Cryogenics for B-Pol S. Masi, reporting from F.X. Desert L. Piccirillo …. Use SAMPAN as a baseline, and look for improvements/variations

FXD BPol Cryogenics Roma30/03/2007p. 2 Bpol Cryogenics : main drivers Provide cooling of the detectors Additional cooling for other parts of the detection chain Stable environment for the optics & baffle Accomplished by a succession of thermal stages  Shields  Passive cooling: V-grooves  Main Cryostat: to reach T < 8 K to lower the optical background  SubKelvin cooler For a total lifetime of 2.5 years + margins François-Xavier Désert (LAOG) Grenoble

FXD BPol Cryogenics Roma30/03/2007p. 3 Cryogenic Architecture The satellite architecture is built around the cryogenics The cold payload needs to be protected from the sun and the SVM with thermal screens, with incidences up to +/- 90° from the satellite axis, and at the same time the cooling philosophy based on passive first stages requires a large factor of view of the payload to the space. Shield, V-grooves, and cryostat = PLM cylindrical SVM Examples drawn from Sampan Phase 0 Study CNRS: F. Bouchet (Sampan leader) M. Piat, N. Ponthieu, M. Bucher, A. Benoit, Ph. Camus CNES/PASO: J. Michaud (Study leader) Alcatel Alenia Space: Ph. Desmet Air Liquide: S. Triqueneaux

FXD BPol Cryogenics Roma30/03/2007p. 4 Constraints Cryogenic needs : 150mK (Integrated power between 2 K & 150 mK) or a bit less 100 mK. 2K: Electronics + optics 8K: Electronics + optics Launch constraints Operations before launch withstanding vibrations Mass/Volume/Cryogenic lifetime Active or passive regulations of thermal stages

FXD BPol Cryogenics Roma30/03/2007p. 5 Constraints Cryogenic needs : 150mK (Integrated power between 2 K & 150 mK) or a bit less 100 mK. 2K: Electronics + optics 8K: Electronics + optics Launch constraints Operations before launch withstanding vibrations Mass/Volume/Cryogenic lifetime Active or passive regulations of thermal stages These numbers depend strongly on the size of the focal plane: Variations have a huge impact

FXD BPol Cryogenics Roma30/03/2007p. 6 SAMPAN Thermal architecture : concept 1 SAMPAN V-grooves to keep the cryostat shell at 40K. Like Planck, but with grooves folded forward, to allow operation from antisun to 90 deg from sun

Schematic Drawing of the Cryostat Note that the SAMPAN telescope is small (30 cm) !! If you increase the size, the cryostat will grow a lot

Main Results for the Cryostat Both cryostats have similar dimensions (helium slightly larger)  Overall mass for LHe / SH2 : LHe about 3 times heavier  Mass of LHe strongly depends on last V-Groove temperature (80K => + 60 kg on the overall mass)  Type of detector (High-Imp or TES) has a reduced impact on overall mass (< 10 %)  Heritage from ISO, Herschel, Studies for JWST  Cryogenic machines could be considered as an intermediate stage: e.g. a 4 K improved version of Planck HFI cooler. But otherwise Sorption machines (no vibrations) are heavy/voluminous and not considered further

SAMPAN SubKelvin Cooler : - Heritage from Planck HFI dilution cooler - Modifications: - more power at mK : 800nW (200nW for Planck) - start from an initial stage at 8 K (if SH2 retained) instead of 4.5 K - store He isotopes into the main cryostat (no more high pressure tanks) - Develop closed cycle dilution to increase lifetime and reduce 3He cost. But not off-the- shelf yet. - ADR is less developed in Europe mK (JT of 3He) is not continuous and reduces sensitivity Planck “demonstrator”

Other option : ADR PROs more power at 100 mK (5  W) – needed if we widen the focal plan to accomodate lower f Intrinsically gravity independent Tested on balloons and rocket flights (McCammon) CONs Cycling and Power required Safety issues for superconducting magnet (but see AMS)

European Expertise CRTBT, RAL, ALCATEL, Air Liquide – see Planck Other possibilities:  in Italy Galileo, ALENIA, RIAL …  In Germany Vericold, MAN …

FXD BPol Cryogenics Roma30/03/2007p. 12 SAMPAN Instrument SAMPAN Internal view Internal view L1 L2 Focal plane Dilution L1 L2 0.5 K baffle Dilution Thermal straps at 0.5 K points Ray-tracing and baffling are key technologies to control sidelobes and straylight

FXD BPol Cryogenics Roma30/03/2007p. 13