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2014 LWS/HINODE/IRIS Workshop, Portland OR, Nov 2-6, 2014

This study investigates the impact of repetitive data-driven chorus elements on the scattering characteristics of energetic radiation belt electrons. The research explores the collective and incoherent wave effects, diffusion surfaces, subpacket structures, and the interactions between waves and particles. The results highlight the importance of nonlinear effects and provide insights into the dynamics of the radiation belts.

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2014 LWS/HINODE/IRIS Workshop, Portland OR, Nov 2-6, 2014

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  1. Understanding the effects of data-driven repetitive chorus elements on the scattering characteristics of energetic radiation belt electrons 2014 LWS/HINODE/IRIS Workshop, Portland OR, Nov 2-6, 2014 Jacob Bortnik, Xin Tao, Wen Li, Jay M. Albert, Richard M. Thorne Many thanks to the NSF/DOE partnership in basic plasma physics, award # ATM-0903802; DE-SC0010578

  2. Radiation belt dynamics: Collective, incoherent wave effects • Particles drift around the earth • Incoherently accumulate scattering effects of: • ULF • Chorus • Hiss (plumes) • Magnetosonic • Characteristic effects of each waves are different and time dependent Thorne [2010] GRL “frontiers” review

  3. The wave environment in space Meredith et al [2004]

  4. Objective Reality, somewhere in this region … 2. Quasilinear theory • Waves are all weak • Wideband & incoherent • Interactions uncorrelated • Global modeling US • 1. Single-wave/test-particle • Waves can be strong • Narrowband & coherent • Interactions all correlated • Microphysics

  5. When are nonlinear effects important? Example simple case: field aligned wave, non-relativistic particles wave adiabatic phase

  6. When are nonlinear effects important? “restoring” force “driving” force Conditions for NL: • Waves are “large” amplitude • Inhomogeneity is “low”, i.e., near the equator • Pitch angles are medium-high

  7. Large amplitude whistler waves Li et al. [2011], Burst mode observations from THEMIS: Large amplitude chorus is ubiquitous, midnight-dawn, predominantly small wave normal angles Cattell et al. [2008], First reports of large amplitude chorus, STEREO B ~ 240 mV/m, ~ 0.5-2 nT Monotonic & coherent (f~0.2 fce, ~2 kHz) Oblique (~ 45 - 60), Transient L~3.5 – 4.8, MLT~2 – 3:45, Lat ~ 21°-26°, AE ~800 nT

  8. Three representative cases(a) small amplitude, pT wave(b) Large amplitude waves(c) Large amplitude, oblique, off-equatorial resonance Bortnik et al. [2008]

  9. [Bortnik et al., 2014]

  10. Diffusion surfaces • Resonant interaction: Which particles are affected? • Non-relativistic form: • Relativistic form: • Resonant diffusion surface: confinement in velocity space • Non-relativistic form:

  11. Resonant diffusion in velocity space [Bortnik et al., 2014]

  12. Subpacket structure: a Two-wave model Two-wave model Tao et al. [2013] subpacket structure modifies the single-wave scattering picture

  13. Subpacket structure: full spectrum model Tao et al. [2012b], GRL

  14. Subpacket structure: full spectrum model Tao et al. [2012b], GRL

  15. Sequence of chorus elements Tao et al. [2014]: Model a sequence of chorus elements, chosen at random from THEMIS observation, randomly chosen initial phase, initiated at equator.

  16. Comparison with quaslinear theory Model the chorus wave power with a fitted Gaussian, and use SDE approach to simulate the “diffusive spread”

  17. Case 1: high repetition, low amplitude Repetition rate δt/τ=0.4 , BRMS=10 pT. Test particle and SDE (QL-diffusion) results agree very well.

  18. Case 2: low repetition, low amplitude Repetition rate δt/τ=1.2 , BRMS=10 pT. Test particle and SDE (QL-diffusion) results disagree: spreading is non-Gaussian, heavy tails and thin core.

  19. Case 3: low repetition, med. amplitude Repetition rate δt/τ=1.2 , BRMS=80 pT. Test particle and SDE (QL-diffusion) results disagree: spreading is non-Gaussian, large positive bias and thin core.

  20. Summary and conclusions • AIM: Bridge the ‘limiting’ paradigms: • Quasilinear theory: weak, broadband waves, linear scattering • Single-wave/test-particle: finite amplitude, narrowband & coherent, linear or nonlinear scattering • Reality: somewhere inbetween? • Subpacket structure: periodicity of amplitude modulation relative to Bw defines mode of interaction. “Realistic” wave packet tends to linearize response. • Repetitive chorus elements: • High repetition rate & low amplitude: QL works well • Low repetition rate & low amplitude: heavy tails, thin core • Low repetition rate & med. amplitude: large +ve bias, thin core

  21. BACK UPS

  22. Large Plasma Device at UCLA • Operated under Basic Plasma Science Facility (NSF/DOE) • 18m long, 60 cm diam • B up to 3.5 kG (0.35 T) 10 independent power supplies • Plasma by diode switch ~1 MW, Ne>2x1012 cm-3, Te=6-15 eV • 450 radial ports, computer controlled scanning probes • 20 kHz-200 MHz wave generator with 20 kW tuned RF amplifier

  23. Experimental setup W-P interaction ω-k||v||=Ωe

  24. 5. Single particle motion example Wave: • Bw = 1.4 pT •  = 0° • 2 kHz (~0.28 fce) • Constant with latitude Particle: • E = 168.3 keV • eq = 70° • 0 =  Cumulative changes when d/dt~0, i.e., resonance

  25. Experimental setup ω-k||v||=Ωe

  26. Outline • Introduction to wave-particle interactions • Diffusion • The wave-particle interaction experiment at the LAPD (Large Plasma Device) Fourier’s monograph on heat diffusion was submitted handwritten to the Institut de France in 1807- rejected! [Phys. Today, 62(7) 2009]

  27. Amplitude threshold of QLT Tao et al. [2012] Quasilinear diffusion coefficients deviate from test-particle results in a systematic way.

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