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Finally someone that's actually in the fusion field. Could you say whether or not the NIF research represents a practical path towards a fusion based power sour

by acadien 13y ago

Finally someone that's actually in the fusion field. Could you say whether or not the NIF research represents a practical path towards a fusion based power source? My understanding is that it would at least be capable of capturing some much needed high pressure empirical data necessary for validating theory. On a side note concerning the NIF funding, the US gov will spend huge sums of money studying Nuclear weapons (including their disposal) regardless of the NIF project. If it is at all possible to combine that research with other fields then really it's a perk. I'm not justifying the expenditure, simply attempting to frame the situation in a different light. Finally, as a fellow scientist with funding woes, I feel your pain.

mrterry 13y ago
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.
- acadien 13y ago
  I thought the goal was to have a self sustaining reaction that would only require laser pulses to hold it in place. Is a continuously pulsed laser necessary to provide thermal energy to drive the reaction? Also I've read (sorry no citation) that the indirect drive was necessary to ensure even dispersal of the heat generated by the initiating laser blast. Any clarification would be much appreciated, this isn't my field.
  - mrterry 13y ago
    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.
    - gameshot911 13y ago
      >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. Well said.
      - raorao 13y ago
        I agree with your general philosophy towards ICF.
      - regularfry 13y ago
        You get the same problem with laser ignition, funnily enough.

by acadien 13y ago

mrterry 13y ago

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.

acadien 13y ago
I thought the goal was to have a self sustaining reaction that would only require laser pulses to hold it in place. Is a continuously pulsed laser necessary to provide thermal energy to drive the reaction? Also I've read (sorry no citation) that the indirect drive was necessary to ensure even dispersal of the heat generated by the initiating laser blast. Any clarification would be much appreciated, this isn't my field.
- mrterry 13y ago
  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.
  - gameshot911 13y ago
    >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. Well said.
    - raorao 13y ago
      I agree with your general philosophy towards ICF.
    - regularfry 13y ago
      You get the same problem with laser ignition, funnily enough.