Two-Plasmon-Decay Hot Electron Generation and Reheating in OMEGA Direct-Drive-Implosion Experiments

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1 Two-Plasmon-Decay Hot Electron Generation and Reheating in OMEGA Direct-Drive-Implosion Experiments r 1/4 ~500 nm Ne To sheath e Laser r e To core 20 nm J. F. Myatt University of Rochester Laboratory for Laser Energetics 40th Annual Anomalous Absorption Conference Snowmass Village, CO June 2010

2 Summary Hot-electron temperatures and preheat caused by TPD have been computed for OMEGA direct-drive parameters An extended Zakharov model of the two-plasmon-decay (TPD) instability is used to predict the saturated Langmuir wave spectrum for OMEGA implosions the Langmuir wave spectrum extends right up to the Landau cutoff after profile modification is complete The hot-electron production is calculated by a test-particle approach using the Zakharov predictions for the electric fields hot-electron recirculation and reheating is an important effect for numerical simulations this effect manifests itself through the boundary conditions Hot-electron temperatures of 30 kev are obtained in comparison with 15 kev when recirculation is neglected TC8642n

3 Collaborators J. A. Delettrez, D. H. Edgell, A. V. Maximov, W. Seka, and R. W. Short, University of Rochester Laboratory for Laser Energetics D. F. DuBois Los Alamos National Laboratory and Lodestar Research Corporation D. A. Russell Lodestar Research Coporation H. X. Vu University of California, San Diego

4 The Zakharov equations are extended when applied to the two-plasmon-decay problem Extended Zakharov equations used in Zak* d : : D -~ ] dn + dng n DE = ` e m jd : 8d_ E : Ei -E d : EB + S LW c 0 0 E 2 2 DIAWdn = d E _ rm i + S d 16 i n TPD source term Dispersion relations for LW and IAW Wave envelopes D LW 2 2 = 92i~ _ 2 + o ) i + 3o d C Eu = 1 2 E^x, y, th exp 9- i`~ tjc + c. c p0 t e e p0 D IAW t i t sd = `2 + 2o ) 2 - c j / Eu = e E 0 y i 0 i exp 9i k : x -i`~ - 2~ jtc 0i 0 p0 TC8454a * D. F. DuBois et al., Phys. Rev. Lett. 74, 3983 (1995); D. A. Russell and D. F. DuBois, Phys. Rev. Lett. 86, 428 (2001).

5 The Zakharov model predicts that a saturated state is formed for OMEGA conditions after several tens of picoseconds n e /n c Laser TC8457c A region of plasma-wave excitation rapidly spreads down the density gradient, modifying the density profile as it does so The LW electric field and the nonlinear density perturbations are averaged over the transverse coordinate x (nm) t = 10 ps t = 30 ps t = 70 ps x (nm) Ion-acoustic spatial frequency ~3 k x (nm) LW intensity ( E 2 ) 0

Test-particle trajectories are integrated in the saturated Zakharov fields showing the importance of boundary conditions Corona Reflected from sheath x (nm) 10 8 6 4 2 0 0 10 20 30 40 x (nm) E

6 Test-particle trajectories are integrated in the saturated Zakharov fields showing the importance of boundary conditions Corona Reflected from sheath x (nm) x (nm) E statvolt/cm # f e (E) keV Maxwellian 15-keV tail Energy (kev) Hot-electron temperature is consistent with RPIC* The heating problem cannot be investigated in isolation. TC8647a *H. X. Vu (this conference)

7 The recirculation at the inner boundary (pointing toward the center of the target) and the outer boundary (pointing into the corona) have a different physical origin Angle b is the angle with respect to the outward normal of the simulation volume Quarter-critical surface Dense shell Simulation domain b v 0 Input r sheath L3 mm b Location of ion sheath Underdense corona r 1/4 ~500 nm Output r 1/4 ~500 nm bʹ vʹ TC8644a The delay at the inner boundary is short, with significant energy loss; the delay at the outer boundary is long, with little energy loss

8 The energy and time of flight of the returning electrons has been tabulated at both boundaries for typical OMEGA cryogenic-implosion parameters For b L 40 : hot electrons with E L 40 kev can easily recirculate through the inner boundary For E >10 kev: electrons can return to the outer boundary Returning energy (kev) TC8646a Inner boundary Flight time (ps) 8 6 Inner boundary b = 0 b < 40 4 b > 40 b > b = Energy (kev) b = Energy leaving (kev) Flight time (ps) Outer boundary Very weak dependence on b Energy (kev)

9 Use of physical boundary conditions leads to a highertemperature test-particle distribution keV Maxwellian f e (E) One pass: 15-keV tail Recirculating: 30 kev Energy (kev) TC8852

10 The coupling of test-particle energy to the target core is increased dramatically when recirculation is included 100 Deposited energy (kev) One-pass trajectories Initial energy (kev) TC8853

11 The coupling of test-particle energy to the target core is increased dramatically when recirculation is included 100 Deposited energy (kev) Multiple-pass trajectories One-pass trajectories Numbers of transits Initial energy (kev) Initial energy (kev) TC8853a

In planar-foil experiments the hot-electron temperature is estimated to be ~20 kev Raw image plate Tungsten Filter Puck 3-mm diam, 1-mm thick with 0.

12 In planar-foil experiments the hot-electron temperature is estimated to be ~20 kev Raw image plate Tungsten Filter Puck 3-mm diam, 1-mm thick with 0.9-mm deep V groove Intensity (arbitrary units) E19017a 20 0 Angle (º) keV fit Lineout of intensity Y (mm) The difference in transmission through the grooved disc suggests a hot-electron temperature of ~20 kev This is much less than the ~60 kev indicated by the HXRD channels for similar shots

13 Summary/Conclusions Hot electron temperatures and preheat due to TPD have been computed for OMEGA direct-drive parameters An extended Zakharov model of the two-plasmon-decay (TPD) instability is used to predict the saturated Langmuir wave spectrum for OMEGA implosions the Langmuir wave spectrum extends right up to the Landau cutoff after profile modification is complete The hot-electron production is calculated by a test-particle approach using the Zakharov predictions for the electric fields hot-electron recirculation and reheating is an important effect for numerical simulations this effect manifests itself through the boundary conditions Hot-electron temperatures of 30 kev are obtained in comparison with 15 kev when recirculation is neglected TC8642

Delay-type boundary conditions are proposed that will mimic the effect of the target in kinetic calculations Exiting particles come back at a later time with a modified velocity vector based on

14 Delay-type boundary conditions are proposed that will mimic the effect of the target in kinetic calculations Exiting particles come back at a later time with a modified velocity vector based on look-up tables Preheat and x-ray accounting will be done For example: consider an electron exiting the inner boundary The test-particle calculations will guide the development of a quasilinear Zakharov model Periodic r 1/4 v 0 To sheath Random x bʹ vʹ Laser vʹ bʹ b x r b To core v 0 TC8643a Periodic

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

An Investigation of Two-Plasmon Decay Localization in Spherical Implosion Experiments on OMEGA An Investigation of Two-lasmon Decay Localization in Spherical Implosion Experiments on OMEGA 1 12 50 23 14 27 18 32 J. F. Myatt University of Rochester Laboratory for Laser Energetics 24 56th Annual Meeting