Simulation and visualization of processes in laser-generated plasma
The advent of laser systems that can deposit within a few nanoseconds energies onto a solid target, which amount to more than one mega-Joule, has placed within our grasp controlled thermonuclear fusion. The direct deposition of this laser energy onto the surface of the fuel capsule, or on a hohlraum target that irradiates it (indirect drive), heats the capsule up to about one hundred million centigrades.
The tremendous thermal pressure of the -instantly vaporized- surface and, more specifically, gradients in the thermal pressure lets the capsule implode. Nuclear fusion processes start in its core, provided that an adequate amount of radiation- and thermal energy reach it. The fusion processes consume the fuel in the core and, ideally, work their way to its surface within picoseconds. The target expansion is negligible during this short time interval and the high temperature and pressure that uphold fusion can be maintained; hence the name inertial confinement fusion. It is anticipated that the ICF experiments at the now operational National Ignition Facility NIF (Lawrence Livermore labs, USA, https://lasers.llnl.gov/ ), will reach in the near future the ignition conditions in fuel capsules composed of deuterium and tritium.
The extreme temperatures in the imploding capsule separate electrons from the atoms of the target material, turning them into positively charged ions. The positive and negative charges can move independently and their ensemble constitutes a plasma. Collisions between individual particles are infrequent during the relevant timescales. They can be neglected outside the core of the imploding capsule and the plasma particles interact predominantly through electromagnetic forces.
Objectives of the project
We investigate in our project, which is supported financially by Vetenskapsrådet (VR), and in close collaboration with research groups at the Queen's University Belfast (UK) and at the Universidad de Castilla-La Mancha (Spain) the plasma acceleration by gradients in its thermal pressure and the interaction of beams of charged particles with a background plasma. We examine wave spectra and the nonlinear structures that develop during these processes and how they act back on the plasma.
Our contribution to the joint research project are particle-in-cell simulations (http://en.wikipedia.org/wiki/Particle-in-cell) and the analysis,visualization and interpretation of their data. The simulations, which are enabled by a computer time allocation by the SNIC ( http://www.snic.vr.se/snic-committees/snac ), are currently performed on the PC clusters of the HPC2N computer center (http://www.hpc2n.umu.se/) in Umeå.