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Fusion Beam

Using inertial confinement to produce spacecraft propulsion
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(Disclaimer: I came up with this independently, then a quick Google showed there have been other expperiments in this direction. I believe my concept is different enough to stand on its own.)

<prelude; skip if you wish>
When I first learned about Project Orion (linky) many years ago, I thought "there must be a better way" - it's like propelling your car with sticks of dynamite.
A few years ago, I was introduced to inertial confinement; using laser beams to stop particles cold.
Then I heard about the NIF (linky), using lasers to create fusion reactions.
</prelude>

The ideas of Project Orion and the NIF suddenly gelled in my mind: using lasers to create fusion explosions to propel a spacecraft.
One of the key components is the ShadowBuilt split-cavity laser (linky). The beam energy inside a laser cavity is far higher than that of the beam which comes out of the cavity, due to the 95% reflective mirror that lets the beam out. So if I use the beam while it's still in the laser cavity, there's more useable energy available.

The other important innovation is using palladium deuteride wire as the fuel. Palladium can absorb a massive volume of hydrogen or deuterium within its atomic structure; I'm not sure about degassing out in space, so maybe coat the wire in Teflon or something to help seal it (Teflon will help later too). Having it as a wire gives an easy method of feeding the fuel into the cavity.

The basic design (linky) is to put a series of split-cavity lasers around a ring, with a deflector plate in the centre to deflect the fusion explosion going on in the middle. Rather than the intermittent, large explosions of the Orion, the will be a (more-or-less) continuous small fusion blast going on to provide the propulsion. Having the palladium in there as well will add some extra mass to the expelled particles.
The 3 (probably, maybe more depending on space) rings of split-cavity lasers, possibly staggered (I thought of that after I built the CAD model) to fit better, would require large amounts of power - that's the main half-baked bit.

So; the lasers work continuously, as the palladium wire is fed through the 'spike' at the centre of the deflector into the point where all the beams cross over (it's at the laser waist, not a focal 'point' as such - minimum size depend on lens properties and beam wavelength). The palladium and its contained deuterium are 'crushed' by the beams, fusing and releasing large amounts of energy, which is mostly the kinectic energy of the fused particles (and the handy, heavy, hot palladium). This energy is transferred to the spacecraft (some directly, some via the deflector plate) creating acceleration - action/reaction and all that.

I'm not sure about the wire actually 'breaking' the laser beams; it may be more of a 'fast intermittent' instead of a 'continuous' process, as the lasers build up photons again.

Also, I have absolutely no sense of the scale of this thing - it could be the size of a car, but it could be the size of an olympic stadium.

ShadowBuilt Fusion Beam - the planets beckon...
neutrinos_shadow, Feb 17 2011

Project Orion http://en.wikipedia...clear_propulsion%29
Nuclear explosive propulsion [neutrinos_shadow, Feb 17 2011]

National Ignition Facility http://en.wikipedia...l_Ignition_Facility
Inertia confinement experiments - huge lasers! [neutrinos_shadow, Feb 17 2011]

Laser comparison http://s1199.photob...Lasers.jpg&newest=1
Comparing a normal laser with the split-cavity laser [neutrinos_shadow, Feb 17 2011]

Overall model of the FusionBeam http://s1199.photob...onBeam.jpg&newest=1
A simple CAD model of the general idea [neutrinos_shadow, Feb 17 2011]

Scale demo using 3 lb. coffee cans of c4. http://www.youtube....watch?v=E3Lxx2VAYi8
<aside> how come I never see mr. C Clarke in any other suit? [2 fries shy of a happy meal, Feb 19 2011]

split cavity laser http://s1199.photob...dia/Lasers.jpg.html
[beanangel, Oct 26 2016]

[link]






       I had a horrible foreboding that I was in for another novella- sized [Vernon] posting, until I scrolled down.   

       The palladium bit is a nice touch - a nod to cold fusion dreams of yore.
MaxwellBuchanan, Feb 17 2011
  

       I croissanted.   

       I'd not worry about the degassing, as the wire would only be outside the ship for a small amount of time.   

       I'd switch over to little pellets instead of wire, if you could. An electric pellet gun could place the bits in the right location. A wire feeder's end would have to be very close to the ignition point, as de-coilers (as they are called in industry) don't leave a nice straight wire.
baconbrain, Feb 17 2011
  

       I imagine a rather thin wire... wouldn't the heat of fusion tend to wreck it ?   

       Liquid would be neat and unlike pellets infinitely'ish variable.
FlyingToaster, Feb 17 2011
  

       /propelling your car with sticks of dynamite/   

       When will there finally be some reduction of this concept to practice?   

       Why does this need to be pushing spacecrafts around? It sounds like this is a way to do fusion energy. Can't we have this in Topeka, powering our plasma TVs?
bungston, Feb 17 2011
  

       If you made the "chamber" perfectly reflective and a section of a sphere, you could get some of each blast to reflect off it and back onto the next pellet/droplet if timing was right.   

       If you make the blasts small enough and often enough, it becomes practically continuous.   

       Nice CAD work.
baconbrain, Feb 17 2011
  

       Ooh, resonating spherical shockwaves - I like that! Maybe pulsed is better...
neutrinos_shadow, Feb 17 2011
  

       Beautiful.
//resonating spherical shockwaves // is setting off red flags for me. I'm not sure why, but I think you would want to throw in a spoiler-wave every so often to prevent resonance amplifying the wave to the point of vibrating the craft apart...sort of like having five prop blades rather than four.
  

       I really like the Orion concept other than the fallout, how would this idea compare when it comes to radiation?
George Dyson's TED talk on Orion is good, and this [link] shows video of some of the scale model testing. (+)
  

       // The palladium and its contained deuterium are 'crushed' by the beams //   

       Without a hohlraum, what will do the crushing? I think if you want to add a hohlraum, it could be a continuous tube surrounding the wire (probably actually two half-tubes that get put together inside the feeder, for practicality of storage and feeding).   

       Also, a Google search for 'ShadowBuilt split cavity laser' only leads back to this page. Is it another of your ideas, which you have yet to write up?
notexactly, Oct 24 2016
  

       Probably Shadowbuilt refers to his moniker. Like BUNGCO but more Sharper Image sounding.
bungston, Oct 24 2016
  

       That is very obvious now. I have no idea why I didn't see that.   

       I would still like to see that split-cavity laser published.
notexactly, Oct 24 2016
  

       [notexactly]; the split-cavity laser is something that came to me in parallel with the Fusion Beam. I didn't think it was complicated enough to warrant its own half-bake. I would like to rig up a test model (but I should have thought of that way back when I was studying laser physics at university; they had the toys to do so).   

       As for the hohlraum, my theory was that if I could get the photons dense and coherent enough, I could manage to achieve fusion without one. From my (brief) research, a hohlraum is not needed, but it does make things a lot better/more efficient.
The main purpose seems to be converting the laser (UV, IIRC) to x-rays, ie: getting the photons as energetic as possible. On-going research into x-ray and gamma-ray lasers will (hopefully) be combined with inertial fusion experiments; depends on the power requirements.
neutrinos_shadow, Oct 24 2016
  

       Bread.
Voice, Oct 25 2016
  
      
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