Learn more about our most recent projects and collaborations.

Hot Electron Scaling and Energy Coupling in Nonlinear Laser Plasma Interaction


Hot electron generation in high power laser-plasma interaction is a fundamental physics problem. In the context of high-energy-density laboratory plasmas (HEDLP), hot electrons can be generated through nonlinear laser plasma instabilities (LPI), such as stimulated Raman scattering (SRS) and two-plasmon decay (TPD).

These hot electrons can preheat the target shell and degrade the implosion, and most previous investigations to date are carried out below the LPI thresholds to avoid the preheating effect. On the other hand, the advanced shock ignition (SI) fusion scheme with a slower implosion velocity and a reduced driver energy requires launching a high intensity ignitor spike pulse at the end of a fuel assembly phase to generate a strong shock to ignite the fuel. Copious hot electrons are expected in the SI-scale high intensity condition. It has been envisaged that moderate energy hot electrons (<200 keV) could further enhance the ablation pressure when depositing their energies in the high density compressed outer shell region and thus augment the ignitor shock, beneficial to SI. There is still lack of understanding of the physical processes in nonlinear LPI and subsequent hot electron generation and energy coupling in this new regime.

In this project, we are studying LPI and the dependence of hot electron generation and energy coupling on high power laser intensity, wavelength, and target ablator material in nonlinear laser-plasma interaction at SI scale high intensity. Experiments are conducted using the high energy OMEGA-EP and OMEGA-60 lasers at the Laboratory for Laser Energetics in the University of Rochester with the beam time awarded via DOE NNSA's National Laser User's Facility (NLUF) program. The temperature and energy of hot electrons generated by LPIs are measured and the hot electron spatial energy deposition is imaged in experiments. Advanced diagnostics including backscattering and angular filter refractometer are used to diagnose the region and the mechanism of the main LPI present in SI conditions. Simulations are planned to be performed on NERSC with the particle-in-cell (PIC) code OSIRIS, a state-of-the-art, fully explicit, multi-dimensional, fully parallelized, fully relativistic PIC code which we have access to. The simulation results can be compared with the results from experiments to have a precise understanding of the LPI mechanisms. This project is expected to have a broad impact on the resolution of basic nonlinear laser-plasma interaction physics issues and particularly important for fusion related HEDLP applications, specifically for the SI scheme.

Systematic study of fast electron energy deposition in imploded plasmas with enhanced EP laser contrast and intensity

DoE/NNSA National Laser Users Facility

In our FY 11 and 12 NLUF project, we developed a platform on the OMEGA laser at the Laboratory for Laser Energetics to visualize fast electron coupling into an imploded CD shell by adding Cu dopant to the inner part of the shell and characterizing the Cu fluorescence emission.

In these experiments, the shell is imploded with the OMEGA long pulse lasers (~18 kJ in UV) and the OMEGA EP short pulse laser (> 1.5 kJ, 10 ps) is injected into a Au cone embedded in the shell, generating a beam of fast electrons. Fast electrons make binary collisions with Cu atoms in the compressed shell causing emission of Cu K-alpha x-rays. A Spherical Crystal Imager (SCI), which was implemented for the first time in the OMEGA chamber for this work, provides 2D images of Cu K-alpha emission from heated regions which can be used to extract information about the fast electron spatial distribution and the coupling efficiency into the core. We will investigate the fast electron coupling into the imploded plasma using the recently improved OMEGA EP laser with enhanced contrast and higher intensity (5x1019 Wcm-2).

Dynamics of high-energy proton beam focusing and transition into solid targets of different materials

DoE/NNSA National Laser Users Facility

Intense, focused proton beams have applications ranging from isochoric heating of plasma to imaging shock waves and magnetic fields. Beam production and use involve a constantly evolving target/plasma topology and hot electron flow as the protons are accelerated from a shaped surface into vacuum and then transition into target plasmas for heating or probing.

The dynamics involved become more complex as the laser energy and resulting beam current increase, and as beam pulse length increases. We have been awarded OMEGA EP laser time at the Laboratory for Laser Energetics to use high energy short pulse laser beams to extend previous proton focusing/transition studies to 10 ps pulse duration. We will be collecting detailed information about the forces that affect such beams, utilizing the second EP beam to produce protons to probe conditions set up by the first EP laser beam. Energy deposition and heating of a solid foil (dense plasma) by the focused proton beam will also be characterized by measuring its induced K-shell fluorescence emission via x-ray imaging and spectroscopy techniques. Our goal is to extend our understanding of the High-Energy Density physics involved facilitating optimal source designs for various medical and energy applications and eventually experiments like NIF integrated proton fast ignition experiments with the Advanced Radiographic Capability (ARC) beam.

