Cryogenics for space radiation shieldsBertrand Baudouy and Romain Bruce

February 7th, 2014

Cryogenics and magnetism at CEA Saclay

Test of R3B-GLAD cold mass in W7X cryostat

• The Accelerator, Cryogenics and Magnets Division at Saclay is in charge of designing and constructing superconducting cavities and magnets for high energy physics projects

CMS cold mass

• “Even if” CEA Saclay was largely involved in the design of the largest magnets in the world (Atlas and CMS)

• “Now” the SR2S magnet is considered as one of the most challenging magnet to be build

Cryogenics and magnetism at CEA Saclay

Atlas cold mass

• Permanent heat loads– Heat fluxes from the Sun and Mars/Earth– Heat fluxes from the human habitat

Human Habitat

Superconducting coil

Sun

1371 W/m

²

Thermal environment of SR2S

10 K

300 KPropulsion Service Temperature sink 7 K

Mars

~500 W/m

²

10 K

10 K

• External passively cooled screen– Space technology screening (sunshield)

• Internal actively cooled screen– Classical terrestrial cryogenic shield

Sun

1371 W/m

²

Conceptual Cryogenics

Mars

~500 W/m

²

Human Habitat

Superconducting coil

10 K

300 KPropulsion Service

10 K

10 K

Internal shield

External shield

Sunshield options (1/2)

• Sunshield located far from the space ship

–V-groove as Webb telescope sunshield• Optical Solar Reflector (OSR) + Multi-layer insulation (MLI) V-shape

–Use the low temperature sink (7 K) of universe–Multi-layer Insulation around the magnet

• Q<1W on the magnet (without conduction)–Solution possible if the sunshield screens both the radiation coming from the Sun and Mars

Human Space

V-groove

Reflective

Magnet 10 K

Sunshield options (2/2)

• Sun shield surrounding the space ship– V-groove sunshield (Webb telescope)

• OSR + MLI V-shape

• Q=10 W on the magnet (without conduction)– Solution less efficient but allows protecting the entire magnet– Solution taken for the rest of the cryogenic design

Human Habitat

Superconducting coil

10 K

300 KPropulsion Service

10 K

10 K

Human habitat heat load (1/2)

• 80 K shield necessary to lower the heat fluxes from the human habitat

100 W to be extracted @ 80 K

10 mm Aluminum80 K internal shield

10 W to be extracted @ 10 K

MLI

MLI

Human habitat heat loads (2/2)

• Thermal conduction heat loads– 1 g resistant “Epoxy-fiberglass” composite mechanical support

10 W to be extracted @ 80 K

10 mm Aluminum80 K internal shield

1 W to be extracted @

10 K

“Epoxy-fiberglass” support

MLI

Cold sources

• Renewable cooling power (no cryogen tank)

• Electrically powered cryo-generators (Stirling, GM, PT)

• Two-stage cryocooler– Stirling (Implemented in space)

• 2nd stage : 200 mW @ 10 K and 1st stage : 8 W @ 80 K

– Gifford McMahon (not implemented in space)• 2nd stage : 10 W @ 10 K and 1st stage : 50 W @ 80 K

– Pulse Tube (not implemented in space)• 2nd stage : 4 W @ 10 K and 1st stage : 50 W @ 80 K

• Half a dozen of “space qualified “ cryocoolers would be enough• Thermal links to distribute the power

Pulse tube cryocooler

Solid Hydrogen

• Possibility of using solid hydrogen as a back-up cold source– Enthalpy reserve at 13 K in case of general electrical failure– Passive particles shielding

• 20 tons is needed for the 2 years flight (ΔHsublimation = 379.6 kJ/kg)

Human Space300 K

Solid hydrogen on the support

structure

Solid hydrogen on the coil mass

Thermal links

• For the cold mass: conductive thermal link from 2nd stage of the cryocoolers

110 W @ 80 K

11 W @ 10 K2nd Stage

1st Stage

• For the 80 K thermal shield : efficient thermal links from the 1st stage of the cryocoolers

Pulsating heat pipe (1/2)

• A pulsating heat pipe is a small tube without wick structure partially filled with a working fluid and arranged in many turns

• Small tube allows formation of liquid plugs and vapor bubbles– Gas bubbles and liquid plugs oscillate back and forth– Liquid plugs penetrate into both condenser and evaporator

• High heat transferred by latent heat and wall convection • PHPs are simpler, cheaper and more reliable

Pulsating heat pipe (2/2)

Pulsating heat pipe for SR2S (1/2)

• First calculation shows that one PHP condenser must be placed every 2 m on the 80 K shield to have a maximum ΔT of 2 K

• A distribution of long PHPs with different length is needed

• Long, gravity free, efficient PHPs around 80 K must be developed for SR2S

80 K internal shield

Evaporators

Crycooler

Condenser

Pulsating heat pipe for SR2S (2/2)

• Cryogenic PHP have been studied– Only small PHPs have been tested (0.2 m in length)– At liquid nitrogen temperature k = 5 to 18 kW/m.K to be compared

with copper k=500 W/mK (RRR=100)

• Gravity effect– Experiments at ambient temperature show no effect of the gravity

when using more than 40 turns PHP (horizontal PHP)– Experiments in parabolic flight show better performance in reduced

gravity than normal or hypergravity

• Long tube efficiency– 2 m long PHP with water or refrigerant gas– 18.7 W/K for 150 W heat input with 16 turns at 300 K

SR2S PHP R&D program (1/2)

• Tests of a long system– Length investigation (1 m to 4 m long) – Number of tubes

• Gravity effect– horizontal and vertical tests

• Geometrical design– Different size for the evaporator and the condenser exchange surface– 3D pipe design

• SR2S will set new standards in cryogenic PHP– New cooling method at low temperature for superconducting devices

SR2S PHP R&D program (2/2)

Existing end cryostat

PHP evaporatorHeating system/measurement

Insert cryostat with the Cryocooler under design

PHP condenser PHP tubes Ø≈1 mmLiquid nitrogen thermal shield

• Use of 4-m horizontal cryostat• Use of 8-m vertical cryostat

Conclusions

• The SR2S project brings one of the most challenging magnet to be built• The cryogenics for such a space superconducting system does not exist yet• SR2S is the opportunity to develop new technology such as

– Long and powerful 80 K PHP technology– 10 to 50-W class spaced qualified cryocoolers

• SR2S will contribute to other communities such as– Low Tc superconducting system– High Tc superconducting system– High Tc transport cable– …