ELECTRON ACCELERATION FROM ELECTRON-ION PLASMA CLOUD MOVING ACROSS A MAGNETIC-FIELD

The dynamics of the electron-ion plasma cloud moving perpendicular to an ambient magnetic field in the background plasma is investigated by means of a three-dimensional, electromagnetic, and relativistic partic le simulation code. The simulation results show that the cloud separat es into electrons and ions due to their gyromotions with Larmor radius of V0/omega(cj) (V-0 is the initial cloud velocity and omega(cj) is t he cyclotron freyuency of species j). Consequently, electromagnetic an d whistler waves are excited from the cloud due to coherent gyration o f cloud electrons. In addition, Langmuir waves are also excited along a magnetic field. It is shown that cloud electrons are accelerated by Langmuir waves along the magnetic field and the population inversion i s created in the velocity distribution of cloud electrons. The acceler ation mechanism of cloud electrons is due to Landau resonance between Langmuir waves and cloud electrons. We apply our results to the electr on acceleration mechanism from plasma cloud produced near a comet nucl eus, which may explain recent observation of X-ray from comet Hyakutak e.