Fusion Science Center for Extreme States of Matter

DoE/Office of Fusion Energy Science

UC San Diego is an integral part of Fusion Science Center (FSC) for Extreme States of Matter. The aim of FSC is to develop an understanding of the physics of creating extreme states of matter using a combination of high-energy drivers (compression) and high-intensity lasers (heating).

Experiments have been conducted at the major national high-energy-density (HED) science facilities (OMEGA-EP, NIF, and Z) in a synergistic relationship with a National Nuclear Security Administration (NNSA) initiative for short pulse HED science. The Center brings academic scientists from around the country into a collaboration that fosters rapid progress in this exciting field. A major long-term goal is to study fast ignition as a potential future energy source. UR Fusion Science Center

Systematic Study of Fast Electron Transport and Magnetic Collimation in Hot Plasmas

DoE/NNSA National Laser Users Facility

Understanding fast electron transport in hot dense plasma is crucial to the success of fast ignition laser fusion. In the FI scheme with MeV energy (fast) electrons, an intense laser pulse (few 00's kJ in a pulse duration of ~10 ps) is used to heat a compressed core created by the irradiation of long pulses.

The FI is expected to achieve a higher gain comparing to the conventional laser fusion (i.e. central hot spot ignition). For the success of FI, The fast electron transport in hot dense plasma needs to be addressed. In the on-going National Laser Users Facility (NLUF) project of our group, the transport of fast electrons generated by 1 kJ level short pulse beam (10 ps duration) will be studied in a hot plasma (Te ~ few 10's eV and Ne ~ 1022 /cm3) with a volume of ~ 0.2 mm3 on the Omega EP laser facility at the Laboratory of Laser Energetics (LLE), the University of Rochester.

Advanced Concept Exploration (ACE)

DoE/Office of Fusion Energy Science

The SCE consortium consists of General Atomics, Lawrence Livermore National Laboratory, the Laboratory for Laser Energetics (LLE), Ohio State University (OSU), UC San Diego, and the University of Nevada at Reno (UNR).

This Consortium addresses physics related to controlling the laser-induced generation of large electron currents and their propagation through high density plasmas. These issues are important for a wide range of HED phenomena, including high energy ion beam generation, isochoric heating of materials, the developement of high brightness backlighters and fast ignition inertial confinement fusion.

Resolving the Issue: The Dynamics of Magnetized Astrophysical Jets through Pulsed Power HEDP Laboratory Studies


This collaboration, known as JetPAC (Jets: A Plasma and Astrophysics Collaboration), is lead by Prof. Adam Frank at Rochester University, and involves the UCSD HEDP Group, the Plasma Physics Group at Imperial College London, and Rice University, TX.

The aim of the 5 year project is to more directly design and carry out experimental studies of plasma jets which have relevance to astrophyical jet formation and propagation, particularly those emanating from Young Stellar Object (YSOs). The project is unique in several ways. For the first time, pulsed power experiments will be carried out (Imperial, UCSD) with computational support from both the plasma (Imperial) and astrophysics (Rochester) communities, and will be guided by observational needs (Rice). The project has also secured shot time at the 26 MA Z machine at Sandia National Laboratories which will generate jets of unprecedented density and Reynolds number, and push experiments significantly further into the turbulent and astrophyically relevent regimes.
Visit the collaboration website for updates at its Wiki Site.

Assessment of Proton Deflectometry for Exploding Wire Experiments

DoE/NSF Basic Plasma Partnership

The development of proton deflectometry has greatly increased the extent to which rapidly spatially and temporally varing electromagnatic field structures can be diagnosed. High energy protons bursts are generated by intensity laser beams (>1019 W cm-2) and the need for such a laser facility has limited diagnosis of experimental fields to laser-driven pump-probe experiments.

This 3 year project, led by the UCSD HEDP Group and carried out the Nevada Terawatt Facility (NTF) , will for the first time use proton probing to diagnose B-field structures in pulsed-power driven exploding wire experiments. NTF has both a MA scale pulsed power generator and a high power, short pulse laser facility, and the proximity of these allows coupling of the two systems. The project will examine the broad space and time evoluion of the B-field in wire plasmas, and address outstanding issues in the distribution of current in ablation and imploding wire array z-pinches.