Z-Pinch Renaissance

Point out news stories, on the net or in mainstream media, related to polywell fusion.

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williatw
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Re: Z-Pinch Renaissance

Post by williatw »

Carl White wrote:
Thu Oct 08, 2020 6:47 am
That's great, but with the requirement of a 2.5 GW power source, I doubt we'll see it any time soon. Not before SpaceX repeatedly lands on Mars, more likely than not.
Okay...but then sailing ships beat steamships to the new world and covered wagons beat railroads to the American west. In this case the change over would likely come much more rapidly than those previous examples. This would be when Mars' population grows from mere hundreds to low thousands to 100's of thousand or even millions very rapidly. Also this technology is more related to the nuclear pulse rocket; your thinking I assume of something like a Tokamak type reactor producing 2500MW; likely that would be pretty heavy. A NPR is more like a serious of controlled (hopefully) nuclear explosions one after another, the power-to-weight ratio is much different than a reactor. Sure Skipjack or Giorgio or some of the other frequent posters could explain it better.

Giorgio
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Re: Z-Pinch Renaissance

Post by Giorgio »

It seems to me that both, you and Carl, are making the same point that this technology is not something we will see anytime soon due to technological limitations. I agree with Carl when he says that we will see SpaceX land on mars several times before people will even think to introduce some new engine system, and I agree with you when you say that as human will expand outside earth, new and improved engines will be offered.
You also open an interesting point regarding "thrust power" to "spacecraft mass" ratio that is generally underestimated by most people.

I am sure that once the need arises we will indeed have nuclear powered spaceships, but I believe that (unless a direct nuclear fission/fusion to electrical energy conversion technology will arise) they will be nowhere near to what they are designing right now.
In my opinion when engineers will start to industrialize solutions to be used in real life applications (and not academic digressions like they are doing now) they will probably go back and revive and optimize solutions like the one offered by the old NERVA program.
With actual level of human technology, and provided that indeed there is plenty of water/volatile trapped in the moon/mars/asteroid soil as expected, this will be the design that makes most sense.


It is true that superheating water and ejecting it will give us the lowest ISP (in respect to superheating H2 as example), but it has a number of inherently interesting advantages:

a) The thrust engine and all related systems have a greatly reduced mass in comparison to other Nuclear-Electric based systems, because the nuclear reactor acts directly as steamer for the water.
b) The Nuclear reactor itself can be much smaller, as you do not need GWe of power for the thrust engine, but with few MWe of power you can easily attain enough Delta-V to travel routes between earth/moon/mars/asteroid belt (including take off and landing from moon/asteroids).
c) The pure electrical production needs are limited to the ship operational systems (so we also have a smaller/lighter electrical conversion unit).
d) Plenty of water onboard as fuel also back ups as extra radiation shielding.
e) No need for a cryo system and related tanks and insulation.
f) Engine maintenance and inspection can be probably designed to be made fully internally from the spacecraft, this would not be thinkable for any of the fusion-based engine design.
g) Order of magnitude less radiator area needed (less electrical production means that less waste heat rejection is needed). This mass saving alone could be invested in a solar panel electricity back up/secondary power system.

Also, coming back to ISP values, a Thermal Nuclear Rocket working on water can probably easily squeeze out an ISP of 300/500 (an maybe more), and if we upgrade it to use H2 we can easily get to a value of 900. Sure, we do not get even near to the 5.000 ISP of the PPR proposal, but the difference in mass of the two spacecraft will probably tend to make the ISP difference less important. I can easily imagine that the mass of a 2,5GW Electric nuclear reactor with all ancillaries for electricity production and waste heat radiators will dwarf everything else in a human rated spacecraft.
And the ISP advantage will drop even more if indeed we will have a cheap water supply in space, and when one consider the extra cost and the additional point of failure that one is introducing with such a multiple-step complicated design.

Of course these considerations can be varied with new technological development or if we don't find water where we are hoping to find it.
Just my 2 cents.
A society of dogmas is a dead society.

