Danny Summers

Publications (3)2.15 Total impact

• Source

  Available from: arxiv.org

  Article: A Model for Generating Relativistic Electrons in the Earth's Inner Magnetosphere Based on Gyroresonant Wave-Particle Interactions

  Danny Summers, Chun-yu Ma
  [show abstract] [hide abstract]
  ABSTRACT: During the recovery phase of a magnetic storm, fluxes of relativistic ($>1$ MeV) electrons in the inner magnetosphere ($3\le L \le 6$) increase to beyond pre-storm levels, reaching a peak about 4 days after the initiation of the storm. In order to account for the generation of these "killer electrons", a model is presented primarily based on stochastic acceleration of electrons by enhanced whistler-mode chorus. In terms of a quasi-linear formulation, a kinetic (Fokker-Planck) equation for the electron energy distribution is derived, comprising an energy diffusion coefficient based on gyroresonant electron-whistler-mode wave interaction and parallel wave propagation; a source term representing substorm-produced (lower energy) seed electrons; and a loss term representing electron precipitation due to pitch-angle scattering by whistler-mode waves and EMIC waves. Steady-state solutions for the electron energy distribution are constructed, and fitted to an empirically-derived relativistic Maxwellian distribution for the high energy "hard" electron population at geosynchronous orbit. The mechanism is expected to be particularly effective for the class of small and moderate storms possessing a long-lasting recovery phase during which many substorms occur.
  11/1999;
• Article: Comment on “Evolution of Langmuir soliton caused by resonant emission of ion sound wave” [Phys. Plasmas 5, 3487 (1998)]

  Chun-yu Ma, Danny Summers
  [show abstract] [hide abstract]
  ABSTRACT: Abstract unavailable.
  Physics of Plasmas 08/1999; 6(9):3721-3723. · 2.15 Impact Factor
• Source

  Available from: ArXiv

  Article: Formation of Power-law Energy Spectra in Space Plasmas by Stochastic Acceleration due to Whistler-Mode Waves

  Chun-yu Ma, Danny Summers
  [show abstract] [hide abstract]
  ABSTRACT: A non-relativistic Fokker-Planck equation for the electron distribution function is formulated incorporating the effects of stochastic acceleration by whistler-mode waves and Coulomb collisions. The stationary solution $f$ to the equation, subject to a zero-flux boundary condition, is found to be a generalized Lorentzian (or kappa) distribution, which satisfies $f\propto v^{-2(\kappa+1)}$ for large velocity $v$, where $\kappa$ is the spectral index. The parameter $\kappa$ depends strongly on the relative wave intensity $R$. Taking into account the critical energy required for resonance of electrons with whistlers, we calculate a range of values of $R$ for each of a number of different space plasmas for which kappa distributions can be expected to be formed. This study is one of the first in the literature to provide a theoretical justification for the formation of generalized Lorentzian (or kappa) particle distribution functions in space plasmas.
  11/1998;