Two-Plasmon Decay Driven by Multiple Incoherent Laser Beams

Transcription

1 Two-Plasmon Decay Driven by Multiple Incoherent Laser Beams 2 # # E^xyt,, h dy dy^arbitrary h n Two coherent e /n c plane waves Dm = 8.8 Å Dm = 17.6 Å Arbitrary 4 Arbitrary 2 Arbitrary t (ps) J. Zhang University of Rochester Laboratory for Laser Energetics 55th Annual Meeting of the American Physical Society Division of Plasma Physics Denver, CO November 213

2 Summary Two-plasmon decay (TPD) driven by multiple incoherent beams in inhomogeneous plasma is investigated Multiple coherent laser beams can share plasma waves in both large -and small*-k regions TPD driven by laser beams with finite temporal bandwidth and spatial incoherence give a higher absolute threshold A more-realistic model including both distributed phase plates (DPP s) and smoothing by spectral dispersion (SSD) is in development TC1856 C. Stoeckl et al., Phys. Rev. Lett. 9, 2352 (23); D. T. Michel et al., Phys. Rev. Lett. 19, 1557 (212). *J. F. Myatt et al., Bull. Am. Phys. Soc. 57, 299 (212); J. Zhang et al., ibid. * R. W. Short et al., Bull. Am. Phys. Soc. 57, 3 (212).

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

4 The Zakharov model is a time-enveloped fluid moment model that describes the coupling between Langmuir and ion-acoustic fluctuations Extended Zakharov model equations Collisional plus Landau damping Density B d: : 2i~ _ 2 + o % i + 3o 2d2 ~ 2 _ dn+ dni/ n DE p t e e p N N / / = e/ 4 m E, E* E, E* e e d: d i t m: md : ~ 2~ ^ h > ^ h H _ pe i + SE m = 1 m = Laser source Noise source 2 2 c2 2 1 n t i t s 16 m E o % 2 d C d = r fd + 4 d E, m p, 5 i m = Landau damping for Ponderomotive force ion-acoustic waves N where the laser field E = / E ^xt, hexp^ i~ th + cc.. L m, m N / TC1648b D. F. DuBois, D. A. Russell, and H. A. Rose, Phys. Rev. Lett. 74, 3983 (1995); D. A. Russel and D. F. DuBois, Phys. Rev. Lett. 86, 428 (21).

5 Multiple laser beams can share plasma waves in both large- and small-k regions Energy spectrum of a Langmuir wave (LW) during the linear growth phase (early time, arbitrary ) k y /k 2 1 " k,1 " k,2 27 GE 2 H Common wave at large k (convectively saturated)* 1 2 Landau cutoff (LC) Common wave at small k (corresponding to Simon s absolutely unstable modes) TC1651b k x /k R. W. Short et al., Bull. Am. Phys. Soc. 57, 3 (212); * J. F. Myatt et al., Bull. Am. Phys. Soc. 57, 299 (212); J. Zhang et al., ibid. *D. T. Michel et al., Phys. Rev. Lett. 19, 1557 (212).

6 The investigation of TPD in incoherent laser beams is broken into three parts Temporal bandwidth is introduced in a way that is similar to SSD* a large bandwidth (Dm á 1 Å) is required to modify absolute growth Spatial incoherence is introduced using a DPP model** the first investigations have looked at a single DPP speckle A model that includes both temporal and spatial bandwidth is under development TC114 *S.Skupsky et al., J. Appl. Phys. 66, 3456 (1989). **H. A. Rose et al., Phys. Fluids B 5, 59 (1993).

7 The effect of temporal bandwidth on the absolute threshold for a single beam is investigated Et ^ h = E exp^id ) sin~ m th; similar to SSD* here d and ~ m are the modulation amplitude and frequency D~ = d~ ; Dm m = D~ ~ 2 m Absolute growth rate for different temporal bandwidth c/~ ( 1 3 ) 1..5 Coherent plane wave Dm = 16.8 Å Dm = 33.6 Å T kev = 2; L nm = 15; normal incidence Temporal bandwidth used here is one order larger than the growth rate Dm = 33.6 Å increases the threshold intensity by ~3 %. TC I 14 (I 14 ) Simon** **S.Skupsky et al., J. Appl. Phys. 66, 3456 (1989). ** Simon et al., Phys. Fluids 26, 317 (1983).

8 Temporal bandwidth must be large to have an effect on the TPD saturation level t (ps) Nonlinear calculations Two laser beams polarized in the same plane (p-polarized) I 14 = 4, L n = 15 nm, T e = 2 kev, i = 27 (Laser intensity is 1.2 above absolute threshold) Two coherent plane waves Dm = 8.8 Å Dm = 17.6 Å Arbitrary 4 Arbitrary 2 Arbitrary Common wave 1 at small k Common wave 5 at large k 2 # # E^xyt,, h dy dy^arbitrary h If the temporal bandwidth is large enough to suppress absolute modes, the saturation level is greatly reduced. TC1858

9 A DPP model* is in development to include spatial incoherence Comparisons are underway between DPP and single speckle y (nm) y (nm) TC1659 An example of 2-D DPP laser beam with f/ Single speckle with f/ Arbitrary Arbitrary threshold ^ peak int ensity h 14 2 I Wcm / Single Gaussian laser beam with different f number: f= ~ a m ; TkeV = 2; Lnm = 15 Plane wave threshold f number So far it appears that the threshold is increased as the speckle f number (width) decreases. *H. A. Rose et al., Phys. Fluids B 5, 59 (1993).

10 Summary/Conclusions Two-plasmon decay (TPD) driven by multiple incoherent beams in inhomogeneous plasma is investigated Multiple coherent laser beams can share plasma waves in both large -and small*-k regions TPD driven by laser beams with finite temporal bandwidth and spatial incoherence give a higher absolute threshold A more-realistic model including both distributed phase plates (DPP s) and smoothing by spectral dispersion (SSD) is in development TC1856 C. Stoeckl et al., Phys. Rev. Lett. 9, 2352 (23); D. T. Michel et al., Phys. Rev. Lett. 19, 1557 (212). *J. F. Myatt et al., Bull. Am. Phys. Soc. 57, 299 (212); J. Zhang et al., ibid. * R. W. Short et al., Bull. Am. Phys. Soc. 57, 3 (212).