## Z-Pinch Renaissance

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

Moderators: tonybarry, MSimon

Skipjack
Posts: 6115
Joined: Sun Sep 28, 2008 2:29 pm

### Re: Z-Pinch Renaissance

What is the destination?

williatw
Posts: 1912
Joined: Mon Oct 12, 2009 7:15 pm
Location: Ohio

### Re: Z-Pinch Renaissance

Skipjack wrote:
Mon Oct 19, 2020 5:21 pm
What is the destination?
Saturn maybe?

Using his figures:
Giorgio wrote:
Sun Oct 18, 2020 4:43 pm
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

Travel time calculated as acceleration till half way and deceleration for other half of the trip.
F=MA
Mass (KG) =30,000,000
Force (N)= 300,000
acceleration (F/M) in m/s^2)= 0.01
acceleration/g =0.0010
time acceler. (sec)= 25,920,000
max velocity km/sec =259.2
time decel (sec)= 14,688,000
Trip distance d=0.5at^2 (total) 4.43792E+12 meters
2,758,184,412 miles

Looks like you could cover almost 3 billion miles in that amount of time; that's pretty far for Saturn and at a max velocity of 259km/sec or 160mile/sec (not counting the 18.5 miles/sec you get from the earth's orbit) hard to believe Saturn is that far away even allowing for the curved trajectory of a Hohmann transfer orbit which with this kind of Delta V you increasingly would not be limited to. On the other hand my calculated acceleration doesn't allow for the deceleration effect caused by the Sun's gravity as you move away from the Sun though that would likely drop off quickly with distance.
Last edited by williatw on Mon Oct 19, 2020 9:01 pm, edited 3 times in total.

Skipjack
Posts: 6115
Joined: Sun Sep 28, 2008 2:29 pm

### Re: Z-Pinch Renaissance

Ok, why such a huge ship?
30,000 tonnes is quite big, IMHO, especially when using only one engine (engine mass is not really that relevant).
At the current distance to Saturn I am roughly estimating about maybe 300 days total trip time for a 660 take off mass ship (30 tonne dry and 630 tonne fuel).
Joe's (great) online DV calculator gives me a total DV of ~152,000 m/s assuming the 5,000 Isp.
Total burn time would be around 85 hours or so, if I did not miscalculate anywhere. Thing is that you can spend a lot more of that time accelerating than you need to spend decelerating since the ship will be much lighter then and you can decelerate at much higher g forces.
And acceleration will increase over time too. So the burn time might actually be quite a bit shorter... Hmmm
I wished Joe's otherwise excellent DV calculator would include the total burn time. Would also be nice to have an option to include deceleration to 0 in the calculation to see what the total burn time is.

williatw
Posts: 1912
Joined: Mon Oct 12, 2009 7:15 pm
Location: Ohio

### Re: Z-Pinch Renaissance

Skipjack wrote:
Mon Oct 19, 2020 8:16 pm
Ok, why such a huge ship?
30,000 tonnes is quite big, IMHO, especially when using only one engine (engine mass is not really that relevant).
At the current distance to Saturn I am roughly estimating about maybe 300 days total trip time for a 660 take off mass ship (30 tonne dry and 630 tonne fuel).
Joe's (great) online DV calculator gives me a total DV of ~152,000 m/s assuming the 5,000 Isp.
Total burn time would be around 85 hours or so, if I did not miscalculate anywhere. Thing is that you can spend a lot more of that time accelerating than you need to spend decelerating since the ship will be much lighter then and you can decelerate at much higher g forces.
And acceleration will increase over time too. So the burn time might actually be quite a bit shorter... Hmmm
I wished Joe's otherwise excellent DV calculator would include the total burn time. Would also be nice to have an option to include deceleration to 0 in the calculation to see what the total burn time is.
What kind of trajectory are you assuming? What I was trying to say is that the more DeltaV you can generate the less like a semi-circle type Hohmann transfer orbit trajectory and the more like a flat ellipse. The orbital mechanics get a lot "flatter" the faster you can go Getting closer to a straight line almost; that would cut down on trip distance and time.

