Space Radiation & It's Effects On Space Systems & Astronauts Course Sampler

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This course is designed for technical and management personnel who wish to gain an understanding of the fundamentals and the effects of space radiation on space systems and astronauts. The radiation …

This course is designed for technical and management personnel who wish to gain an understanding of the fundamentals and the effects of space radiation on space systems and astronauts. The radiation environment imposes strict design requirements on many space systems and is the primary limitation to human exploration outside of the Earth’s magnetosphere. The course specifically addresses issues of relevance and concern for participants who expect to plan, design, build, integrate, test, launch, operate or manage spacecraft and spacecraft subsystems for robotic or crewed missions. The primary goal is to assist attendees in attainment of their professional potential by providing them with a basic understanding of the interaction of radiation with non-biological and biological materials, the radiation environment, and the tools available to simulate and evaluate the effects of radiation on materials, circuits, and humans.

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  • 1. SPACE RADIATION AND ITS EFFECTS ON SPACE SYSTEMS AND ASTRONAUTS Instructor: V.L. PisacaneATI Course Schedule: http://www.ATIcourses.com/schedule.htm
  • 2. Single Particle Motion SPACE RADIATION AND ITS EFFECTS ON SPACE SYSTEMS AND ASTRONAUTS Single Particle Motion by V. L. PisacaneSpace Radiation and its Effects on Space Systems and Astronauts 5─ 1 ©VLPisacane,2012
  • 3. Single TOPICS Particle Motion  Introduction  Equation of Motion  Gyration Motion  Guiding Center Motion  Mirror Points  SummarySpace Radiation and its Effects on Space Systems and Astronauts 5─ 2 ©VLPisacane,2012
  • 4. INTRODUCTION Single Particle Background Motion  Trapping of particles by magnetic fields was first studied by Kristian Birkeland in Norway in ~1895 – He aimed beams of electrons at a magnet inside a vacuum chamber and noted that they seemed to be channeled towards its near magnetic pole  Birkeland interested Poincaré who analyzed the motion of charged particles in a magnetic field and showed that they spiraled around field lines and were repelled from regions of strong field  Birkeland also interested Carl Stormer who carried out more detailed analyzes  Existence of trapped radiation was confirmed by the Explorer 1 and Explorer 3 missions in early 1958, http://www.centennialofflight.gov/essay/Dictionary/R under Dr. James Van Allen at the University of Iowa ADIATION_BELTS/DI160.htm  As a consequence, the trapped radiation are often called the Van Allen radiation beltsSpace Radiation and its Effects on Space Systems and Astronauts 5─ 3 ©VLPisacane,2012
  • 5. INTRODUCTION Single Particle Summary Motion Motion  Motion of the trapped radiation as illustrated in Figure 6.4 consists of three primary components: – Gyration ~ milliseconds • Particles rotating around field lines – Mirroring ~0.1 ─ 1.0 s • Particles traveling from one hemisphere to the other and back – Longitudinal drift ~ 1 ─ 10 min • Particles driting east or west Figure 6.4 Motion of charged particles trapped 5– 4 in the Earth’s magnetic field,Space Radiation and its Effects on Space Systems and Astronauts 5─ 4 ©VLPisacane,2012
  • 6. EQUATION OF MOTION Single Particle Introduction Motion  Force on a particle in a magnetic and av electric field with charge q is given by the Lorentz force FL  qE  v  B  where B = magnetic flux density or magnetic field vector, T E = electric field, V m-1 FL = Lorentz force, N q = charge, C v = velocity, m s-1 F = applied force  Equation of motion with the addition of an applied force F is then dv m  F  q(E  v  B) dtSpace Radiation and its Effects on Space Systems and Astronauts 5─ 5 ©VLPisacane,2012
