Speaker
Giovanni Lapenta
Description
See the full Abstract at http://ocs.ciemat.es/EPS2018ABS/pdf/P4.4002.pdf
New Developments of the Energy Conserving Semi Implicit (ECsim)
method
G. Lapenta, D. Gonzalez, M.E. Innocenti, J. Amaya, E. Boella
Center for mathematical Plasma Astrophysics, Department of Mathematics, KULeuven,
Belgium
The Energy Conserving Semi Implicit (ECsim) method [1, 2] is a new approach to particle
in cell plasma simulation based on a exactly energy conserving formulation. The method uses a
new implicit particle mover and a mass matrix formation of the current to discrete the coupled
particle-field equations with a semi-implicit temporal scheme.
The new lines of investigation reported are: sub-cycling of the particle motion with respect to
the field solution, stabilisation of spurious instabilities present in a drifting plasma, preservation
of the Poisson constraint and detailed local charge conservation.
Subcycling is the process whereby particles are moved multiple times during a field evolution
time step. In the present case, this feature can be implemented in a different way for each
particle and leads to a modification of the algorithm to compute the mass matrix. The procedure
is beneficial in three ways: it increases the accuracy, it can lead to charge conservation and it
can be modified to lead to a gyro-averaged approach
Drifting cold plasmas are notoriously hard to model with PIC because of the insurgence of
the finite grid instability. We report a new method developed within our ECsim approach to
eradicate this nuisance.
The Poisson eqaution and the solenoidal condition for the magnetic field are constraints that
need to be valid at all times. In kinetic particle in cell the second is trivially enforced by choosing
a discretisation of the curl whose discretised divergence is zero. But the first is a more complex
matter, requiring to design an interpolation method for the charge and the current consistent
with each other via the local charge conservation equation. We report our approach to resolve
this issue.
References
[1] Lapenta, G. (2017). Exactly energy conserving semi-implicit particle in cell formulation. Journal of Compu-
tational Physics, 334, 349-366.
[2] Lapenta, G., Gonzalez-Herrero, D., & Boella, E. (2017). Multiple-scale kinetic simulations with the energy
conserving semi-implicit particle in cell method. Journal of Plasma Physics, 83(2).
