[Ferret]

opensource wrote: What we’re talking about I think – to be quite vague – is a technology that best converts between energy and matter. The more of the latter you have, the more effective the propulsion system will be in this sea of gas and gravitation. Sound right?

Generally, a rocket engine is more effective in terms of fuel used when it puts more energy into less matter. Energy means kinetic energy. Thus, an efficient rocket engine has higher exhaust speeds for less matter exhausted. For atmospheric engines things change a bit, since air may be taken in and used as the exhaust. But basically you still want to use the least amount of fuel.

Now for FF atmospheric propulsion, one would probably have to send the FF ion jets into a heating chamber, where they heat the air, which is then expelled to the back. It is much like a turbojet or a ramjet engine, only you use the FF exhaust to heat the air instead of burning some petroleum fuel. In terms of fuel used, this is much more efficient than a jet engine, since you use nuclear energy and the fuel quantity is some 1 000 000 times smaller. It remains to be seen whether it is more efficient in terms of engine mass, too. You don’t want a huge, heavy engine to do the same work as a jet engine. If you wanted that, the solution were right around the corner: a thermal nuclear fission reactor powering an aircraft engine. Think about an aircraft carrier power source on an airplane.

[Ferret]

Well, that’s exactly what happens when more pinches are formed. The total current has to provide a high enough intensity to each pinch. This can be done if the current is high enough and it is quite constant during the formation of pinches. The pinches would then be hot even if the plasma sheath were not moving at the same speed, as long as the plasma feeding each pinch arrives at the same time. Since the pinches separate due to plasma instabilities, how could the distance at which they form be estimated? On the other side, the number of pinches may also depend on the current intensity, which is a factor in plasma instabilities.

[Ferret]

zapkitty wrote: Hmmm… how about something less ambitious?

Let’s try powering a small commercial space station in LEO first.

There you can learn about whatever quirks lie within the system in a working environment of vacuum and microgravity… but you have auxiliary systems on hand in case of teething pains… and Earth is only an hour away by capsule if things go really south on you.

Attached is a rorschach test… see what you can make of it… I don’t see so well myself but everything should be in place…

This would be an interesting and useful application of DP devices. And it may work without fusion already. It will then have under-unity energy efficiency, but there may be some advantages compared to already applied systems: probably less weight (far lighter compared to classical chemical propulsion), the fact that it is fed with electricity produced on the ship, far less fuel required, thus less fuel weight…

[Ferret]

On the same note of hybridizing the ICF and DPF, there exists the possibility of replacing ICF lasers with DPF – like particle guns. So instead of huge inefficient lasers there would be a couple of dense plasma devices that may not achieve nuclear fusion themselves but fire jets of particles at a solid fuel target, burning its outer layer and inducing inertial confinement and fusion in the target. Several such devices placed around the target would fire synchronously. The idea came from http://en.wikipedia.org/wiki/Railgun#Trigger_for_Inertial_Confinement_Fusion

The main advantage: possibly much smaller and more efficient DP devices compared to lasers. And simpler and cheaper too.

Main disadvantages:
– synchronous firing: how well could it be achieved?
– target acquisition: they have to fire straight, not around corners.
– particle beams are not neutral, but positively charged. Electron beams fire the opposite way. So electrons may have to be added to the particle beam in order to make it neutral (or maybe this is not necessary).
– in some conditions, firing plasma at targets generates an electric field that effectively shields the target from the plasma. Would the same happen here? Neat stuff, anyway. And quite new too: http://phys.org/news/2012-07-deflector-shields-lunar-surface.html

Post your opinions on this. And hey, if you run out of activities or you simply get some funds / benefits from this, you could consider “feeding” some of the ICF projects with DP devices of this sort. I know some X-ray generators have been developed from DP machines.