Skipjack
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Re: Z-Pinch Renaissance

Post by Skipjack »

I think the most interesting fusion engine concept so far is the one based on the Sheared Flow Stabilized Z- Pinch. That thing has an Isp of ~370,000 seconds and a respectable thrust of 330 KN in a tiny package (by fusion reactor standards anyway). You would likely have to inject some extra propellant to cool the engine. That will lower the Isp but will increase thrust a lot too. I would favor that over large cooling panels. Also wondering if this could be used in the atmosphere as some sort of Project Pluto equivalent (use air for cooling and thrust). A combined cycle of that with a pure rocket engine could enable SSTO (and more). If the power supplies are not too heavy.

williatw
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Re: Z-Pinch Renaissance

Post by williatw »

Skipjack wrote:
Thu Oct 08, 2020 11:29 pm
I think the most interesting fusion engine concept so far is the one based on the Sheared Flow Stabilized Z- Pinch. That thing has an Isp of ~370,000 seconds and a respectable thrust of 330 KN in a tiny package (by fusion reactor standards anyway). You would likely have to inject some extra propellant to cool the engine.
The one with the 3.3TW that is 3300GW power output? Yes you would indeed have to inject "extra propellant" to prevent overheating. The original NPR from the 1950's the issue of reaction chamber overheating was solved by there being no reaction chamber to overheat. The bombs exploded outside the ship close to the massive pusher plate (which also served as protection for the payload/crew). The gradual ablation of the massive pusher plate produced thrust even in the vacuum of space; of course it was never built/tested as far as I know. It was the only design until relatively recently that theoretically gave high thrust and SI. Theoretical terminal velocities of single digit percent "C" being possible. Even the much lower energy John Sough's design the Lithium blanket would absorb the radiation/heat of the fusion burn but what happens to the EM radiating from the then superheated Li plasma? Where does that go? What protects the reaction equipment/ship to say nothing of the crew?

Giorgio
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Re: Z-Pinch Renaissance

Post by Giorgio »

What I liked of the FuZe engine proposal was the lack of magnetic nozzle at the engine end that indeed would simplify a lot the engine, but everything else that was into the 2006 paper was honestly not so exciting for a real life application.
The 2006 paper was based on the results of a MS thesis supervised by Shumlak. In that thesis the fusion dynamics was explored by developing a code to simulate MHD, fusion and radiation equations. Due to the lack of real life data, the writer had to implement few hypothesis to simplify the code and get some meaningful results in a suitable time frame.
Some of those hypothesis are for me a bit too much optimistic, the most important of which was the "no thermalization effect for the fusion alphas".

I guess everyone here can make up his own mind on this hypothesis. To me it is just unrealistic.

In the FuZe engine 2006 paper, the main issues for me are:
1) Fusion z-pinch radius of 1 mm (to try to keep valid the hypothesis of NO Alpha thermalization), but this in turn has limited potential fusion gains to a Q <2.
2) To get the 330.000 N of thrust (the 3.300 GW power output you mentioned) an input energy of 1.800 GW for the pinch is than required....
3) No mention of pinch frequency rate.

I was never able to get my hands on a copy of the 2018 FuZe engine paper, but someone who had occasion to read it told me it was the same as the 2006 paper. If that was true it would mean that experimental results so far was not enough to update the above mentioned data.

I guess we will need until FuZe-Q results to get a better understanding also for the engine proposal.
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williatw
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Re: Z-Pinch Renaissance

Post by williatw »

Giorgio wrote:
Fri Oct 09, 2020 9:29 am
2) To get the 330.000 N of thrust (the 3.300 GW power output you mentioned) an input energy of 1.800 GW for the pinch is than required....
Minor correction that is 3.3TW not GW; yes that engine would need some serious coolant:

Input Power 1.8×1012W
Fusion Power 3.3×1012W (for the D-He3 burn.)

http://www.projectrho.com/public_html/r ... p#fszpinch

This would not be a small machine...looks like many thousands of tons. I suppose you could protect the crew/passengers by having the drive section separated from the habitation ring by a long pylon, maybe a kilometer long? Though how would you keep the engine from vaporizing putting out 3500GW of power? Have a really short boost phase with lots of cool down between shots? After all in the original NPR designs the pusher plate was massive; in the largest examples I believe it massed out in the millions of tons range.

