Plasma-based Accelerators and Radiation Sources
In Plasma-Based Acceleration a laser or a particle beam excites a plasma wake, thereby generating a structure that can support accelerating fields more than three orders of magnitude above those of conventional accelerators. A (second) particle beam properly loaded into the wake, can be accelerated to very high energy in a short distance. This mechanism makes it possible to develop compact accelerators for high-energy physics, for studying new materials and for medical applications. Read more.
Inertial Fusion Energy
In Inertial Confinement Fusion a capsule of hydrogen isotopes (DT) implodes under ablation pressure and the isotopes fuse, releasing energy. Fast Ignition has been proposed to decouple the compression from the ignition process. It relies on the electrons at the surface of the compressed target to absorb the energy of an ultra-intense laser pulse, travel through the dense plasma, and deposit that energy to the pellet’s core. Read more.
High Performance Computing
High Performance Computing (HPC) refers to obtaining the best performance possible in solving scientific problems on the most powerful computers. Our research relies on Particle-in-Cells (PIC) codes, which model plasmas by calculating the trajectories of billions of particles as they respond to external forces and to the forces particles exert on each other. Read more.
Continuation of the Application of Parallel Pic Simulations to Laser and Electron Transport through Plasma under Condition Relevant to ICF and HEDS
The UCLA simulation group develops and uses state-of-the-art simulation tools to study laser and beam interactions in high energy density plasmas. These tools run extremely efficiently on more than 100,000 processing cores. Understanding how a laser interacts with a high energy density plasma and the related generation of energetic electrons is essential for the success of the National Ignition Facility and of Inertial Fusion Energy and it is a of fundamental importance to the nonlinear optics of plasmas.
A laser propagating in plasma can effectively couple to plasma waves through instabilities named stimulated Raman scattering, two-plasmon decay, and the high-frequency hybrid instability. These are extremely complicated processes because they involve waves coupling to waves, particles surfing on waves, and the highly dispersive nature of plasma waves in density gradients. An ultra-intense laser provides pressures on a plasma in excess 100 Billion Atmospheres and it wiggles electrons at energies in excess of 100 Mega Electron Volts. Due to the complexity of these interactions, computer simulations that track individual trajectories of plasma particles are necessary to make sense of it all.
Using our massively parallel particle-in-cell codes, we discovered that packets of plasma waves behave very differently than their idealized cousins which are infinitely long and wide. They erode away and localize due to complex wave-particle interactions which can profoundly alter the reflectivity of the laser. We discovered that higher than expected electron energies occur when the laser scatters both backward and forward and this scattered light rescatters, generating a spectrum of plasma wave packets. Electrons first surf on the slower wave and then progressively bootstrap their way onto the faster waves. We found that for parameters expected in the future for inertial fusion energy that extremely strong absorption into energetic electrons can be generated near the so-called quarter critical density. We also found a new absorption mechanism for an intense laser impinging a sharp solid density plasma interface and studied how these electrons are transported forward.