Resonant scattering of particles and second phase acceleration in the solar corona

✍ Scribed by D. B. Melrose

• Publisher: Springer
• Year: 1974
• Tongue: English
• Weight: 714 KB
• Volume: 37
• Category: Article
• ISSN: 0038-0938
• DOI: 10.1007/bf00152495

✦ Synopsis

Effective acceleration of particles by hydromagnetic turbulence requires that the particles be scattered at a rate v comparable with the frequency o9 of the turbulence. The only effective scattering process is due to resonant wave-particle interactions. The resonant waves are HM waves for ions with fl >>flA (tic --particle speed, pAc = Alfv6n speed) and for electrons with 7,6 ~> 43fl0 (rio ~ 43flA), and are whistlers for electrons with P0 ~ 7fl < 43/?o. The resonant waves can be generated by an anisotropic distribution of particles provided that the anisotropy factor A exceeds a threshold anisotropy A0 ~ flA/P for HM waves and Ao ~po2/flz7 for whistlers. Turbulence with relative magnetic amplitude e causes acceleration at a rate va ~ o)e~fia/fl provided the following conditions are satisfied: (a) fl>> fla for ions, fl >> fl0 for electrons; (b) e >> A0; (c) nl/ne < o9/f2~ or nl/ne >> (co/s (Tfl/43f10) 2 for scattering by HM waves or whistlers respectively (nl = number density of accelerated particles, f2~ = ion gyrofrequency).

The injection energy for electrons (fl > fl0) implies that second phase acceleration can be operative for electrons resulting from first phase acceleration (energies ~< 40 keV) only in regions with Alfv6n speed ~ 3 • 103 km s -1 (PA < 10-3). Acceleration on a time scale of a few minutes can result from turbulence with typical periods in the range 0.1 s to 10 s, whose presence is indicated by pulsations of metre-wave continuum radiation.