Z-Pinch Renaissance

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

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Skipjack
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Re: Z-Pinch Renaissance

Post by Skipjack »

williatw wrote:
Sat Oct 10, 2020 10:34 pm
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.
Yeah, I meant Saturn's gravity well. I am still not sure whether mining Saturn for He3 is cost effective. I think it will be cheaper to breed it in D+D reactors on Earth, at least until demand increases dramatically with hundreds of D+He3 ships flying around and mining at the outer planets becomes easier/cheaper because of all this.

Giorgio
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Re: Z-Pinch Renaissance

Post by Giorgio »

Skipjack wrote:
Sat Oct 10, 2020 4:43 pm
I think that asteroids containing Carlsbergite might be the source of nitrogen on Earth
I didn't know about Carlsbergite and I didn't expect that it was a CrN compound... Quite unusual and intriguing.
At 21% N content this could indeed be an excellent starting raw material.
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williatw
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Re: Z-Pinch Renaissance

Post by williatw »

Skipjack wrote:
Sun Oct 11, 2020 4:30 am
I am still not sure whether mining Saturn for He3 is cost effective. I think it will be cheaper to breed it in D+D reactors on Earth, at least until demand increases dramatically with hundreds of D+He3 ships flying around and mining at the outer planets becomes easier/cheaper because of all this.
Given your Z-pinch drive's capabilities doubt if Saturn's gravity well would be that big of an issue. Would think that taking off from & navigating the thick turbulent atmosphere of Titan with a full load would likely cause more headaches than eithers' gravity well would. Would bet Titan has some killer wind vortexes. Wonder if instead of landing ships might just dive into Titan's atmosphere fill up their tanks and then blast back into orbit. The whole point of developing a high thrust/SI system like you Z-pinch drive would be to open up the whole solar system for development. The mineral rich Asteriod belt, outer planets and their retinue of volatile rich moons even the Kuiper belt would become easy pickings. Hundreds if not thousands of said ships of various sizes would be inevitable. And as I said before even if earth derived He3 would initially be cheaper the "spacers" wouldn't like being kept on a leash held by earth. Especially as the issue of who owns off planet resources like the Asteroid belt would increasingly be a bone of contention. Earth might use the clout of being the only filling station to keep said spacers in line. Would think that you would get your He3 by breeding Tritium from Lithium and then letting it decay to He3. Probably easier than getting it as a side reaction for the De+De reaction. Although I suppose you could mean using that burn to make Tritium from Lithium; would think you would prefer the easier De+Tritium burn for that.
Last edited by williatw on Wed Oct 14, 2020 7:21 pm, edited 1 time in total.

williatw
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Re: Z-Pinch Renaissance

Post by williatw »

Giorgio wrote:
Sun Oct 11, 2020 9:38 am
Skipjack wrote:
Sat Oct 10, 2020 4:43 pm
I think that asteroids containing Carlsbergite might be the source of nitrogen on Earth
I didn't know about Carlsbergite and I didn't expect that it was a CrN compound... Quite unusual and intriguing.
At 21% N content this could indeed be an excellent starting raw material.
Probably more Nitrogen (& other useful volatiles) in Titan's atmosphere and surface than all the N2 in the entire asteroid belt, all in one place.

Giorgio
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Re: Z-Pinch Renaissance

Post by Giorgio »

williatw wrote:
Wed Oct 14, 2020 7:15 pm
Probably more Nitrogen (& other useful volatiles) in Titan's atmosphere and surface than all the N2 in the entire asteroid belt, all in one place.
That might be true, but the Asteroid belt is between 180 and 300 million km far from Earth, while Titan is 1300 Million km far.
We can imagine a 6 to 8 month trip to reach Asteroid belt area and maybe (with cheap fuel) we can squeeze it to 5 moth for a near earth object.
So, going to the belt would still be affordable time-wise, but the trip to actually go and mine Titan would be prohibitively long with our actual technology level, we are speaking about 30 to 36 month travel time just to go there if we are plenty of cheap fuel.

