Z-Pinch Renaissance

[Skipjack]

Well, the FuZE prototype is really small. The expensive part is the experiments right now. Once they worked out the kinks, these things should be really cheap to mass produce. May be not as cheap as a fusor, but they will (hopefully) produce a lot more neutrons.

[crowberry]

I wonder what the relative difficulty/cost of getting fusion neutrons from a Z-pinch machine is compared to getting them from a Hirsch-Farnsworth fusor. Is there any other confinement concept for which the barrier to entry is as low (or nearly so) as the fusor? (An accelerator, perhaps, but that's not really a confinement concept.)

A DPF device could also be rather small and inexpensive. The plasmoid confines itself for a very short time and can give neutron pulses:

Palm top plasma focus device as a portable pulsed neutron source

Development of a palm top plasma focus device generating (5.2 ± 0.8 ) × 10^4 neutrons/pulse into 4π steradians with a pulse width of 15 ± 3 ns is reported for the first time. The weight of the system is less than 1.5 kg. The system comprises a compact capacitor bank, a triggered open air spark gap switch, and a sealed type miniature plasma focus tube. The setup is around 14 cm in diameter and 12.5 cm in length. The energy driver for the unit is a capacitor bank of four cylindrical commercially available electrolytic capacitors. Each capacitor is of 2 μF capacity, 4.5 cm in diameter, and 9.8 cm in length. The cost of each capacitor is less than US$ 10. The internal diameter and the effective length of the plasma focus unit are 2.9 cm and 5 cm, respectively. A DC to DC converter power supply powered by two rechargeable batteries charges the capacitor bank to the desired voltage and also provides a trigger pulse of −15 kV to the spark gap. The maximum energy of operation of the device is 100 J (8 μF, 5 kV, 59 kA) with deuterium gas filling pressure of 3 mbar. The neutrons have also been produced at energy as low as 36 J (3 kV) of operation. The neutron diagnostics are carried out with a bank of 3 He detectors and with a plastic scintillator detector. The device is portable, reusable, and can be operated for multiple shots with a single gas filling.

http://dx.doi.org/10.1063/1.4808309

[Skipjack]

New Paper for the 46thEPS Conference on Plasma Physics in Milan:
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1102.pdf

[Skipjack]

LLNL provides their opinion on the Sheared Flow Stabilized Z- Pinch:
https://pls.llnl.gov/news/sustained-nuc ... on-z-pinch

[Skipjack]

New paper from Uri's team:
Kinetic simulations of sheared flow stabilization in high-temperature Z-pinch plasmas:
https://aip.scitation.org/doi/full/10.1063/1.5092241

Looks like more accurate simulation techniques confirm their approach and match experimental results.
Also worth noting is that they are about to reach 300kA, the limit of the FuZE prototype. They will have to move on to a new prototype after that.

[AcesHigh]

Has any paper mentioned some mission profile?

I would like to see what they expect with 10 million ISP and 1 meganewton of thrust.

and I wonder how many of these could you put in a ship...

[paperburn1]

Has any paper mentioned some mission profile?

I would like to see what they expect with 10 million ISP and 1 meganewton of thrust.

and I wonder how many of these could you put in a ship...

Not many, still limited by that vaccum bottle effect , only way to get rid of heat is by radiation

[AcesHigh]

Any torchship (high thrust high Isp) will have to deal with heat disposal problems.

Aside that... what can we do with 10 million Isp and 1 MN thrust?


Suppose SpaceX would find some way to install 2 of these on Starship (the upper stage), without modifying Starship payload space or weight.

Starship
Launch mass 1,335,000 kg (2,943,000 lb)
Dry mass 85,000 kg (187,000 lb)


So, what would be travel times to Mars, Jupiter and Saturn (lets suppose closest approach, just for sake of dealing with a single distance), considering time to accelerate and decelerate, and a payload of 100 tons of cargo?

[paperburn1]

These are very rough numbers ( with huge assumptions ) but your looking at 60 days will get about to Jupiter. 90 days will get you to Saturn. with a flip and slowdown because what is the point of going without stopping for a visit.

[paperburn1]

I found this list of destination for one g travel
The Moon / Luna:
Closest to Earth (Supermoon): 356,577 km
Travel time (at 9.80665 m/s2, no deceleration): 2h 22m 12s
Travel time (at 9.80665 m/s2, decelerating halfway): 3h 20m 24s

Mercury:
Closest to Earth: 77.3 million km
Travel time (at 9.80665 m/s2, no deceleration): 1d 10h 52m 48s
Travel time (at 9.80665 m/s2, decelerating halfway): 2d 1h 19m 12s

Venus:
Closest to Earth: 40 million km
Travel time (at 9.80665 m/s2, no deceleration): 1d 1h 5m 2s
Travel time (at 9.80665 m/s2, decelerating halfway): 1d 11h 28m 48s

Mars:
Closest to Earth: 65 million km
Travel time (at 9.80665 m/s2, no deceleration): 1d 7h 58m 5s
Travel time (at 9.80665 m/s2, decelerating halfway): 1d 21h 13m 1s

Jupiter:
Closest to Earth: 588 million km
Travel time (at 9.80665 m/s2, no deceleration): 4d 0h 11m 2s
Travel time (at 9.80665 m/s2, decelerating halfway): 5d 16h 2m 2s

