Calculation of Half-Harmonic Emission Generated by the Two-Plasmon Decay Instability at exit boundary

Transcription

1 Calculation of Half-Harmonic Emission Generated by the wo-plasmon Decay Instability ^ h E D~ at exit boundary Arbitrary units inear conversion Nonlinear conversion homson down-scattering 40 Red shift J. Zhang University of Rochester aboratory for aser Energetics D~ Df = / r Hz ( ) 56th Annual Meeting of the Blue shift American Physical Society Division of Plasma Physics New Orleans, A 7 31 October 014

2 Summary Half-harmonic emission generated by two-plasmon decay (PD) is calculated with a new code, EMZAK Half-harmonic emission is one of the few experimental* observables of PD he Zakharov equations** are expanded to include transverse fields and are solved with a new code Half-harmonic emission can be generated by three different mechanisms linear conversion nonlinear conversion homson down-scattering For the case shown, nonlinear-mode conversion is dominant. C11571 * W. Seka et al., Phys. Rev. ett. 11, (014). ** D. F. DuBois, D. A. Russell, and H. A. Rose, Phys. Rev. ett. 74, 3983 (1995); D. A. Russell and D. F. DuBois, Phys. Rev. ett. 86, 48 (001); J. Zhang et al., Phys. Rev. ett. 113, (014).

3 Collaborators J. F. Myatt, R. W. Short, and A. V. Maximov University of Rochester aboratory for aser Energetics H. X. Vu University of California, San Diego, CA D. F. DuBois and D. A. Russell odestar Research Corporation, Boulder, CO

4 he generation of half-harmonic transverse waves occurs near quarter-critical density where PD angmuir waves (W s) turn n e /n c 0.31 aser Simulation box n c / x (nm) Damping region Simulation region n e = n 0 + dn(x) Damping region 6 y (nm) Parameters are relevant to an OMEGA spherical implosion Single laser beam I h 14 = 8; = 150 nm; = = ; m n e, kev i, kev = e,kev I n nm 14. ; o 4 ei = 188. # 10 ~ 0 C1157

5 he electrostatic Zakharov equations are extended* to include the transverse field (in -D so far) Electromagnetic Zakharov equations here E = E + E contains both longitudinal and transverse components - dn density inhomogeneity - dn density fluctuation i D 3V c 4r m e ; ~ pe0 ^ t + oeh + te ^dd : h ^d# d# h ^dn + dnhe E = e e 8d E E* E* E e i i t S 4m ^ 0 : h ^d : h ~ 0B + E e PD, stimulated Raman scattering (SRS), and homson down-scattering (DS) E 1 Dt i Dt cs d 6 + o % dn = + 16rm 4 i d E 16rm 0 i C11573

6 EMZAK is able to simulate the three competing half-harmonic generation mechanisms (dne ) : linear-mode conversion (inverse resonance absorption); ~ = ~ ^k h = ^k h = = (dne ) : nonlinear-mode conversion; ~. ~ k = k + k IAW 8^d : E* he B : homson down-scattering; 0 ~ = ~ ~ 0 k = k k 0 C11574

7 he simulation is first run without coupling to transverse fields to obtain the saturation stage of PD # # E^x, ~ h = b E^x, ye h i~ tdt dyl ; D~ = ~ ~ E ^x, h 0 ps (before restart) ~ 0.45 D~/~ Maximal growth region for PD* C n x (nm) c / *D. A. Russell and D. F. DuBois, Phys. Rev. ett. 86, 48 (001).

8 he wave spectrum shows strong signatures of the angmuir wave decay instability # # E^x, ~ h = b E^x, ye h i~ tdt dyl ; D~ = ~ ~ E ^x, h 0 ps (before restart) ~ 0.45 D~/~ Maximal growth region for PD W s after angmuir decay instability* C11575a x (nm) n c / *D. A. Russell and D. F. DuBois, Phys. Rev. ett. 86, 48 (001).

9 he frequency spectrum of W s at their turning points can be determined # # E^x, ~ h = b E^x, ye h i~ tdt dyl ; D~ = ~ ~ E ^x, h 0 ps (before restart) ~ 0.45 D~/~ Maximal growth region for PD W s after angmuir decay instability urning point of W s based on the perturbed density (dn + dn) C11575b n x (nm) c /4 0.50

10 he simulation is restarted with coupling to the half-harmonic emission enabled aser E ^x, ~ h 1 ps (after restart) D~ = ~ ~ 0 / 0.04 dne" linear conversion 1.6 dne" nonlinear conversion 0.4 (d E) E 0 homson down-scattering 1.6 D~/~ Observer x (nm) x (nm) x (nm) n c /4 n c /4 n c /4 Exit boundary dn 3.0 urning point of W s based on perturbed density C11576

11 he half-harmonic emission is collected at the left (exit) boundary E ^x = 6 nm, D~ h D~ = ~ ~ 0 / Arbitrary units C Red shift D~ Df = / r Hz Blue shift ( ) inear conversion Nonlinear conversion homson down-scattering For this case, nonlinear conversion is the dominant generation mechanism.

12 More conclusions can be inferred through manipulating some parameters Incorporating all three sources in a single run, half-harmonic emission is the sum of the three shown in the previous slide, indicating that the three sources act independently In another set of simulations with smaller collisional damping, the level of half-harmonic emission is higher; the reason is that more W s are able to propagate to the turning point and convert to half-harmonic light C11764

13 Summary/Conclusions Half-harmonic emission generated by two-plasmon decay (PD) is calculated with a new code, EMZAK Half-harmonic emission is one of the few experimental* observables of PD he Zakharov equations** are expanded to include transverse fields and are solved with a new code Half-harmonic emission can be generated by three different mechanisms linear conversion nonlinear conversion homson down-scattering For the case shown, nonlinear-mode conversion is dominant. C11571 * W. Seka et al., Phys. Rev. ett. 11, (014). ** D. F. DuBois, D. A. Russell, and H. A. Rose, Phys. Rev. ett. 74, 3983 (1995); D. A. Russell and D. F. DuBois, Phys. Rev. ett. 86, 48 (001). J. Zhang et al., Phys. Rev. ett. 113, (014).