Superconductive Radiation Space Shielding
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Transcript of Superconductive Radiation Space Shielding
Superconductive Radiation Space
Shieldingfor Exploration Missions
R. BattistonINFN-TIFPA and University of Trento
Italian Space Agency
COSPAR 2014 Moscow
Friday 15 August 14
The Consortium
SPA 2012 2.2.02 Key technologies for in-space activities
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FP7 SR2S program (2013-‐15)
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Radia7on effects on biological 7ssues
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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 radia:on 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 contribu:on to the ionizing radia:on encountered in space are
• Solar Par:cle Events (SPE)• Galac:c Cosmic Rays (GCR)•
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Distribu=on 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 resul=ng from varying solar ac=vity (Physics Today, Oct. 1974, p. 25)
Par=cle spectra observed in SPE compared with the GCR spectrum
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Galac7c cosmic radia7on
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% of death due to cancer -‐ 95% CL
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Durante & CucinoUa, Nat. 2008
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Doses for explora7on 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 loca:on
• ON THE MOON SURFACE : 223 mSv/yr (22,3 rem/yr) with oscilla:ons of ± 10 rem/yr as a func:on of solar ac:vity
–for comparison: ISS about 18 rem/yr -‐-‐> 6 month expedi7ons
•
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Projec7on of risk of radia7on on
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95% CL
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3% REID limit =>increase of P(cancer death)
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Mars Mission 1000 days in space
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SR2S mission scenarios
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SR2S mission scenarios
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Shield in space if it is “thin” ... .......then it “adds” dose
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Shield in space if it is “thin” ... .......then it “adds” dose
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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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Advanced materials can help SPE not GCR
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Spacecrafts structures 2 - 6 cm Al eq
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So we turn to ac7ve radia7on shields
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Ac7ve magne7c shielding
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Magne7c shield configura7ons
• The angular deflec:on in the magne:c field may be compared to the kine:c energy lost by ioniza:on, where BL replace the electromagne:c and nuclear radia:on 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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The ATLAS superconduc7ng toroid
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Previous Monte Carlo Studies
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Ac7ve magne7c shielding
• Principle of opera=on
• B field tangent to the shielded volume bends par7cle away
• 1) toroidal B field, orthogonal to Hab axis
• 2) solenoidal B field, parallel to Hab axis
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1) TOROIDAL-‐ORTHOGONAL FIELD
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eg. racetrackstoroid
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...but also
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double helix donut
double handle
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2) SOLENOIDAL-‐PARALLEL FIELD
eg. coaxial solenoids
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...but also
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mul:solenoid axial mul:donut
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Shielding power : ∫BdL
Re
Ri
For an ideal toroid, the shielding power is defined as
-‐-‐> large radius-‐-‐> large B we would reach effec:ve
shielding with ∫BdL≈15 Tm
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Magnet mechanical structure
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• • P(Pa) = B2/ 2μo (T2)
Toroidal field !B non uniform! 1-large inward pressure !structural mass
2-low leakage field
Solenoidal field ! B is uniform !1-‐large outward forces
2-‐large leakage field! compensaNon coil
Avoid stresses on superconducNng cable !coil support
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SRS2 tradeoff -‐> racetrack toroid system
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Magnet mechanical structure
• Magnet design iteraNons in SR2S
• Structure design opNmizaNon:
–minimize the material traversed by GCR to avoid secondary producNon
–maximize the BdL to deflect away Z<3 parNcles
–exploit the passive material to absorb Z>2 parNcles (stopping power)
• Perform Monte Carlo calculaNons of the dose reducNon factor for GCR and SPE
• Improve the use advanced materials and mechanical soluNons to reduce mass.
