![]() ![]() The thermal architecture is separated into a two-stage pulse tube cryocooler The epoxy is machined to the correct thickness and laser diced to 1cm squares to mitigate differential thermal contraction between alumina and the epoxy.įigure 6: Cutaway view of the BICEP3 cryogenic receiver. The alumina filter is coated with a mix of Stycast 10FT. The original design was a stack of metal-mesh filters, which was replaced in 2017.įigure 5: AR coated alumina filter in BICEP3. This photo shows the current configuration, with each layer composed of 3.17mm thick HD-30 foam, glued onto a stack of aluminum frames with 3.17mm spacing. ![]() The 300K metal-mesh filters were replaced by a stack of 10 Zotefoam filters in 2017, which improved both the IR loading on the cryostat, and the in-band power incident on the detectors.įigure 4: Stack of 10 layers room temperature IR filters installed in BICEP3, immediately behind the vacuum window. In both photos, two ball-end rod joints act as torque arms to transmit the azimuth rotation to the rotor of the HRJ.įigure 3: Ray diagram including the elements of the optical chain. Right: Static section with the 4 connections for the high and low pressure helium and their respective guard channels. Left: Two 30-degree bends rotate with the azimuth axis and go on to the receiver through the elevation and boresight axes. The three-axis mount previously used in BICEP1 and BICEP2 allows for motion in azimuth, elevation, and boresight rotation.Ī co-moving absorptive forebaffle extends skyward beyond the cryostat receiver to intercept stray light outside the designed field-of-view.Īdditionally, the telescope is surrounded by a stationary reflective ground shield which redirects off-axis rays to the cold sky.įigure 2: Photos of the 4-channel helium Rotary Joint system. The insulating environmental shield shown in the bottom right photo is hidden in the CAD layout. ![]() Figure 1: The BICEP3 telescope in the mount, looking out through the roof of the Dark Sector Laboratory (DSL) located \(\sim 800\)m from the geographic South Pole.
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