  • 7. GYRATION MOTION Single Particle Introduction Motion  For a uniform magnetic flux density and no electric field, the force will be constant and perpendicular to the motion resulting in circular motion  Speed will remain constant  Positive particles will rotate clockwise around an out of plane field line  Negative particles will rotate counterclockwise around an out of plane field line g g Positive charge Negative chargeSpace Radiation and its Effects on Space Systems and Astronauts 5─ 6 ©VLPisacane,2012
  • 8. GYRATION MOTION Single Particle Gyro-Frequency and Larmor Radius Motion  Gyro-frequency or relativistic cyclotron frequency wc and Larmor radius rc follow from the gyration equation of motion dv g rlwc  v g m  qv g  B dt vg qv gB   mrl w 2 rl  c wg qrlwg  B   mrl w2 c v gm0 g  mc  m0 gc rl    qB  qB  qB  v2 qB  qB  qB  wg    1 2 m m0 g m0 c v gm0 g p pc 1 R rl     qB  qB  q cB cB qB  qB  vc q q B  vc q B  c2 wg    B  vc   m mvc pc q R q R where F = force, N m = gm0, relativistic mass, kg rl = Larmor radius, m m0 = rest mass, kg R = magnetic rigidity, V a = acceleration, m s-2 g ≡ (1-v2/c2)─1/2 q = charge, C wg = gyrofrequency, s-1 v = magnitude of particle velocity, m s-1 fc = wc/ 2p, gyrofrequency, Hz vg = magnitude of gyration velocity, m s-1 B = magnetic flux density perpendicular to plane of motion, TSpace Radiation and its Effects on Space Systems and Astronauts 5─ 7 ©VLPisacane,2012
  • 9. GYRATION MOTION Single Particle Gyro-Frequency for Electrons and Protons Motion  For electrons qB  qB   1.60  10 19 B  B wg     1.76  1011  rad s -1 m m0 g 9.11  10 31 g g w B fg  c  2.80  1010  Hz 2p g  For protons qB  qB  1.60  10 19 B  B wg     9.58  107  rad s -1 m m0 g 1.67  10 27 g g w B fg  c  1.52  107  Hz 2p g  Ratio of gyro-frequencies for the electron and proton is fg ,electron m0 ,proton 1.67  10 27    1833 fg ,proton m0 ,electron 9.11  10 31 where me= 9.11 x 10-31 kg qe = ─ e = ─1.60 x 10-19 C mp= 1.67 x 10-27 kg qp = e = 1.60 x 10-19 CSpace Radiation and its Effects on Space Systems and Astronauts 5─ 8 ©VLPisacane,2012
  • 10. GYRATION MOTION Single Particle Larmor Radii for Electrons and Protons Motion  For electrons m0 gc 9.11  10 31 gc gc rl ,electron    5.68  10 12 qB   1.60  10 19 B B  For protons m0 gc 1.67  10 27 gc gc rl ,protons    1.04  10 8 qB  1.60  10 19 B B  Ratio Larmor radii for the electron and proton is rl ,proton m0 ,proton 1.67  10 27    1833 rl ,electron m0 ,electron 9.11  10 31 where me= 9.11 x 10-31 kg qe = ─ e = ─1.60 x 10-19 C mp= 1.67 x 10-27 kg qp = e = 1.60 x 10-19 CSpace Radiation and its Effects on Space Systems and Astronauts 5─ 9 ©VLPisacane,2012
  • 11. GYRATION MOTION Single Particle Larmor Radii and Gyro-frequency in Terms of Magnetic rigidity Motion  Examples of Larmor radii and gyro-frequency for any charged particle with a given rigidity at  Sun  near Earth  surface of the Earth Larmor Radius, Re = Earth radii Magnetic Kinetic Speed Rigidity Energy [% of c] Corona Interplanetary Earth (10 mT) 1 AU (5 nT) Surface (30 μT) 1 GV 0.43 GeV 73% 330 m 6.6x108 m ≈ 100 Re 1.1x105 m ≈ 0.017 Re 5 GV 4.1 GeV 98% 1.65 km 3.3x109 m ≈ 520 Re 5.5x105 m ≈ 0.086 Re 20 GV 19.1 GeV 99.8% 6.60 km 1.3x1010 m ≈ 2100 Re 2.2x106 m ≈ 0.340 Re Gyro-frequency Magnetic Kinetic Speed Rigidity Energy [% of c] Corona Interplanetary Earth (10 mT) 1 AU (5 nT) Surface (30 μT) 1 GV 0.43 GeV 73% 105.6 kHz 0.053 Hz 316.9 Hz 5 GV 4.1 GeV 98% 28.4 kHz 0.142 Hz 85.1 Hz 20 GV 19.1 GeV 99.8% 7.2 kHz 0.004 Hz 21.7 HzSpace Radiation and its Effects on Space Systems and Astronauts 5 ─ 10 ©VLPisacane,2012
  • 12. GYRATION MOTION Single Particle Summary Motion in Uniform Magnetic Field Motion  Orbit of a charged particle in a uniform, static magnetic field is a spiral trajectory  Particle gyrates in plane perpendicular to magnetic field in a circular orbit  Radius of orbit is the Larmor radius, rl  Sense of gyration depends on sign of the particle’s charge  Positive and negative charged particles will rotate in opposite directions  Gyro-frequency is given by wg or fg  Gyro-period given by 1/fg or 2p/ wg  Tangential velocity is constant  Particle’s energy is conservedSpace Radiation and its Effects on Space Systems and Astronauts 5 ─ 11 ©VLPisacane,2012
