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

Postby Skipjack » Wed Oct 02, 2019 2:39 am

Giorgio wrote:The numbers are probably right, but according the way of working of the FuZe reactor is seems more to be an "Impulse ISP" than a prolonged time working engine ISP.
If you get a shot every 10 seconds it still is a pretty impressive ISP value for space application, but nowhere useful to get out of earth gravity well.

Theoretically, the SFS- Z- Pinch can operate like continuous thruster. The pulse length is extremely short and the pulses can come in such quick succession that you essentially get continuous thrust. That is at least my understanding. I think the potential problem with that is with the reactor components getting extremely hot. But maybe that is not as bad as it seems (the papers are not really going into that). There are also potential ways to mitigate that problem.

AcesHigh
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Re: Z-Pinch Renaissance

Postby AcesHigh » Wed Oct 02, 2019 3:22 am

in all scenarios however, it would still open the Solar System for human colonization (which I do not really think Starship does... it opens the Star System for exploration by scientists, miltiary, bases creation, etc...

but I don't think it's feasible to transport 100 civilians who were NOT screened psychologically, on 1000 m³ for 6 months. And that, to Mars!

Giorgio
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Re: Z-Pinch Renaissance

Postby Giorgio » Wed Oct 02, 2019 3:30 am

Skipjack wrote:
Giorgio wrote:The numbers are probably right, but according the way of working of the FuZe reactor is seems more to be an "Impulse ISP" than a prolonged time working engine ISP.
If you get a shot every 10 seconds it still is a pretty impressive ISP value for space application, but nowhere useful to get out of earth gravity well.

Theoretically, the SFS- Z- Pinch can operate like continuous thruster. The pulse length is extremely short and the pulses can come in such quick succession that you essentially get continuous thrust. That is at least my understanding. I think the potential problem with that is with the reactor components getting extremely hot. But maybe that is not as bad as it seems (the papers are not really going into that). There are also potential ways to mitigate that problem.


I didn't express myself properly.
What I meant to say is that anyhow the "Thrust generating" instance (the time during which the fusion event takes place) of such an engine is extremely small in respect of the time frame of operation of the engine itself.

The fusion event length is just few microseconds, all the other time is spent just to prepare for the fusion event, hence there is no thrust.

If the fusion last for 5 uSec, even if they get to reach a frequency of 50 Hz for the shooting (which per se would already be an amazing technological feat), we are still getting a ratio of 4.000 for the "no thrust/thrust" time indicator ( 1.000.000 uSec / {50 shots x 5 uSec = 4.000} ), hence the real ISP value will have to be downgraded by 4.000 times in respect to the reported single shot theoretical ISP.
And we are still not taking into consideration the other important value for any engine willing to leave earth gravity well, the engine thrust/weight ratio.

Anyhow, I hope now is more clear what I meant. Of course these are all assumptions based on the few info/numbers we are getting for the FuZe operating parameters. Maybe in the end they will surprise us with totally different (and hopefully more favorable) numbers.
A society of dogmas is a dead society.

Skipjack
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Re: Z-Pinch Renaissance

Postby Skipjack » Wed Oct 02, 2019 12:32 pm

Giorgio wrote:
Skipjack wrote:
Giorgio wrote:The numbers are probably right, but according the way of working of the FuZe reactor is seems more to be an "Impulse ISP" than a prolonged time working engine ISP.
If you get a shot every 10 seconds it still is a pretty impressive ISP value for space application, but nowhere useful to get out of earth gravity well.

Theoretically, the SFS- Z- Pinch can operate like continuous thruster. The pulse length is extremely short and the pulses can come in such quick succession that you essentially get continuous thrust. That is at least my understanding. I think the potential problem with that is with the reactor components getting extremely hot. But maybe that is not as bad as it seems (the papers are not really going into that). There are also potential ways to mitigate that problem.


I didn't express myself properly.
What I meant to say is that anyhow the "Thrust generating" instance (the time during which the fusion event takes place) of such an engine is extremely small in respect of the time frame of operation of the engine itself.

