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Electron Acceleration inside Jupiter’s Radiation Belt and the Origin of Synchrotron Radiation Richard B. Horne 1 R. M. Thorne 2, S. A. Glauert 1, J. D. Menietti 3, Y. Y. Shprits 2, and D. A. Gurnett 3 1. British Antarctic Survey 2. University of California, Los Angeles 3. University of Iowa R.Horne@bas.ac.uk REPW, Rarotonga, 8th August 2007

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Application to Jupiter’s Radiation Belts

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The Problem [Bolton et al., Nature, 2002] How do you produce ~1 MeV electrons at L ~ 15? Synchrotron radiation indicates: –50 MeV electrons at L=1.4 Current theory –Betatron and Fermi acceleration by inward transport Requires a source –> 1 MeV at 10 – 15 Rj

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Inward Radial diffusion Flux at 90 at L=15.75 from Pioneer and Voyager Assume inward radial diffusion and at L=8.25 the flux should vary as the dotted line Some evidence for local plateau in flux Additional acceleration? Cannot be sure due to uncertainty over variability Radial diffusion also found to agree well with observations

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Whistler Mode Waves at Jupiter

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Resonant Diffusion Scaling similar to Earth Energy transfer via whistler mode waves from low to high energy and large pitch angles Trapping inside magnetic field at high energy

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Galileo Wave Data

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Bagenal [1994] Density Model

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Density Model – Latitude Variation

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Galileo Data Survey of all Galileo data, 1996-2002 Chorus wave power peaks outside orbit of Io –Waves generated by flux interchange instabilities Wave power high where fpe/fce drops –Energy diffusion more efficient

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Diffusion Rates Diffusion rates –PADIE code [Glauert and Horne, 2005] –Model wave spectrum from Galileo 13:20-13:30 SCET –30 o angular spread of waves –Landau +-5 cyclotron resonances –Bounce average over 10 o latitude Energy diffusion peaks outside Io –Wave acceleration Fokker-Planck equation

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Wave Acceleration at Jupiter Evolution of electron flux –Initial flux from Divine and Garrett [1983] –Fixed boundary conditions at 0.3 and 100 MeV –Flux=0 inside loss cone and flat gradient at 90 o Timescale ~ 30 days for flux of 1 - 6 MeV electrons to increase by a factor of 10 Timescale is comparable to transport timescale (20 - 50 days) for thermal plasma Predict anisotropic pitch angle distribution

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Conclusions Wave acceleration by whistler mode chorus is a viable process for producing ~ MeV electrons inside Jupiter’s radiation belt for t ~ 30 days Magnetic flux interchange instability provides energy to drive the waves Acceleration is most effective outside the moon Io Wave acceleration predicts pitch angle distributions peaked near 90 o Trapped inside magnetic field Energy dependent Wave acceleration is part of a multi-step process to produce synchrotron radiation from Jupiter And Saturn, Uranus, Neptune, exoplanets, ….???

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