  • 13. GUIDING CENTER MOTION Single Particle Introduction Motion  When geomagnetic field in not constant and uniform and electric field is not zero, motion is more complicated  However, when the variation in the forces over distances comparable to the Larmor radius is small, these effects can be treated as perturbations  Partitioning the motion into gyro motion and motion of the guiding center where – Gyration motion – circular motion of the particle around the magnetic field in the plane perpendicular to the magnetic field, vg – Guiding center motion – motion of the center of the gyrating particle (all motion but gyration motion), vgc  Let v  v g  v gc so that the equation of motion dv m  F  qE  qv  B dt can be approximated by dv gc dv g m  F  qE  qv gc  B m  qv g  B dt dtSpace Radiation and its Effects on Space Systems and Astronauts 5 ─ 12 ©VLPisacane,2012
  • 14. GUIDING CENTER MOTION Single Particle Guiding Center Equations Motion  Equation of motion of the guiding center is dv gc m  F  qE  qv gc  B dt  Partitioning the velocity and force into components parallel and normal to the magnetic field v  v gc||ε||  v gc  F  F ε||  F || E  E||ε||  E gives dv gc|| dv gc m  F||  qE|| m  F  qE  qv gc  B dt dt  If for E|| and F|| are constant, guiding center motion parallel to the magnetic field is F||  qE|| v gc||  t  v gc||(0) m  Forces parallel to magnetic field accelerates particle along the field line with direction depending on sign of the force or charge of the particle  Forces perpendicular to the magnetic field will accelerate the particle orthogonal to the magnetic field lineSpace Radiation and its Effects on Space Systems and Astronauts 5 ─ 13 ©VLPisacane,2012
  • 15. GUIDING CENTER MOTION Single Particle Motion in Uniform Magnetic Field Motion  General motion of proton and electron in a constant magnetic field with an initial velocity along the field line results in the direction of the magnetic field results in helical motion g gSpace Radiation and its Effects on Space Systems and Astronauts 5 ─ 14 ©VLPisacane,2012
  • 16. GUIDING CENTER MOTION Single Particle Orthogonal Drift Velocities of the Guiding Center 1/2 Motion  Gyration without perturbations (see A)  General Force Drift (see C) – Drift due to presence of general force F FB v gc ,F  qB 2  Electric Field Drift (see B) – Drift due to presence of electric field E EB F  qE v gc ,E  B2  Gradient Drift (see D) – Drift due to gradient in t magnetic field ∇B – Dominates for the Earth B mv 2 v gcB   3 B  B 2qB http://en.wikipedia.org/wiki/File:Charged-particle-drifts.svgSpace Radiation and its Effects on Space Systems and Astronauts 5 ─ 15 ©VLPisacane,2012
  • 17. GUIDING CENTER MOTION Single Particle Orthogonal Drift Velocities of the Guiding Center 2/2 Motion  Gravitational drift – Drifts due to presence of gravity vector g mg  B v gcg  qB 2  Magnetic Curvature Drift B || – Drift due to Rc radius of curvature of magnetic field 2 2 mv|| mv|| v gcR  2 2 Rc  B  4 B  B   B qB Rc qB Drift out for positive charge Drift into for negative charge  Polarization Drift – Drifts due time derivative of the electric field dE/dt 1 dE m dE v gcp   2 wgB dt qB dt dE dtSpace Radiation and its Effects on Space Systems and Astronauts 5 ─ 16 ©VLPisacane,2012
  • 18. MIRRORS POINTS Single Particle Introduction Motion  If the electromagnetic fields do not vary in time, the energy of the particle is constant so that dE 0 dt  The energy can be expressed as 1/2 v||   (E  B  q)  vD  2 E  mv||  vD   B  q 1 2 2 2 m    2  in regions where 1 2 E  mv D  B  q 2 charged particles can drift in either direction along magnetic field-lines  However, particles are excluded from regions where v|| is imaginary 1 2 E  mv D  B  q 2  Charged particles must reverse direction at those points on magnetic field-lines, these points are termed bounce points or mirror points E = Energy  = electric field potential, E = ─ t = time Vm = magnetic field potential m = particle mass q = charge v|| = velocity parallel to field line = orbital dipole moment of particle vd = drift velocity =IA = 2riwc/2, I = current, A = areaSpace Radiation and its Effects on Space Systems and Astronauts 5 ─ 17 ©VLPisacane,2012