Skipjack
Posts: 6115
Joined: Sun Sep 28, 2008 2:29 pm

### Re: Z-Pinch Renaissance

Assuming a straight line for now. It is easier.
Maybe I miscalculated something somewhere?

Giorgio
Posts: 2784
Joined: Wed Oct 07, 2009 6:15 pm
Location: China, Italy

### Re: Z-Pinch Renaissance

williatw wrote:
Mon Oct 19, 2020 6:55 pm
F=MA
Wrong formula and also you didn't include the fuel mass in the calculations.
For a rocket you need to use Tsiolkovski rocket equation [ dV=Ve x ln(Mi/Mf) ]as acceleration will increase while total mass decreases over time.

Skipjack wrote:
Mon Oct 19, 2020 8:16 pm
Ok, why such a huge ship?
30,000 tonnes is quite big, IMHO, especially when using only one engine (engine mass is not really that relevant).
I estimated the mass according the ZAP engine estimate you made few posts before:

Reactor power : 5 GW (I assume you mean GWe and not GWth)
Distance : 1.3 to 1.5 billion km
Thrust : 300,000 N
ISP : 5,000 s

From these we can easily derive also
Ve : 49,000 m/s (exhaust speed)
Fuel flow : 6.12 Kg/s

For the ship I estimated 20,000 Tons for infrastructure, power generator, cooling system and fluids for the reactor and the engine, electrical transformation and distribution and accumulators, life support system, radiation shielding, mass of tanks for fuel and mined products, ship spare parts, living quarters and so on.

Engine is indeed a small part of the mass of the ship as most of the mass will be taken by the 5 GWe reactor and all related sub-components.
Consider that the best of actual submarine nuclear reactor technology is estimated to be an amazing 12Tons/MWe only for the reactor without shielding.
In my estimates i theorized an almost 10 times reduction in mass to 1.5 Tons/MWe x 5,000 MWe = 7,500 Tons only for the core mass of the 5 GWe reactor. And to be honest I am afraid that this is already a big underestimate of what will be the real mass.

The 10,000 Tons left is the payload that includes also any unaccounted overdraft for the ship infrastructure and everything related to the mining side and conversion side of the operation, including the lander, machinery, equipment and reactors to transform/purify the mined products, consumables, fuel and all spare parts for the mining operations.

Additionally, if we take as example a standard earth operation in a remote area, the minimum crew should be at least 5 for managing, maintenance and care of the ship (and the crew), and 10 to 15 for the mining/refining team. Being so far the number will probably need to be bigger, especially if some of the operations will be required to run 24h/day (like the refining/catalytic reactors for the fuel refining/manufacture).

When you start to factor inside all what is needed for a stand alone prospect operations these numbers do not look so big anymore already here on Earth, imagine in space.

Skipjack wrote:
Mon Oct 19, 2020 8:16 pm
At the current distance to Saturn I am roughly estimating about maybe 300 days total trip time for a 660 take off mass ship (30 tonne dry and 630 tonne fuel).
With only 30 tons of dry mass you can't fit a reactor able to give you 300 KN thrust at 5,000 ISP. Than all the assumptions and calculations I made are not anymore meaningful.

Skipjack wrote:
Mon Oct 19, 2020 8:16 pm
I wished Joe's otherwise excellent DV calculator would include the total burn time.
Would also be nice to have an option to include deceleration to 0 in the calculation to see what the total burn time is.
You can quickly calculate Fuel flow rate as = Thrust / (ISP x 9.8 ) , result is fuel flow in kg/s, Thrust is in Newton.
Than from your fuel mass you can easily get the burning time.

I have made a quick spreadsheet where you can input basic data and after defining the number of intervals it will calculate for each interval the travel time, the Dv, the fuel left, the actual acceleration at the end of the interval, distance traveled in the interval, progressive distance, leftover distance at destination and other stuff.
If you are interested I can optimize it during weekend and upload it.

