An Investigation of Two-Plasmon Decay Localization in Spherical Implosion Experiments on OMEGA

Transcription

1 An Investigation of Two-lasmon Decay Localization in Spherical Implosion Experiments on OMEGA J. F. Myatt University of Rochester Laboratory for Laser Energetics 24 56th Annual Meeting of the American hysical Society Division of lasma hysics New Orleans, LA October 2014

2 Summary Three-dimensional calculations demonstrate the spatial localization of the two-plasmon decay (TD) instability in spherical implosions Multibeam laser plasma instabilities (LI s) must be studied in three dimensions The laser plasma simulation environment (LSE) code describes TD in 3-D fast, makes efficient use of memory, and extensible includes 3-D visualization tools three-dimensional calculations can be performed in ~1 h The TD localization in spherical targets is consistent with experimental observations. TC11469

3 Collaborators J. Shaw, J. Zhang, A. V. Maximov, R. W. Short, W. Seka, D.. Edgell, and D.. Froula University of Rochester Laboratory for Laser Energetics D. F. DuBois, D. A. Russell Lodestar Research Corporation. X. Vu University of California, San Diego

4 The effects of multibeam TD on direct-drive implosion designs must be quantified (~ pump, k pump ) (~ EW1, k EW1 ) e (~ EW2, k EW2 ) EW: electron plasma wave e In-line models of TD that can be implemented in hydrocodes are required quantify the effects of TD on time-dependent drive account for hot-electron preheat TC11296a A model that can be used to search for and test TD mitigation strategies is required linear threshold* nonlinear saturation *R. W. Short et al., O , this conference.

5 LSE is a practical model that is being used to address these questions It solves the fundamental TD equations for linear response in an arbitrary hydrodynamic profile (density, temperature, velocity) with an arbitrary number of beams LSE includes nonlinear saturation mechanisms that are related to the coupling of Langmuir waves (LW s) to low-frequency density fluctuations performance (one run in ~1 h on 96 Intel cores) setup (either planar or spherical target simulations are automated) connected to experiment via diagnostics package tools for the exploration/visualization of large 3-D datasets LSE is extensible a hot-electron package has recently been implemented TC11297

6 The simulation volume is determined by the density scale length and the Langmuir wave correlation length Multiple beams 15 nm n e = 0.19 n c ne = 0.27 nc 15 nm OMEGA cryogenic implosion y z x 50 nm n c /4 Dense shell Few 10s nm r ~ 0 nm i.e., it is a local analysis in the neighborhood of a point r = (r,i,z) on the quartercritical surface Laser r ~ 500 nm Laser Times up to 100 ps TC11243a

7 Interaction conditions vary along a path on the n c /4 surface (e.g., a line of longitude) because of the beam-spot shapes and beam symmetry Radius (nm) Shot 62737, LILAC at t = 2.2 ns Radius (nm) n c /5 n c /4 Distributed phase plate (D) = SG4 Multibeam TD favors symmetry bisectors of beam pairs centers of EX or ENT ports Impact parameter I 14 ~ 2±17.5% 150-J/beam, triple-picket, 2.5-ns pulse n c /5 I E21347e

8 A series of runs computed the effects of an excursion across 17 with both large (SG4) and small (SG2) spot phase plates End of simulation box: ne = 0.19 nc nm z y nm TC R = 500 nm i = z = x

9 A series of runs computed the effects of an excursion across 17 with both large (SG4) and small (SG2) spot phase plates End of simulation box: ne = 0.19 nc nm nm TC110a R = 500 nm i = z = z y x

10 A series of runs computed the effects of an excursion across 17 with both large (SG4) and small (SG2) spot phase plates End of simulation box: ne = 0.19 nc nm R = 500 nm i = z = z nm TC110b y x

11 The LSE simulations show that TD depends on the beam spot shape (at constant power and hydrodynamics) SG4 phase plates have a focal spot that is close to the target diameter in size; SG2 phase-plate spots are roughly half the diameter Can be compared with the observations of local temperature islands * E 2 rms (arbitrary units) Saturated LW rms (root-mean-square) energy density on the position of the 165 n c /4 surface Azimuth = 54 SG2 SG olar angle ( ) TC11244b *W. Seka et al., hys. Rev. Lett. 112, (2014).

12 The LSE simulations predict a similar structure to that observed in half-harmonic images* through a hex port** Room-temperature C target (880-nm diam), SG2, SSD off Room-temperature C target (870-nm diam), SG4, SSD on 2.5-ns triple-picket pulse, kj, I 14 (nominal) ~ 9.5 I 14, single beam ~1.3 TC115a Distance (nm) Distance (nm) Distance (nm) Distance (nm) SG4 SG2 E 2 rms (arbitrary units) Azimuth = 54 SG4 SG olar angle ( ) * J. Zhang et al., O , this conference. ** W. Seka et al., hys. Rev. Lett. 112, (2014); W. Seka et al., O , this conference.

13 Summary/Conclusions Three-dimensional calculations demonstrate the spatial localization of the two-plasmon decay (TD) instability in spherical implosions Multibeam laser plasma instabilities (LI s) must be studied in three dimensions The laser plasma simulation environment (LSE) code describes TD in 3-D fast, makes efficient use of memory, and extensible includes 3-D visualization tools three-dimensional calculations can be performed in ~1 h The TD localization in spherical targets is consistent with experimental observations. TC11469