Year two instrument status of the SPT-3G cosmic microwave background
  receiver
  The South Pole Telescope (SPT) is a millimeter-wavelength telescope designed
for high-precision measurements of the cosmic microwave background (CMB). The
SPT measures both the temperature and polarization of the CMB with a large
aperture, resulting in high resolution maps sensitive to signals across a wide
range of angular scales on the sky. With these data, the SPT has the potential
to make a broad range of cosmological measurements. These include constraining
the effect of massive neutrinos on large-scale structure formation as well as
cleaning galactic and cosmological foregrounds from CMB polarization data in
future searches for inflationary gravitational waves. The SPT began observing
in January 2017 with a new receiver (SPT-3G) containing $\sim$16,000
polarization-sensitive transition-edge sensor bolometers. Several key
technology developments have enabled this large-format focal plane, including
advances in detectors, readout electronics, and large millimeter-wavelength
optics. We discuss the implementation of these technologies in the SPT-3G
receiver as well as the challenges they presented. In late 2017 the
implementations of all three of these technologies were modified to optimize
total performance. Here, we present the current instrument status of the SPT-3G
receiver.
