Superconductive

Radiation Space

Shielding

for Exploration

Missions

R. Battiston

INFN-TIFPA and University of Trento

EASITrain School2, CEA Saclay

October 1st 2019

“Anything a man could imagine,

other men could make it possible”

Jules Verne

The SR2S Consortium

Istituto Nazionale di Fisica Nucleare CERN

Commissariat a l’Energie Atomique

Thales Alenia Space Italia

Compagnia Generale dello Spazio

Columbus Superconductors

Carr Communication

The Consortium

SPA 2012 2.2.02 Key technologies for in-space

activities

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Radiation effects on biological tissues

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Radiation effects on biological tissues

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The interplanetary travel case

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• The evidence for cancer risks from humans who are exposed to low-LET radiation is extensive for doses above 100 mSv (10 rem).

• The doses that are to be expected on space missions, as well as the nuclear type and energies, are quite well understood.

• The main contribution to the ionizing radiation encountered in space are

• Solar Particle Events (SPE)

• Galactic Cosmic Rays (GCR)

•

Distribution of energies of GCR. This is a graph of the more abundant nuclear species in CR as measured near Earth. Below a few GeV/nucleon these spectra are strongly influenced by the Sun. The different curves for the same species represent measurement extremes resulting from varying solar activity (Physics Today, Oct. 1974, p. 25)

Particle spectra observed in SPE compared with the GCR spectrum

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Galactic cosmic radiation

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Radiation doses in different missions

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% of death due to cancer - 95% CL

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Durante & Cucinotta, Nat. 2008

3% REID

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Doses for exploration missions.....

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• FREE SPACE: equivalent doses in excess of 1.2 Sv /yr (120 rem/yr)

• SPACECRAFT (thin) SHIELDING: about 700-800 mSv/yr (70-80 rem/yr)

• ON THE MARS SURFACE: between 100 and 200 mSv/yr (10 and 20 rem/yr), depending on the location

• ON THE MOON SURFACE : 223 mSv/yr (22,3 rem/yr) with oscillations of ± 10 rem/yr as a function of solar activity

–for comparison: ISS about 18 rem/yr --> 6 month expeditions

•

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Projection of risk of radiation on biological tissues

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95% CL

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3% REID limit =>increase of P(cancer death)

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Various form of shielding

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Passive shield in space if it is “thin” ..........then it “adds” dose

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Spacecrafts

structures

2 - 6 cm

Al eq

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Advanced materials can help SPE not GCR

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Spacecrafts

structures

2 - 6 cm Al eq

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Mars Mission 1000 days in space =>increase of P(cancer death)

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SR2S mission scenarios

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So we turn to active radiation shields

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Active magnetic shielding

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Magnetic shield configurations

• The angular deflection in the magnetic field may be compared to the kinetic energy lost by ionization, where BL replace the electromagnetic and nuclear radiation length to characterizing the shielding performance of the material

• Unconfined Field (e.g. Earth’s field), very large volume (L), lower field strength (B)

• Confined field: small volume (L), higher field (B) and larger mass

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Superconductivity

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The ATLAS superconducting toroid

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Superconductivity in space : why?

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Analytical and Monte Carlo analyses

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See M. Giraudo talks

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Magnetic shielding of a SPE event

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• The Columbus habitat was surrounded by the full model already used in the past, without considering hydrogen and endcaps

• The density of every component was reduced:– 0% of the total

– 25% of the total

– 50% of the total

– 75% of the total

– Total (around 315 tons)

Simulation A: varying the mass

10/3/2019

10/3/2019

Simulation Team & Software

Simulations are simultaneously run on different processors

Results are saved in ROOT histogram for post processing

Geant4 Radiation Analysis for Space

MC toolkit for the simulation of interaction of particles in matter

Simulation Team & Software

Simteams

TAS-Italia:• Marco Vuolo• Martina Giraudo

Results on different magnetic configurationsIterations :1. changing materials (solid hydrogen,

boron rich, etc.) 2. changing Physics Lists (different models

to simulate physical processes).3. Using different GCR models: CRÈME 96

and ISO 15390.

