Stochastic transport of high-energy particles through a turbulent plasma
Journal of Plasma Physics Cambridge University Press (CUP)
Authors:
LE Chen, AFA Bott, P Tzeferacos, A Rigby, A Bell, R Bingham, C Graziani, J Katz, M Koenig, CK Li, R Petrasso, H-S Park, JS Ross, D Ryu, D Ryutov, TG White, B Reville, J Matthews, J Meinecke, F Miniati, EG Zweibel, S Sarkar, AA Schekochihin, DQ Lamb, DH Froula, G Gregori
Abstract:
The interplay between charged particles and turbulent magnetic fields is
crucial to understanding how cosmic rays propagate through space. A key
parameter which controls this interplay is the ratio of the particle gyroradius
to the correlation length of the magnetic turbulence. For the vast majority of
cosmic rays detected at the Earth, this parameter is small, and the particles
are well confined by the Galactic magnetic field. But for cosmic rays more
energetic than about 30 EeV, this parameter is large. These highest energy
particles are not confined to the Milky Way and are presumed to be
extragalactic in origin. Identifying their sources requires understanding how
they are deflected by the intergalactic magnetic field, which appears to be
weak, turbulent with an unknown correlation length, and possibly spatially
intermittent. This is particularly relevant given the recent detection by the
Pierre Auger Observatory of a significant dipole anisotropy in the arrival
directions of cosmic rays of energy above 8 EeV. Here we report measurements of
energetic-particle propagation through a random magnetic field in a
laser-produced plasma. We characterize the diffusive transport of these
particles and recover experimentally pitch-angle scattering measurements and
extrapolate to find their mean free path and the associated diffusion
coefficient, which show scaling-relations consistent with theoretical studies.
This experiment validates these theoretical tools for analyzing the propagation
of ultra-high energy cosmic rays through the intergalactic medium.
