Simulation Studies of Shock Formation due to Interactions of Two Plasmas in a Magnetic Field and Modified Two-Stream Instabilities

Shock formation due to interactions between exploding and surrounding plasmas and evolution of modified two-stream instabilities are studied using two-dimensional (2D) electromagnetic particle simulations. After the exploding ions penetrate the surrounding plasma, a strong magnetic-field pulse forms near the front of the exploding plasma. Because of modified two-stream instabilities, electromagnetic fluctuations grow to large amplitudes in this pulse. At Ωit ≅ 1, where Ωi is the ion cyclotron frequency, the pulse starts to reflect ions and to split into two pulses, which then develop into forward and reverse shock waves. For various values of the initial exploding plasma velocity and of the angle between the velocity and external magnetic field, 2D simulations are performed. The parametric dependence of the properties of the generated pulses and of magnetic fluctuations is discussed