The CMB-S4 South Pole Large Aperture Telescope (SPLAT) team has recently authored two key scientific publications [ref. 1, ref. 2] related to the telescope and mirror designs and is working on a third publication describing the detailed optics design. In addition, Eric Chauvin Consulting has submitted to the project a SPLAT preliminary engineering design report which includes mechanical design details as well as engineering analysis. In Fig. 1, below, the SPLAT design, originally conceived by S. Padin [ref. 3] is based on a three-mirror anastigmat design with a large field of view. To reduce systemic errors the telescope incorporates co-moving shields, boresight rotation, and monolithic aluminum mirrors.
Fig. 2, below, is an example of the SPLAT structural analysis evaluating deflections and pointing errors. The image shows modal analysis results displaying the mount’s first resonance shape.
The South Pole Large Aperture Telescope incorporates a novel combination of features which will allow CMB measurements over a wide range of angular scales. The telescope’s large (~5 m) primary mirror provides the necessary angular resolution to determine the angular distortions in CMB caused by gravitational lensing from the large scale structure in the universe. These distortions lead to a low level of B-mode polarization signal that must be subtracted from the CMB measurements to detect the primordial B-mode signal. As a novel development, the telescope will provide exceptional control of systematic errors by providing co-moving shields and baffles, boresight rotation capability, and uniquely fabricated monolithic aluminum mirrors. The combination of these new features will enable unprecedented levels of sensitivity for LAT measurements of B-mode polarization on large angular scales. Fig. 3, below, shows the optical layout of the three mirror anastigmat configuration (left) plus lens arrangement of the 85 receiver optics tubes (right) located at the telescope’s final focus.
Recently, a full-scale prototype monolithic mirror was machined to required precision and delivered to the University of Chicago. Deformation tests including a mirror support structure will be performed in the near future. The photos below show the recently-completed SPLAT prototype mirror. The upper image shows the surface of the mirror after machining while the lower image shows the structural support on the backside of the mirror.
Key Dates and Upcoming Activities
The project started preparations for a Director’s Review at LBNL (November 14th to 17th, 2023). A
sequence of external subsystem conceptual design reviews is also planned for late summer to fall.
Thanks to everyone who supports the preparations for these reviews!
- CMB-S4 Summer Collaboration Meeting (at SLAC) – July 31 – Aug 3, 2023
- Subsystem Conceptual Design Reviews – July – September, 2023
- Director’s Review (at LBNL) – November 14 – 17, 2023
Originally posted in the CMB-S4 June 2023 Newsletter