M. Vuolo M. Giraudo. June 17 th, /06/2015. Ref.: DOC-TAS-EN-001

Transcription

1 DOC-TAS-EN-001 M. Vuolo M. Giraudo June 17 th, /06/2015 Ref.:

2 Introduction Cancer risk caused by radiation exposure is the main obstacle to interplanetary travel No simple and effective countermeasures Significant uncertainties Space radiation hitting the crew (primary particles): protons, alpha and High Charge and Energy Particles (HZE). Secondary particles produced as radiation interacts with matter secondary protons, neutrons, gamma, electrons and recoil nuclei Whole body dose of 1 to 2 msv/day accumulated in interplanetary space

3 Space Radiation in Deep-Space Solar particle events (SPEs) Mainly energetic protons, helium nuclei and heavier nuclei Highest intensity at solar maximum Relative short fluxes of particles Energies from 1 to 100 MeV Not currently predictable Easily shielded by passive and active shields Galactic cosmic rays (GCR) Continuous source Energies ranging from ~10 MeV n -1 to ~ MeV n -1 High-LET radiation Biological effects poorly known Most significant deep-space missions radiation hazard Modulated by the Sun cycle Not easily shielded

4 E, msv Deep Space Effective Dose Estimations When considering passive shielding option: 800 Effective dose for Male behind Shielding SPE easily shielded 700 GCR requires enormous mass to be shielded because of high energies and secondary radiation Mission at solar maximum Thick shielding: Annual GCR at Solar Minimum Aluminum Polyethylene Annual GCR at Solar Maximum Aluminum E(NASA Q) E(NASA Q) E(ICRP2007 Q/Wt) E(ICRP2007 Q/Wt) Mass problems to spacecraft launch systems 200 Polyethylene Bad GCR effective dose reduction Current shield approach: NOT a solution x, g/cm 2 Annual GCR Effective doses or NASA Effective dose in deep space vs. depth of shielding for males. Values for solar minimum and maximum are shown. Credit to Francis A. Cucinotta (NASA, Lyndon B. Johnson Space Center)

5 Superconducting shielding Idea of magnetic shielding field dates back to 1960 Proposed in several configurations Magnetic field ability to deflect particles Interaction of radiation with the magnet materials Structures and subsystems necessary to generate the field SR2S: effective shielding capability studied : Magnetic field Matter of + + spacecraft Realistic supporting structures

6 Toroidal magnetic shield From initial trade-off between active shielding structures toroidal magnetic configuration Toroidal field advantages: isotropic protection around the habitat very low fringe field inside the internal module endcaps of the habitat module free of the field Shielded module Smaller end cap toroids Other modules attached in series Coils

7 Active Shielding: toroidal magnetic field Perfect matching between analytical previsions and simulation results

8 Simulations Team & Softwares SR2S Simulations INFN-Perugia: Filippo Ambroglini William J. Burger TAS-I: Martina Giraudo Marco Vuolo Results on different magnetic configurations Iterations : 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 Monte Carlo code used: Geant4.10 and GRAS (Geant4 Radiation Analysis for Space) H 2 O Cylinder (Diameter 24 cm, Length 180 cm) ICRP 123 conversion coefficients Fluence on a Sphere Detectors used

9 Magnetic models evolution Toroidal Field Configuration A: 10 m Main struct. mat.: Titanium Mass = 300 tons BL: 7.9 Tm Configuration B1: 10 m Main struct. mat.: Kevlar Mass= 100 tons BL: 7.9 Tm Configuration B2: 10 m Main struct. mat.: Kevlar Mass= 150 tons BL: 11.9 Tm Pumpkin Field Configuration C: Main struct. mat.: Kevlar Estimated Mass = 40 tons Multi Toroid 3 Coils 4

10 Coils modeling details Configuration A Configuration B1 New advanced model for the coils, including the bandage reproduction Coil Mat. Al=6mm 1mm Kevlar Instead of using the eq. coil material (Conf.A), each coil detail has been modeled

11 Source and assumptions made End Caps Region SR2S ref spherical source, confined to a cylinder placed outside the region occupied by the magnet Results given in terms of dose reduction (as % of Free Space dose) Barrel Region Dose is estimated using the fluence computed on a virtual sphere

12 Dose and Dose Equivalent Estimation ICRP 123- Phantom Fluence on a Sphere Protons, neutrons, pions, alpha, HZE, etc. Fluence to dose (in Gy) conversion coefficients ICRP 123 for each organs and tissues computed using a voxelized phantom

13 Configuration A PARAMETRIC ANALYSIS VARYING THE MASS The following relative densities were taken into consideration, as a percentage of the real one: Only Crew Module 0% 25% 50% 75% 100% % Density of Coils and supporting structures N.B. Only 100% dens. model is dimensioned to support the mechanical stresses!