Edited:
Fixed the thousand indicator to "," style to prevent confusion
A society of dogmas is a dead society.

williatw
Posts: 1912
Joined: Mon Oct 12, 2009 7:15 pm
Location: Ohio

### Re: Z-Pinch Renaissance

Giorgio wrote:
Tue Oct 20, 2020 12:16 am
williatw wrote:
Mon Oct 19, 2020 6:55 pm
F=MA
Wrong formula and also you didn't include the fuel mass in the calculations.
For a rocket you need to use Tsiolkovski rocket equation [ dV=Ve x ln(Mi/Mf) ]as acceleration will increase while total mass decreases over time.
I deliberately didn't use the fundamental equation of rocketry because you said the ship mass was:

"Ship Mass: 30.000 Tons
Fuel Mass: 240.000 Tons"
and "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:"

I apparently mistakenly thought you were saying that the ship mass was 30K (30,000) tons and the fuel mass was only 240 tons (D+He3). That is with the fuel being less than 1% total mass decided I could ignore the difference of change of mass as the ship burned fuel. Didn't know you were including an unspecified amount of propellant mass expelled as exhaust. Sorry for misunderstanding your figures.

Skipjack
Posts: 6115
Joined: Sun Sep 28, 2008 2:29 pm

### Re: Z-Pinch Renaissance

Giorgio wrote:
Tue Oct 20, 2020 12:16 am
Skipjack wrote:
Mon Oct 19, 2020 8:16 pm
At the current distance to Saturn I am roughly estimating about maybe 300 days total trip time for a 660 take off mass ship (30 tonne dry and 630 tonne fuel).
With only 30 tons of dry mass you can't fit a reactor able to give you 300 KN thrust at 5,000 ISP. Than all the assumptions and calculations I made are not anymore meaningful.
Based on the vague info that I have, I estimated the mass of the ZAP engine at ~15 tonnes. It is really just two 10 meter long hollow and thin tungsten tubes. The heaviest part would be the power supply and switches. I don't understand how you would estimate it based on a submarine nuclear reactor. Those are completely different technology (fission and not fusion).
You would not need much heavy power conversion equipment since the D+He3 reaction produces charged particles that can be directly converted into electricity. The reactor would also be 5GWth, not 5GWe You only need to get enough electric power for the next shot and a bit extra for systems and stuff.

williatw
Posts: 1912
Joined: Mon Oct 12, 2009 7:15 pm
Location: Ohio

### Re: Z-Pinch Renaissance

Skipjack wrote:
Mon Oct 19, 2020 8:16 pm
Ok, why such a huge ship?
30,000 tonnes is quite big, IMHO, especially when using only one engine (engine mass is not really that relevant).

Would have to agree:
The SpaceX BFR (Big Falcon Rocket or Big frick Rocket) has a planned payload of 150,000 kg (330,000 lb) when flying reusable or 250,000 kg (550,000 lb) when flying expendable, making it a super heavy-lift launch vehicle.
viewtopic.php?f=10&t=3957&p=130405&hili ... +5#p130405

So 330K pounds is 169 tons of payload launched to orbit. 30K/169 yields 178 launches to put the components into orbit to be assembled into your 30K tons beast. Given a sufficient number of rockets and launches at some point that might be doable perhaps but that would take some time. I am just assuming that even if the the modified Z-pinch designs ever reached the stage of being capable of greater than one-gee acceleration that safety concerns would forbid it being allowed to launch itself to orbit. Probably something in the neighborhood of 1000 to perhaps 5000 tons might be more practically foreseeable in the relatively near future. Greater than 100K tons ships might become practical once we have in space manufacturing capabilities using off-planet resources for raw materials; but that will take awhile. If we can use such eventually to build large multi-gigawatt SPS and large space colonies you would obviously be able to build large ships using the same facilities.

