detector stack, including corrugated feedhorns and pixel fabrication, are well-described in previous publications. 12,14…”

“…9 The second flight is scheduled for December 2018 and will re-deploy three proven SPI-DER-1 telescopes alongside three NIST-fabricated feedhorn-coupled 280 GHz TES focal plane units (FPUs). 12 Otherwise, SPIDER-2 will have effectively the same construction as the first instrument.…”