H2O Cylinder (Diameter 24 cm, Length 180 cm)

ICRP Voxelized phantom throughICRP123 conversion coefficients

Different detectors used

Monte Carlo code: Geant4.10 and GRAS (Geant4 Radiation Analysis for Space)

INFN-Perugia:• Filippo Ambroglini• William J. Burger

• ISO 15390 GCR spectrum –solar minimum

• SR2S reference sphericalsource, confined to a cylinderplaced outside the regionoccupied by the magnet

• Results given in terms of dosereduction (as % of Free Spacedose)

Bar

rel R

egi

on

End Caps Region

Dose estimated using the fluencecomputed on a “virtual” sphere

Source and assumptions made

ICRP Pub123 coefficients inclusion in the Analyses

Taking into account reviewers’ recommendations

ICRP - Phantom

Structures evolution: Performed Analyses

Configuration A - Varying the mass in a parametric way

Necessity to optimize the materials

Configurations B1 and B2

Necessity to optimize the mass distribution

Overcoming the toroidal concepts..

Pumpkin configurations MT3 and MT4

Activities DescriptionStudied Active Shielding Configurations

Results

Structures evolution: Performed Analyses

Main evolution of the studied concepts in chronological order following the optimization approach

Configuration A.

Based on titanium structures to support the coils (total mass 315

tons, then parametrically varied).

Configuration B1.

Based on aramid fibers support structure reducing the total mass to

104 tons for a bending power of 7.9.

Configuration B2.

Based on aramid fibers support structure (as the B1) increasing the

Bending Power to 11.9 Tm and the total mass to 147 tons.

Configuration MT3.

Multi Toroid 3 coils configuration to generate a “pumpkin” magnetic

field. The support structures are based on aramid fibers.

Configuration MT4.

Multi Toroid 4 coils configuration to generate a “pumpkin” magnetic

field. The support structures are based on aramid fibers.

Magnetic models evolution

Why a parametric analysis varying the mass/density?

Positive charged Ions

Negative charged Ions and e-

Neutral particles (n and gamma)

Iron GCR hitting the aluminummodule producing a secondaryparticles shower

Fragmentation process and secondary particles production

Intra-nuclear Cascade

Heavy ion

γ

μ+/-

Electromagnetic Cascade

αnp

π+/-

π0

γ

e-

e+

e-e+

Extra-nuclear Cascade with additional target nuclei

γγ β Decay

α Decayγ Decay

Induced Radioactivity

Evaporations Nucleons

Compound Nucleus Decayn

p

Recoil nucleus

Configuration A – Parametric analysis

PARAMETRIC ANALYSIS VARYING THE MASS

Different structure relative densities taken into consideration, as a percentage of the real one:

Only Crew Module

% Density of Coils and supporting structures

0% 25% 50% 100% 75%

N.B. Only 100% dens. modelis dimensioned to supportthe mechanical stresses!

Configuration A Results

Magn Field ON

Magn Field OFF

Very high neutrons contribution, not deflected by magnetic field

~30% ~15%

Total dose reduction (100% dens.) :~45% = 30% (Material)+ 15% (Field)

Possible solutions:• Absorb secondary neutrons• Produce less neutrons using

lighter structures

Configurations B1 and B2

Configurations B1 and B2

SIMULATION OF THE MATERIAL OPTIMIZED CONFIGURATION

• Mechanical structures B1 and B2

• Attempt to minimize high energy neutrons production with low Z materials (e.g. Kevlar)

• Preliminary simulations to study secondaries production

• 2 simulations sets:

Configuration B1:

BL = 7.9 Tm

Configuration B2:

BL = 11.9 Tm

Results Configuration B1,B2 vs Configuration A

B1

Primary: Z=1-2

Primary: Z=3-26

Off OffOn On Off On

B2 A

Results Configuration B1,B2 vs Configuration A: All GCR

Primary: Z=1-26

Off

On

Off

On

Off

On

B1

B2

A

Configuration

Dosereduction

Material contributi

on

Field contributi

onTotal Mass

A 45% 30% 15% 300 t

B1 42% 24% 18% 100 t

B2 44% 22% 22% 150 t

Dose Eq. NASA

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Multi Toroid 3 Coils Configuration

B2 C

• Reduced secondaries production • Reduced material contribution due to the coils

spatial distribution• Improved magnetic field efficiency

• Higher primaries contribution

• Less fragmentation

Multi Toroid 3 Coils Configuration

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Kevlar Bandage

Aluminum Alloy

Estimated

MT3 magnetic field contour lines and BL

Multi Toroid 4 Coils Configuration

MT4 Desing Mass Budget

Superconductor 31 tons

Coil formers 17.6 tons

Tie rods 1.6 tons

Supporting bars 1.6 tons

Connecting mechanicalstructure

2.1 tons

TOTAL 52 tons

Kevlar Bandage

Aluminum Alloy

10/3/2019

MT6 …..higher number of coils, better magnetic coverage

Three different versions of the MT4 configuration simulated.