Giorgio
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Re: Z-Pinch Renaissance

Post by Giorgio »

williatw wrote:
Fri Oct 09, 2020 11:27 am
Minor correction that is 3.3TW not GW; yes that engine would need some serious coolant:
Many countries (including mine) use "." to separate thousands and "," for decimal. Many other countries (including US and UK) have an opposite system. There has been several attempts to standardize this issue but with little success so far.

Working with people from different countries and continents we mostly adapted to each other by using indifferently "," or "." with the rule that if the annotation is followed by 1 or 2 digit than it has a decimal meaning, if followed by 3 digits is has a thousand meaning.
So to me 3.300 GW=3,30TW=3.3TW= 3.30×1012W

I will try to make indications more obvious in their meaning in the future to avoid confusion.


williatw wrote:
Fri Oct 09, 2020 11:27 am
Though how would you keep the engine from vaporizing putting out 3500GW of power? Have a really short boost phase with lots of cool down between shots?
This is a pulsed engine if we do not know the exact time frame over which that power has been calculated than it is a pretty meaningless number because we can't see the real joule content.

williatw wrote:
Fri Oct 09, 2020 11:27 am
After all in the original NPR designs the pusher plate was massive; in the largest examples I believe it massed out in the millions of tons range.
I see the original NPR more as an attempt to stimulate thoughts, I don't see anyway where it could have actually worked to move people or goods between the solar system because it was lacking the basic need for a rocket, that is attitude control and thrust control/vectoring. Normal system would hardly work with the mass of that beast.
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Skipjack
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Re: Z-Pinch Renaissance

Post by Skipjack »

williatw wrote:
Fri Oct 09, 2020 12:16 am
The one with the 3.3TW that is 3300GW power output? Yes you would indeed have to inject "extra propellant" to prevent overheating.
I am not sure how big of a deal the heating really is for this design. Unfortunately the paper does not go into details on that.
But let's assume that they have about half of that left over as heat. Then they have 1.65 TW of waste heat.
The pulse only lasts about 20 microseconds. So that is 33 MW per second if we assume one pulse per second and I did not miscalculate that.
At 150 Hz, that is 5 GW. That was the specification for NERVA 2. I think a NERVA type engine should be doable at 5GW continuous power with today's materials. If we extrapolate what we know from research into open cycle nuclear gas core rocket engines (which I think this design would be comparable to), we can assume an Isp of up to 5,000 seconds and extremely high thrust. During atmospheric flight, one could operate this at a lower pulse rate and use air for cooling. The idea is not unprecedented (Project Pluto). It could get the space craft to super sonic speeds and high altitude without spending any of the reaction mass that is needed once it reaches the vacuum (the amount of fuel for the reactor is negligible in comparison). So in atmospheric flight the Isp could be in the millions.

hanelyp
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Re: Z-Pinch Renaissance

Post by hanelyp »

Giorgio wrote:
Thu Oct 08, 2020 10:10 pm
It is true that superheating water and ejecting it will give us the lowest ISP (in respect to superheating H2 as example), but it has a number of inherently interesting advantages:
...
Anhydrous ammonia is an interesting comparison. A bit harder to store than water, but respectable density can still be had with modest pressure or refrigeration. In deep space a simple radiator system my be enough for the latter. In the engine it thermally decomposes to lower molecular mass diatomic molecules, N2 and H2, favoring higher exhaust velocity than water for a simple nozzle. A downside, depending on where you're getting propellant, is sourcing. I know of no natural concentration this side of Jupiter, so it would have to be synthesized.
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Giorgio
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Re: Z-Pinch Renaissance

Post by Giorgio »

hanelyp wrote:
Sat Oct 10, 2020 6:30 am
Anhydrous ammonia is an interesting comparison. A bit harder to store than water, but respectable density can still be had with modest pressure or refrigeration. In deep space a simple radiator system my be enough for the latter. In the engine it thermally decomposes to lower molecular mass diatomic molecules, N2 and H2, favoring higher exhaust velocity than water for a simple nozzle.
Good point, indeed NH3 will give about 25% more exhaust velocity than water and the storage issues might be a good compromise in respect to handling liquid H2.
Just as a comparison term, H2 gives you double the exhaust velocity than water but the infrastructure mass to handle its storage is probably cutting a good chunk out of the deltaV gains from the unit of fuel.
Storage for both (NH3 and H2) is also a well understood technology, so I guess that a detailed analysis of the needed infrastructure can be quickly made to evaluate which of the 3 fuels fuel offers the better trade off in economic and mass terms with our technology level.


