indirect drive ignition at the national ignition facilityocs.ciemat.es/eps2016abs/pdf/i1.002.pdf ·...

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Page 1: Indirect Drive Ignition at the National Ignition Facilityocs.ciemat.es/EPS2016ABS/pdf/I1.002.pdf · Indirect Drive Ignition at the National Ignition Facility * Nathan Meezan 1 1 Lawrence

Indirect Drive Ignition at the National Ignition Facility*

Nathan Meezan1

1 Lawrence Livermore National Laboratory, Livermore, California, USA

This talk reviews scientific results from the pursuit of indirect-drive ignition on the National

Ignition Facility (NIF) and describes the program’s forward looking research directions.

Inertial Confinement Fusion (ICF) is a grand challenge with the potential to open new

frontiers in the study of matter at extreme density, temperature, and pressure. In laser-driven

indirect-drive ICF, laser beams heat an x-ray enclosure called a hohlraum that surrounds a

spherical pellet. The x-ray radiation ablates the surface of the pellet, imploding a thin shell

of deuterium/tritium (DT). The DT layer must accelerate to high velocity (v > 350 km/s)

and compress by a factor of several thousand. Since 2009, substantial progress has been

made in understanding the major challenges to ignition: Rayleigh Taylor (RT) instability

seeded by target imperfections and low-mode asymmetries seeded by systematic and

random perturbations in the hohlraum x-ray drive, particularly from laser-plasma

instabilities (LPI). Requirements on velocity, symmetry, compression, and stability have

been demonstrated separately on the NIF but have not been achieved simultaneously.

We now know that the RT instability, seeded mainly by the capsule support tent, severely

degraded DT implosions from 2009-2012. Experiments using a “high-foot” drive with

demonstrated lower RT growth improved the thermonuclear yield by a factor of 10,

resulting in yield amplification due to alpha particle heating by more than a factor of 2.

However, large time dependent drive asymmetry in the LPI-dominated hohlraums remains

unchanged, preventing further improvements. High fidelity 3D hydrodynamic calculations

now explain these results. Future research focuses on: improved capsule mounting

techniques; hohlraums with little LPI and controllable symmetry; and lower convergence

implosions to better understand the physics of alpha heating. In parallel, we are pursuing

improvements to the basic physics models used in the design codes through focused physics

experiments. We are confident that this approach, including a diverse portfolio of

experimental, theoretical, and computational physics efforts by teams from around the

world, will lead to further advances in solving the challenges of ICF. *This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

43rd EPS Conference on Plasma Physics I1.002