cmbpol technology v2

Technology Requirements for CMBpol: 

Technology Requirements for CMBpol Sarah Church Stanford University May 7th 2002 With input (and pictures) from Jamie Bock, Andrew Lange, Harvey Moseley, Lyman Page

The sensitivity increase required: 

The sensitivity increase required 40 20† 20-100 Exact number will be the result of studies A lot of the sensitivity increase for MAP and Planck has come from improvements in detector sensitivity, but Planck is close to the background limit Polarization sensitivity 30K† per 5 arcmin pixel to Q and U MAP COBE †Planck spec. Mission-realized sensitivity is expected to be much better

The Planck HFI: 

The Planck HFI 50 feeds in a focal plane of ~ 1kg at 100mK Focal plane area ~ 2 square degrees Instantaneous sky coverage per polarization-sensitive frequency about: 0.1 square degrees The HFI also has channels at 100, 545 and 850 GHz that are not polarization sensitive

Slide4: 

Assuming 0.5K RJ instrument background, 50% optical efficiency for the bolometers and 30% bandwidth for both bolometers and HEMTs Numbers from Lange, unpublished proceedings of Monterey detector workshop, April 2002 Bolometers or HEMTs or something else? Bolometers have the highest raw sensitivity, especially at higher frequencies. Array technology is more developed. HEMTs are somewhat easier to operate, but x5 longer mission time required. The Planck solution of technology mixing in the focal plane should be avoided.

So how can a x100 sensitivity increase be achieved?: 

So how can a x100 sensitivity increase be achieved? 3 over Planck spec by reducing the detector noise close to the CMB BLIP limit Requires a cold telescope (10K) and careful control of stray-light Alternative detector technologies (TES bolometers, Kinetic Inductance Detectors) may come closer to the BLIP limit than Ge bolometers. 16 if the instantaneous sky coverage per frequency is increased from 0.1 to 25 square degrees Requires arrays of > 2000 polarization-sensitive detectors at each frequency frequency multiplexing to obtain 50-500 GHz from each pixel simultaneously An optimized focal plane array of 5 5 degrees 2 from increase in mission lifetime

Frequency-multiplexing: 

Frequency-multiplexing Dichroic beam-splitters can be used, but the instrument becomes large, Frequency multiplexing of bolometers using microstrip filters is under investigation A design (courtesy J. Bock) for a frequency-selective polarization-sensitive array coupled to TES bolometers

Other Technology Requirements for CMBPol: 

Other Technology Requirements for CMBPol Readout electronics CMBPol could have > 10,000 detectors – 200 times more than the HFI. Need low power, multiplexed readout – SQUIDs? Optical Coupling Cold optics: Instrument loading degrades the HFI sensitivity by 60% compared to the CMB BLIP Low cross-polarization and instrumental polarization Polarization modulation may be desirable to reduce systematics Cryogenics 100mK operating temperature if bolometers are used Very stable control of intermediate temperature stages used to cool filters and shields.

Other Technology Requirements for CMBPol (cont): 

Other Technology Requirements for CMBPol (cont) Learn how to use this technology and how to make the measurements “Sensitivity to polarization does not a polarimeter make”attributed to Roger Hildebrand

The importance of coupling correctly to the sky with low spillover onto cold optics: 

The importance of coupling correctly to the sky with low spillover onto cold optics Filled arrays are attractive to maximize use of focal plane space, but instrument loading is an issue

Polarization Modulation: 

Polarization Modulation Spacecraft rotation: Modulates location of pixels on the sky as well as the orientation of the polarimeter Cold rotating waveplate or an equivalent solid-state polarization rotation system Separates the functions of polarization modulation and spatial modulation Both of these methods will be hard to implement in a satellite.

Cooling technology: 

Cooling technology Technology overlap with Con-X 10K mechanical cooler + ADR Cooler options: pulse tube, turbo-Brayton ADR has more cooling power than the Planck dilution fridge Intermediate stages of will cool optics, telescope. CMBpol requirements 100mK operating temperature if bolometers are used Very stable control of intermediate temperature stages used to cool filters and shields.

The role of ground and balloon based experiments in previous missions: 

The role of ground and balloon based experiments in previous missions MAP Boomerang Planck Saskatoon

Technologies that will be tested on the ground or in balloons before CMBpol or Planck: 

Technologies that will be tested on the ground or in balloons before CMBpol or Planck Experiments existing or under construction Polarization-sensitive bolometers (Boomerang, QUEST, BICEP) Polarization modulation techniques Warm waveplates (DASI, CBI) Cold waveplate (MAXIPOL, QUEST) Faraday rotation in cylindrical waveguide (BICEP) HEMT arrays (CAPMAP) Planned Experiments Antenna-coupled, frequency selective bolometers (Polarbear and others) Ground-based experiments can operate continuously for periods comparable to CMBPol – vital for testing component lifetimes, and to investigate systematic effects.