Giorgio
Posts: 2784
Joined: Wed Oct 07, 2009 6:15 pm
Location: China, Italy

### Re: Z-Pinch Renaissance

williatw wrote:
Tue Oct 20, 2020 3:43 pm
Skipjack wrote:
Mon Oct 19, 2020 8:16 pm
Ok, why such a huge ship?
30,000 tonnes is quite big, IMHO, especially when using only one engine (engine mass is not really that relevant).
Would have to agree:
I think we will have to agree before if we are doing a "theoretical analysis" based on yet to come technologies or implementing a practical application based on the "state of the art" technology we have available today.
If it is a theoretical analysis than we can take all my numbers and throw them away, but if we want to evaluate what would take to set up tomorrow a human mission to make a mining prospect on Titan than we need to stick to actual technology limitations.

Let me go through the points you raised:

First, the reason why I added a fission reactor is that you need anyhow enough electrical power to "start" the first fusion reaction, so you need anyhow a secondary continuous and reliable electrical source whenever you need to start the reactor.

Second, the fusion energy gain limit (Q) is equal to 2 and this is a "physics limit" of the ZAP that (apparently) cannot be overcome.
So any input energy will get doubled, but a good chunk will escape through the nozzle, what's left goes to the direct energy conversion step, filtered, rectified, and transported back to the next pulse. All of this is anyhow subject to an efficiency factor. The biggest loss should be in the direct conversion process that (to the best of my knowledge) can reach a 60% efficiency. But even if you should reach a 80 or 90% conversion, the limiting factor is still that starting Q=2.
In other words, I do not see any possibility to generate enough electrical power in a direct way to feed the following cycle, let alone to do it 150 times every second. Meaning you will always need some extra power to start up the following cycle.

Third, an ISP of 5000 is not that great in terms of fuel efficiency.
Unless we can reach an ISP of one or 2 order of magnitude bigger, the fuel will "always" be the predominant factor of the ship, and we can't escape this point due to the very definition of ISP.

Fourth, there is still the huge and yet unanswered issue of the thermalization of the Alphas that could prevent continuous operation and force to use a slower pulsed operation moving most of the electrical load needs to a secondary generator as default design.

I am not trying to make it difficult, I am just trying to be realistic in the design.
A society of dogmas is a dead society.

Skipjack
Posts: 6115
Joined: Sun Sep 28, 2008 2:29 pm

### Re: Z-Pinch Renaissance

Giorgio wrote:
Wed Oct 21, 2020 12:34 am
First, the reason why I added a fission reactor is that you need anyhow enough electrical power to "start" the first fusion reaction, so you need anyhow a secondary continuous and reliable electrical source whenever you need to start the reactor.
Capacitor bank.
Giorgio wrote:
Wed Oct 21, 2020 12:34 am
Second, the fusion energy gain limit (Q) is equal to 2 and this is a "physics limit" of the ZAP that (apparently) cannot be overcome.
I don't think that this is some sort of hard physics limit. It is just all that they need. AFAIK you can make the reactor longer and/or increase the input current to increase the fusion power and Q, but why do more than what is needed? I think Uri chose the Q of 2 to have just enough fusion power for the system.
Giorgio wrote:
Wed Oct 21, 2020 12:34 am
All of this is anyhow subject to an efficiency factor. The biggest loss should be in the direct conversion process that (to the best of my knowledge) can reach a 60% efficiency. But even if you should reach a 80 or 90% conversion, the limiting factor is still that starting Q=2.
I am not sure where you get 60% efficiency from. D+He3 releases almost all of it's energy in charged particles. Those can be directly converted into electricity.
I am pretty sure that Uri assumes direct conversion and feeding that energy back into the reactor in his paper and not a fission reactor to power the ship. That would be really inefficient.
Giorgio wrote:
Wed Oct 21, 2020 12:34 am
Third, an ISP of 5000 is not that great in terms of fuel efficiency.
Unless we can reach an ISP of one or 2 order of magnitude bigger, the fuel will "always" be the predominant factor of the ship, and we can't escape this point due to the very definition of ISP.
5,000 is pretty much top of the line of any propulsion system we have ever had and this ship would have a comparably enormous amount of thrust.
Extrapolating from Project Rover, I would expect about 100 tonnes of thrust from an engine like this but at 6 times the Isp. Staying with an assumed 15 tonnes of engine mass, we would get a T/W ratio of 6.6 (about double that of Rover). Not too shabby and I actually think that it could be even better.
Giorgio wrote:
Wed Oct 21, 2020 12:34 am
Fourth, there is still the huge and yet unanswered issue of the thermalization of the Alphas that could prevent continuous operation and force to use a slower pulsed operation moving most of the electrical load needs to a secondary generator as default design.
The reactor is by it's nature pulsed. It just can do a lot of pulses per second. I am not sure how that makes a separate power generator necessary. The P(in) vs P(out) should be the same either way.

