Upper bounds on particle energization?
Abstract
Cosmic rays have energies up to 10^20 eV. Much attention has been devoted to astrophysical accelerators; exotic origins have been sought in cosmology. Diverse plasma processes have long been identified that will produce energetic particles. It appears not to be known, however, what limitations exist on paricle energization by random electric fields in turbulent classical plasmas. Isotropic random electric fields can accelerate charges indefinitely unless "emission" terms, similar to the dynamical friction Fokker-Planck coefficients, exist to permit the re-radiation of energy by a test particle. These terms are well in hand for stable electrostatic plasmas via the Balescu-Lenard equation, but the expressions diverge as the zeros of the dielectric function cross the real axis. No agreed-upon formalism apparently is available for a turbulent or unstable plasma that will prohibit some particles' running away in energy. Candidate processes such as Cerenkov or synchrotron radiation, or radiative reaction, seem not to have been developed in convincing detail. Numerical experiments might usefully be performed on relativistic particle acceleration in electrostatic fields that either were modeled or obtained from sustained turbulence simulations, in order to find limitations, if any, on acquired particle energies.
- Publication:
-
APS Division of Plasma Physics Meeting Abstracts
- Pub Date:
- November 2004
- Bibcode:
- 2004APS..DPPBM2002M