Transcript Document
LSP modeling of the electron beam propagation in the nail/wire targets FSC Mingsheng Wei, Andrey Solodov, John Pasley, Farhat Beg and Richard Stephens Center for Energy Research, University of California, San Diego LLE, University of Rochester, General Atomics, San Diego Electron beam propagation and heating of the background plasmas in method 1 Motivations - Use LSP hybrid code to simulate large scale plasma that is comparable to the real experiments. - Study the electron beam transport in the nail/wire target - Benchmark code against the experiments Nail target, Cu2+ plasma, 20μm diameter wire Wire target, Cu2+ plasma, 50 μm diameter wire t=0.5ps (pulse center) t=1ps t=1ps t=0.5ps (pulse center) t=1ps We aim to accurately model the nail/wire experiments That means properly describing the experiment as well as properly simulating the physics Target geometry Laser pulse - including prepulse Properly generate current Analyze in terms of diagnostics Preformed plasma produced by the laser prepulse has been modeled using the 2d rad hydro code h2d. Density contour in low region high region Courtesy of P. Patel at LLNL Initial target position at z=0 r =7μm r =0 Two methods used for modeling the experiment with LSP code r =25μm Energetic electron beam production, propagation and heating of the background plasmas in method 2 (preliminary results) Method 1: Hot electron beam promoted from the background electrons using the empirical scaling LASER pulse: Gaussian, 0.5 ps (FWHM) energy: 81 J spot size: 16.4 µm (FWHM) intensity: 51019 W/cm2 r =17μm r =0 r =10μm kinetic electron density r=0.9 µm r=7.6 µm r=25 µm Background electron temperature Hot electron current vs time ELECTRON BEAM conversion efficiency: 30% average energy: Th~2.23 MeV angular spread: 34 (half-cone angle) t = 0.5 ps t = 1.0 psc t = 1.4 ps t = 0.5 ps t = 1.0 ps Method 2: Hot electron beam produced from the laser plasma interaction 12 µm underdense plasma kinetic electrons 300 µm Ti wire Target: - 12 µm kinetic electrons (underdense to critical density) - background solid density Ti(+15) with Tinitial 100 eV, electrons as the fluid species 50 µm 10% of laser energy is transferred to hot electrons which cause significant reduced heating compared to that using the excitation model. MA current is carried by hot electrons. Hot electron density drops quickly (by 10 fold) in the first 20 µm. Strong azimuthal B field and radial E field are generated on the wire surface. Laser beam launched from the left boundary - Focal spot size: r0=7.5 µm - 65 J in the focal spot - 0.5 ps (top hat profile) - I~ 7.361019 W/cm2, a0=7.4 Grid szie: - r: 0.312 -0.615 µm - z: 0.182 - 1 µm -Time step: 0.03um B ~ 25 MG Er ~ 2.5 MV/µm Future work: Simulation for the longer wire case Including the self-consistent ionization model Analyze the simulation data in terms of diagnostics used in the experiments t = 1.0 psc * This work is supported by the U.S. Department of Energy under Contract No. DE-FG03-00ER54606, No. DE-FC02-04ER54789, and No. DE-FG02-05ER54834 This work is also partially supported by the National Center for Supercomputing Applications under grant number PHY050034T and utilizes the computer facilities in SDSC. t = 1.4 ps