[Ferret]

I played a bit with the Lee Model simulation, just to get used to it. It complained about pressures higher than 20 Torr, so I erased the complaint from the program. Next it complained about the run time being too long compared to the discharge time. I played a bit with the parameters until the axial run time was OK. This is what I got: cathode radius 5 mm, anode radius 2 mm, anode length 2.1 mm so that current I is at its maximum at the end of the axial phase, charging potential 120 kV (not 10 kV as I wanted it), pressure 760 Torr (I squeezed it out of the anode length 🙂 ), maximum current 0.5 MA. I used L = 5 nH, C = 0.1 uF and r0 = 1/4 sqrt(L/C) = 1.77 mOhm. The fuel was Deuterium. The only products I see are Joule heat and Bremsstrahlung radiation, the last being 0. The plasma went to a temperature of 4.5E6 (Kelvins I guess).

This is just the first shot. I’ll have to play with it a bit more. At least the simulation took those parameter values (except for the pressure, I forced it into it). The voltage is far too high for what I aimed.

Next week I’ll try a few more guesses and see what I’ll get.

[Ferret]

The functioning of a DPF device is controlled by the so-called “drive factor”: D = I / ( a sqrt(p) ), where I is the peak current, a the anode radius and p is the pressure inside the device. For optimum neutron yield in deuterium, D = 78.46 kA / ( cm sqrt(mbar) ). In order to use the normal atmospheric pressure p = 760 Torr instead of 7 Torr, p has to increase 100 times. Thus, either I increases 10 times too or a decreases 10 times. I would go for a decrease of a. Say a = 0.2 cm (anode diameter of 0.4 cm), a catode 0.5 cm in radius (1 cm diameter) and p = 1000 mbar, it follows I = 0.5 MA. Up to now it should work with deuterium fuel at normal atmospheric pressure. For decaborane, maybe a higher I is necessary, say 1-2 MA.

Of course, there are problems with such a device. For one thing, the anode has to be a solid bar, i.e. no cooling hole in the center. That way it could take some of the mechanical stress from the plasmoid. Next, it may not last long. As Mr. Olsen found out, the current passing through it and the X-rays will vaporize a layer at its surface each time the device is fired. But it should take a few pinches.

One advantage of having a smaller anode is that the device needs far less energy. If I’m correct, the energy scales as a^3, thus a 10 times decrease of a means a 1000 times decrease for the energy. Instead of, say, 5-10 kJ used in other devices, only 5-10 J would be required. Thus, the capacitor bank may be reduced to just one capacitor.

That is, if the pinch does occur. Why would it not occur? This is a real question, not rethorical.

There is one possible reason: the flow of plasma along the anode may be disrupted by the higher pressure, somehow. Is it the case? Or maybe other reason?

PS: The capacitor fires at about 10 kV in air, quite a high voltage. Its capacity: about 100 nF or 0.1 uF.

[Ferret]

Breakable wrote: You do know that sun is driven by fusion reactions don’t you? 😉

Aaa… it slipped past me. 🙂

Well, I guess coal burning can be thought as nuclear fusion energy too, since carbon is formed in stars. Just to stretch it even more. 🙂

Anyway, you have a point. My questions still remain: how do we make the bomb with the help of the Sun? 🙂

[Ferret]

So where’s the nuclear fusion in the solar part? 🙂 I’m afraid I fail to see it.

Actually I’m really curious how solar-driven nuclear fusion can be achieved. A straightforward approach wouldn’t work: bombarding a target of anything with solar radiation would heat it to at most 5600 K, which is the Sun’s temperature and the solar radiation’s temperature too. Concentrating it would not help – the same maximum temperature holds. Yet I would not say it’s impossible to do it.

One way to achieve solar nuclear fusion would be to concentrate solar radiation on a laser. The laser radiation can next be used to achieve nuclear fusion.

Another would be to attempt to do inertial confinement on a fuel pellet with concentrated solar radiation. That way the bet would not go on the heating only.

The fact is solar radiation has a lot of energy and having a way to drive nuclear fusion with it could be very useful.

Any other ideas? Maybe some practical ones? Mine are not very practical, I would say.

[Author]

Posts