Z-Pinch Renaissance

[paperburn1]

not my work but relevant underlined comments are mine.
Consider a 1,000 ton spacecraft with a 10,000 km/s exhaust velocity and an acceleration of 0.722 m/s/s. For a 1 AU trip at constant acceleration, flipping at the midpoint, it will take 10.5 days and consume 66 tons of propellant/fuel.

Now let's add extra mass into the exhaust stream, so that the spacecraft uses propellant at 16 times the rate but expels it at 1/4 the exhaust velocity (thus keeping the same power). This brings the acceleration up to 2.89 m/s/s. We will accelerate for 1/10 the distance, drift for 8/10 the distance, and then decelerate for 1/10 the distance. The trip now takes 7 days and uses 240 tons of propellant, of which only 7 tons is fuel.
in this case propellant is not fuel, we are talking a new way of doing things, we tend to get this confused because in chemical rockets propellant is fuel but in our case they are now different

Bulk inert (non-fuel) propellant is probably cheap (water or hydrogen). Fuel is probably expensive (He-3 and D). The second option gets you there faster and cheaper.

[paperburn1]

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

This is from Advanced Space Propulsion Based on the Flow-Stabilized Z-Pinch Fusion Concept (2006) and Sustained neutron production from a sheared-flow stabilized Z-pinch (2019)

[AcesHigh]

I contacted ProjectRho administrator to talk about the Shared Flow Stabilized ZPinch. He was unaware of the 2006 paper with the torch ship like properties.

This was like 1 week ago.

[paperburn1]

I contacted ProjectRho administrator to talk about the Shared Flow Stabilized ZPinch. He was unaware of the 2006 paper with the torch ship like properties.

This was like 1 week ago.

LOL tiny circles in everybody's world.

[AcesHigh]

https://www.youtube.com/watch?v=b21pxLKnQ30

[williatw]

This is my current favorite John Sough's design:

Magneto Inertial Fusion Drive Rocket




Fusion Drive Rocket (FDR)

This is from Electromagnetically Driven Fusion Propulsion, J. Slough, Pancotti, A., Kirtley, D., Votroubek, G., International Electric Propulsion Conference, IEPC-372 (2013).

This fusion ship uses John Slough et al's innovative Magneto Inertial Fusion engine. The engine has most of the advanages of both magnetic confinement and inertial confinement fusion with very little of the disadvantages. Instead of trying to crush the fusion fuel with wobbly magnetic fields or a spherical firing squad of lasers, then attempting to heat the propellant by toasting it over the explosion, it tries a more clever method.

Instead it magnetically crushes a foil ring of lithium metal (called a "liner") such that it also crushes a blob of fusion fuel in a mighty fist of metal. Then as the fusion explosion occurs, the lithium becomes propellant, conveniently totally enclosing the blast and doing a fantastic job of converting fusion energy into propellant energy. This also allows the rocket to use open cycle cooling, so it does not need acres of heat radiators like other fusion rockets.

In addition, carrying inert rolls of compact lithium foil propellant is infintely easier than trying to keep huge cryogenic tanks of liquid hydrogen from boiling dry.

Each lithium foil liner has a mass of something between 0.28 to 0.41 kilograms. The crush speed is about 3 kilometers per second, resulting in a solid cylinder of lithium with a fusion explosion going off in its heart.

☢

Using a fusion rocket means the entire mission will take about 210 days, instead of the 540+ days you'd need with a fission rocket. Which means the crew won't max out their career radiation exposure limit in one lousy mission.

For the specified mission a specific impulse of 5,000 seconds is needed. A complicated equation (in the paper) calculates this mandates a fusion gain factor of 200. This means if you want 36 megawatts of jet power coming out of the engine, you will have to feed in 36,000,000 / 200 = 180 kilowatts of electricity. This can be supplied with a low-mass arrangement of a solar photovoltaic array charging a capacitor energy storage bank (instead of being forced to use a weighty nuclear reactor or something). Remember that sunlight is weaker at Mars orbit, you'll need an array rated for 400 kilowatts at Terra orbit in order to eke out 180 kW at Mars.

☢

The crew habitat module appears to be a bog-standard inflatable TransHab module, which is hardly surprising. It can house a crew of six for about 18 months in about 33 metric tons. The rest of the payload is a 30 metric ton Mars Excursion Vehicle. Basically it is using the payload package specified in NASA's Mars Design Reference Architecture 5.0.

And this rocket is totally resuable, unlike those insane designs using fission rocket staging.

TRANSIT HABITAT is a TransHab module
SPLINE TRUSS is the backbone of the ship
LINER/PROPELLANT are the big rolls of lithium foil propellant


SHADOW SHIELD protects ship from radiation
FRC FORMATION makes the puff of fusion fuel for detonation (stands for Field Reversed Configuration if anybody cares)
SHOCK ABSORBERS are needed since this engine pulses BANG! --- BANG! --- BANG! at 13.3 second intervals instead of a steady burn
LINER/PROPELLANT INJECTOR converts a length of lithium foil into a ring and throws it over the compression coils
MAIN COMPRESSION COILS grabs the ring of lithium foil and brutally squeezes it over the puff of fusion fuel
MAGNETICALLY INSULATED EXPANDER channels the blast of lithium plasma into a rocket exhaust


White area is protected by the shadow shield. Note how radiators are trimmed at an angle to keep them inside the protective shadow.





http://www.projectrho.com/public_html/r ... ive_Rocket

[Skipjack]

I love the Fusion Driven Rocket. It is foil liner compressed FRCs. It has a lot of thrust compared to other fusion engine designs and a Isp of 5000 is still plenty good.
That said, if the Sheared Flow Stabilized Z- Pinch works, it would have this design beat in terms of Isp and thrust, which is quite crazy.