The fusion event length is just few microseconds, all the other time is spent just to prepare for the fusion event, hence there is no thrust.

If the fusion last for 5 uSec, even if they get to reach a frequency of 50 Hz for the shooting (which per se would already be an amazing technological feat), we are still getting a ratio of 4.000 for the "no thrust/thrust" time indicator ( 1.000.000 uSec / {50 shots x 5 uSec = 4.000} ), hence the real ISP value will have to be downgraded by 4.000 times in respect to the reported single shot theoretical ISP.
And we are still not taking into consideration the other important value for any engine willing to leave earth gravity well, the engine thrust/weight ratio.

Anyhow, I hope now is more clear what I meant. Of course these are all assumptions based on the few info/numbers we are getting for the FuZe operating parameters. Maybe in the end they will surprise us with totally different (and hopefully more favorable) numbers.

No, I understood you. But I believe to have read that the operation of this SFS Z-Pinch is essentially continuous because the shots come in such a quick succession. But you are right, this is not 100% clear from the available publications and I am therefore not entirely sure of that.
T/W ratio should be above 1 from my estimates (if the thrust is indeed continuous).

Giorgio
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Re: Z-Pinch Renaissance

Postby Giorgio » Wed Oct 02, 2019 3:34 pm

Skipjack wrote:I believe to have read that the operation of this SFS Z-Pinch is essentially continuous because the shots come in such a quick succession.

I am concerned mainly by the ability to dissipate heat load as the frequency of the pulses increases.
If by any chance you get to talk to them again you might drop the question of what is their expected shooting rate for the commercial reactor and the rocket engine variant.
A society of dogmas is a dead society.

Skipjack
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Re: Z-Pinch Renaissance

Postby Skipjack » Thu Oct 03, 2019 3:26 am

Giorgio wrote:
Skipjack wrote:I believe to have read that the operation of this SFS Z-Pinch is essentially continuous because the shots come in such a quick succession.

I am concerned mainly by the ability to dissipate heat load as the frequency of the pulses increases.
If by any chance you get to talk to them again you might drop the question of what is their expected shooting rate for the commercial reactor and the rocket engine variant.

Yes, I do understand the heat load being a problem, but I suppose one could use some kind of active-passive cooling combination to deal with that.
I mean chemical rocket engines also operate at extreme heat loads.

Giorgio
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Re: Z-Pinch Renaissance

Postby Giorgio » Thu Oct 03, 2019 7:20 pm

Skipjack wrote:
Giorgio wrote:
Skipjack wrote:I believe to have read that the operation of this SFS Z-Pinch is essentially continuous because the shots come in such a quick succession.

I am concerned mainly by the ability to dissipate heat load as the frequency of the pulses increases.
If by any chance you get to talk to them again you might drop the question of what is their expected shooting rate for the commercial reactor and the rocket engine variant.

Yes, I do understand the heat load being a problem, but I suppose one could use some kind of active-passive cooling combination to deal with that.
I mean chemical rocket engines also operate at extreme heat loads.


True, but in chemical rockets the combustion is with high flow of mass which brings away a large chunk of the heat and additionally it creates a boundary layer effect around the walls of the combustion chamber/nozzle, that effectively controls the heat flux and protect them.

In a FuZe style rocket (or in any fusion based device for what it matters), the flow of mass is minimal, while the thermal load to be managed is exponentially higher due neutron and radiation induced heating (in case of D+D or D+T fuel), as well as the need for cooling for all electric load bearing equipment that is ancillary to the fusion reactor.

I found back this 2012 NASA paper titled "FUSION PROPULSION Z-PINCH ENGINE CONCEPT":
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20120002875.pdf

Shot frequency was 10Hz and net ISP was 19400 (with some assumptions).
Limiting factors for increasing frequency of pulses seemed to be the charging time for the capacitor bank for the following pulse and thermal radiator size/mass and thermal management in general.

It's an interesting read if you have some spare time during a coffee break.
A society of dogmas is a dead society.

