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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
6
Radiation effects on biological tissues
6
77
8
Radiation effects on biological tissues
8
9
The interplanetary travel case
9
• 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
11
Galactic cosmic radiation
11
12
Radiation doses in different missions
12
13
% of death due to cancer - 95% CL
13
Durante & Cucinotta, Nat. 2008
3% REID
14
Doses for exploration missions.....
14
• 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
•
15
Projection of risk of radiation on biological tissues
15
95% CL
16
3% REID limit =>increase of P(cancer death)
16
17
Various form of shielding
17
18
Passive shield in space if it is “thin” ..........then it “adds” dose
18
Spacecrafts
structures
2 - 6 cm
Al eq
19
Advanced materials can help SPE not GCR
19
Spacecrafts
structures
2 - 6 cm Al eq
20
Mars Mission 1000 days in space =>increase of P(cancer death)
20
21
SR2S mission scenarios
21
22
So we turn to active radiation shields
22
23
Active magnetic shielding
23
24
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
24
2525
Superconductivity
26
The ATLAS superconducting toroid
26
2727
Superconductivity in space : why?
28
Analytical and Monte Carlo analyses
28
See M. Giraudo talks
29
Magnetic shielding of a SPE event
29
• 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
46
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
47
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
61
Superconducting cable for space applications
61
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Superconductors for space
62
63
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)
64
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
65
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
66
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
67
Cryogenics and thermal control system
67
• 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
72
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
73
– 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
74
Identify critical technologies and TRL
74
• 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
75
Critical technologies and TRL
75
• Improvement of SC cable : MgB2, YBCO
•Development of large, light coils
76
Critical technologies and TRL
76
•Deployable technologies
•Low heat leakage cryostats and cryogen-free technologies
77
Critical technologies and TRL
77
•Flux pump power supplies
•Quench protection systems for HT SC
78
Ground demonstrator philosophy
78
79
Radiation shield development plan
79
80
Conclusions (1)
80
•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
81
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
81
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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
83
Thank you !
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backup
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SC cables