Dartmouth Events

Space and Plasma Seminar - Radhika Chirakkara, University of Toronto

Topic: Turbulent Dynamo | Title: Properties of magnetic field amplification in collisionless plasma

5/26/2026
3:30 pm – 4:30 pm
Wilder 202 and Zoom
Intended Audience(s): Public
Categories: Lectures & Seminars, School of Arts and Sciences

Abstract: Weakly collisional plasmas, such as the intracluster medium of galaxy clusters, have dynamically strong magnetic fields. In collisional plasmas, which can be approximated in the magnetohydrodynamical (MHD) limit, the turbulent dynamo mechanism can amplify seed magnetic fields of much weaker strength of astrophysical or primordial origin to strong dynamical levels efficiently by converting turbulent kinetic energy into magnetic energy. However, the viability of this mechanism in weakly collisional or completely collisionless plasma is much less understood. In this talk, I will discuss the properties of the collisionless turbulent dynamo using three-dimensional hybrid-kinetic particle-in-cell simulations with the "AHKASH" code. 

I will describe "AHKASH" - a new Hybrid particle-in-cell (PIC) code 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. 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 describe the properties of the collisionless turbulent dynamo in the kinematic regime for different values of the magnetic Reynolds number, initial magnetic-to-kinetic energy ratio, and initial Larmor ratio, i.e. the ratio of the Larmor radius to the size of the turbulent system. The nature of the collisional turbulent dynamo in the subsonic and supersonic regimes can differ significantly, as demonstrated by numerical MHD studies. I will discuss the features of turbulence and magnetic field amplification from the collisionless turbulent dynamo in both the subsonic and supersonic regime.

Hosted by Assistant Professor Muni Zhou 

Zoom Link: https://dartmouth.zoom.us/j/99960465228

For more information, contact:
Samantha Marcotte
samantha.j.marcotte@dartmouth.edu
Permanent URL to this event: https://physics.dartmouth.edu/events/event?event=81279

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