Shock Fast-Ignition of Thermonuclear Fuel with High Areal Density FSC RX prepulse Fuel assembly pulse Shock ignitor pulse 3rd FSC Meeting January 26-27, 2006 Rochester, NY C. Zhou, R. Betti LLE-University of Rochester J. Perkins, LLNL

Summary High density/areal density fuel can be ignited with a spherically convergent shock driven by a laser intensity spike FSC High density/areal density fuel can be assembled through low velocity, low adiabat implosions. 1-D simulations show that such a fuel assembly can be ignited by a spherically convergent shock. Two designs are presented with 100kJ and 500kJ fuel assemblies ignited by a 60kJ and 200kJ shock respectively. 2-D simulations are being performed to evaluate the target robustness to inner surface roughness and laser imprinting.

Low implosion velocity targets have better performance (small RT growth and high gain if ignited). But these targets are difficult to ignite by standard direct drive ICF implosions. FSC Low velocity = high gain G Low velocity = low RT growth. Ne = number of RT e-folding. However, low velocity = large energy for ignition. Eign is the energy required for ignition. R. Betti, GO1.07 M.C.Herrmann et al., Nucl. Fusion 41, 99 (2001)

A 100kJ RX-shaped pulse can assemble fuel with ρR=1 A 100kJ RX-shaped pulse can assemble fuel with ρR=1.6g/cm2 through a slow (Vi=2.5×107 cm/s), low adiabat implosion (α=0.7) FSC Driver laser intensity CH CH(DT)6 DT ice DT gas 2μm 80μm 147μm 453μm 100kJ fuel assembly pulse Energy In-flight aspect ratio Max. areal density (g/cm2) Implosion velocity (cm/s) Gain (not ignited) 100kJ 29 1.6 2.5×107 5%

The slow implosion velocity leads to small Rayleigh-Taylor growth during the laser flat top FSC Bubble front thickness / target thickness Laser shuts off Results from RT postprocessor based on Haan-Goncharov models and OMEGA laser nonuniformities with 1THz SSD.

Laser Power and Intensity A spherically convergent shock driven by a 60kJ spike in the laser intensity can ignite the hot spot of the 100kJ fuel assembly FSC Laser Power and Intensity 60kJ 200ps shock ignitor pulse 100kJ fuel assembly pulse Energy gain = 68 (1-D LILAC simulation)

The laser-driven shock collides with the return shock, generating a high pressure reflected shock propagating to the hot spot FSC Before collision After collision incoming shock high pressure shock continues to the hot spot ρ return shock ρ P P The igniter pulse drives an incoming shock, which collides with the return shock inside the shell. A high-pressure shock resulting from the collision continues to propagate to the central hot spot, leading to ignition.

The high pressure shock heats the hot spot above the ignition threshold FSC Hot spot temperature Hot spot pressure With shock With shock Without shock Without shock

Ignition is sensitive to the launching time of the ignitor shock FSC ~250ps Total driver energy is kept constant at 160kJ

The ignitor and return shocks must be synchronized to collide in the region of peak density FSC G=0.1 G=62 G=0.06 Implosion without ignitor shock Implosion with ignitor shock

A 500kJ NIF size fuel assembly is ignited by a 200kJ ignitor shock to produce a gain of 116 FSC Laser Power and Intensity CH CH(DT)6 DT ice DT gas 2μm 153μm 253μm 772μm 200kJ 690ps shock ignitor pulse Energy In-flight aspect ratio Max. areal density (g/cm2) Implosion velocity (cm/s) Gain 700kJ 29 2.6 2.5×107 116

Preliminary work on the effect of ice surface roughness shows encouraging results with respect to design robustness FSC 5 10 15 20 1 1.5 0.5 Mode number Amplitude (m) 0.5 1 1.5 2 2.5 3 10 20 30 40 50 60 70 80 Gain RMS Multimode l=2-24, RMS=1-3m

2-D simulations including laser nonuniformities yield good shell integrity at the end of the acceleration phase FSC Modes l=4-100, DPP+DPR, 1THz SSD

FSC R r Z  r- view R-Z view The bubble front penetration is only a small fraction of the shell thickness at the end of the acceleration phase when the ignitor shock is launched. FSC R r 13g/cc 5.5g/cc Z  R-Z view r- view

Summery/Conclusions High density/areal density fuel may be ignited with a spherically convergent shock driven by a laser intensity spike FSC High density/areal density fuel can be assembled through low velocity, low adiabat implosions. 1-D simulations show that such a fuel assembly can be ignited by a spherically convergent shock. Two designs are presented with 100kJ and 500kJ fuel assemblies ignited by a 60kJ and 200kJ shock respectively. 2-D simulations are being performed to evaluate the target robustness to inner surface roughness and laser imprinting.