How Do Space Plasmas Create High-Energy Particle Accelerators?

The acceleration of charged particles to high energy due to explosive energy releases, such as solar flares and magnetospheric substorms, often occur in cosmic plasmas. It implies that cosmic plasmas have ability to create powerful high energy particle accelerators. The acceleration of charged particles cannot be driven by magnetic fields. Parallel electrostatic fields related to the charge-separation are the most powerful means to directly and efficiently accelerate particles. We have developed a dynamical theory which explains how the parallel electric field, E, can be generated, with the required conditions being low plasma density, high magnetic shear, and continuous energy supply. In the theory we emphasize the role of the displacement current, JD = (1/4)E/t, as shown in the parallel component of Amperes law, in generating E, which has been ignored previously. This development has opened a door to understand the mechanism of particle acceleration in cosmic plasmas. Due to the mobility of charged particles, the electric field that are produced will quickly short themselves out by motion of free charges. Thus, the particle acceleration requires the generation of long-lasting electrostatic fields, in addition to continuous energy supply. We will present a dynamical theory of the formation of double layers (DL), which are Alfvenic electromagnetic plasma structures generated by Alfvenic interaction in inhomogeneous acceleration regions, and serve as the particle accelerators. The Alfvenic DL consists of localized electrostatic fields related to charge separation embedded in low density cavities surrounded by enhanced reactive stresses. The Poynting flux carried by Alfven waves continuously supplies energy to the acceleration region, supporting the DLs, leading to strong long-lasting electrostatic fields. In exploring the mechanisms of the phenomena, we have applied fundamental physical laws of electromagnetic plasmas without using the unnecessary magnetic reconnection hypothesis. We suggest that the phenomena that have the ability to create and maintain electrostatic fields can occur in the active plasma which is far from thermodynamic equilibrium.