This austral summer season at Pole, our primary objective is to install the SPT-3G camera. SPT-3G is the third generation camera to be installed on the South Pole Telescope. This camera will be a major step forward in mapping and studying the Cosmic Microwave Background. How well we can measure this cosmic signal scales with the number of detectors in our camera; SPT-3G will increase the number of detectors by 10-fold over the previous SPTpol camera. Additionally, each detector is sensitive to one of three frequencies of light; 3G has roughly the same sensitivity to these three frequencies. With these improvements, I am very excited about analyzing the data we will take with this camera!
In my first month here at Pole, we assembled the 3G camera. Here is a photo-essay of the assembly process.
Removing SPTpol:
As the first step, we took down the SPTpol secondary mirror cryostat and camera.
[Removing the SPTpol secondary mirror cryostat from the receiver cabin]
[Loading 3G and unloading SPTpol crates using a fork-lift on a snow ramp]
Optics Bench Installation:
The optics bench holds the secondary and tertiary mirror, and has the ability to move so we can focus the camera. The optics bench was assembled outside the telescope building, then lifted into place with a crane.
[After assembly, Josh and Jessica measure the optics bench before it is installed.]
[Lifting the optics bench into place on the telescope.]
[Looking up at the newly installed optics bench from inside the receiver cabin.]
Camera Assembly (milli-Kelvin stage, detectors, cold detector readout):
Grossly over-simplifying, the camera consists of detectors that absorb the CMB light, and electronics that read out the detectors. These detectors operate at 0.260 Kelvin, just above absolute zero.
[The detector array. The small white domes are lenslets that focus light onto each pixel. Each pixel in turn contains 6 detectors: 3 frequencies and two polarizations per frequency. Here we have installed 2 detector wafers; the full focal plane will contain 10 wafers.]
[Cold readout electronics (specifically the LC towers) are mounted below the detectors.]
[The full focal plane and mili-Kelvin stage]
[Amy and Josh after assembling the detector stage.]
[The detector stage is then mounted into the camera cryostat body so it can be cooled and operated.]
Fridge Assembly:
The camera is cooled in several stages. The final stage is cooled to 260 mili-Kelvin with a Chase Fridge.
[Chase Fridge, ready to be installed]
[Installing the fridge in the camera cryostat.]
[View of a physicist: Josh installing heat-straps on the fridge.]
[Just finished sealing up the gaps after installing the fridge.]
Lens Assembly:
A series of lenses are used to focus incoming light onto the detectors.
[Preparing a lens for mounting.]
[Matt working on a lens mount.]
[The team mounting an optics tube over a lens Photo: Robert Guyser]
Finished camera Assembly:
[The camera, fully assembled. Photo: Robert Guyser]
[The team and the camera!]
Test Mount of the camera:
We tested lifting all ~2500 lbs of the camera assembly into the telescope receiver cabin and mounting it in place. It took all day, but it fit!
[Adam, Matt, and Amy, mounting the warm readout electronics.]
[John and Josh preparing to lift the camera into the cabin.]
[Jessica, Eric, Amy, Brad and JT start lifting the camera using chain-hoists.]
[Starting the lift.]
[It fits! Dinner time, then we took it right back down.]
Now that the camera is assembled, we are working hard to make it work well. Stay tuned!
