[KeithPickering]

Thanks for the research on this, jamesr. Probably easier than finding a material that absorbs x-rays would be finding a material that is *almost* transparent to x-rays (but not quite!), so that it could handle the flux. With enough layers, you could get good absorption overall without saturating any one layer. In fact, I suspect that a thin enough foil layer might be just the ticket. Studies of x-ray absorption by various metals has been done, eg here:

http://scripts.iucr.org/cgi-bin/paper?a04630

[KeithPickering]

Methane is less toxic than ammonia, and there already is a large scale existing infrastructure. And you can power your car on methane with very simple modifications. All you need is a way to make methane from renewables, or from FF.

But there is such a way already … if you grow methanogenic archaea in an electrolytic cell and add 1 volt, they make methane like gangbusters. About 80% efficient in initial lab tests, which is better than electrolysis of hydrogen. And they haven’t even started selective breeding of the little critters yet.

http://www.sciencedaily.com/releases/2009/03/090330111257.htm

[KeithPickering]

The biggest technical challenge may not even be cable strength. It will be impact resistance/avoidance from gazillions of pieces of junk in Low Earth Orbit. A paint fleck at 17,000 mph can ruin your whole day. Shuttle damage is trivial by comparison, since the shuttle tends to travel in the same direction as other LEO objects, lessening the relative velocity. The cable for a space elevator isn’t moving at orbital speed until you’re up at 22,000 miles. Take a look at this diagram:

Now imagine having to move the cable bottom to avoid each and every one of those little dots, simultaneously. And those dots are all moving! Clearly it’s an impossible task. But if you don’t do it, your cable takes impacts. So how long can the cable survive under such bombardment? Not long, is the guess here. And the problem is only going to get worse as time goes on and more and more junk ends up in orbit.

[KeithPickering]

Dr_Barnowl wrote: BBC News Story as title

I have mixed feelings about this one. They could still fund multiple LPP style experiments out of just this years budget shortfall. Probably out of the shortfall in the tea and biscuits budget. But is it nice to see that they are still willing to try?

This is very good news. They could have let it dawdle along in underfunded limbo for years. And there’s a decent chance it will work.

[KeithPickering]

jamesr wrote: Can somebody tell me why there needs to be more than one switch?

They are all wired to the anode on the other side of the switches. One big switch has to handle the whole current load, but it completely eliminates synchronization issues.

There are no commercially available plasma switches that can handle the current requirements. Hence the need for multiple switches that must fire simultaneously.

[KeithPickering]

The switch has to go from fully-off to fully-on in something like 20 nanoseconds. This pretty much rules out all normal physical processes, and fluid flow is most especially ruled out.

[KeithPickering]

vansig wrote: or place the reactors in the tail section, then have just a single shield for the bunch

Misses the point. About half of the energy from FF derives from capture of the X-rays using the onion-skin. So the space issue is real, as each FF must have its own onion-skin. Twenty of those would easily fill a 747, leaving no room for payload.

Much easier to use FF as an energy source from which to create hydrocarbon fuel.

[KeithPickering]

Salgado wrote: Hi guys,

I am a close follower of the Focus Fusion initiative and also other approaches working to unleash the tremendous energies entrapped in the nuclei of atoms.

Not being a particle physicist, I would like to throw a question to the forum: how come all fusion experiments and ideas revolve around high energy plasma?
Obviously, you need energy to overcome the electrostatic repulsion of the nuclei for them to fuse, but why does that mean having both reagents at high energy?

As an example of what I am asking, consider this: why would not just shooting high energy protons down a crystalline boron shaft release enough energy (mainly thermal) to sustain the original proton accelerator?
Would the crystalline boron shaft need to be as long as the Earth? Or be as sphere as big as the Earth? Would the proton accelerator waste too much energy?

I would appreciate your thoughts, please don’t be too nasty. 🙂

It’s not easy to fuse nuclei. First, because normal atoms are protected by electron shells, and in order to get at the nucleus, you need to strip away the electrons. When you do that, for any gas light enough to fuse, you have a plasma by definition. Even your protons are a plasma, as they are simply ionized hydrogen gas, i.e., another plasma.