• Current design configuraNon: BdL ≈ 8 Tm
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Superconduc7ng cable for space applica7ons
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Superconductors for space
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Columbus cable for SPACE applica7ons
FROM 17 TO 10.2 grams,
40% weight reducNon
FROM:
3x0,5 nickel clad wire
3x0,2 copper stabiliza:on
TO:
3x0,5 :tanium clad wire
3x0,5 alluminium stabiliza:on
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Example of mass op7miza7on
First Design:•24 Coils ! High loads on the racetrack
! Concentrated Loads on the Tube " ! High Local DeformaNon ! More sensiNve at mechanical tolerance
Smart
SoluNo
n
New Design:• 120 coils ! Lower loads on the racetrack
! Loads uniformly distributed on the tube ! Lower DeformaNon ! Less SensiNve at mechanical tolerance
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Analy7cal and Monte Carlo analyses
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See M. Giraudo talks
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Magne7c 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)
Simula:on varying the mass -‐ M. Giraudo, M. Vuolo
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• Par:cles were generated on a cylinder around the habitat ! No evalua:on of the radia:on shielding at the endcaps:– For this reason, the obtained dose values are valid only to perform a comparison between the different studied configura:ons, they are not absolute values of dose per event in space.
Source
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• Various components of the primary radia:on field in space par:ally absorbed in the walls of the spacecrai
• Secondary radia:on produced by scajering and reac:ons of the primary radia:on in the walls and other materials within the spacecrai
• GCR: about 90% hydrogen nuclei; 9% alpha par:cles and 1% are the nuclei of heavier elements
High energy protons and neutrons:
• Knockout and spalla:on reac:on– Built-‐up of light par:cles and heavy ion target fragments with high LET
and low ranges.
About radia:on field inside the spacecrai
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HZE: predominant processes in their penetra:on through majer are energy loss through atomic and molecular collisions, and absorpNon and parNcle producNon from nuclear interacNons with spacecrai materials and :ssues•E>100 MeV/u dominant reac:on mode: fragmenta:on
– Nuclear absorp:on cross sec:on ̴ A1/3
•E<100 MeV/u dominant reac:on modes: elas:c scajering, compound nucleus forma:on, and excita:ons of discrete nuclear levels that decay by gamma emission or par:cle emission
•Transport of HZE highly modulated by nuclear reac:ons in passing through majer
HZE
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• In case of thick shielding important source of dose
• Low-‐energy neutrons from evapora:on processes where a neutron is boiled off from the nucleus because it contains an excess of energy from its last interac:on
• High energy neutrons from high-‐energy collisions (ten’s of GeV/nucleon) where the result of the interac:on is a spray of nuclear fragments and par:cles
• H approximately the same mass as the neutron ! the best neutron-‐scajering medium available– The hydrogen-‐bearing materials reduce the number of higher energy
neutrons in the 500 keV to 20 MeV energy range that penetrate the shield materials considered. In fact, the more hydrogen, the bejer the overall shielding characteris:cs.
Neutrons
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Preliminary Results Varying Mass: Protons + He GCRAll doses presented are EffecNve sex averaged doses according ICRP123
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FIELD ON
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Preliminary Results Varying Mass: Protons + He GCRAll doses presented are EffecNve sex averaged doses according ICRP123
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FIELD OFF
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Preliminary Results Varying Mass: Ions (z=3 to 26) GCRAll doses presented are EffecNve sex averaged doses according ICRP123
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FIELD ON
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Preliminary Results Varying Mass: Ions (z=3 to 26) GCRAll doses presented are EffecNve sex averaged doses according ICRP123
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FIELD OFF
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Preliminary Results Varying Mass: TOTAL dose
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Normaliza:on extended to all the solid angle. Note that we are genera:ng par:cles from a lateral source. In this preliminary analysis we are not considering ‘endcaps effect’!
