Positron acceleration to ultrarelativistic energies by an oblique magnetosonic shock wave in an electron-positron-ion plasma

Positron acceleration in a shock wave in a plasma consisting of electrons, positrons, and ions is studied with theory and simulations. From the relativistic equation of motion, it is found that an oblique shock wave can accelerate some positrons with the energy increase rate proportional to E?B. They move nearly parallel to the external magnetic field, staying in the shock transition region for long periods of time. Then, this acceleration is demonstrated with one-dimensional, relativistic,electromagnetic particle simulations with full particle dynamics. Some positrons have been accelerated to ultrarelativistic energies sg,1000d with this mechanism. Parametric study of this acceleration is also made

Persistent acceleration of positrons in a nonstationary shock wave

Long-time evolution of positrons accelerated in an oblique shock wave in an electron-positron-ion plasma is studied with relativistic, electromagnetic, particle simulations. In the early stage, some positrons move nearly parallel to the external magnetic field in the shock transition region and gain energy from the parallel electric field. The acceleration can become stagnant owing to the deformation of the wave profile. After the recovery of the shock profile, however, the acceleration can start again. By the end of simulation runs, omega_pet=5000, positron Lorentz factors reached values ~2000. In this second stage, three different types of acceleration are found. In the first type, the acceleration process is the same as that in the early stage. In the second type, positrons make gyromotions in the wave frame and gain energy mainly from the perpendicular electric field. In the third type, particle orbits are similar to curtate cycloids. Theoretical estimate for this energy increase is given

Particle acceleration by a large-amplitude wave associated with an ion beam in a magnetized plasma

Large-amplitude waves associated with a relativistic ion beam in a magnetized plasma are investigated by means of relativistic electromagnetic particle simulations. In the simulations, it is shown that electromagnetic fields are induced by an ion bunch which has Gaussian density distribution and that their profiles are similar to those of magnetosonic solitons. Further, when an ion beam propagates obliquely to the external magnetic field, it is found that an induced electric field has a parallel component along the magnetic field. Then, as the next step, giving another positron bunch, it is observed that some particles in a positron bunch are accelerated by the parallel electric field

Metamagnetic jump in the spin-1/2 antiferromagnetic Heisenberg model on the square-kagome lattice

The magnetization process of the spin-1/2 antiferromagnetic Heisenberg model on two-dimensional square-kagome lattice is studied theoretically. The metamagnetic jumps exist in the magnetization process at the higher edge of the 1/3 and 2/3 plateaus. The parameter-dependencies of the critical field and the magnitude of the magnetization jump at the higher edge of the 1/3 plateau are obtained by using the approximated state in the unit cell and compared with the nu- merical results of the exact diagonalization of 42 sites.Comment: 10 pages, 10 figure