Speaker
Description
I will describe Astrophysical Hybrid-Kinetic simulations with the flASH code (AHKASH) - a new Hybrid particle-in-cell (PIC) module developed within the framework of the multi-physics code FLASH. Our new second-order accurate hybrid PIC method uses the Boris particle integrator and a predictor-predictor-corrector algorithm for advancing the Hybrid-kinetic equations. It also employs the constraint transport method to ensure that magnetic fields are divergence-free. We employ the cloud-in-cell stencil for interpolation operations between particles and the computational grid and have implemented a $\delta f$ method to study instabilities in collisionless plasmas. I will present code tests for standard physical problems such as the motion of a charged particle in the presence of magnetic fields, propagation of Alfv'en and whistler waves, and Landau damping of ion-acoustic waves. We introduce turbulence driving, modelled using the Ornstein-Uhlenbeck process, in the new Hybrid PIC code. To investigate steady-state turbulence with a fixed Mach number, it is important to maintain isothermal conditions, and we introduce a novel cooling method for PIC codes to achieve this. I will present tests of the cooling method and demonstrate the importance of using it when turbulence is introduced in a collisionless plasma. Additionally, I will discuss the numerical convergence of turbulence driving experiments with varying grid and particle resolutions and test the computational scalability, the hybrid precision method, and the efficiency of the new code.
