Cryogenics for B-PolS. Masi, reporting from

F.X. DesertL. Piccirillo

….

Use SAMPAN as a baseline, and look for improvements/variations

FXD BPol Cryogenics Roma30/03/2007 p. 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 Roma30/03/2007 p. 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 StudyCNRS: F. Bouchet (Sampan leader) M. Piat, N. Ponthieu, M. Bucher, A. Benoit, Ph.

Camus

CNES/PASO: J. Michaud (Study leader) Alcatel Alenia Space: Ph. DesmetAir Liquide: S. Triqueneaux

FXD BPol Cryogenics Roma30/03/2007 p. 4

Constraints

Cryogenic needs :1µW @ 150mK (Integrated power between 2 K & 150 mK) or a bit less power @ 100 mK.800µW @ 2K: Electronics + optics12mW @ 8K: Electronics + optics

Launch constraintsOperations before launchwithstanding vibrations

Mass/Volume/Cryogenic lifetimeActive or passive regulations of thermal stages

FXD BPol Cryogenics Roma30/03/2007 p. 5

Constraints

Cryogenic needs :1µW @ 150mK (Integrated power between 2 K & 150 mK) or a bit less power @ 100 mK.800µW @ 2K: Electronics + optics12mW @ 8K: Electronics + optics

Launch constraintsOperations before launchwithstanding vibrations

Mass/Volume/Cryogenic lifetimeActive 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 Roma30/03/2007 p. 6

Thermal architecture : concept 1SAMPANSAMPAN

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

Dilution

300 mm

350 mm

350 mm

540 mm

20°

< 5

00 m

K2

K

< 8 K

2K

< 8K

320 mm

phi int réservoir : 500 mm

L2

FPhau

teu

r ré

serv

oir

: 1

200

mm

L1

Cryostat: enceinte au vide

2K

Structure 100K

SVM

SH2

GHeGHe DCCU

100mK

2K

8K

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 heavierMass 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 JWSTCryogenic 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

Cryostat Param

Nb of shields (CVV -> Tank)

Inner Temp

(K)

CVV Temp

(K)

Tank Inner P

(Pa)

Cryogen flow

(mg/s)

Cryogen* Overall Tank IDCVV OD

CVV height

SH2 2 8 43 15 0,21 21 109 0,5 0,92 1,71LHe 3 2 34 3,1 0,74 88 352 0,5 1,26 1,66

* Main Cryogen only

Main Dim(m)

Mass(kg)

SAMPAN SubKelvin Cooler :- Heritage from Planck HFI dilution cooler- Modifications: - more power at 100 - 200 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- 300 mK (JT of 3He) is not continuous and reduces sensitivity

Planck “demonstrator”

Other option : ADRPROs 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 Roma30/03/2007 p. 13