Btw, I am fully convinced now that this would enable an SSTO.
GLOW: 100 tonnes
Dry mass 45 tonnes.
Payload about 15 tonnes.
Mass break down:
Hydrogen tank 8 tonnes. Based on shuttle ET (13 tonnes ET was able to carry 100 tonnes of hydrogen * 0.6 since only need about half of that).
Engine mass 15 tonnes.
Payload fairing 2 tonnes (F9 fairing is 1900 kg, but this one will need motors and stuff for it to open and close).
Landing legs 2 tonnes (Falcon 9 landing legs are 2.4 tonnes but they are much larger than what is needed for this relatively small rocket).

Leaves 18 tonnes margin for other stuff like radiation shielding, turbo pump, foam TPS, mass growth, etc.

A vehicle like this would not even need to use air breathing and would still get a DV of 25,000 m/s. That is enough to go to the GEO and then get back and land propulsively (no thermal protection system needed).

Giorgio
Posts: 2784
Joined: Wed Oct 07, 2009 6:15 pm
Location: China, Italy

### Re: Z-Pinch Renaissance

Skipjack wrote:
Wed Oct 21, 2020 8:19 am
Giorgio wrote:
Wed Oct 21, 2020 12:34 am
First, the reason why I added a fission reactor is that you need anyhow enough electrical power to "start" the first fusion reaction, so you need anyhow a secondary continuous and reliable electrical source whenever you need to start the reactor.
Capacitor bank.
I think those are already included in the design of the ZAP, but you still need to charge them from a source before the reactor first shot and also in any event when there is not enough energy charge to allow for another shot.
We do not have enough data from ZAP to evaluate the size needed for the single shot, but these capacitor banks tend to become quite big and heavy pretty quickly.

Skipjack wrote:
Wed Oct 21, 2020 8:19 am
Giorgio wrote:
Wed Oct 21, 2020 12:34 am
Second, the fusion energy gain limit (Q) is equal to 2 and this is a "physics limit" of the ZAP that (apparently) cannot be overcome.
I don't think that this is some sort of hard physics limit. It is just all that they need. AFAIK you can make the reactor longer and/or increase the input current to increase the fusion power and Q, but why do more than what is needed? I think Uri chose the Q of 2 to have just enough fusion power for the system.
With no physical limits having a greater Q means immediately having an higher thrust and an higher ISP so it is an highly desirable situation.
I got back Uri paper of 2006 and into it is explained from where the limit to the an higher Q is coming from.

The stabilizing mechanism which is the heart of the ZAP concept requires that to have a stable plasma its axial velocity has to satisfy this limit:

Vmax > 0.1 VA k a

VA = Alfven speed,
k = axial wave vector
a = pinch radius (here lies the limit)

In the same paper (figure 9) they delineate the Q gain in respect to the pinch radius "a" and the Thrust/Ve values in respect to the Q obtained .
You can clearly see that the smaller the pinch radius the higher the Q you can get and the more Ve/Thrust you obtain (as I was stating before), but the smaller the pinch radius, the more difficult to maintain the parameters of the stabilizing mechanism.
Additionally the length of the pinch to ensure a complete fuel burn increases as the axial velocity increases.
The balance between these values strictly forces the Q to a lower level. In the 2006 paper the pinch radius was 1 mm, and the relative Q was 1.8.
In the following paper they pushed the pinch radius down to 0,6 mm and this allowed them to rise the Q to 2.1 (but they had to highly increase the pinch length making even more difficult to maintain a stable shear flow over all the length).
As far as I know they was able to demonstrate stability only in the test machine that has a 10 mm pinch radius. This is another big technical issues I am still wondering how they plan to face.