1. MT4 configuration designed, with realistic values of currents

2. MT4 2x

3. MT4 4x – With the same magnets of the MT4 configuration, but with currents

increased of a factor 2 and 4, respectively

– Goal: to study the effect of a higher magnetic field achievement, to understand whether this path was convenient for future studies.

Multi Toroid 4 Coils Configuration

Results MT3, MT4, MT4x2, MT4x4

Relative effective dose obtained using a lateral source with protons/alphaparticles and with GCR with Z>2, for free space, Columbus module, configurationMT3, MT4 and MT4 with 2x and 4x current, using the NASA Quality factors.

protons/alpha particles

GCR with Z>2

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

Dose Equivalent NASA

IONS PROTONS NEUTRONS PIONS

Results MT3, MT4, MT4x2, MT4x4

Relative effective dose obtained using a lateral source with the whole GCRspectrum, for free space, Columbus module, configuration MT3, MT4 and MT4with 2x and 4x current, using the NASA Quality factors.

All GCR

Comparison against passive shielding

• High Density Polyethylene (HDPE)cylinder placed around the sameColumbus-like habitat

• Different thicknesses of materialconsidered in the Monte Carlosimulations

• Dose reduction calculation

Material

Density

Rmin

S [cm] Rmax [cm] g/cm2 Mass [t]

1 5 255 5 5

2 9 259 9 10

3 14 264 14 16

4 23 273 22 27

5 45 295 44 56

6 60 310 58 76

7 80 330 78 105

8 145 395 141 212

9 200 450 194 317

10 250 500 243 425

11 295 545 286 532

HDPE

0,97 g/cm2

250 cm

Conversion Table

Comparisons against passive shielding

• Relative effective dose

• lateral source

• ISO15390 GCR

Spectrum, in solar

minimum

• Columbus module and

passive shielding

configurations

increasing the mass

Energy distribution of secondary neutrons dose

10/3/2019

1.0E-03

2.0E+04

4.0E+04

6.0E+04

8.0E+04

1.0E+05

1.2E+05

1.4E+05

1.6E+05

1.00E-03 1.00E-02 1.00E-01 1.00E+00 1.00E+01 1.00E+02 1.00E+03 1.00E+04 1.00E+05 1.00E+06 1.00E+07 1.00E+08 1.00E+09 1.00E+10 1.00E+11

pG

y

eV

Neutron Fluences and doses

Relevant contribution

Dose after B4C/Al

Dose after C Epox.

Dose No Mat

Lin-Log scale

Negligible contribution

below 100 KeV

• In order to reduce neutron contribution we must consider generation and absorbtion of n in different materials

• Heavy materials as lead (Pb) have a large absorbtion cross section but in case of high energy protons (GCR) they produce more neutrons (large secondaries generation). Generation > Absorbtion

• Boron rich materials are efficient neutron absorber only in the low energy region where dose contribution is negligible.

Conclusions

10/3/2019

• Using Carbon Epoxy in place of Titanium reduces significantly the neutron production but increases protons contribution.

• The magnetic field is off in this configuration and proton contribution may be decreased by the field.

• The choice of structural materials is fundamental

• Materials and field must work in synergy in order to improve the dose reduction avoiding secondaries production

Conclusions

10/3/2019

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Superconducting cable for space applications

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Superconductors for space

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Columbus cable for magnet applications

•MgB2 superconducting cable for magnet applications:

•Flat tape (3x0,5mm) multifilamentary tape, nickel clad

•Overall dimensions: 3x0,7mm

19 MgB2 filamentsNickel cladding

OFHC copper tape laminated (by tin soldering)

Overall weight per 1m of MgB2 standard cable: 17 grams

(See G. Grasso talk)

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Columbus cable for SPACE applications

Which way is it possible to reduce the averall weight for reducing the launching load?

