Relativistic Particle Beam Generation from Short Pulse High Intensity Laser-Solid Interactions and Transport through Dense Plasma

Event Date: October 16, 2013
Speaker: Dr. Farhat Beg
Speaker Affiliation: Professor of Engineering Physics
Department of Mechanical & Aerospace Engineering, University of California San Diego
Type: Joint
Time: 3:30 p.m.
Location: WTHR 200

When a high intensity (Ipeak>> 1018 W/cm2) short pulse laser is irradiated on a solid target where the laser electric field is much stronger than the atomic field, the target surface is instantaneously ionized, creating ablative plasma. The laser energy  is  absorbed  and partly transferred into energetic electrons produced in the interaction. The hot electrons propagate away from the interaction region into the target, producing bremsstrahlung radiation up to several 10’s MeV range. As these hot electrons exit the rear surface of the target, they create the field [eE Th/max(Li,λDh ) , where Li is the ion scale length, Th is the hot electron temperature and λDh is the hot electron Debye length] that accelerates the impurities (protons and ions) to 10’s of MeV energies. These exotic properties of high intensity laser-matter interaction, and energetic particle generation has generated significant interest due to a number of applications (e.g. proton acceleration, electron- positron pair production, high energy K-alpha and gamma ray sources, table top electron accelerators and fast ignition). Most of these applications depend on the efficient transfer of laser energy into energetic particles. The efficient conversion efficiency depends on a number of factors, including laser prepulse, laser pulse length and intensity.

The focus of this talk will be on the underlying physics involving relativistic hot electrons generation and transport pertinent to fast ignition inertial confinement fusion. In the fast ignition (FI) scheme of inertial confinement fusion (ICF), compression of the fuel to high density and heating are achieved in separate processes. Similar to conventional ICF, a number of long pulse lasers can be used to compress the fuel shell to create high density plasma. Subsequently, a high energy (over 10 kJ), high intensity (over  1020 W/cm2),  short  (~10  ps)  laser  pulse  is  used  to  create  high-energy  (MeV) particles: electrons or ions, which then heat the compressed fuel plasma  to  initiate ignition. The requirements on the symmetry of the target are less stringent in FI compared to conventional ICF due to the external heating source. In addition, higher gain is expected with the FI scheme because more fuel mass can be assembled with less compression energy. This scheme involves some of the most challenging and complex physics of laser-matter interactions and energetic particle transport in varying density plasmas, both experimentally and numerically.

Bio: Farhat Beg received the Ph.D. degree in plasma physics from Imperial College, London. He was a Research Associate and then a Research Fellow  with Imperial College London. In 2003, he joined the faculty at the Department of Mechanical and Aerospace Engineering, University of California at San Diego, La Jolla, where he is currently the Vice Chair and a Professor of engineering physics. He has published over 170  articles  in  high  quality  journals—including  Nature,  Nature  Physics,  and  Physical Review Letters—and has been cited more than 4700 times in peer refereed journals. Dr. Beg has been fellow of the American Physical Society since 2009 and the Institute of Electronics and Electrical Engineers (IEEE) since 2011. He received the Department of Energy Early Career Award in 2005 and IEEE Early Achievement Award in 2008.


2013-10-16 15:30:00 2013-10-16 16:30:00 America/Indiana/Indianapolis Relativistic Particle Beam Generation from Short Pulse High Intensity Laser-Solid Interactions and Transport through Dense Plasma WTHR 200