Skipjack wrote:
Wed Oct 21, 2020 8:19 am
Giorgio wrote:
Wed Oct 21, 2020 12:34 am
All of this is anyhow subject to an efficiency factor. The biggest loss should be in the direct conversion process that (to the best of my knowledge) can reach a 60% efficiency. But even if you should reach a 80 or 90% conversion, the limiting factor is still that starting Q=2.
I am not sure where you get 60% efficiency from. D+He3 releases almost all of it's energy in charged particles. Those can be directly converted into electricity.
Energy needs anyhow to be extracted from the charged particles, be it with a "Venetian Blind" type of converter or an Inverted cyclotron converter (ICC from TriAplha design).

Venetian blind type was actually built and it demonstrated 40% efficiency with a theoretical upper limit of 70%.
ICC has never been built is a paper design and has a theoretical "extraction efficiency" of 90% if (and this is a big IF) there is no thermalization of the Alphas. Than you still need to rectify and transform the electrical flow into something usable for the next shot, as well as feed al the ICC ancillary equipment.
The trade off is that the ICC is massive in respect to the "venetian blind" solution. Here is the link to the Trialpha interesting patent for the ICC.

Skipjack wrote:
Wed Oct 21, 2020 8:19 am
I am pretty sure that Uri assumes direct conversion and feeding that energy back into the reactor in his paper and not a fission reactor to power the ship. That would be really inefficient.
I totally agree that it would be inefficient, especially with those low ISP values is not practical. My feeling is that (like many scientists) he simply didn't stop to evaluate the whole picture but just focused on the engine design. This is a trend I see in the 99,9% of the publications I read. They focus on the research object but the integration is always demanded to another phase/paper/research grant that has to evaluate the technical or economical feasibility of the proposed solution.
I hope to be wrong, but I guess we will discover it only when they actually give us more data to crunch.

Skipjack wrote:
Wed Oct 21, 2020 8:19 am
Giorgio wrote:
Wed Oct 21, 2020 12:34 am
Fourth, there is still the huge and yet unanswered issue of the thermalization of the Alphas that could prevent continuous operation and force to use a slower pulsed operation moving most of the electrical load needs to a secondary generator as default design.
The reactor is by it's nature pulsed. It just can do a lot of pulses per second. I am not sure how that makes a separate power generator necessary. The P(in) vs P(out) should be the same either way.
I didn't express myself in a clear way.
Thermalization of the Alpha would drastically drop the Q (even under 1).
This will create more dependence (need more time) from auxiliary electric generator to charge the system for the next shot, hence reducing the number of pulses available for second.

Skipjack wrote:
Wed Oct 21, 2020 8:19 am
Giorgio wrote:
Wed Oct 21, 2020 12:34 am
Third, an ISP of 5000 is not that great in terms of fuel efficiency.
Unless we can reach an ISP of one or 2 order of magnitude bigger, the fuel will "always" be the predominant factor of the ship, and we can't escape this point due to the very definition of ISP.
5,000 is pretty much top of the line of any propulsion system we have ever had and this ship would have a comparably enormous amount of thrust.
Extrapolating from Project Rover, I would expect about 100 tonnes of thrust from an engine like this but at 6 times the Isp. Staying with an assumed 15 tonnes of engine mass, we would get a T/W ratio of 6.6 (about double that of Rover). Not too shabby and I actually think that it could be even better.
Skipjack wrote:
Wed Oct 21, 2020 8:19 am
Btw, I am fully convinced now that this would enable an SSTO.
I strongly doubt. The 15/18 tons would probably not be enough even only for the capacitor bank and related equipment, let alone for all the other components of the engine. Than again to make a real evaluation we need more data and (possibly) experimental data.
A society of dogmas is a dead society.

