2009-07-03
| Professor Chuang Ren |
| Department of Mechanical Engineering, Department of Physics and Astronomy, University of Rochester |
| Time: 9:30 am, July 3, 2009 |
| Place: Rm. 616 Meeting Room |
| Abstract: We present particle-in-cell (PIC) and fluid simulations on the two-plasmon-decay (TPD) instability under conditions relevant to direct-drive inertial confinement fusion experiments. Under these conditions, the PIC simulations show a wide TPD spectrum, with modes whose perpendicular mode number k^ larger than the cutoff predicted by the linear theory for absolute modes. The fluid simulations, solving the full set of the linear equations of TPD, clearly show that these large- k^ modes are convective and have linear growth rates comparable to the absolute modes. The convective modes grow at the lower density region and can cause pump depletion, reducing the growth of the absolute modes. Even though they saturate before reaching the convective limit, the convective modes are energetically dominant in the nonlinear stage. The PIC simulations show that both the absolute and convective modes saturate due to ion density fluctuations, which can turn off TPD by raising the instability threshold through mode coupling and lead to intermittent growth. The results show that the convective modes of TPD are important to the performance of current and future direct-drive experiments. This work was supported by U.S. Department of Energy under Grants Nos. DE-FG02-06ER54879 and DE-FC02-04ER54789. The research used resources of the National Energy Research Scientific Computing Center. |
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