[Giorgio]

Zap Energy got the grant in November 2018, so it should almost be time for an update.
If they can prove that the nature of neutrons generated was indeed coming from Deuterium fusion and that the system can scale as expected while keeping stability, we might have indeed the technological base for a new leap in our evolution.

I am eager and curious to see what their next paper will say.

[Skipjack]

Zap Energy got the grant in November 2018, so it should almost be time for an update.
If they can prove that the nature of neutrons generated was indeed coming from Deuterium fusion and that the system can scale as expected while keeping stability, we might have indeed the technological base for a new leap in our evolution.

I am eager and curious to see what their next paper will say.

That video above is from May. They have proven that the neutrons are from D2 fusion.

[Giorgio]

That video above is from May. They have proven that the neutrons are from D2 fusion.

I will need to check it back again, I seem to remember that also in the video they said (like in the 2018 paper) that the neutron flux was "coherent" with Deuterium fusion occurences, but there was no definitive proof.
I personally agree with their logic and conclusions, but I would be more satisfied if they could actuallly prove it in an unquestionable way.

[Skipjack]

That video above is from May. They have proven that the neutrons are from D2 fusion.

I will need to check it back again, I seem to remember that also in the video they said (like in the 2018 paper) that the neutron flux was "coherent" with Deuterium fusion occurences, but there was no definitive proof.
I personally agree with their logic and conclusions, but I would be more satisfied if they could actuallly prove it in an unquestionable way.

Have you seen this paper? They revised it in February.
https://arxiv.org/abs/1806.05894
It seems to me that the increase of neutron production with the square of deuterium concentration (in accordance with expectations) should be proof enough, no?

[Giorgio]

[Have you seen this paper? They revised it in February.
https://arxiv.org/abs/1806.05894
It seems to me that the increase of neutron production with the square of deuterium concentration (in accordance with expectations) should be proof enough, no?

Let me state again that I agree with the logic they used to sustain the hypothesis that the neutron flux measured is indeed coming from Deuterium fusion. To refresh my mind today I took the time to revise once more the paper and the video.

In the paper they correctly point out few experimental measurements that support the hypothesis that the neutron flux is coming indeed from fusion occurrences, but for each one of them they prudently (and professionally) restrain themselves to state that it has been experimentally proved.

A) The no signal observed for the 0% Deuterium case:
"This result strongly indicates that the measured scintillator detector signals are from neutron emissions, and are not due to X-rays."

B) The coherent time frame and time span of the measured scintillator flux:
"This sustained neutron emission, coincident with the lack of m=0 and m=1 instabilities, suggests (that) a thermonuclear fusion process may be responsible for the neutron observation, (and) not a beam-target fusion process...."

C) The increased neutron production with increase in Deuterium concentration:
"(The) neutron production results follow the expected nD2 dependence, which provides additional evidence of possible thermonuclear fusion with the deuterium mixture plasmas. However, further investigation is needed to better characterize the energy spectrum of the observed neutrons."

Because of the above findings they correctly stated in their conclusions that it "indicate consistency with a thermonuclear fusion process" but they didn't give it for granted (and similar statements are made in the video).
In other words, they saw 3 smoking guns and some holes, they expect that there must be bullets shot from these guns to make the holes, but they didn't really see the bullets.

After all scintillators are not direct neutron counters, but indirect detectors generally used for the determination of the upper energy side of the x-ray spectrum, and thus susceptible to measure a plethora of other events.
Even if the scintillator they used was calibrated at the High Flux Neutron Generator (see note 28 of the paper) and used a specific set of models to characterize the incoming flux, the correct interpretation of a scintillator data stream is a matter of great complexity and subject to a great deal of discussions, interpretations and publications among the one expert in the issue. If you want to give a look to these issues there is a 2019 publication that gives a good overview of these complexities and is available HERE.

The above is what I believe is pushing them to be cautious and even if also for me there is little room left for a different interpretation, I greatly appreciate their not giving for granted something they still didn't officially see and prove. I have strong belief that this will be the first point that they will try to pinpoint with the 2018 grant they received.

Personally this is the way I love seeing science done.

[Skipjack]

ZAP is generally cautious and tries to avoid over hyping things. So your point is valid (and their wording makes sense).
That said, they are already moving on to higher currents, it seems. I am a bit surprised by that. I was under the impression that FuZE can't handle currents over 300 kA.

[Giorgio]

Maybe they didn't fully disclose the abilities of FuZE or it was built in a way to be easily upgradeable.
After al they are now a commercial company and if I was in their shoes I would also not fully disclose what I am able to do unless i discuss with a qualified investor.

[Skipjack]

Maybe they didn't fully disclose the abilities of FuZE or it was built in a way to be easily upgradeable.
After al they are now a commercial company and if I was in their shoes I would also not fully disclose what I am able to do unless i discuss with a qualified investor.

Well, it is what Uri told me when we talked last year. IIRC, he said that they would need a new prototype to go (significantly) above 300 kA because of material issues at the higher currents. But maybe they upgraded it or they already have a new device. They also needed new capacitors, though that is not directly related to the device itself.