1- REDUCE THE WEIGHT:

-substitute nickel cladding with a lighter metal (titanium)

-substitute copper stabilizer with aluminum stabilizer

2- IMPROVE CRITICAL CURRENT DENSITY:

-If we are able to improve the current density, we can reduce the overall amount of conductor to be wound in the magnet

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Columbus cable for SPACE applications

Materials densities:

titanium: ρ= 4.5 g/cm3

alluminium: ρ= 2.7 g/cm3

MgB2: ρ= 2.55 g/cm3

Materials percentages:

titanium: 40%

alluminium: 50%

MgB2: 10%

Materials weights per component (per meter):

titanium: 5.4g

alluminium: 4.0g

MgB2: 0.77g Global weight per 1m of MgB2 SPACE app. cable: 10.2 grams

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Columbus cable for SPACE applications

FROM 17 TO 10.2 grams,

40% weight reduction

FROM:

3x0,5 nickel clad wire

3x0,2 copper stabilization

TO:

3x0,5 titanium clad wire

3x0,5 alluminium stabilization

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Cryogenics and thermal control system

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• External passively cooled screen

– Space technology screening (sunshield)

• Internal actively cooled screen

– Classical terrestrial cryogenic shield

Cryogenics concept

Human Habitat

Superconducting coil

10 K

300 K

Propulsion Service

10 K

10 K

Internal shield

External shield

(See B. Baudouy talk)

Thermal links

• Conductive thermal link between the cold mass of the magnet and the 2nd stage of the cryocoolers

110 W @ 80 K

11 W @ 10 K2nd Stage

1st Stage

• Efficient thermal links between the 80 K thermal shield and the 1st stage of cryocoolers

• No gravity, high heat transfer, passive (no pump) and long thermal link

• Pulsating Heat Pipe

R&D on large Cryo-Pulsating Heat Pipes

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

R&D on Cryo-PHP

Existing end cryostat

PHP evaporator

Heating 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

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R&D on Cryo-Loop Heat Pipe

Selected TCS devices

LHP is based on the fluid evaporation inside a porous wick

• Completely Passive System

• Self regulating heat transport (e.g. valves)

• Possible long transportation line

• Highest thermal conductance

• Highest heat trasport capability

POWER

POWER

Vapor line transporter

Liquid linetransporter

CONDENSER/RADIATOR

Compensation Chamber

Evaporator block

Fluid direction

see F. Zanetti talk

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– 4 Cryocooler (Stirling Cycle)

– 8 LHP lines : 4 (main)+ 4(red) lines

– Radiator with embedded LHP (Area ~6m2)

R&D on AMS-02 Loop Heat Pipe

Similar TCS concept for SR2S

.

• Cryocooler Temperature Limit [-30°C / +40°C]

• Cryocooler Power to be dissipated ~630W

TCS solution adopted

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Identify critical technologies and TRL

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• We have identified 10 Critical Technologies which would need significant R&D to meet the requirements of an active shield for Space Exploration.

• Critical Technology #1 ITSC and HTSC wires of better suitable quality (MgB2, YBCCO)

• Critical Technology #2 Lightweight coils, congifuration, design and assembly

• Critical Technology #3 Cryogenically stable, light mechanics

• Critical Technology #4 Gas/liquid based recirculating large cooling systems

• Critical Technology #5 Cryo-coolers operating a low temperature

• Critical Technology #6 Magnetic field flux charging devices

• Critical Technology #7 Quench protection for ITS/HTS coils

• Critical Technology #8 Space deployment and assembly of magnetic elements

• Critical Technology #9 Super cryo-insulation, radiation shielding, heat removal

• Critical Technology #10 Superconducting Cable splicing in space

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Critical technologies and TRL

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• Improvement of SC cable : MgB2, YBCO

•Development of large, light coils

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Critical technologies and TRL

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•Deployable technologies

•Low heat leakage cryostats and cryogen-free technologies

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Critical technologies and TRL

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•Flux pump power supplies

•Quench protection systems for HT SC

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Ground demonstrator philosophy

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Radiation shield development plan

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Conclusions (1)

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•The SR2S project brings one of the most challenging magnet systems to be built

•Various of the technologies for such a space superconducting system do not exist yet

•SR2S is an extraordinary technology development field and technology driver

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Conclusions (2)

•Active Radiation Shielding for exploration is a necessity

•Passive shielding for GCR is not adequate and for SPE can only protect limited volumes

•Active magnetic shielding becomes effective at high ∫ BdL values and only if the material thickness traversed by the GCR is “small”

• Interplay between active and passive shielding is complex and detailed simulations are needed to understand it

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Conclusions (3)

• Optimization of magnetic and structural forces is mandatory

• During the first year SR2S has developed the basic tools for active shield analysis, started a sistematic investigation and achieved important technological developments

• We are analyzing a toroidal configuration: other magnetic configurations would also deserve careful study

• A R&D path towards future developments for light, high field, modular toroidal shield design has been identified

• Collaboration and synergy with NASA, ESA and EU 82

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Thank you !

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backup

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SC cables