So, once you’ve got your plasma — i.e., your bare nuclei — then with no electrons in the way, they can fuse, right?

Wrong.

Nuclei are all positively charged, which means the repel each other by electrical force — and the closer they get, the stronger the repulsion. You need to get those nuclei close enough so that the strong nuclear force overcomes the electrical force, which means they need to get very, very close indeed. And generally the way to do that is to get them very hot, which is to say, get them moving very fast. If their kinetic energy is great enough, occasionally some nuclei will run into other nuclei fast enough to overcome the electrical repulsion, and they fuse.

The crystalline boron shaft (or any shaft made of neutral materials) won’t work, because those positively charged protons will be attracted to the electrons in the shaft material and won’t go down the middle. The proton will simply collide with the wall, pick up an electron, and revert to normal hydrogen again. If the plan is to collide protons together, magnetic confinement is the way to go, like a linear accelerator. And yes, some of them will fuse, but almost certainly not enough to reach break-even.

[KeithPickering]

vansig wrote: The current alternative is VASIMR, which already consumes lots of electricity; can a below-unity FF reactor achieve greater specific impulse than VASIMR on the same input power? maybe it can.

VASIMR’s specific implulse is about 5000 seconds optimally, according to wikipedia, compared to about 1.2 million seconds (optimally) from p-B11 reactions. Thrust from p-B11 will be low, like other forms of ion drive. VASIMR’s advantage is higher thrust.

[KeithPickering]

vansig wrote:

thrust will be very low, since amount of material expended per pinch is very low, but FF becomes a viable form of propulsion even before it reaches break-even.

This last is doubtful, since power is always at a premium aboard a spacecraft, and if the engine is an energy hog, the spacecraft will have inherent difficulties. Theoretically possible, but sooo much easier if you’re beyond breakeven, and hopefully well beyond.

[KeithPickering]

I would assume that we engineer this something like a solar cell, i.e., separate the foil with diodes, forcing any current to flow only one way, doing work in the process.

[KeithPickering]

KeithPickering wrote:
Specific impulse and thrust depend on how much and how rapidly fuel is burned. I don’t believe we know the answers to those questions yet.

Amending my own post: specific impulse is 1/g times the exhaust velocity. At 11781 km per second, or 11,781,000 meters per second, specific impulse would be about 1,201,334 seconds. But of course, that’s still very much a best-case scenario.

[KeithPickering]

Breakable wrote: Even if RPM reduces, it does not mean its a hoax.
It could be possible that the inventor found a way to convert magnetic potential into energy. Most of physical processes are reversible. As we know how to convert electrical energy into magnetic potential, it is possible that somebody might found a reverse process.

We can covert magnetism into electricity any day of the week. It’s called a generator. And, having an energy output, it requires an energy input to run.

If the official explanation were true, the entire magnetic potential would quickly be converted to kinetic energy, and then the motor would stop.

The problem here is that the motor “as advertized” breaks the first law of thermodynamics. And the second.

[KeithPickering]

Breakable wrote: http://www.youtube.com/watch?v=QOyuZSzkWRU
I usually don’t believe in ZPE or magnetic machines, but the demo seems to be pretty well done. I wonder what is happening there?

There’s a lot of room to hide a battery in there. I’d want to put a tach on the motor and measure its rpm change over a 12 hour period. That would either kill the hoax or win the Nobel prize. Any bets that Muammar is going to run that test?

[KeithPickering]

Brian H wrote: From Talk-Polywell, this proposal:
http://www.talk-polywell.org/bb/viewtopic.php?t=1944&highlight=beams+wiffleball+beta+electron
Starts with Thorium230, proceeds on to alpha-beta emitting decay products. Lasts 100 years.

This whole thing strikes me as a theoretical method to make neutronic fusion actually useful, even though it really isn’t.

It’s much easier to create a Th-232/U232 breeder directly. In fact, the US built one in the 1960’s; they are inherently safe, can’t melt down (because the fuel is already liquid salt), and produce virtually zero long-term waste. So why do we need the extra neutrons from D-T fusion to run that cycle? We don’t. But the D-T boys need something for their neutrons to do, besides creating another long-term waste headache.

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