Stochastic Acceleration of 3He and 4He in Solar Flares by Parallel Propagating Plasma Waves: General Results
Abstract
We study the acceleration in solar flares of 3He and 4He from a thermal background by parallel propagating plasma waves with a general broken power-law spectrum that takes into account the turbulence generation processes at large scales and the thermal damping effects at small scales. The exact dispersion relation for a cold plasma is used to describe the relevant wave modes. Because low-energy α-particles only interact with small scale waves in the 4He-cyclotron branch, where the wave frequencies are below the α-particle gyro-frequency, their pitch angle averaged acceleration time is at least one order of magnitude longer than that of 3He ions, which mostly resonate with relatively higher frequency waves in the proton-cyclotron (PC) branch. The α-particle acceleration rate starts to approach that of 3He beyond a few tens of keV nucleon-1, where α-particles can also interact with long wavelength waves in the PC branch. However, the 4He acceleration rate is always smaller than that of 3He. Consequently, the acceleration of 4He is suppressed significantly at low energies, and the spectrum of the accelerated α-particles is always softer than that of 3He. The model gives reasonable account of the observed low-energy 3He and 4He fluxes and spectra in the impulsive solar energetic particle events observed with the Advanced Composition Explorer. We explore the model parameter space to show how observations may be used to constrain the model.
Turn this paper into a full lesson
ArcXiv compiles a staged curriculum from this paper: 8-12 lessons across beginner → advanced, synthesised section guides, visuals, flashcards, a quiz, exercises, and on-demand deep dives per section. Grounded in the abstract, never invented.