Speaker：Dr. Rui Yan (University of Rochester)

Chair Person: Wei Kang (Distinguished research fellow)

Date：September 11, 15:30-16:30

Place：Room 210 COE Building No.1

Report Introduction:

Laser plasma instabilities (LPI) are critical concerns in inertial confinement fusion (ICF).We present a series of 2-D particle-in-cell (PIC) simulations using the full PIC code OSIRIS on the long-term (~10-ps) nonlinear behaviors of LPI near the 1/4-critical-density surface, especially the two-plasmon-decay (TPD) instability, for parameters relevant to direct-drive inertial confinement fusion. When the TPD threshold is exceeded, the simulation results show that significant laser absorption and energetic electron (>50-keV) generation occur in the nonlinear stage. The energetic electrons are mostly forward oriented, which poses a preheating risk for targets. The hot electrons are stage-accelerated from the low-density region to the high-density region. New modes with small phase velocities develop in the low-density region after saturation. These modes can couple to background thermal electrons and form the first stage for electron acceleration. In the PIC simulations the ion-density fluctuations are observed to be driven by plasma waves through the ponderomotive forces. Electron-ion collisions are shown to significantly reduce the efficiency of this acceleration mechanism. The shock ignition regime involves higher laser intensities. Long-term simulations show an intermittent bursting pattern of laser–plasma instabilities, resulting from a coupling of the modes near the quarter-critical surface and those in the lower-density region via plasma waves and laser pump depletion. The majority of the hot electrons are found to be from stimulated Raman scattering and of moderate energies. However, high energy electrons that threaten to preheat the fuel can still be generated by the two-plasmon decay instability.

About Speaker:

Rui Yan: Graduated from the University of Science and Technology of China in 2005, department of modern mechanics, Bachelor degree. Graduated from the Rochester University, department of mechanical engineering in 2011, doctor degree. Now work in the Rochester University as a Research Associate.