Skipjack
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Re: Z-Pinch Renaissance

Postby Skipjack » Thu Oct 03, 2019 9:40 pm

Giorgio wrote:
Skipjack wrote:
Giorgio wrote:I am concerned mainly by the ability to dissipate heat load as the frequency of the pulses increases.
If by any chance you get to talk to them again you might drop the question of what is their expected shooting rate for the commercial reactor and the rocket engine variant.

Yes, I do understand the heat load being a problem, but I suppose one could use some kind of active-passive cooling combination to deal with that.
I mean chemical rocket engines also operate at extreme heat loads.


True, but in chemical rockets the combustion is with high flow of mass which brings away a large chunk of the heat and additionally it creates a boundary layer effect around the walls of the combustion chamber/nozzle, that effectively controls the heat flux and protect them.

In a FuZe style rocket (or in any fusion based device for what it matters), the flow of mass is minimal, while the thermal load to be managed is exponentially higher due neutron and radiation induced heating (in case of D+D or D+T fuel), as well as the need for cooling for all electric load bearing equipment that is ancillary to the fusion reactor.

I found back this 2012 NASA paper titled "FUSION PROPULSION Z-PINCH ENGINE CONCEPT":
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20120002875.pdf

Shot frequency was 10Hz and net ISP was 19400 (with some assumptions).
Limiting factors for increasing frequency of pulses seemed to be the charging time for the capacitor bank for the following pulse and thermal radiator size/mass and thermal management in general.

It's an interesting read if you have some spare time during a coffee break.


Uri assumes D+He3 as the idea fuel for a SFS- Z- Pinch rocket engine. The Q and T/W are higher than with an engine using PB11 (which they also examined). Neutron fluxes with D+He3 are much lower. I don't have numbers for the SFS- Z- Pinch, but I have them for the PPPL DFD (with kind permission from Michael Paluszek). Unfortunately this board does not seem to allow the attachment of PDFs, or I could post the whole Poster, which is super interesting...
Here are the reactions and their rates in the DFD. I assume they will be similar for the SFS- Z- Pinch, maybe even better since pulse durations are so short and fusion products are expelled out the back at a very high velocity.
The percentage value at the end indicate the anticipated percentage for each reaction in the DFD.
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%

Also interesting in this context is the radiator mass that Princeton Satellite Systems is proposing for their DFD powered Pluto orbiter. That mass 133kg for their 2 MW engine. One could probably extrapolate from that for the SFS Z- pinch. But I want to add that the PSS Pluto Orbiter design is assuming a conventional steam cycle for conversion of the fusion energy into electricity. That will require bigger radiators than they would need to just radiate away the excess engine heat (since the temperature differential needs to be much higher for the steam cycle to work well).
The SFS Z- Pinch fusion engine would use direct conversion, which does not add as much weight and would charge up the capacitors much quicker than a steam cycle would.

You are right about chemical engines working differently, but I would like to argue that a Z- Pinch derived engine could be configured in a similar way.
Plus most of the heat would still get carried away quickly by the exhausted fuel. One could also trade some Isp by injecting extra cold fuel into the flow or in between pulses to cool the engine and generate extra thrust (or more continuous thrust if pulse frequency is indeed a problem). That would make it work a bit like a "conventional" nuclear thermal engine. Some newer NT designs are aiming for 1000 seconds Isp (some even 4000 but I am not sure they would be applicable), which is still really good. Combine that with the much higher Isp for the actual fusion "mode" and you would still get a very powerful system. Even if that reduced the overall Isp of the engine by a factor of 10, it would still be an amazing engine with incredible Isp. Also note that the thrust from the NERVA mode would be higher than from the pure fusion mode (though the Isp would be lower), which _may_ be able to offset the total increase in GLOW of a spacecraft derived from that.