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williatw
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Re: Z-Pinch Renaissance

Post by williatw »

Giorgio wrote:
Thu Oct 15, 2020 1:28 am
That might be true, but the Asteroid belt is between 180 and 300 million km far from Earth, while Titan is 1300 Million km far. We can imagine a 6 to 8 month trip to reach Asteroid belt area and maybe (with cheap fuel) we can squeeze it to 5 moth for a near earth object. So, going to the belt would still be affordable time-wise, but the trip to actually go and mine Titan would be prohibitively long with our actual technology level, we are speaking about 30 to 36 month travel time just to go there if we are plenty of cheap fuel.
First you have to locate the asteroid containing the volatiles you are looking for then cost/time to reach it and setup operations there. After you deplete said asteroids' limited resources you have to locate the the next one and repeat the process. We already know where Saturn & Titan are and would only have to setup operations there once. Didn't think we were talking about that long of a trip time to Saturn with a modified Z-pinch delivering several thousand seconds SI and high thrust operated in something approaching a "torch-ship" mode. The longer the intended trip the longer the acceleration/deceleration boost phase; nothing close to a linear relationship for ship travel time with distance. Assuming the engine over-heating issue can be resolved. Furthermore mining Titan would be an outgrowth of the primary reason you are at Saturn mining the extremely valuable He3 from Saturn's atmosphere. You can refuel at Saturn both He3 + De fuel and propellant as needed. He3 (& De) would probably be harvested from Saturn with a space elevator attached (or sky-hook) to the processing facility probably floating in Saturn's atmosphere. You would only send up the elevator the separated He3 (and/or whatever else you want) topside to the waiting orbiting ship(s). A ship (once the facilities were operational) could arrive at the Saturn virtually empty refuel then boost from Titan/Saturn with full tanks of propellant/fuel/cargo. Unlike an Asteroid you wouldn't need to carry fuel/propellant for the round trip to the asteroid and back, or just gamble you can find fuel/propellant as needed on said Asteroid.

williatw
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Re: Z-Pinch Renaissance

Post by williatw »

Skipjack wrote:
Sun Oct 11, 2020 4:30 am
I am still not sure whether mining Saturn for He3 is cost effective. I think it will be cheaper to breed it in D+D reactors on Earth, at least until demand increases dramatically with hundreds of D+He3 ships flying around and mining at the outer planets becomes easier/cheaper because of all this.
Found this: Tritium is very expensive: Currently it costs $30,000/gram [1]! Deuterium is produced from seawater. It is cheap: Currently it costs about $1/gram. deuterium is negligible, it is insignificant for these computations.

https://vixra.org/pdf/1702.0190v1.pdf

So since it decays to He3 Tritium produced on earth from Lithium and therefore the He3 decay product cost $850K per ounce; quite a bit more than gold/platinum. Sure with increased demand for said He3 economies of scale would lower earthside production cost but still. Very big potential profit margin; at some point the spacers would not only be able to supply themselves with fuel but could sell it back to earth

Skipjack
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Re: Z-Pinch Renaissance

Post by Skipjack »

That is actually a nice side effect of the D+D reaction for making He3 (I think I mentioned that before). D+D produces He3 in one branch and Tritium in the other. Selling that Tritium would make a ton of money. There is a high demand for military and medical applications and possibly D+T fusion reactors operating on Earth might need some extra T in the inventory, especially if a lot of new ones are built and need to get started.
So doing D+D on Earth will be even more cost effective and probably really hard to beat by mining space. I don't think T is more common out there (mainly because of it's short half life), but I might be wrong.
Deuterium is cheap and everywhere on Earth. Heavy water reactors have entire pools full of that stuff.

williatw
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Re: Z-Pinch Renaissance

Post by williatw »