Saturn:
Closest to Earth: 1.2 billion km
Travel time (at 9.80665 m/s2, no deceleration): 5d 17h 25m 1s
Travel time (at 9.80665 m/s2, decelerating halfway): 8d 2h 20m 24s

Uranus:
Closest to Earth: 2.57 billion km
Travel time (at 9.80665 m/s2, no deceleration): 8d 9h 6m 0s
Travel time (at 9.80665 m/s2, decelerating halfway): 11d 20h 24m 0s

Neptune:
Closest to Earth: 4.3 billion km
Travel time (at 9.80665 m/s2, no deceleration): 10d 20h 7m 48s
Travel time (at 9.80665 m/s2, decelerating halfway): 15d 7h 52m 48s

Pluto:
Closest to Earth: 4.28 billion km
Travel time (at 9.80665 m/s2, no deceleration): 10d 19h 31m 12s
Travel time (at 9.80665 m/s2, decelerating halfway): 15d 7h 1m 12s

[AcesHigh]

Lol, 90 days to Saturn is already better than expected. But 8 days to Saturn??? Screw impossible physics engines. There is a whole Star System to colonize.

I was not even thinking 1g acceleration were possible

Speaking of which... did you consider 1g just for fun or did you make some calculations regarding acceleration? What would be the possible acceleration of a Starship with one of these engines?

My physics is quite rusty. Isn´t acceleration thrust (N) divided by mass (kg)?

Starship is 85 metric tons. Its about 1.2 thousand metric tons considering fuel.

We don´t need so much fuel for this behemoth engine. Let's consider instead 85 metric tons + two 50 ton landers + 15 tons rover - 200 tons dry mass.

And 300 tons of fuel.

Total 500 tons.

So 1.000.000 N / 500.000 kg = 2 m/s².

Still pretty good.

[paperburn1]

one g was for fun
the other figure was making so many assumptions it probably not realistic.

[Skipjack]

I do not know where people are seeing 10 million Isp. I read an Isp of ~360,000 seconds and 330 kN of thrust for the D+He3 configuration.
There are two big unknowns to me. They need 5 MA input current for a few microseconds. I have no idea what size of a power supply they would need for that. I did a vague estimate of about 14 tonnes based on the size and mass of their current power supply, but I may be off a bit.
The other big problem could be the heat generated by the thing. I mean we are talking 1.8 TW input power plus 3.3 TW fusion power for 5.1 TW total.
IMHO, this would produce a lot of heat that would radiate away only very slowly in space. Granted, most of it would probably be exhausted out the back, but there would still be 100s of Gigawatts of heat trapped in the system. The best idea that I could come up with is to operate the engine in short pulses, then transport of the heat with liquid hydrogen, like in a NERVA engine. With current materials, that would limit the Isp to about 1000, maybe 1200 seconds during the "NERAVA" mode. However, the thrust would be a lot higher. For atmospheric flight during a launch from Earth, they could maybe get away with air cooling for part of the way. Maybe combined with a He precooler like Reaction Engines is planning. That could enable SSTOs with a very high payload fraction IF the power supplies are remotely within the weight range that I estimated.
I calculated that at the average distance of Mars to Earth (not when they are closest), at 1g, a trip would take about 4 days (with turning around half way).
IF the engine miraculously does not suffer from heat problems for some reason and we assume a 0.2g constant acceleration, then a ship with this engine could make the trip to mars in 8 days (decelerating half way) with about 70 tonnes of fuel with a ship dry mass of about 30 tonnes. Trip times could potentially be a bit shorter, since you are spending fuel and thus acceleration at constant thrust would increase over time. So you could accelerate for longer, then decelerate with more g.
Of course, there is the problem with finding ~35 tonnes of He3 somewhere (and for a reasonable price). One could probably build dedicated D+D reactors that are mainly meant to produce He3 and do not produce (economic) power on their own.

[Skipjack]

Lol, 90 days to Saturn is already better than expected. But 8 days to Saturn??? Screw impossible physics engines. There is a whole Star System to colonize.

I was not even thinking 1g acceleration were possible

Speaking of which... did you consider 1g just for fun or did you make some calculations regarding acceleration? What would be the possible acceleration of a Starship with one of these engines?

My physics is quite rusty. Isn´t acceleration thrust (N) divided by mass (kg)?

Starship is 85 metric tons. Its about 1.2 thousand metric tons considering fuel.

We don´t need so much fuel for this behemoth engine. Let's consider instead 85 metric tons + two 50 ton landers + 15 tons rover - 200 tons dry mass.

And 300 tons of fuel.

Total 500 tons.

So 1.000.000 N / 500.000 kg = 2 m/s².

Still pretty good.

Why do you need a lander with Starship? Starship is the lander. Also most of the 85 tonnes dry mass of Starship is tanks. If you only need 85 tonnes in fuel, you get away with much smaller tanks. In return, we have an engine mass of about 20 tonnes (by my calculation). You might need several engines though to get out of Mars' gravity well for the return trip, assuming that you are mating with a fully fueled tank in LEO.

[AcesHigh]

Are you Elmar?

The above post was very similar to the one posted at NSF forums.

I talked about a lander because I mentioned changing Starship to have a z pinch fusion engine, which I don't know if it would be ideal for take off and landings at planets.