Small update from Lawrenceville Plasma Physics

[DeltaV]

Have you looked at LACE? Liquify the air and separate it or not, store some for high altitude, dump the rest as liquid into the alpha stream for cooling and thrust.

Hadn't thought about cruise-phase air liquifaction. Would reduce the takeoff weight, since the boost-phase propellant tank could start out empty. The alphas are hopefully all going to the direct converter grid to power the ducted fans and, later, the REB. If Prins-style VHT superconductors are not available, the liquified air could be used to cool the coils of the Halbach rim-drive fan motors at cruise speed, and later the REB heating chamber when the real work begins.

The best work I've ever seen comparing the various possible continuous cycles is certainly this:

http://www.amazon.com/Future-Spacecraft ... 301&sr=8-1

With the FF, because it's not intended to run in stasis but is pulsed, you actually have an opportunity for a pulsed detonation of liquid air. Czysz and Bruno talks quite a bit about about pulse engines too. It's an excellent book and easily worth the price if you're seriously interested in this.

Interesting, but no mention of Woodward/MLTs in the index. The military has done a good job of supressing enthusiasm for nontraditional propulsion since that big, standing-room-only antigravity conference in the mid-1950s drew too much attention.

[GIThruster]

Interesting, but no mention of Woodward/MLTs in the index. The military has done a good job of supressing enthusiasm for nontraditional propulsion since that big, standing-room-only antigravity conference in the mid-1950s drew too much attention.

Woodward has made almost no effort to promote his ideas. I say "almost" because he does publish every year. This year, he'll be publishing and presenting 2 works at SPESIF, and one of them, the one explaining how to build traversable wormholes; he's getting a double session for presentation of his over-length, 26 page paper.

The best way to understand why it is Woodward does not promote himself is that he's an older guy, with a couple kinds of terminal cancer, who's financial needs are all cared for. If/when his work becomes an astonishing success, this will be primarily a lot of fuss and distraction for him, people pushing, worrying about IP and money, etc. Though he works hard at what he does, I think he knows the best times will end when he succeeds at what he does, and this likewise affects the fact he is not a self-promoting person.

As far as Czysz and Bruno, it's all traditional aerospace. All the challenges in it are in engineering. There is nothing I can think of that is held out as a possible option based upon unresolved physics.

[chrismb]

I'm sure this is of interest.... to someone.... possibly even earthlings or other near-terrestrial hominids..... alive, dead or otherwise.... but maybe we should keep a thread for posting recent DPF updates?

[chrismb]

On the LPP website:
billion-degree pinches achieved.

In regards the video that I've just watched, linked to in that text, at the end it shows Mr Lerner holding up a dosimeter with around 40 bubbles in it. Earlier, the dosimeter that one of the chaps walked out of the chamber with says 29 bub/mrem on it.

If a 29bub/mrem dosimeter was placed 1 metre from the reactor, then 40 bubbles would be a neutron output of 2x10^9 neutrons. If it had been 50cm from the reactor then it'd've been 5x10^8 neutrons. It'd be nice to know whereabouts that was located. 10^9 neutrons is a nice number, but I got the impression from the links to that video that it showed a 10^11 run?

[D Tibbets]

DPF reactor weight of ~ 14 kilograms?. That sounds very generous. Remember that you need a vacuum vessel for each if you plan to use it in atmosphere. And you need the x-ray recovery system surrounding each reactor. Plus any other direct conversion equipment (say only for the electron beam. You need to have some way to dissipate all that energy (converted from X-rays and election beams), plus the waste heat. The you need all the vacuum pumping equipment , etc. Add the weight of a VASMIR type engine to usefully eliminate all that energy, additional mass if you are using dilluted fusion product thrust, relativistic electron beam heating, radiaters, etc, etc and the weight per reactor would go way up. A hundred KG per reactor may be very conservative. .

If you stay out of atmosphere the challenges are a lot less.

The major problem with DPF, perhaps to the extent that Polywells would quickly surpass them, is that the power out is modest to the power in. If you get 25 MW power out, you eill need to use perhaps 10-15 MW of that power for the next shot. This is about 1 MW consumed for each 2 MW produced. A Polywell ()P-B11) optimistically might consume 1 MW for each 20 MW produced. This 10 X advantage adds up, especially where you need a lot of thrust. The fusion products alone do not make much thrust, You have to augment it with some working fluid. I think this essentially gives the Polywell a 10:1 weight advantage. 10 X 100KG DPF = 1X 1000 KG Polywell. It is doubtfull that either would be this light, but the DPF may have an advantage. But, you also have to concider the waste heat . Those 10 DPF reactors would be producing 10X the waste heat. So, you need to add the weight of cooling systems.
If you are using maximum thrust in atmosphere only for only short times, you might use your inert fuel as a heat sink and minimize other cooling systems.....

