1. 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

2. 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.

3. 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)

4. 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%

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.

6. 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)

8. 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.

9. 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

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

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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.