Elizabeth George


SPT-SZ on the South Pole Telescope

SPT-pol on the South Pole Telescope

The SPT is a 10-meter telescope that has surveyed 2500 square degrees of sky at 1.4, 2.0, and 3.0 mm wavelengths with arcminute resolution and micro-Kelvin sensitivity. The first phase of the SPT project will produce three main science products: 1) a measurement of primary and secondary CMB anisotropies, 2) a survey of galaxy clusters found via the SZ effect, and 3) a survey of high-redshift mm-wave bright star forming galaxies. The SPT survey was completed in November 2011, and data analysis of the complete survey is ongoing.

Photo (left): SPT, the dark sector lab, and the full moon.

I deployed to the South Pole twice for SPT-sz, each time installing new detectors that were built and tested in the lab in Berkeley to increase the sensitivity of the focal plane. The detectors used in SPT-sz are transition edge sensor (TES) spiderweb bolometers cooled to 250mK. The TESes are an AlTi bilayer which is tightly coupled to a Bandwidth Limiting Interface of Normal Gold (BLING). There are a total of 960 detectors split between three bands at 90, 150, and 220 GHz. I am currently working on the high-ell power spectrum data analysis of the complete 2500 square degree survey.

Photos (below, left to right): 1) TES thermisitor with Al leads and gold bling. 2) Spiderweb absorber. 3) Array of 160 bolometers with LC board and horn array. 4) Assembled focal plane with bandpass filters on mK stage assembly.

In January 2012, the SPT was equipped with a polarization receiver, SPT-pol. It will map 600 square degrees at 2 and 3 mm wavelength to a depth four and six times deeper, respectively, than the SPT-sz survey. The primary science goals are to measure the mass of the neutrino and to search for primordial gravity waves from inflation, by measuring their signatures in the polarization of the CMB.

I worked on the SPT-pol detector development and focal plane design, and deployed to the south pole in December 2011 to deploy the SPT-pol receiver on SPT, and again in November 2012 to upgrade the SPT-pol camera for higher sensitivity. Analysis of the first year data is ongoing.

The detectors for SPT-pol are TESes which employ two technologies to couple to polarized radiation. The 90 GHz detectors (fabricated at Argonne national lab) are dipole absorbers in a waveguide coupled to a contoured feedhorn. The 150 GHz detectors (fabricated at NIST) are orthomode transducers that are waveguide coupled to silicon micromachined corrugated feedhorns.

Photos (below, left to right): 1) 150 GHz pixel with othomode transducer, and X,Y, and Dark TESes. 2) 150GHz TES with gold bling. 3) Silicon micromachined feedhorns. 4) 90 GHz pixel with two dipole absorbers. 5) 90GHz dipole absorber for one polarization.


Photo (above): Me aligning optical filters on the receiver cryostat.