Universities Space Research Association Page 1 HAWC Optical and Photometric Specifications 27 July 2007

Universities Space Research Association Page 2

Universities Space Research Association Page 3 Results from June 07 Lab Tests Observed per-pixel backgrounds from external radiation (as determined from iv curves) are 84% to 134% of predicted values for lab conditions (based on analysis of data from backplane QRST-- limited data from other backplanes are consistent with the comparable QRST data). Internal backgrounds are too high (comparable to those expected for SOFIA external backgrounds). Likely cause is high temperature of OMS structure (10-12K). We expect to be able to reduce this by increasing the thermal conductivities of the OMS structure and adding additional 4K baffling (need ~ 4-5 times reduction in power). Performance of 200mK baffle meets requirements. Background observed when baffle is covered by a mirror is less than or equal to 2-3 pW. Mechanisms work well, but position sensors need to be replaced with a more reliable, lower power system. Temperature rise caused by lens carousel and pupil carousel motors is relatively small. Thermal effect of PRL mechanism motor is more significant, but not mission critical. Substitution of motors with superconducting windings is expected to reduce the effects to negligible levels. Time for JFET drawers to reach operating temperature is ~20-30 minutes. Increasing the current capacity for the circuits driving the heater resistors is expected to ameliorate the problem. Can probably do this without risk to bridge chips.

Universities Space Research Association Page 4 Optics Modifications for Polarimetery Current HAWC optics can accommodate 32x32 pixel detector out to the longest wavelength of 216 microns. A larger detector could be accommodated in the short-wavelength bands. The diameter of the pupil carousel can be increased by several inches if the mechanism is driven by a spur gear rather than a geneva mechanism. If the maximum thickness of half- wave-plate rotating mechanisms is less than about 1.25 inches, they could fit within the currently available space within the OMS. Fabrication of a new pupil plate (the sky-side bulkhead of the OMS system) would minimize the down-time for a conversion. Dual detectors can fit within the current volume between OMS and helium cold plate if we use TES detectors rather than ion-implanted silicon detectors (the size reduction results primarily from substitution of multiplexed SQUID readouts for JFETS). Upgrading to polarimetry can be accomplished in stages. For example: installation of cold half-wave plates, installation of a larger TES detector, installation of dual TES detectors. The time to implement stage one would be limited only by the time to fabricate the mechanisms (and available funding). Possibly of order one year for fabrication and component testing and 3-6 months for integration and testing within HAWC (?). Time scale for detectors is probably somewhat longer (2-3 years ?).