Skipjack
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Re: Z-Pinch Renaissance

Postby Skipjack » Thu Oct 03, 2019 9:57 pm

Another thing to consider is that by my most conservative estimate, the total engine mass for the D+He3 Z-Pinch engine would be about 20 tonnes. But probably a lot less.
Most of that is power supplies and support systems. The actual reactor core mass is relatively minor. One could double or triple up the number of reactor cores to increase the pulse frequency that way. They could all share the same support systems and then just cycle. Doing trade studies between these different solutions would probably keep several grad students busy for years ;)

Skipjack
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Re: Z-Pinch Renaissance

Postby Skipjack » Fri Oct 04, 2019 5:05 am

This seems relevant related news:
Congrats to Professor Uri Shumlak for becoming an APS Fellow!
https://www.aa.washington.edu/news/arti ... ety-fellow

Giorgio
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Re: Z-Pinch Renaissance

Postby Giorgio » Fri Oct 04, 2019 4:43 pm

Skipjack wrote:Uri assumes D+He3 as the idea fuel for a SFS- Z- Pinch rocket engine. The Q and T/W are higher than with an engine using PB11 (which they also examined).


You are totally right, indeed the pB11 has theoretical worst characteristics as a fuel, but is also the fuel that has been less investigated so far; I do believe it is still the field where "surprises" can come out once some real experimental test start to be done.
I didn't even take into consideration 3He route because right now on earth the only 3He source is from the natural decay of Tritium (which has about 12 years half life) thus is not a fuel that we have ready available and we will not have it in the coming future, so whatever engine we will use in the first stage of solar system exploration will have to be based on available commodities.

Regarding the paper you are referring to, I believe is this one, correct me if I am wrong:
https://www.nasa.gov/sites/default/files/atoms/files/niac_2016_phasei_thomas_fusiontopluto_tagged.pdf

For the radiators mass I am not convinced by the assumptions in their paper.
They assume to reject to space only about 25% of the fusion power generated with a D-3He fusion.
They assume radiator weight based on a new carbon-carbon radiator with 5 times less mass than actual technology (but still is just theoretical).
They assume (very optimistically) that both sides of the radiators will be in a optima radiate situation.
These assumptions are offsetting the needed mass of radiators by a factor of 10 and the needed area by a factor of 3 compared to existing technology that would require about 1400 Kg of mass and 140 M2 for the radiators; and this just to get 5 N of thrust.
Now let's imagine the mass and area needed for the radiators for a 50 KN engine for a human rated vessel.......

I greatly hope to be proven wrong in the immediate future, but radiators technology for space applications is in my opinion one of the most underestimated and underfunded field of space research but whose importance I place on the same level as the reactor. That is, unless we have a reaction that can get rid of most of these thermal issues.
And if you look it under this light p-B11 fuel starts to look very attractive, even if it is greatly more difficult to ignite.


Skipjack wrote:One could also trade some Isp by injecting extra cold fuel into the flow or in between pulses to cool the engine and generate extra thrust (or more continuous thrust if pulse frequency is indeed a problem). That would make it work a bit like a "conventional" nuclear thermal engine.
.......
One could double or triple up the number of reactor cores to increase the pulse frequency that way.


I like both ideas, even if the thermal dissipation requirements will still be quite big there could be a sweet spot somewhere that could make the design more affordable.
Worst case, let's fit the ship with a set of NT reactors, find some water rich asteroid to mine and just steampunk our way around the solar system. Maybe not greatly efficient, but what an amazing view would such a ship be! 8)
A society of dogmas is a dead society.

Giorgio
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Re: Z-Pinch Renaissance

Postby Giorgio » Fri Oct 04, 2019 4:44 pm

Skipjack wrote:This seems relevant related news:
Congrats to Professor Uri Shumlak for becoming an APS Fellow!
https://www.aa.washington.edu/news/arti ... ety-fellow

Congratulations indeed! Hopefully this will make more easy for him and his team to source extra funds for research!
A society of dogmas is a dead society.

Skipjack
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Re: Z-Pinch Renaissance

Postby Skipjack » Fri Oct 04, 2019 7:02 pm

Giorgio wrote:
Skipjack wrote:Uri assumes D+He3 as the idea fuel for a SFS- Z- Pinch rocket engine. The Q and T/W are higher than with an engine using PB11 (which they also examined).