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Dose Eq. Results
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• Carbon Epoxy cylinder has the best performance in reducing the number of secondary neutrons
• The effect of Boron is not influen:al on the results
• We have to inves:gate the energy distribu:on of neutrons and the cross sec:ons for the simulated configura:ons
Cross sec:ons comparison
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Energy distribu:on of secondary neutrons dose
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Lin-‐Log scale
Negligible contribuNon below 100 KeV
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Cross sec:ons for different materials ENDF-‐VII (n,Total)
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Considering different materials configura:ons :
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1. Carbon Epoxy, same geometry (No Titanium)
• Pb internal cylinder (3 cm thick – 75 tons)
• All Carbon Epoxy (Coils and structures)
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Material componentMaterial componentMaterial componentMaterial component Other featuresOther featuresOther features
ConfiguraNon COILS STRUCT. 1 STRUCT. 2 Solid H2 Par:cle Field G4 Phisiscs List
B4C/Al Coil Eq. Mat Titanium B4C/Al -‐ H OFF QBBC
C Epoxy Coil Eq. Mat Titanium C Epoxy -‐ H OFF QBBC
C Epoxy HP Coil Eq. Mat Titanium C Epoxy -‐ H OFF QGSP_BERT_HP
No Mat Coil Eq. Mat Titanium -‐ -‐ H OFF QBBC
Lead Coil Eq. Mat Titanium Lead -‐ H OFF QBBC
All Carbon Carbon Epoxy Carbon Epoxy Carbon Epoxy -‐ H OFF QBBC
Carbon_NoTi Coil Eq. Mat Carbon Epoxy Carbon Epoxy -‐ H OFF QBBC
Hydro+B4C/Al Coil Eq. Mat Titanium B4C/Al 10 tons H OFF QBBC
Hydro+B4C/Al+Field Coil Eq. Mat Titanium B4C/Al 10 tons H ON QBBC
C Epoxy Field (H) Coil Eq. Mat Titanium C Epoxy -‐ H ON QBBC
C Epoxy Field (H+He) Coil Eq. Mat Titanium C Epoxy -‐ H+He ON QBBC
C Epoxy Field x2 (H+He) Coil Eq. Mat Titanium C Epoxy -‐ H+He ON (double) QBBC
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STRUCT. 1
Solid H2
STRUCT. 2
COILS
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Effec:ve Doses: All Configura:ons
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Freespace H, normalized on the lateral region (47% of total solid angle)
Field Off
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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 superconduc:ng system do not exist yet
•SR2S is an extraordinary technology development field and technology driver
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Conclusions (2)
•Ac:ve Radia:on Shielding for explora:on is a necessity
•Passive shielding for GCR is not adequate and for SPE can only protect limited volumes
•Ac:ve magne:c shielding becomes effec:ve at high ∫ BdL values and only if the material thickness traversed by the GCR is “small”
•Interplay between ac:ve and passive shielding is complex and detailed simula:ons are needed to understand it
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Conclusions (3)•Op:miza:on of magne:c and structural forces is mandatory
•During the first year SR2S has developed the basic tools for ac:ve shield analysis, started a sistema:c inves:ga:on and achieved important technological developments
•We are analyzing a toroidal configura:on: other magne:c configura:ons would also deserve careful study
•A R&D path towards future developments for light, high field, modular toroidal shield design has been iden:fied
•Collabora:on and synergy with NASA, ESA and EU 56
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• In order to reduce neutron contribu:on we must consider genera:on and absorb:on of n in different materials
• Heavy materials as lead (Pb) have a large absorb:on cross sec:on but in case of high energy protons (GCR) they produce more neutrons (large secondaries genera:on). GeneraNon > AbsorbNon
• Boron rich materials are efficient neutron absorber only in the low energy region where dose contribu:on is negligible.
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Conclusions (4)
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• Using Carbon Epoxy in place of Titanium reduces significantly the neutron produc:on but increases protons contribu:on.
• The magne:c field is off in this configura:on and proton contribu:on 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 reduc:on avoiding secondaries produc:on
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Conclusions (5)
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Thank you !
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backup
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SC cables
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