Skipjack wrote:
Thu Oct 15, 2020 7:38 am
That is actually a nice side effect of the D+D reaction for making He3 (I think I mentioned that before). D+D produces He3 in one branch and Tritium in the other. Selling that Tritium would make a ton of money. There is a high demand for military and medical applications and possibly D+T fusion reactors operating on Earth might need some extra T in the inventory, especially if a lot of new ones are built and need to get started.
So doing D+D on Earth will be even more cost effective and probably really hard to beat by mining space. I don't think T is more common out there (mainly because of it's short half life), but I might be wrong.
Deuterium is cheap and everywhere on Earth. Heavy water reactors have entire pools full of that stuff.
But what is the cost of producing Tritium? I am assuming if you can sell it for such an exorbitant amount it must be expensive to make. De and Lithium are cheap but that doesn't mean the products are cheap. For instance graphite is cheap; doesn't mean that carbon fiber (or diamonds) made from such are cheap, obviously they are not. I mean how long do you have to run a 1000MW D+D fusion reactor to even get one KG of Tritium (or He3)? After all if it were cheap to make from lithium using existing fission reactors someone right now would be making tons of it and getting rich. If I recall most if not all of the Tritium produced by the D+D fusion reaction is consumed in the reactor by reacting with more De...little of it recoverable as a discreet product for sale. A first generation fusion Tritium+De reactor like the proposed ITER the reaction chamber is surrounded by a blanket of Lithium to breed more Tritium. How much of that net is produced how quickly and is available to harvest as product for sale would be the question.

Skipjack
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Re: Z-Pinch Renaissance

Post by Skipjack »

williatw wrote:
Thu Oct 15, 2020 1:07 pm

But what is the cost of producing Tritium? I am assuming if you can sell it for such an exorbitant amount it must be expensive to make. De and Lithium are cheap but that doesn't mean the products are cheap. For instance graphite is cheap; doesn't mean that carbon fiber (or diamonds) made from such are cheap, obviously they are not. I mean how long do you have to run a 1000MW D+D fusion reactor to even get one KG of Tritium (or He3)? After all if it were cheap to make from lithium using existing fission reactors someone right now would be making tons of it and getting rich. If I recall most if not all of the Tritium produced by the D+D fusion reaction is consumed in the reactor by reacting with more De...little of it recoverable as a discreet product for sale. A first generation fusion Tritium+De reactor like the proposed ITER the reaction chamber is surrounded by a blanket of Lithium to breed more Tritium. How much of that net is produced how quickly and is available to harvest as product for sale would be the question.
Depends on the reactor. If you have a reactor capable of burning D+He3, then Tritium is an unwanted byproduct.
In pulsed reactors like Helion's the Tritium burn up rate would be quite low. They would extract the Tritium between pulses.
I presume that if ZAP managed to do D+He3 (like they hope to do for their engine), they would do the same.
In PPPL's FRC the Tritium would be transported off by the scrape off layer. They claim a less than 1%(can't remember the exact number but it is tiny) T burn up rate. They too would extract the T from the fusion products, I presume.
I think in Tokamaks this would be really hard to do.
As for the exact amounts of T produced, I am not sure. I think it again depends on the reactor. From all I have read, I would guess it is somewhere on the magnitude of 30 kg of T per year for a reactor(s) producing 1 GW. That is 900 million dollars worth of Tritium a year. Granted, at that point the price of Tritium will likely fall and one would probably want to keep some of it to decay into He3 anyway, but it would be a pretty good income for the first few reactors on the market.

williatw
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Re: Z-Pinch Renaissance

Post by williatw »

Skipjack wrote:
Fri Oct 16, 2020 9:09 am
As for the exact amounts of T produced, I am not sure. I think it again depends on the reactor. From all I have read, I would guess it is somewhere on the magnitude of 30 kg of T per year for a reactor(s) producing 1 GW. That is 900 million dollars worth of Tritium a year. Granted, at that point the price of Tritium will likely fall and one would probably want to keep some of it to decay into He3 anyway, but it would be a pretty good income for the first few reactors on the market.


D + 3He ➞ 4He (3.6 MeV) + p (14.7 MeV) 98.4%
D + D ➞ T (1.01 MeV) + p (3.01 MeV) 0.88%
D + D ➞ 3He (0.82 MeV) + n (2.45 MeV) 0.72%
D + T ➞ 4He (3.5 MeV) + n (14.1 MeV) 0.05%

I assume you mean the D+D reactor to produce the 30kg of Tritium per year since the D + 3He ➞ 4He doesn't have a step that produces Tritium I didn't think. If your figures are accurate about the 30kg of T per year per 1GW reactor looks like you were right about my plan to extract He3 from Saturn (or Uranus or Neptune which have even more concentrated He3 less gravity/radiation belts). It wouldn't be practical without a huge increase in demand for He3 far more than terrestrial power plant usage would seemingly indicate. It would have to be as you suggested 100(s) of 3TW burning Z-pinch rockets; unless the spacers before then get really desperate to secure an off-planet filling station.