Skipjack
Posts: 6115
Joined: Sun Sep 28, 2008 2:29 pm

### Re: Z-Pinch Renaissance

Giorgio wrote:
Wed Oct 21, 2020 9:41 pm
I think those are already included in the design of the ZAP, but you still need to charge them from a source before the reactor first shot and also in any event when there is not enough energy charge to allow for another shot.
I disagree with that.
Giorgio wrote:
Wed Oct 21, 2020 9:41 pm
Energy needs anyhow to be extracted from the charged particles, be it with a "Venetian Blind" type of converter or an Inverted cyclotron converter (ICC from TriAplha design).
Nope, the plasma is charged particles that are moving. Put a magnetic coil around the tube and induce a current.
Venetian blinds are needed when the plasma motion is without a direction, which is not the case in this reactor (things move in a direction).

Giorgio wrote:
Wed Oct 21, 2020 9:41 pm
I totally agree that it would be inefficient, especially with those low ISP values is not practical. My feeling is that (like many scientists) he simply didn't stop to evaluate the whole picture but just focused on the engine design.
Knowing Uri, this is unlikely.

Giorgio wrote:
Wed Oct 21, 2020 9:41 pm
I didn't express myself in a clear way.
Thermalization of the Alpha would drastically drop the Q (even under 1).
This will create more dependence (need more time) from auxiliary electric generator to charge the system for the next shot, hence reducing the number of pulses available for second.
I still don't see that as a thing to necessarily happen.

Giorgio wrote:
Wed Oct 21, 2020 9:41 pm
I strongly doubt. The 15/18 tons would probably not be enough even only for the capacitor bank and related equipment, let alone for all the other components of the engine. Than again to make a real evaluation we need more data and (possibly) experimental data.
If you look at my numbers, you can see that the 18 tonnes would be additional reserves in case the 15 tonnes I put aside for the engine are not enough.
I agree that the size of the capacitors is an unknown. They tend to be big, but then we are not talking about a lot of energy per shot, just a lot of power. That latter part is what is worrying me, though capacitors are generally good at power density and bad at energy density.

Giorgio
Posts: 2784
Joined: Wed Oct 07, 2009 6:15 pm
Location: China, Italy

### Re: Z-Pinch Renaissance

Skipjack wrote:
Thu Oct 22, 2020 1:47 am
Giorgio wrote:
Wed Oct 21, 2020 9:41 pm
I think those are already included in the design of the ZAP, but you still need to charge them from a source before the reactor first shot and also in any event when there is not enough energy charge to allow for another shot.
I disagree with that.
We agree that we disagree, we will just need to wait until more info will become available.

Skipjack wrote:
Thu Oct 22, 2020 1:47 am
Giorgio wrote:
Wed Oct 21, 2020 9:41 pm
Energy needs anyhow to be extracted from the charged particles, be it with a "Venetian Blind" type of converter or an Inverted cyclotron converter (ICC from TriAplha design).
Nope, the plasma is charged particles that are moving. Put a magnetic coil around the tube and induce a current.
Venetian blinds are needed when the plasma motion is without a direction, which is not the case in this reactor (things move in a direction).
Giorgio wrote:
Wed Oct 21, 2020 9:41 pm
Thermalization of the Alpha would drastically drop the Q (even under 1).
I still don't see that as a thing to necessarily happen.
Your point on energy extraction is valid only in absence of thermalization effect, but thermalization is a real issue that was recognized as a potential big concern from Clifton Lilly when he made his MS thesis under Uri Shumlack supervision (his thesis is the base of the ZAP engine design).
He clearly stated this into section 2.2.2, 2.2.3 and especially 3.4.3 of his thesis.

2.2.2 Energy Equation
Our energy conservation equation covers each of these terms explicitly, in the form of heat conduction, ohmic heating, convection of the fluid energy, radiation, and fuel ion destruction, with the exception of the alpha heating. The alpha heating is neglected on the assumption that the alpha particles will escape the pinch before thermalizing.

