[Tulse]

belbear wrote: A FF powered scramjet does not do chemical combustion at all, so this problem does not pose itself, because it would work by simple heating of incoming air (using either electricity, X-rays or ion beam) And that always work.
Instead of fuel injection it could be using a tungsten heat exchanger, operating at very high temperature (2000°C) to transfer heat from the source to the airflow.

Thanks for clarifying that. I wonder if instead of a heat exchanger if something like a plasma torch would be more efficient, as it would use the FF electricity directly.

I’m also still not clear on the power required, however. What kind of power density does one have to reach to match that of hydrocarbon fuel? Is such density practically achievable?

I also wonder if FF won’t be far more useful in deep space, where low thrust electric propulsion systems are more practical, and where one might not need a lot of the support gear on needs in an atmosphere. For example, I presume it wouldn’t be necessary to have a vacuum pump to keep the reaction chamber evacuated in space, or to have the reaction chamber heavily reinforced to fight against implosion from atmospheric pressure. I would think a space-based FF reactor could be much lighter and smaller in space. (The one issue that might be more of a problem is dealing with the waste heat, as it it more difficult to radiate it away in a vacuum.) I would also think that the inherent simplicity of the system would be attractive, relative to fission reactors that require complex systems to turn their heat into electricity.

[Tulse]

Phil’s Dad wrote: Could we have a ‘Quote of the Week’ thread;

I submit for an example this from Tulse 😉 who posted on 03 November 2009 at 03:05 PM

“…the only thing that FF would be doing is providing an alternate(sic) power source.”

The only thing!!! :-/

(Alternative – since you ask)

I’ll certainly take the grammatical correction, but I think the point in context stands — the issue with scramjets is not how to power them, and using FF in a scramjet would not really solve the major obstacles with that technology.

[Tulse]

texaslabrat wrote: If the power density of the fusion power sources were sufficiently high (in terms of MW/m^3 and/or MW/kg) , that’s definitely feasible from at least a basic conceptual point of view (ignoring the complexities of the actual aircraft and propulsion system design). A lot of optimization and miniturization of the fusion source will be necessary to make this kind of system do-able for atmospheric flight propulsion.

One of the “advantages” of conventionally fueled craft is that they get lighter as they travel. With a FF powerplant instead, all the weight is constant. I presume there is some crossover point where a specific fixed weight fusion generator is more efficient than than a powerplant running on conventional fuel that gets lighter over time. But it is not immediately obvious that such crossover point can be easily reached — my guess is the fusion plant in such instance would have to be very light relative to its on-the-ground, fixed instantiation.

And I’m still not convinced that there would be any major advantage to such a system. As I noted earlier, the real problem with most launch systems isn’t lack of power per se (at least not power on the scale that an FF device would generate).

[Tulse]

belbear, in the system you describe the only thing that FF would be doing is providing an alternate power source. As I understand it, the problems with scramjets aren’t in that area, but instead in the engineering of the hypersonic air passage. Perhaps I’m wrong, though — someone else here may be more knowledgeable on this topic.

[Tulse]

Brian H wrote: once FF’s operating full blast, going to space (moon, Mars, asteroids) will be a piece of cake.

I’m not sure that’s true — once in space FF may make technologies like VASIMR far more practical, but the big problem will always be getting into space. I don’t see how FF will significantly change the problems of launching to orbit, at least not without other major technological advances (such as space elevators or huge magnetic launch tracks).

[Tulse]

Breakable wrote: It would be interesting to see the FF reactor to go open source, and people building one for their own community in 10-15 years.

Perhaps it’s a misperception on my part, but it seems to me that one of the most exciting things about focus fusion is its relatively technical simplicity. That’s not to say that there is not a lot of very hard work needed to do the research and get it operational, but if/when it does work, the actual device appears pretty simple, arguably much simpler than any other fusion design, and simpler even than most power generation technologies. All of the individual technological pieces are pretty well understood and easily produced to whatever specs one needs. My guess is that, once there is a demonstration of substantial over-unity energy from FoFu, it will be very difficult to prevent these devices from popping up all over the place. (I suppose that’s a real risk for the business side of Lawrenceville Plasma Physics — if this approach works, it may be so easy to reproduce that it is difficult for LPP to profit from.)

[Tulse]

All the above points are indeed true, but I’m still not clear how far over unity one needs to be for economic viability, nor where other fusion approaches would sit on that curve. (For that matter, I’m not sure what the relative “mine to outlet” energy gain is for coal-fired or nuclear powerplants — does anyone have estimates on that?)

[Tulse]

If you assume a conversion efficiency of 80% for both and no other losses inside the system the net gain on each shot is 25%. This is certainly better than unity but not very comfortably so.

I’m not clear on the economics of this — why would 25% over unity not be “comfortable”?

What are the hypothesized maximums for other fusion approaches? I have to believe that a process involving direct electrical generation from the fusion reaction will be much more efficient and economical than the MCF and ICF approaches of creating suns to boil water to drive a turbine to turn a generator.

Also, if you have low overall gain the waste heat that is generated is going to be very large compared to the net electrical output.

Of course, the “waste” heat itself can be used either to generate further electricity, or for heating and industrial applications, making the system more economical than figures for just direct electricity generation might suggest.

[Tulse]

The element produced is He3. It could be used for dirigibles

Fusion-powered zeppelins that never need refilling — awesome!

[Tulse]

I realize the helium ions get ejected through the coil, but the interior of the coil must be open to the main chamber, no? Does the main chamber essentially continually “leak” into the evacuated chamber beyond the coil? And is it simply that the amount of leakage isn’t significant enough to be a problem?

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