This is for a Tokomak:
ITER will procure the tritium fuel necessary for its expected 20-year lifetime from the global inventory. But for DEMO, the next step on the way to commercial fusion power, about 300g of tritium will be required per day to produce 800 MW of electrical power. No sufficient external source of tritium exists for fusion energy development beyond ITER, making the successful development of tritium breeding is essential for the future of fusion energy.
https://www.iter.org/mach/TritiumBreeding

Reason I posted it is 0.3kgX (1.0/0.8) X 365 = 136KG of Tritium (& approx. the same mass of He3 for that kind of reaction) per year for a 1GW reactor.

136/36=3.8; approx. 4 D + D reactors to supply every D +He3 reactor. Or actually half that no. since it would produce He3 in equal amount of the Tritium. If you had a 1000 D+He3 reactors you would need approx. 1.4 metric tons a year of He3
Last edited by williatw on Fri Oct 16, 2020 3:35 pm, edited 2 times in total.

Skipjack
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Re: Z-Pinch Renaissance

Post by Skipjack »

That is what Helion is planning to do. Their reactor will be a little above break even with pure D+D but the real oomph comes when they feed the He3 back into the reactor for the next shot. Then they (at least hope to) get a Q above 5, which will be enough for their reactor design to be economically competitive with gas, probably even solar and wind (but if they can just replace the gas plants that take over for Renewables then they already have a huge market).
The Tritium could be stored until it decays into more He3 in the future, or it could be sold. Tritium is (at least right now) much more expensive than He3. So they could sell the T and buy He3 instead and still make a good profit from just that.

As for the metric of how much He3 you need, it is not quite that simple. A reactor burning He3 like Helion's can use direct conversion. Helion's reactor is presumably really efficient in that way, since it can even recoup a good measure of the energy that goes into the plasma. That is why they should be able to get away with a much lower than Q than a Tokamak (Toks will need a Q of about 30 or so to be economic).
So you can't necessarily extrapolate from a D+T Tokamak to a D+He3 reactor with direct conversion.

Giorgio
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Re: Z-Pinch Renaissance

Post by Giorgio »

williatw wrote:
Thu Oct 15, 2020 3:24 am
First you have to locate the asteroid containing the volatiles you are looking for then cost/time to reach it and setup operations there. After you deplete said asteroids' limited resources you have to locate the the next one and repeat the process. We already know where Saturn & Titan are and would only have to setup operations there once.
That unfortunately is not so straightforward.
While we have a rough idea about Titan composition, but we do not know the exact chemical nature and real composition of the environment where the operation will take place. This includes eventual trace of other chemicals/materials that might influence the extraction/transformation/catalytic process of the end product we need to extract/manufacture.
Like all mining activities we will need to send a prospect team to verify and test the area and the process to be implemented before even evaluating the possibility to set up a full human mission.
The real main limit I see on implementing operations on such a large time scale, is the extreme startup costs, and in the end it might be order of magnitude cheaper to just source them from earth (He3 being the exception, but we still need to prove that there is enough there to be economically mined).


williatw wrote:
Thu Oct 15, 2020 3:24 am
Didn't think we were talking about that long of a trip time to Saturn with a modified Z-pinch delivering several thousand seconds SI and high thrust operated in something approaching a "torch-ship" mode. The longer the intended trip the longer the acceleration/deceleration boost phase; nothing close to a linear relationship for ship travel time with distance.
Yes, I already put that into account.
With our actual level of technology an high ISP/high thrust engine design has the trade-off of a huge increase in mass (for energy generation/ancillary equipment) that will generally nullify the extra ISP (or the extra thrust) benefit. Any engine proposed so far that overcome one of these limits is designed with technologies we do not posses yet nor we are anywhere near to posses.
The consequence is a very slow acceleration even in the most optimistic scenario where you can use the engine 24h/365d. To to gain speed will take a very long time, to the point where for short distance travels (say Mars or the asteroids) a chemical rocket is more "time wise" efficient.

