HLRB Project h0842
Kinetic Simulation
Max-Planck-Institut für Aeronomie, Katlenburg-Lindau
Proposing Institution
Max-Planck-Institut für Aeronomie, Katlenburg-Lindau
Project Manager
Prof. Jörg Büchner
Max-Planck-Str. 2
37191 Katlenburg-Lindau
Abstract
Structure formation in the Universe is dominated by a mysterious dark matter component, which is aboutsix times more abundant than all the known matter made up of standard model particles. Most of thepast research has focused on the assumption that the putative dark particle should be thermally cold andmassive. However, there are some observational clues that this model has shortcomings on small scales.One possible solution from particle physics is for the dark particle to be lighter and retain some thermalvelocity. This scenario is dubbed Warm Dark Matter (WDM). We propose to explore cosmic structureformation in the WDM scenario through a suite of ambitious high resolution N-body simulations. Thesesimulations will be aimed at uncovering the details of how structure formation behaves from the very largestscale structures, down to the free-streaming mass scale and out to high redshift for the first objects. Thiswill enable us to greatly extend our knowledge about large and small scale structures in WDM and alsomixed cold plus warm dark matter (C+WDM) cosmologies. This work will also help direct and indirect dark matterdetection experiments to calculate expected cross-sections for these particle candidates.Astrophysical energy release processes, like flares or jets out ofAGN, require kinetic treatment since the plasma is collisionless and binary collisions are inefficient. As a result micro-turbulent processes have to be considered. The strongly nonlinear character, e.g. of the formation of coherent phase space structures, is largely unaccounted yet in existing descriptions of transport and acceleration in collisionless plasmas, in particular due to the high inherent noise level of the usually used particle-in-cell (PIC) kinetic codes. We intend to study anomalous transport properties and particle acceleration in collisionless astrophysical plasmas {ab initio} by means of four/five dimensional (2D2V/2D3V and 2D2P/2D3P, where D stands for spatial, V for velocity space and P for the momentum space dimensions in relativistic approaches) Vlasov-code simulations.Five-dimensional Vlasov-code simulations of collisionless plasma turbulence, energy conversion, transport and acceleration are grand computational challenges which require the use of the best available codes and state-of-the-art supercomputers. Our project has been prepared by 1D1V and 2D2V electrostaticimplementations of our newly developed Vlasov code. We have developed an innovative unsplit conservative finite volume method to directly solve the Vlasov equation. We have already successfully utilized the 1D1V electrostatic versionof the code on up to 128-CPU ALTIX machines. In our previous runs the code reached a practically linear scaling and a top performance of more than 70\% for 128 CPUs. We have now started to improve the code and to further increase itsperformance in order to efficiently use 512 CPUs. On such configuration we will be able to consider for the first time obliquely propagating modes (2D) as well as electromagnetic effects on micro-turbulence, structure formations, transport and acceleration by means of a five-dimensional Vlasov-code. To study the influence of turbulence and phase space structuring onto the anomalous transport and acceleration processes in collisionless astrophysical plasmas we plan to perform a series of simulations in dependence on realistic plasma parameter, such as drift velocities, magnetic field, temperature anisotropy, first for four-dimensional and than for five-dimensional systems and electromagnetic turbulence.Major goals of this project are, in particular, the derivation of anomalous dissipation and resistivity in collisionless astrophysical plasmas, i.e. of the microscopic momentum exchange and heating rates. This should include the ab initio consideration of strongly nonlinear effects like phase space structuring of the microscopic plasma turbulence, for which a Vlasov approach is mandatory. The derived macroscopic transport properties in dependence on macroscopic plasma parameters will provided for their incorporation in macroscopic fluid models of, e.g. of reconnection but we will also directly derive the spectra of accelerated energetic particles.