2.2.3 Alpha Heating
There is some question as whether the alphas would be thermalized in the dense plasma of the Flow Through Z-Pinch, or whether the alpha’s would escape. Work by Robson suggested that they would be thermalized. ....[omissis].... What can be said from this basic calculation is that some alphas will be confined and some will escape. The associated alpha heating is not included in this model.

3.4.3 Comments on Fusion Burn
The assumption of no alpha heating in the system is a crucial one. As discussed in Sec.2.2.3, some alphas may be thermalized. The effects of the alpha heating have not been included in the model studied here. If the alphas were to begin thermalizing, a significant increase of the plasma radius would be expected.

An higher radius induced by thermalization will oblige the plasma to a new equilibrium state with a lower current density and magnetic field. This will bring a drastic drop in Q (which is already low!)

While I do understand (and agree) on not including such a complicated issue in a short work like this thesis, it is an issue that cannot be ignored (as Clifton correctly stated and as Shumlack knows). Understanding the degree of thermalization is essential to ensure the feasibility of the proposed engine system.
A good comparison will be with laminar and turbulent flows into a pipeline. The smaller the diameter, the slower the speed of flow to keep laminar flow (no thermalization), the smaller the "Q" you get. To increase "Q" you need to increase speed but than your flow will become turbulent (particles will thermalize). As of today we lack in knowledge and technology to get both (high speed and high Q) at the same time.
A society of dogmas is a dead society.

williatw
Posts: 1912
Joined: Mon Oct 12, 2009 7:15 pm
Location: Ohio

### Re: Z-Pinch Renaissance

Giorgio wrote:
Thu Oct 22, 2020 10:28 am
Skipjack wrote:
Thu Oct 22, 2020 1:47 am
Giorgio wrote:
Wed Oct 21, 2020 9:41 pm
I think those are already included in the design of the ZAP, but you still need to charge them from a source before the reactor first shot and also in any event when there is not enough energy charge to allow for another shot.
I disagree with that.
We agree that we disagree, we will just need to wait until more info will become available.
Not to interrupt you gentlemen's interesting technical discourse but what about a compromise? Say one of those small modular nuclear reactors of the type that Trump just approved funding for?

In the NuScale reactor, a core is kept cool by circulating normal fresh water, as happens in today’s operating nuclear plants on a much, much larger scale. Inside huge nuclear towers, most of the space is dedicated to cooling. The NuScale reactor uses gravity and buoyancy to naturally circulate the cooling water. The size difference is staggering: “About the size of two school buses stacked end to end, you could fit around 100 of them in the containment chamber of a large conventional reactor,” Wired reports. The reactor technology itself isn’t completely different than before, it’s just wildly more efficient and up to date. Each NuScale reactor rates 60 MWe, which sounds small because the reactor is small by design. Plants can install dozens at a time.

https://www.popularmechanics.com/techno ... r-reactor/

60MWe would be more than enough to initially charge up the capacitor bank even if it took time to do so and top it off as needed between burns assuming you can't extract enough juice from the charged particle products of the fusion burns. Wouldn't hurt to have a back-up power supply in case the main went off line for whatever reason. Backup systems tend to be the older more reliable tech (fission) as opposed to the newer, better less proven tech (fusion). Maybe wed that small fission reactor to a backup drive like the VASIMR or/NEXT ion thruster. Kind of like I remember seeing old wooden steamships that still had sails rigged; as if someone didn't trust the new steam engines yet with their lives. After all if the main drive bites the dust a billion miles out from Earth, better to limp home 3X time later than expected on "impulse" then not get home at all. As an aside, iIf I recall a former fave of mine the ICANII used solar panels to get the initial electric power.

http://ffden-2.phys.uaf.edu/213.web.stu ... usion.html
Last edited by williatw on Thu Oct 22, 2020 5:03 pm, edited 2 times in total.