Stochastic Acceleration by Turbulence

• Published in: Space science reviews Vol. 173; no. 1-4; pp. 535 - 556
• Main Author: Petrosian, Vahé
• Format: Journal Article
• Language: English
• Published: Dordrecht Springer Netherlands 01.11.2012; Springer Nature B.V
• Subjects: Acceleration; Aerospace Technology and Astronautics; Astrophysics and Astroparticles; Computational fluid dynamics; Cosmic background radiation; Cosmic rays; Energetic particles; Fluid flow; Particle accelerators; Physics; Physics and Astronomy; Planetology; Plasma physics; Space Exploration and Astronautics; Space Sciences (including Extraterrestrial Physics; Stochastic processes; Stochasticity; Turbulence; Turbulent flow; Particle acceleration
• ISSN: 0038-6308; 1572-9672
• DOI: 10.1007/s11214-012-9900-6

The subject of this paper is stochastic acceleration by plasma turbulence, a process akin to the original model proposed by Fermi. We review the relative merits of different acceleration models, in particular the so called first order Fermi acceleration by shocks and second order Fermi by stochastic processes, and point out that plasma waves or turbulence play an important role in all mechanisms of acceleration. Thus, stochastic acceleration by turbulence is active in most situations. We also show that it is the most efficient mechanism of acceleration of relatively cool non relativistic thermal background magnetized plasma particles. In addition, it can preferentially accelerate electrons relative to protons as is needed in many astrophysical radiating sources, where usually there are no indications of presence of shocks. We also point out that a hybrid acceleration mechanism consisting of initial acceleration by turbulence of background particles followed by a second stage acceleration by a shock has many attractive features. It is demonstrated that the above scenarios can account for many signatures of the accelerated electrons, protons and other ions, in particular 3 He and 4 He, seen directly as Solar Energetic Particles and through the radiation they produce in solar flares.