FSC Channeling in the Corona of Fast Ignition Targets G. Li, R. Yan, and C. Ren, UR/LLE T. Wang, J. Tonge, and W. B. Mori, UCLA

FSC High-intensity ignition pulse can lose energy in underdense corona The ignition pulse power greatly exceeds self-focusing threshold –P/P c ~10 6 P(PW) n/n c >>1 –Indicating highly nonlinear interactions Ignition pulse can lose its energy and being reflected through underdense corona underdense plasma ~1 mm

FSC Channeling makes ignition pulse more effective Two ways of avoiding loss in corona –Using attached-cone targets –Using a channeling pulse Key questions –What are the channeling speeds? Density- and intensity-scalings –Where does the pulse energy go? Absorption vs reflection channeling/hole-boring pulse ignition pulse

FSC Channeling in  m plasmas is simulated for different laser intensities Previous PIC simulations on channeling used 100-  m plasmas We are doing PIC simulations with  m plasmas – =1  m, I= W/cm 2, W 0 =  m, t~10 ps –Plasma density rises from 0 to 1 n c in ~ 1000  m exponentially ~exp( x/430  m) M i /m e =4590 (DT), T i =T e = 1 keV Two types of simulations in 2D –Two separate density region ( n c & n c, 10 particles/cell) –Single region ( n c, 1 particle/cell)

FSC New results in the last 6 months Previously I=10 19 W/cm 2 runs illustrated basic channeling process –Channel bifurcation and self-correction –V c is significantly slower than V g of linear waves Since we have examined and W/cm 2 cases –laser energy tracking (absorption vs reflection) –density- and intensity-scalings of V c

FSC Channeling process at different intensities is similar Ion density plot (n 0 =0.3-1 n c ), I=10 20 W/cm 2, ~6.4 ps 250  m 500  m

FSC At I=10 18 W/cm 2, channeling is much slower 250  m 500  m Ion density plot (n 0 =0.3-1 n c ), I=10 18 W/cm 2, ~9.2 ps

FSC How do we measure V c ? x1x1 ncnc Density at channel center Define channel as n<n r

FSC V c decreases as n 0 increases W/cm 2

FSC Channel advancing is stochastic Longitudinal advancing involves many highly nonlinear processes –Plasma piling-up –Laser hosing/channel bending –Channel bifurcation –Channel smoothing (self-correcting)

FSC V c decreases as I L decreases W/cm W/cm 2

FSC Without channeling, most of pulse energy would be absorbed by electrons W/cm W/cm 2

FSC Work underway Find the optimized intensity for channeling –Density- and intensity-scalings of V c –Ignition pulse propagation in a preformed channel –3D effects Other simulations –Circularly-polarized laser heating –Weibel instabilities of an e - -beam in rising densities

FSC Clean channel can be established ( n c ) Ion density plot, CW laser, ~8 ps 250  m 500  m

FSC Laser can propagate unperturbed in channel ( n c ) Laser e-field (s-pol)

FSC Clean channel can be established (0.3-1 n c ) electron density plot, CW laser, ~7.8 ps

FSC Clean channel can be established (0.1-1 n c ) electron density plot, CW laser, ~12 ps 1000  m

FSC Relativistic SF/Filament Stages of channeling process E laser nene nini

FSC Relativistic SF/Filament Ponderomotive SF/Filament Stages of channeling process E laser nene nini

FSC Relativistic SF/Filament Ponderomotive SF/Filament Central filament widening & shock launching Stages of channeling process E laser nene nini

FSC Channel advancing is stochastic Regular Transverse expansion –V t ~0.03c ~2C s (at 500 keV) –Channel wider than laser width Longitudinal advancing involves many highly nonlinear processes –Plasma piling-up n i /n c

FSC Channel advancing is stochastic Regular Transverse expansion –V t ~0.03c ~2C s (at 500 keV) –Channel wider than laser width Longitudinal advancing involves many highly nonlinear processes –Plasma piling-up –Laser hosing/channel bending –Channel bifurcation –Channel smoothing (self-correcting)

FSC How long does it to take to get to 1n c ? p-pol s-pol The 14  m-wide beam shows uneven advancing speed –V  0.1c->t=30 ps –V>(mn c /Mn) 1/2 a=0.04c (for n=n c ) t<80 ps 3D effects (p-pol vs s-pol) –V s >V p –W s <W p

FSC It will take blue light to channel to cm -3 Hole-boring from 1n c to 10 n c takes >300 ps Tripling the frequency of channeling pulse can channel to cm -3

FSC Summary Clean channel can be created for I=10 19 W/cm 2 Channel advancing is stochastic but self-correcting Channeling to n=10 22 cm -3 requires  m light