mrterry

ICF is intrinsically pulsed (magnetic confinement like ITER is completely different). You use a laser to spherically compress a 1 mm diameter spherical capsule. The capsule implodes, stagnates, and blows (releasing energy in the explosion). Then you do do it again 0.1 seconds later.

NIF uses an "indirect drive" design. Instead of directly illuminating the spherical target with a bunch of lasers, you blast the inner surface of a gold cylinder with the shell at the center of the cylinder. The cylinder gets hot, emits x-rays, which are absorbed by the capsule. The x-ray drive tends to be "smoother" than direct illumination.

The big problem with ICF is hydrodynamic stability. It is like trying to squeeze a water balloon with your fingers. If you don't squeeze it perfectly symmetrically, it will squirt through your fingers and pop rather than getting compressed by a factor of 20.

it is unlikely that fusion energy will be cheaper than current tech. however, it does not emit CO2, is not a proliferation risk, and cannot have a nuclear meltdown.

"50-100 more energy out than in to make up for inefficiencies in electricity generation using this kind of scheme."

Completely true. Theoretically, the NIF target has enough fuel to produce 10-20x the amount of laser energy driving it. Once things work, it isn't a huge step to get to an energy gain (energy_out/energy_in) of ~50. That said, the real world is always more complicated and NIF has yet to ignite.

I've worked in ICF for a nearly a decade. I think NIF research is a necessary step to a ICF based power source. If NIF demonstrates ignition, it can be used to validate our physics models of ICF (turbulence, fusion product transport, thermal conduction, etc). These physics questions are shared by all ICF approaches. However, a fusion power plant will use entirely different laser technology [1], and most likely a different target design [2]. After showing that the physics works, there is still a lot of engineering work needed before building a reactor.

[1] An ICF power plant will be pulsed at 1-10 Hz. NIF is a flash-lamp pumped glass laser, which takes ~12 hours to cool between shots. A power plant would likely be diode-pumped sold state laser since these can meet the required repitition-rate.

[2] The indirect drive target that LLNL is pursuing on NIF is not very efficient. You spend a lot of energy heating the hohlraum. Directly driven targets (blast the capsule directly rather than heating a gold can to make x-rays) should be much more efficient. There are also several ideas for ways to ignite a target more efficiently (shock ignition, fast ignition), but these need additional laser hardware.

@sam Though I work in ICF, I was sad to see the innovative confinement concepts (magnetic confinement) cut a couple years ago. I think it is short sighted. Fusion need to work and get smaller and we should keep our options open. Hope you managed to get a thesis out before the walls fell.

This is true. The reactor work is very low priority, and the LLNL's reactor project "LIFE" has more fairy dust than I prefer. However, fusion and other NIF experiments are important.

I haven't seen enough details to have a good opinion, but I'm skeptical (but would happily eat my hat if it works). We abandoned mirror fusion in the 80's because confinement is really hard if you have open field lines [1]. I do think high beta confinement concepts ([2], [3]) are very cool and could drive power plants small enough for power companies to be interested.

[1] http://en.wikipedia.org/wiki/Mirror_Fusion_Test_Facility [2] http://en.wikipedia.org/wiki/Spheromak [3] http://en.wikipedia.org/wiki/Spherical_tokamak

Lasers gets fired at the inner surface of a cylinder (called a hohlraum). The laser heat the surface of the hohlraum which then emits x-rays. The x-rays then deposit energy on the surface of a spherical capsule (this is the "energy absorbed" number).

You start with ~2,000 kJ of laser energy, but some of that gets "backscattered" and never makes it into the hohlraum. Other energy is spent heating the walls of the cylinder. Additionally, some of the x-rays leak out of the hohlraum and do not drive the capsule implosion. After all these losses are taken into account, only about 15 kJ is absorbed in the capsule.

I can think of two off the top of my head. Low temperature plasma processing (used in semiconductor fab) got it start as the-mess-created-when-a-plasma-confinement-experiment-fails. Adaptive optics were developed for high intensity lasers and are now used in telescopes.

Just a couple quibbles from a former NIF scientist.

NIF is much higher on the priority list than that. LLNL is already in the doghouse due to NIF failing to ignite on schedule. As goes the 5 giga-buck NIF, so goes LLNL (and the management knows it).

Technologically, I'd put inertial and magnetic fusion about the same place. Even if the physics works, neither has a chamber first wall material that can stand up to the huge neutron loads that a power plant will create. Economically, both are hosed. Fusion wants to be big. Most reactor designs are for >1,000 MW. Electric companies are mostly interested in plants in the 50-400 MW range.

The showers continue. Budget pressures have NIF down to shooting three days a week. To make matters worse, DoE has decided to cut funding for high energy density physics, ie the field covering the physics needed to make NIF ignite and turn laser fusion into a viable electricity source.