Ultra-short pulsed laser-plasma systems as Hyperspectral Radiography Sources: 3D Particle-In-Cell Simulations

In order to investigate or control the extremely fast (10**(-15)) and/or small-scale (sizes of molecules) processes such as implosions, strong shock waves, solid microstructure transformations and microbiological changes, one needs the diagnostic equipment with comparable, very high, resolution. The requirement of high resolution calls for the development of super-short (for temporal resolution) point-like (for spatial resolution) sources of probing radiation. The latest developments in laser technology ensure that the next generation of radiographic imaging and tomography applications will be based on tabletop super-powerful pulsed lasers*. Such systems provide excellent resolution while being powerful, compact and controllable.

* PetaWatt lasers with the intensities above 10**19 W/cm 2 can accelerate beams of electrons to multi-MeV energies at mJ laser energy scale at a 1 kHz repetition rate. The corresponding brightness of the electron beams can be the highest ever achieved. At the same time, the laser-based systems allow for coherent control of the relativistic motion of charged particles and precise focusing of the particle beams.

In addition to bright radiation sources, the tabletop laser systems can serve as beam accelerators for inertial material confinement fusion (fast ignition), nuclear physics (separating short-lived isotopes), hadron radiation therapy in medicine and other novel applications.

The technology of laser-induced bright sources and beam accelerators involves complex multi-step physical processes. These processes include the interaction of a high-intensity ultra-short laser pulse with a complex solid target, plasma formation, laser-plasma interaction, generation of high-energy electrons, ions and x-rays, generation of neutrons in the subsequent nuclear reactions, and the propagation of the secondary radiation through the laser-excited material of the multi-layer target.

In order to form an efficient source of radiation, the above processes must be configured and matched in an optimal way. Because experimental optimization is costly and slow, realistic computer simulations become a major part of this effort.

BTG solves the problem of optimizing the design of the laser-based bright point-like pulse sources of radiation and particle beams by a coupled series of computer simulations.

In our new project, we are applying our proprietary multi-dimensional (2D and 3D) relativistic, fully implicit, massively parallel Particle-In-Cell (PIC) code MANDOR to investigate laser-pulse interaction with plasma and the resulting generation of the high order harmonics, plasma-emitted X-rays and particle (electron, ion and neutron) beams. Monte-Carlo methods (MCNPX code) will be used to further calculate the propagation of the secondary heavy particles.



Results of our 2D PIC calculations of the laser-beam propagation through the overdense plasma. Left top pictures show spatial distribution of the electromagnetic energy density without channel formation. Right top panel shows the evolution of magnetic field distribution with channel formation. Bottom: Spatial distribution of electron density without (upper) and with channel formation