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DISTRIBUTION D: Distribution authorized to Department of Defense and DoD contractors (Administrative or Operational Use); 10 Dec 2010. Other requests for.

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Presentation on theme: "DISTRIBUTION D: Distribution authorized to Department of Defense and DoD contractors (Administrative or Operational Use); 10 Dec 2010. Other requests for."— Presentation transcript:

1 DISTRIBUTION D: Distribution authorized to Department of Defense and DoD contractors (Administrative or Operational Use); 10 Dec 2010. Other requests for this document shall be referred to Air Force Research Laboratory/RVBX, 3550 Aberdeen Ave SE, Kirtland AFB, NM 87117- 5776. Radiation Belt Modeling and Wave-Particle Interactions Michael J. Starks Space Vehicles Directorate Air Force Research Laboratory

2 Distribution D – See Distribution Statement on Cover 1 of 16 Outline Radiation Belt Dynamics Wave-Particle Interactions Radiation Belt Modeling Terrestrial VLF Transmitters Space VLF Transmitters Lightning Summary

3 Distribution D – See Distribution Statement on Cover 2 of 16 Radiation Belts The Earth’s radiation belts are variable but robust. Energetic electrons are stably trapped by the Earth’s magnetic field. These electrons pose substantial hazards to spacecraft.

4 Distribution D – See Distribution Statement on Cover 3 of 16 ELF/VLF Waves Control Particle Lifetimes L shell = distance/R E Particles mirroring below 100 km are “lost” Electromagnetic waves Particle pitch-angle Electromagnetic waves in the Very Low Frequency (VLF) range (3-30 kHz) scatter and accelerate radiation belt electrons through cyclotron resonance interactions Wave-Particle Interactions Waves from CRRES (1990)

5 Distribution D – See Distribution Statement on Cover 4 of 16 Diffusion coefficient along field lines Quantitative maps of ELF- VLF wave power distribution are crucial for radiation belt specification & forecasting Wave power in the magnetosphere Diffusion coefficients along field lines Particle lifetime along field lines (approximate 1D solution) Full 3D global, time dependent particle distributions X i = (L, E,  ) Wave-particle resonance condition Diffusion coefficients = sum over resonances Complex dependence on energy, frequency, and pitch angle Distribution of Resonant Wave Vectors Transmitters Natural VLF Radiation Belt Modeling

6 Distribution D – See Distribution Statement on Cover 5 of 16 ≠ Abel & Thorne (1998) Starks, et al. (2008) Ground transmitter VLF needed in the inner magnetosphere… but where is it? Could lightning be more effective than previously thought? Terrestrial Transmitters The 20 dB Problem

7 Distribution D – See Distribution Statement on Cover 6 of 16 Apogee (altitude in km)12,000 Perigee (altitude in km)6,000 Inclination (degs)120 Argument of perigee (degs)357.9 (90) Right ascension of the ascending node (degs)TBD (90) True anomaly (degs)TBD (180) Start time (UT)12:00:00 01 Oct 2012 Period (hours)5.277 The DSX Mission

8 Distribution D – See Distribution Statement on Cover 7 of 16 Wave-Particle Interactions (WPIx) – VLF transmitter & receivers – Loss cone imager –Vector magnetometer Space Weather (SWx) –5 particle & plasma detectors Space Environmental Effects (SFx) – NASA Space Environment Testbed – AFRL effects experiment FSH HST Y-Axis Booms VLF E-field Tx/Rx Z-Axis Booms VLF E-field Rx AC Magnetometer –Tri-axial search coils DC Vector Magnetometer Loss Cone Imager - High Sensitivity Telescope - Fixed Sensor Head VLF Transmitter & Receivers -Broadband receiver -Transmitter & tuning unit ESPA Ring Interfaces between EELV & satellite The DSX Satellite

9 Distribution D – See Distribution Statement on Cover 8 of 16 S=0 m i /m e R R X L X R R L XO R L O L=0 X Vacuum limit Cold Plasma Regime Where is DSX?

10 Distribution D – See Distribution Statement on Cover 9 of 16 Vacuum Linear cold plasma – current distribution on antenna specified Linear cold plasma – voltage on antenna specified, current distribution on antenna calculated consistently Sheath& plasma heating effects included Antenna Modeling

11 Distribution D – See Distribution Statement on Cover 10 of 16 Linear Cold Plasma Radiation Patterns 3.5 kHz B x y z antenna 50 kHz B x y z antenna Parallel Perpendicular  c = 89.4  – 68.3 , = 3.2 kHz (LH resonance) – 50 kHz vacuum

12 Distribution D – See Distribution Statement on Cover 11 of 16 Evidence for Resonance Cones Fisher and Gould, Resonance Cones in the Field Pattern of a Short Antenna in an Anisotropic Plasma, Phys. Rev. Lett., 22, 1092-1095, 1969. Koons, et al., Oblique resonances excited in the near field of a satellite-borne electric dipole antenna, Radio Sci., 9, 541-545, 1974. B0B0 B0B0 Resonance cones In the laboratory In space

13 Distribution D – See Distribution Statement on Cover 12 of 16 Vacuum current, Constant dielectric current, Radiated Power Computations Cold plasma dielectric current, ???? UNCLASSIFIED Normalized Radiation Resistance normalized radiation resistance [log Ohms] Normalized Power Normalized power [log Watts] 0 2 4 6 8 10 12 0 2 4 6 8

14 Distribution D – See Distribution Statement on Cover 13 of 16 Space transmitters produce much more complex wave fields than terrestrial transmitters The resulting wave field complicates the computation of wave-particle interactions Accurate space transmitter models are a prerequisite to understanding the behavior of DSX AFRL has focused substantial resources on solving these questions in preparation for the DSX mission VLF Transmitters in Space

15 Distribution D – See Distribution Statement on Cover 14 of 16 January August Satellite-Derived (LIS/OTD) Monthly Global Lightning Climatology (1995 – 2003) Lightning couples an enormous amount of VLF energy into the inner magnetosphere, driving radiation belt dynamics Flashes Km -2 Year The Role of Lightning in the Inner Magnetosphere DSX will help to quantify the lightning VLF flux and determine whether it represents the “missing power”

16 Distribution D – See Distribution Statement on Cover 15 of 16 Lightning Contributions The prevalence of lightning is known, but the coupling of VLF to space is not as well understood

17 Distribution D – See Distribution Statement on Cover 16 of 16 Summary Important questions remain regarding radiation belt dynamics Some existing models are known to be deficient; others may yet be overturned AFRL views carefully validated models as the only route to predictive capabilities The balance of power in the inner magnetosphere between terrestrial transmitters, lightning and hiss has been overturned Outstanding science questions about each influence need answers

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