  • 19. MIRRORS POINTS Single Particle Mirror Points in Dipole Field Motion  Distance a particle travels from the equator before mirroring is determined by its pitch angle at the equator  Equatorial pitch angle for a particle that mirrors at a given magnetic latitude in a dipole field is cos6 lm Pitch Angle sin a eq  2 1  3sin2 lm 1 / 2 60o where lm = magnetic latitude of mirror point aeq = pitch angle at the equator 80 60 40 Mirror Latitue, degs 20 Pitch Angle 0 -20 40o -40 -60 6 – 18 -80 0 10 20 30 40 50 60 70 80 90 Equatorial Pitch Angle, degs Mirror magnetic latitude as function of magnetic equatorial pitch angle From: http://www.altfuels.org/sampex/losscone/index.htmlSpace Radiation and its Effects on Space Systems and Astronauts 5 ─ 18 ©VLPisacane,2012
  • 20. MIRRORS POINTS Single Particle Mirror Points in Dipole Field Motion How far the particle travels from magnetic equator before Particle with equatorial pitch angle 90 degrees, will mirror at "mirroring" is determined by pitch angle at the equator equator and remain in magnetic equatorial plane If pitch angle close to 0 or 180 degrees (nearly aligned with Mirror points occur at same field strength on each bounce, magnetic field), mirror point will fall below planet surface i.e., at same magnetic latitude and drift equatoriallySpace Radiation and its Effects on Space Systems and Astronauts 5 ─ 19 ©VLPisacane,2012
  • 21. MIRRORS POINTS Single Particle Equatorial Loss Cone Motion  Equatorial Loss Cone is a cone of velocities of charged particle whose apex is on the equator and axis along a magnetic field line that represents the charged particles that will be lost due to interaction with the atmosphere or the surface in a dipole field  Loss-cone angle for intersection with the Earth depends solely on L-shell value and not on particle mass, charge or energy where http://www-spof.gsfc.nasa.gov/Education/wtrap2.html sin alc  4L6  3L5  1 / 4 a lc Loss -one geometrySpace Radiation and its Effects on Space Systems and Astronauts 5 ─ 20 ©VLPisacane,2012
  • 22. MIRRORS POINTS Single Particle Mirror Points of Trapped Radiation 1/2 Motion  Spenvis simulation  Initial Conditions – L-shell: 2 Re – Equatorial pitch angle: 30o 3D view of L shell Altitude of mirror points 6 – 21 Footprints in Northern and Southern hemisphere Cylindrical projection of the shellSpace Radiation and its Effects on Space Systems and Astronauts 5 ─ 21 ©VLPisacane,2012
  • 23. MIRRORS POINTS Single Particle Mirror Points of Trapped Radiation 2/2 Motion  Spinvis simulation  Initial Conditions – L-shell: 2 Re – Equatorial pitch angle: 15o  Mirror Points – Some mirror points subsurface 3D view of L shell Altitude of mirror points Footprints in Northern and Southern hemisphere Cylindrical projection of the shellSpace Radiation and its Effects on Space Systems and Astronauts 5 ─ 22 ©VLPisacane,2012
  • 24. SUMMARY Single Particle Typical Particle Characteristics Motion 6 – 23 Table 6.5 Characteristics of typical radiation belt charged particlesSpace Radiation and its Effects on Space Systems and Astronauts 5 ─ 23 ©VLPisacane,2012
  • 25. SUMMARY Single Particle Summary Single Particle Motion Motion  Motion along uniform magnetic field – Uniform B, no E: constant speed along B – Uniform B, E parallel to B: charge dependent acceleration along B  Gyration motion – Circular orbit in plane perpendicular to B – Sense of gyration depends on charge sign – Larmor radius rl and gyration frequency fg  Drift motion orthogonal to magnetic flux density B from force F – Drift perpendicular to B and F according to vF  F  B qB2 may depend on charge sign – If F proportional to q then drift motion independent of charge – If F not proportional to q then drift motion dependent on charge sign  Non-uniform and time-varying magnetic field – Gradient drift perpendicular to B and ∇B depends on charge sign – Converging/diverging B: deceleration/acceleration along B with mirroring 6 – 24  In a dipole field – Charged particles will mirror at a latitude depending on the equatorial pitch angle – Particles will intersect Earth if equatorial pitch angle is within equatiorial loss coneSpace Radiation and its Effects on Space Systems and Astronauts 5 ─ 24 ©VLPisacane,2012
  • 26. Single Particle Motion DISCUSSIONSpace Radiation and its Effects on Space Systems and Astronauts 5 ─ 25 ©VLPisacane,2012