14 Why a parametric analysis varying the mass/density? Fragmentation process and secondary particles production Heavy ion Iron GCR hitting the aluminum module producing a secondary particles shower Intra-nuclear Cascade π +/- μ +/- Recoil nucleus Evaporations Nucleons n p Compound Nucleus Decay p n α π 0 γ γ e+ e- e+ e- Electromagnetic Cascade Induced Radioactivity Extra-nuclear Cascade with additional target nuclei Positive charged Ions γ γ Decay γ α Decay β Decay Negative charged Ions and e- Neutral particles (n and gamma)

15 Sex averaged effective dose results : Pions OFF ON Primary: Z=1-2 Neutrons Protons Heavy Ions 0% 25% 50% 75% 100% Primary: Z=

16 Comments on Configuration A Results ~30% OFF ON ~15% Total dose reduction (100% dens.) : ~45% = 30% (Material)+ 15% (Field) Neutrons contribution is very high Neutrons are not deflected by magnetic field Possible solutions: Absorbe secondary neutrons Produce less neutrons using lighter structures

17 Configuration B SIMULATION OF THE MATERIAL OPTIMIZED CONFIGURATION Mechanical structures B1 and B2 Idea of minimizing high energy neutrons production with low Z materials (e.g. Kevlar) 2 simulations sets: Configuration B1: BL = 7.9 Tm Configuration B2: BL = 11.9 Tm

18 Results Configuration B1,B2 vs Configuration A B1 B2 A Primary: Z=1-2 Off On Off On Off On Primary: Z=3-26

19 Results Configuration B1,B2 vs Configuration A: All GCR Primary: Z=1-26 B1 B2 A Off On Off On Off On Mat.

20 Comments on Configurations B1 & B2 Results Tot. dose reduction are quite similar but there are obtained with 3 different configurations The masses are very different: The Bending Power are different: ~300 tons (A) ~100 tons(b1) ~147 tons (B2) 7.9 Tm (A) 7.9 Tm (B1) 11.9 Tm (B2) Configuration B2 shows the best magnetic field efficiency and the reduction due to the magnetic field is similar to the one obtained by the mass B2 configuration is the best compromise between the Bending Power and the mass Greater efforts must be focused on a new magnetic configuration increasing the magnetic field efficiency and reducing the mass!!!

21 SR2S: Multi Toroid 3 Coils Configuration Estimated Kevlar Bandage Aluminum Alloy 21

22 SR2S: pumpkin magnetic field 3D view of magnetic field lines and Bending Power computation by V. Calvelli INFN Genova

23 Preliminary results All GCRs Z=1-26 Dose Eq [csv/y] NASA B2 C Preliminary results The secondaries production is reduced The material contribution is reduced because of the coils spatial distribution The magnetic field efficiency is improved 23 Due to this the primaries contribution is higher Less fragmentation

24 Conclusions after the preliminary results Mat. ~300 tons ~100 tons ~147 tons ~39 tons The total dose reduction is reduced for the pumpkin configuration The mass is more suitable for a space mission if compared to the other configurations The pumpkin configuration seems to have an high magnetic efficiency An optimization of mass and field must be performed in future works Find new solutions to increase the Bending Power and magnetic field!

25 Future Works Multi Toroids MT4-large Configuration Increase the Bending Power Optimization of the magnetic field (orientation) Improve conductor properties To be continued.

26 THE END Thank you for your attention Questions?

27 Summary Radiation space environment and risk Introduction to the active shielding Monte Carlo simulations: source model, detectors and configurations evolution. Description and results of the 2 most studied systems (toroidal configuration A and B) Simulations varying mass on conf. A Simulations on conf. B The Pumpkin configuration (Multi Toroid 3 coils) Future works

28 Toroidal configurations details CONFIGURATION CONFIGURATION CONFIGURATION A B1 B2 Total Mass 315 tons 104 tons 147 tons Height 10m 10m 10m Winding Cable 57 %Al, 9% MgB2, 57 %Al, 9% MgB2, 57 %Al, 9% MgB2, Material 23% Ti, 11%SiO2 23% Ti, 11%SiO2 23% Ti, 11%SiO2 Former Titanium Aluminum Aluminum Struct. cylinder mat Al honeycomb B4C/Al B4C/Al Toroid int. Radius 2.70m 2.80m 2.80m Toroid ext. Radius 6.30m 6.40m 8.75m Bending Power 7.9 Tm 7.9 Tm 11.9Tm Variable density: MC Simulation 100%, 75%, 50%, Real design density Real design density 25%, 0%. Field ON and OFF Field ON and OFF Field ON and OFF

29 Bending Power Analysis Integrated BL over barrel solid angle Comparison between MultiToroidal Magnets with 3 toroid (MT3) 4 large toroid (MT4-large) On the whole barrel solid angle covered, they are equivalent to an ideal toroid with MT4 is doubling BL MT3 2.7 Tm MT4-large 4.1 Tm But there is a big gain if we consider ½ barrel solid angle! MT4 = 7.3 Tm Non pumpkin configuration Ω barrel = π By V.Calvelli

30 Possible shielding strategies Passive Shielding: Active Shielding: Shielding Materials Particle deflected Force field Habitat Habitat Habitat External Shielding: SPE/GCR During whole mission Radiation env. Internal Shelter: SPE Few Hours/Days Active shielding: SPE/GCR During whole mission Biological countermeasures: Drugs Dietary supports : antioxidant rich diet (vitamin E and C, melatonin and selenium) Appropriate crew selection

31 Coil section & cable composition 31

32 Shielding high energy neutrons: Boron rich materials Boron capture cross section for neutron is very high when the energy is below 100 KeV Simulations showed that neutrons contribution to dose in this range of energy is very low Boron is not effective to shield high energy neutrons Negligible contribution below 100 KeV

33 Main differences between configuration A and B Configuration A Configuration B1 Titanium equivalent cylinder Aramid fibers bandage

34 Other Non-Cancer Effects: CNS effects Possible acute or late damages to CNS (Central Nervous System) from low dose rate (< 50 mgy/h) of HZE particles in deep space as one of the main concerns for manned exploration missions in deep space Possible acute effects: limited motor function behavioural changes altered cognitive functions Possible late CNS risks: neurological disorders premature aging Alzheimer s diseases 34