"The Multi Domain method, a semi-implicit adaptive method for fully kinetic Particle In Cell simulations," by Maria Elena Innocenti (University of Leuven)

Thursday, December 3, 2015 - 2:00pm to 3:00pm
Plasma Seminars

Plasma Seminar

Physics and Astronomy Building (PAB) Room 4-330
Thursday, December 3, 2015
2-3 PM

Guest Speaker: Maria Elena Innocenti (University of Leuven)

Talk Title: "The Multi Domain method, a semi-implicit adaptive method for fully kinetic Particle In Cell simulations"


Fully kinetic Particle In Cell (PIC) simulations with the ambition of realistically representing both ion and electron dynamics have to be able to cope with the huge scale separation between electron and parameters while respecting strict stability constraints. This often results in computational costs so high to seriously limit the extension and duration of the simulations. Many alternatives are available to reduce the computational costs of PIC simulations. Semi implicit methods (Vu and Brackbill, 1992; Lapenta et al., 2006; Cohen et al., 1989) can bypass the strict stability constraints of explicit PIC codes. Adaptive Mesh Refinement (AMR) techniques (Vay et al., 2004; Fujimoto and Sydora, 2008) can be employed to change locally the resolution of the simulation. 

We focus here on the Multi Level Multi Domain (MLMD) method introduced in Innocenti et al. (2013), Beck et al. (2014), Innocenti et al (2015). The method combines the advantages of semi-implicit algorithms and adaptivity. Two grid levels are fully simulated with fields and particles. Different spatial and temporal resolutions are used at the different levels, with jumps in spatial and temporal resolution reaching up to 14 and 10 respectively. These large resolution jumps are allowed by the Implicit Moment Method used. The aim is to resolve ion scale processes in the less resolved grid, electron scale processes in the higher resolution areas.

MLMD simulations with standard parameters have been measured to be 70 times cheaper than their single grid, semi-implicit counterparts.

The MLMD method is demonstrated with simulations of collisionless magnetic reconnection and turbulence generated by the Lower Hybrid Drift Instability. In magnetic reconnection, the characteristic Ion and Electron Diffusion Regions (IDR and EDR) develop at the ion and electron scales respectively (Daughton et al., 2006): electron scale resolution can be used in the EDR only. In turbulence simulations, a mixed grid spectrum is obtained by joining the solutions calculated on the grids evolved with the different resolutions. This extends the simulated wavenumber range of a factor proportional to the resolution jump at a cost only roughly double with respect to simulating the low resolution grid alone.

All the simulations shown have realistic mass ratio, domains of the order of tens of ion skin depths and higher resolution of the order of fractions of the electron skin depth.

Stefano Markidis (KTH Royal Institute of Technology, Stockholm, Sweden)
Giovanni Lapenta (University of Leuven, Leuven, Belgium) 

PAB 4-330