hanelyp wrote:
Sat Oct 10, 2020 6:30 am
A downside, depending on where you're getting propellant, is sourcing. I know of no natural concentration this side of Jupiter, so it would have to be synthesized.
This I believe is the main point.
Not only Ammonia is extremely rare on the inner side of solar system, but for what is my knowledge also Nitrogen is nowhere to be found, either bonded or free (Venus is probably the only meaningful place outside earth where to find it, but I doubt it will be more economical to source it than from Earth).
Is worth mentioning that a cheap source of Nitrogen outside earth would be one of the most important factors to enable cheap Space farming.
A society of dogmas is a dead society.

williatw
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Re: Z-Pinch Renaissance

Post by williatw »

Giorgio wrote:
Sat Oct 10, 2020 9:02 am
This I believe is the main point.
Not only Ammonia is extremely rare on the inner side of solar system, but for what is my knowledge also Nitrogen is nowhere to be found, either bonded or free (Venus is probably the only meaningful place outside earth where to find it, but I doubt it will be more economical to source it than from Earth).
Is worth mentioning that a cheap source of Nitrogen outside earth would be one of the most important factors to enable cheap Space farming.
The atmosphere of Mars is the layer of gases surrounding Mars. It is primarily composed of carbon dioxide (95.32%), molecular nitrogen (2.6%) and argon (1.9%). ... The atmosphere of Mars is much thinner than Earth's. The surface pressure is only about 610 pascals (0.088 psi) which is less than 1% of the Earth's value.

https://en.wikipedia.org/wiki/Atmosphere_of_Mars

Pretty thin 2.6% of 1% relative to Earth but you could probably make it work for Agriculture; don't know about propellant.

Skipjack
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Re: Z-Pinch Renaissance

Post by Skipjack »

Giorgio wrote:
Sat Oct 10, 2020 9:02 am
Is worth mentioning that a cheap source of Nitrogen outside earth would be one of the most important factors to enable cheap Space farming.
This is very off topic, but I agree about the nitrogen part. I think that asteroids containing Carlsbergite might be the source of nitrogen on Earth and we could- maybe- find some more somewhere in the solar system.

williatw
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Re: Z-Pinch Renaissance

Post by williatw »

Skipjack wrote:
Sat Oct 10, 2020 4:43 pm
Giorgio wrote:
Sat Oct 10, 2020 9:02 am
Is worth mentioning that a cheap source of Nitrogen outside earth would be one of the most important factors to enable cheap Space farming.
This is very off topic, but I agree about the nitrogen part. I think that asteroids containing Carlsbergite might be the source of nitrogen on Earth and we could- maybe- find some more somewhere in the solar system.
The atmosphere of Titan is the layer of gases surrounding Titan, the largest moon of Saturn. It is the only thick atmosphere of a natural satellite in the Solar System. Titan's lower atmosphere is primarily composed of nitrogen (94.2%), methane (5.65%), and hydrogen (0.099%).
https://en.wikipedia.org/wiki/Atmospher ... _chemistry

Skipjack
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Re: Z-Pinch Renaissance

Post by Skipjack »

Yes, but mining titan would be harder than mining asteroids. Deeper gravity well.

williatw
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Re: Z-Pinch Renaissance

Post by williatw »

Skipjack wrote:
Sat Oct 10, 2020 6:52 pm
Yes, but mining titan would be harder than mining asteroids. Deeper gravity well.
The gravity of Titan is 1.352m/s2 actually less than the moon's although you probably mean Saturn's gravity well which Titan is obviously in as well. Titan is large but made of low density materials. Titan can hold onto a thick atmosphere (pressure at the surface is actually greater than Earth's) in spite of its low gravity because it is so cold there. Of course if we already had mining operations setup at Saturn to mine the copious amounts of He3 in Saturn's atmosphere to fuel your Z-Pinch drive the infrastructure used for that could obviously be used to mine/transport N2 (and other volatiles like CH4) from Titan. "Piggy-backed" onto it so to speak.

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