SAT Thermal Analysis

and Verification

John Groh (he/him)�May 2, 2024

1

Quick design recap

• 3 optics tubes per mount with shared vacuum space and sub-Kelvin refrigeration
• 1 x Bluefors SD400 (or similar)
• 2+1 x Cryomech PT410s
• Cryogenic design largely driven by power footprint, which is dominated by the PTCs

75.5 kW + 12 kW + 6 kW = 93.5 kW ≤ 93.5 kW

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• Aggressive cryogenic design w/ notable risk
• Mitigating w/ R&D into alternative configurations and prototyping

2

Project workshop | May 2024

(SSAs likely to mount at 4k instead)

(slight PTC geometry change since this rendering)

100mK

1K

4K

50K

300K

Cryostat

Mount

Readout

Steady state total

SAT site budget

Steady state

• Current status:
• Nodal estimate structure for estimating heat loads
• IR: adapted/updated from BICEP model
• Supports: spreadsheet macro integrals w/ hand-curated material properties
• Radiation: idealized MLI w/ no conduction terms
• Readout: from Readout L3 via readout_load_calculator
• Large uncertainties & tight budget!
• Initial estimates have been made of gradients across metal bodies w/ FEA and basic formulae
• Possible directions for future development:
• Update as design evolves (e.g. strut geometries, wire count)
• Iterate on model assumptions and methods based on prototype tests (esp. IR, MLI, (+readout))
• Enable generating full set of thermal loads w/ new assumptions from single program
• Document methods and assumptions
• Account for fridge capacity curves
• Progress beyond nodal description

3

Project workshop | May 2024

FEA study reference

(Some inconsistencies and omissions found while filling this table - revisit needed…)

50K and 1K budgets currently tightest w/ largest estimated contribution from optical loading

Steady state: optical loading

• Methodology from Jamie Bock, Denis Barkat, Lingzhen Zeng, David Goldfinger
• “Conventional” model integrating over photon distributions, featuring:
• Radial temperature gradients
• Non-constant thicknesses
• Temperature dependent thermal conductivities (hand curated)
• Constant optical properties w/ temperature (hand curated)
• Link to reports and model code
• Would be interesting to compare to other calculators (incl. the ACT/SO-style ray tracing method)

4

Project workshop | May 2024

Cooldown time

• Naive scaling from Simons Observatory SAT suggests unaided cooldown (~8 days) will be too long
• We have ~3x the payload and ~3/4ths the cooling power
• Initial requirement from I&C scheduling concerns (CMBS4-L3-467): <11.25 days
• Ongoing study of speedup options
• Survey of turnkey and custom heat switch and precooling options
• Network model-based simulation tool

5

Project workshop | May 2024

gas-gap

mechanical

LN2 precool

Toy model

R&D and Prototyping

• R&D efforts targeting PTC risks:
• Alternative low-power model
• Optimization w/ inverter compressor
• Water cooling of PTC exterior
• Study of tilt, helium charge, motor frequency dependence of candidate models w/ realistic hoses & joints
• Optics testbed cryostat:
• Iterate on optical load model based on measurements
• Prototype SAT cryostat:
• Iterate on radiative, conductive, cabling model inputs based on measurements
• Retire thermal risk of 3-tube design w/ constrained cooling
• High-level plan captured in SAT logic flow chart

6

Project workshop | May 2024

Tiltable PTC test cryostat

Presentation reference

Mutual benefit opportunities w/ LATR, HTCs

• Overall strategy as we progress beyond a basic nodal model
• Refrigerator optimization & alternative studies
• IR loading knowledge
• Material property assumptions (utilize S4 conductivity database?)
• Cooldown speedup solutions

7

Project workshop | May 2024

Backup

8

Project workshop | May 2024

References

• SAT thermal modeling for AoA: https://docdb.cmb-s4.org/cgi-bin/private/ShowDocument?docid=847
• SAT cryostat slides from SAT CDR: https://indico.cmb-s4.org/event/54/contributions/1318/attachments/961/2463/2023%20SAT_CDR_L3_Cryostat.pdf
• SAT optics slides from SAT CDR: https://docs.google.com/presentation/d/1G8cgx9YWiJifnVZJ8gP_XCC-eKMh4FLN1uL-UiBy0Jg/edit?usp=sharing
• Google Drive folder with misc useful files: https://drive.google.com/drive/folders/10KxVsEhJfecy7Btz14RNAJxdxElwA13V?usp=drive_link
• Most recent compilation of thermal loads: https://docs.google.com/spreadsheets/d/15IV1jR5E6NEL_WG9X53E_PbOpryO6w9y2sIIjZYqrgo/edit?pli=1#gid=801597198
• Dynamic thermal model code: https://github.com/CMB-S4/cryostat_transient_thermal_model
• Readout load model code: https://github.com/CMB-S4/readout_load_calculator
• SAT IR modeling code: https://drive.google.com/drive/folders/1p3RdNvr43BH5AAHi-fJs0NOipFDCAE7t?usp=drive_link
• SAT prototyping & production plan in flowchart form: https://app.diagrams.net/#G1JzAjjNPBiMsqwdDwrYyndZyr8lJbIBrh#%7B%22pageId%22%3A%22jqsFjZIWBPyZVIjakhJL%22%7D
• preSAT prototyping plans: https://docs.google.com/presentation/d/1D5SITa1mwMVHvqKLV_OKmG0c87pyMDhyRA_BI6RJPKs/edit?usp=sharing

9

Project workshop | May 2024

IR thermal model

10

Project workshop | May 2024

Reference: https://docs.google.com/presentation/d/1G8cgx9YWiJifnVZJ8gP_XCC-eKMh4FLN1uL-UiBy0Jg/edit#slide=id.gdbb4434b1a_3_82

(modulo some refinements since the PBDR)

Cryostat cross section

Project workshop | May 2024

11

Reference: https://docs.google.com/presentation/d/1G8cgx9YWiJifnVZJ8gP_XCC-eKMh4FLN1uL-UiBy0Jg/edit#slide=id.gdbb4434b1a_3_82

(modulo some refinements since the PBDR)