The same proposed ZAP engine is a good example of these limits and if you run some calculations (by estimating what could be the thrust duration in a given second) you can see it clearly where my numbers come from.
It is true that we do not have any official number from ZAP about engine repetition rate, but existing technology puts strong limits on the range of those numbers.
The time frame I gave you is in truth a very very optimistic one. In a real application I doubt we will get even near to those numbers due to the limits of ship mass /repetition rate as I mentioned above.

We can open a new thread if you are interested in going through the calculations.

williatw wrote:
Thu Oct 15, 2020 3:24 am
A ship (once the facilities were operational) could arrive at the Saturn virtually empty refuel then boost from Titan/Saturn with full tanks of propellant/fuel/cargo. Unlike an Asteroid you wouldn't need to carry fuel/propellant for the round trip to the asteroid and back, or just gamble you can find fuel/propellant as needed on said Asteroid.
Any engine operating on ISP of 370.000 does not have many fuel issues for such a short (distance wise) round trip.
For a 30000 tons ship (say 20000 Tons of infrastructures and 10000 Tons payload) it would take between 1000 and 1600 tons of fuel (depending on engine repetition rate), so is still manageable in respect to total ship mass.
The problem is still the time for the humans onboard.
A society of dogmas is a dead society.

Skipjack
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Re: Z-Pinch Renaissance

Post by Skipjack »

Giorgio wrote:
Sun Oct 18, 2020 1:19 pm

Yes, I already put that into account.
With our actual level of technology an high ISP/high thrust engine design has the trade-off of a huge increase in mass (for energy generation/ancillary equipment) that will generally nullify the extra ISP (or the extra thrust) benefit. Any engine proposed so far that overcome one of these limits is designed with technologies we do not posses yet nor we are anywhere near to posses.
The consequence is a very slow acceleration even in the most optimistic scenario where you can use the engine 24h/365d. To to gain speed will take a very long time, to the point where for short distance travels (say Mars or the asteroids) a chemical rocket is more "time wise" efficient.

The same proposed ZAP engine is a good example of these limits and if you run some calculations (by estimating what could be the thrust duration in a given second) you can see it clearly where my numbers come from.
It is true that we do not have any official number from ZAP about engine repetition rate, but existing technology puts strong limits on the range of those numbers.
The time frame I gave you is in truth a very very optimistic one. In a real application I doubt we will get even near to those numbers due to the limits of ship mass /repetition rate as I mentioned above.
As I said in an earlier post, I think that the ZAP rocket engine, when operated like a gas core NTR could sustain a pulse rate of 150 Hz and achieve an Isp of 5,000 seconds. Thrust should be good enough to make use of fast transfer options.

Giorgio
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Re: Z-Pinch Renaissance

Post by Giorgio »

Skipjack wrote:
Sun Oct 18, 2020 1:34 pm
As I said in an earlier post, I think that the ZAP rocket engine, when operated like a gas core NTR could sustain a pulse rate of 150 Hz and achieve an Isp of 5,000 seconds. Thrust should be good enough to make use of fast transfer options.
I can't comment on what would be the thrust level of a gas core NTR but the main issue I see is the estimated ISP of 5000.
If we assume for easy of calculations that the ship mass at destination still to be 30000 Tons and keep the engine thrust to 300 KN than we have with rough calculations:

Ship Mass: 30.000 Tons
Fuel Mass: 240.000 Tons

Acceleration phase (first half):
Best time to destination: ~300 days
Average time to destination: ~400/450 days (depends on planetary relative position)

Deceleration phase:
Best time to destination: ~170 days
Average time to destination: ~200/220 days (depends on planetary relative position)

Total time:
Best time to destination: ~470 days
Average time to destination: ~600/670 days (depends on planetary relative position)

Still not viable solution in my opinion.

Edited to add:
Travel time calculated as acceleration till half way and deceleration for other half of the trip.
A society of dogmas is a dead society.

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