You are totally right, indeed the pB11 has theoretical worst characteristics as a fuel, but is also the fuel that has been less investigated so far; I do believe it is still the field where "surprises" can come out once some real experimental test start to be done.
I didn't even take into consideration 3He route because right now on earth the only 3He source is from the natural decay of Tritium (which has about 12 years half life) thus is not a fuel that we have ready available and we will not have it in the coming future, so whatever engine we will use in the first stage of solar system exploration will have to be based on available commodities.


If you have a reactor that can "burn" D+He3, then you can also fuse D+D.
D+D-> n + He3
D+D-> p + T

For a space propulsion like that, I would probably have dedicated D+D reactors somewhere on Earth that do nothing but produce He3.
One could either wait for the T in the other branch to decay to more He3, or sell it. T is worth a lot more than He3 right now. So there is a business opportunity there. Plus, those reactors would even produce some electricity from the neutrons and the charged particles created by the reaction. They would be a lot less efficient than D+He3 reactors, but it could still help them produce He3 fuel for essentially free. To make matters even more interesting, one could also try to capture the neutrons in a Lithium blanket to produce even more T... Lots of options to make this whole thing relatively affordable.

Giorgio wrote:Regarding the paper you are referring to, I believe is this one, correct me if I am wrong:
https://www.nasa.gov/sites/default/files/atoms/files/niac_2016_phasei_thomas_fusiontopluto_tagged.pdf

For the radiators mass I am not convinced by the assumptions in their paper.
They assume to reject to space only about 25% of the fusion power generated with a D-3He fusion.
They assume radiator weight based on a new carbon-carbon radiator with 5 times less mass than actual technology (but still is just theoretical).
They assume (very optimistically) that both sides of the radiators will be in a optima radiate situation.
These assumptions are offsetting the needed mass of radiators by a factor of 10 and the needed area by a factor of 3 compared to existing technology that would require about 1400 Kg of mass and 140 M2 for the radiators; and this just to get 5 N of thrust.
Now let's imagine the mass and area needed for the radiators for a 50 KN engine for a human rated vessel.......

I am not expert on radiators. So you may very well be right there. On the positive side, there is a new magnetic nozzle design that I saw in the recent NIAC presentation on PUFF that would probably bring some improvements to the concept there.

Giorgio wrote:I greatly hope to be proven wrong in the immediate future, but radiators technology for space applications is in my opinion one of the most underestimated and underfunded field of space research but whose importance I place on the same level as the reactor.

And I agree with you there, but I believe that even under ideal circumstances you are limited by the black body radiation limits no matter what you do. From what little I understand, I believe the key to reducing radiator mass is (paradoxically) to run hotter. Hotter radiators radiate more.

Giorgio wrote:That is, unless we have a reaction that can get rid of most of these thermal issues.
And if you look it under this light p-B11 fuel starts to look very attractive, even if it is greatly more difficult to ignite.

Just like D+He3 reactors, PB11 reactors would still produce heat that would have to be radiated into space.
Uri Shumlak's team compared the masses for PB11 and DHe3 and DHe3 came out with a lower total system mass. In their case it is the need for a larger reactor that would have a lower Q. DHe3 seems to be a good middle ground between the smaller D+T that suffers from extreme neutron flux and PB11, which has less neutrons but is also much larger. There are some other issues too. Both fuel mixes can use direct conversion. So you don't have to radiate enough heat away to have a nice heat gradient for the Carnot cycle. You "just" have to keep the reactor at an acceptable operating temperature. For the Z- Pinch and it's extreme Pin / Pout values, that too could potentially be a challenge. I wished Uri would answer that in an updated paper on the topic. That and the projected total system mass (including capacitors, switches, etc).

paperburn1
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Re: Z-Pinch Renaissance

Postby paperburn1 » Sun Oct 06, 2019 1:31 am

I am not a nuclear physicist, but play one on the internet.

Skipjack
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Re: Z-Pinch Renaissance

Postby Skipjack » Sun Oct 13, 2019 12:47 am

Looks like ZAP is hiring, some of the jobs mention their next generation (scientific break even) device:
https://careers.aps.org/jobs/?keywords= ... 0Inc%2E%22


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