Dan Tibbets

[Aero]

Yes, 14 kg seems light so lets see if we can devise a more realistic mass estimate. Remember, the situation is one of ganging hundreds or thousands of thrusters, so some of the equipment can drive multiple thrusters. Vacuum pumps, for example.

Yes, I was thinking that the 7th power of radius scaling would result in Polywell far out performing FF thrusters. But FF thrusters start producing power at a much lower mass than does a Polywell. Do the numbers, you can't build a 2 meter radius Magrid using only one metric ton of mass so your 1000 kg Polywell produces at most a few milliwatts of power. The volume of a two meter radius magrid is 2.1 cubic meters assuming 20% shadow. That is, 0.4 meter coil minor diameter. You pick the density, water comes in at 2.1 mton, copper at almost 10 times as much. On a post several months ago, MSimon and I came up with 3 to 5 metric tons per cubic meter, or 6.3 to 10.5 metric tons for a two meter radius Magrid. The balance of plant is not included in these numbers.

I'll use your 100 kg mass FF thruster to illustrate my point. By ganging FF thrusters and assuming a net 10 MW per 100 kg thruster, you get into the range of 600 MW to 1 GW before the Polywell of equal mass is physically large enough to produce even 100 MW. Beyond this size I would expect the Polywell to quickly catch up, but mass increases quickly with radius and the FF thrusters have a running head start in power/mass. You will note that if each FF thruster massed 1000 kg, then 100 MW worth of FF thrusters would mass just about the same as a 100 MW Polywell, in the same ball park, at least.

[Aero]

A further note. Very often the cost of mature mechanical product can be estimated by the mass of materials needed to build it. In this regard, and assuming that both FF thrusters and Polywell perform satisfactorily, the low mass of FF thrusters does not bode well for Polywell.

[GIThruster]

I think if we're talking about fusion rockets, as opposed to power sources for something like VASIMR, then it really matters more which, FF or Poly; is easier to get the power out of. For a rocket, you really want the alphas to go through a coil to power the cap banks, then use what energy is left to vaporize a working liquid propellant, be it air, oxygen, whatever. You also hope to capture the x-rays for use, but that's the same issue with regards both approaches.

Seems to me it's in how you capture and handle the alphas that makes all the real difference. Which approach, FF or Poly is likely to make this simpler, lighter, more efficient?

In any case, FF is the only approach for very small applications. Still seems to me that the scaling laws for the Poly demand it will at some point be a better approach.

[chrismb]

I think if we're talking about fusion rockets..

We're not. Why not start another thread, and maybe you can power-point your way to building starship enterprise wormhole whatever. There I was thinking this thread was about Lawrenceville plasma....

[GIThruster]

Chris, how many times to you need to be ignored when you whine, in order to stop your whining?

This is a thread on FF. Conversations about fusion rockets are fair game, and even if they weren't, you are not a moderator. Grow up.

[happyjack27]

Chris, how many times to you need to be ignored when you whine, in order to stop your whining?

This is a thread on FF. Conversations about fusion rockets are fair game, and even if they weren't, you are not a moderator. Grow up.

you'll need to ignore me, too, then.

[GIThruster]

Yes well, my apologies. I tried to delete the post and you copied it before I was able. But honestly, do we really need thought police here complaining every time someone posts on a related subject that someone else doesn't like? Discussions of FF rockets may not be "news" but they're certainly on topic. If the mods want them to be moved, they'll move them.

Personally, I think if you have a complaint, you should send it to the mods rather than whine in public. At least that way, you don't leave everyone wondering if you need a diaper change.

[chrismb]

Chris, how many times to you need to be ignored when you whine, in order to stop your whining?

This is a thread on FF. Conversations about fusion rockets are fair game, and even if they weren't, you are not a moderator. Grow up.

No whining on my part. I'm just talking about being plain and decent.

By what non-sequitur oddities are there recirculating in your brain to lead you to say that talking about fusion rockets is fair game in a thread on FF?

Problem these days is that you seem to hijack almost every thread into something about aeroplanes or spaceships or something. Take it to the 'General' where I can then ignore you.

This section is NEWS, buddy. What NEWS are you talking about here?

I'm a bit tired of having to wade through 25 pages per thread of you blithering on about thrust this and M-E that and wormholes to get to something about FUSION NEWS!!!

If you demand moderation then..... Moderator!, please moderate...

[GIThruster]

Okay Chris, I'll do my best to keep it in General. You need to sympathize though, that people digress by accident on most occasions, and those of us who aren't anal retentive don't much care. So try to keep the whining to a minimum.

[chrismb]

Okay Chris, I'll do my best to keep it in General. You need to sympathize though, that people digress by accident on most occasions

Thank you. I give you my sympathy. Some digression is par for the course here, I agree, but my concern is that the digression is now 50% of the thread, and not news.