Let’s talk about fusion fuels in relation to the recent discussion of building a spacecraft engine. A direct fusion drive (DFD) system using magnetic mirror technologies is, as we saw last time, being investigated at the University of Maryland in its Centrifugal Mirror Fusion Experiment (CMFX), as an offshoot of the effort to produce fusion for terrestrial purposes. The initial concept being developed at CMFX is to introduce a radial electric field into the magnetic mirror system. This enhances centrifugal confinement of the plasma in a system using deuterium and tritium as fusion fuel.
Out of this we get power but not thrust. However, both UMD’s Jerry Carson and colleague Tom Bone told the Interstellar Research Group’s Montreal gathering that such a reactor coupled with a reservoir of warm plasma offers prospects for in-space propulsion. Alpha particles (these are helium nuclei produced in the fusion reaction) may stay in the reactor, further energizing the fuel, or they can move upstream, to be converted into electricity by a Standing Wave Direct Energy Converter (SWDEC). A third alternative: They may move downstream to mix with the warm plasma, producing thrust as the plasma expands within a magnetic nozzle.
Image: The fusion propulsion system as shown in Jerry Carson’s presentation at IRG Montreal. Thanks to Dr. Carson for passing along the slides.
We also know that fusion fuel options carry their own pluses and minuses. We can turn to deuterium/deuterium reactions (D/D) at the expense of neutron production, something we have to watch carefully if we are talking about powering up a manned spacecraft. The deuterium/tritium reaction (D/T) produces even more neutron flux, while deuterium/helium-3 (D/He3) loses most of the neutron output but demands helium-3 in abundances we only find off-planet. Tom Bone’s presentation at Montreal turned the discussion in a new direction. What about hydrogen and boron?
Here the nomenclature is p-11B, or proton-boron-11, where a hydrogen nucleus (p) collides with a boron-11 nucleus in a reaction that is aneutronic and produces three alpha particles. The downside is that this kind of fusion demands temperatures even higher than D/He3, a challenge to our current confinement and heating technologies. A second disadvantage is the production of bremsstrahlung radiation, which Bone told the Montreal audience was of the same magnitude as the charged particle production.
The German word ‘bremsen’ means ‘to brake,’ hence ‘bremsstrahlung’ means ‘braking radiation,’ a reference to the X-ray radiation produced by a charged particle when it is decelerated by its encounter with atomic nuclei. So p-11B becomes even more problematic as a fuel, given the fact that boron has five electrons, creating a fusion plasma that is a lively place indeed. Bone’s notion is to take this otherwise crippling drawback and turn it to our advantage by converting some of the bremsstrahlung radiation into usable electricity. To do this, it will be necessary to absorb the radiation to produce heat.
Bone’s work at UMD focuses on thermal energy conversion using what is called a thermionic energy converter (TEC), which can convert heat directly into electricity. He pointed out that TECs are a good choice for space applications because they offer low maintenance and low mass coupled with high levels of efficiency. TECs operate off the thermionic emission that occurs when an electron can escape a heated material, a process Bone likened to ‘boiling off’ the electron. An emitter and collector in the TEC thus absorb the heat from the bremsstrahlung radiation to produce electricity.
Image: A screenshot from Dr. Bone’s presentation in Montreal.
I don’t want to get any deeper in the weeds here and will send you to Bone’s presentation for the details on the possibilities in TEC design, including putting the TEC emitter and collector in tight proximity with the air pumped out between them (a ‘vacuum TEC’) and putting an ionized vapor between the two (a ‘vapor TEC’). But Bone is upfront about the preliminary nature of this work. The objective at this early stage is to create a basic analytical model for p-11b fuel in a propulsion system using TECs to convert radiation into electricity, with the accompanying calculations to balance power and efficiency and find the lowest bremsstrahlung production for a given power setting.
The scope of needed future work on this is large. What exactly is the best ratio of hydrogen to boron in this scenario, for one thing, and how can the electric and magnetic field levels needed to light this kind of fusion be reduced? “It’s not an easy engineering problem,” Bone added. “It’s certainly not a near-term challenge to solve.”
True enough, but it’s clear that we should be pushing into every aspect of fusion as we learn more about confining these reactions in an in-space engine. Experimenting with alternate fusion fuels has to be part of the process, work that will doubtless continue even as we push forward on the far more tractable issues of deuterium/tritium.
Proton–boron fusion passes scientific milestone (March, 2023)
However, from the article:
and,
And we were so excited when it was thought cold fusion was real 30 years ago. And before that, muon-catalyzed fusion, that Clarke thought would power spaceliners in 2061: Odyssey 3 (pub. 1987).
Controlled fusion to release net energy is hard. We have been trying almost since before I was born and shortly after successfully achieving uncontrolled fusion with H-bombs. If ITER fails, then I have to wonder if we won’t have to give up without some radical new technology. If it proves easier to manufacture anti-matter in bulk, maybe we should just bypass fusion?
A failure at ITER really would change the landscape, wouldn’t it? And getting serious about antimatter production at the required scale would certainly offer a huge potential reward. Interesting thought.
Carbon fuels, fissionable elements, and anti-matter all easily generate energy with little effort. In contrast, fusible elements are extremely hard to generate energy by fusion. The only known natural way that such elements fuse and release their energy in a continuing stable way is to accumulate a star’s mass of the element and let gravity compress it to the conditions that allow fusion.
With fusion, we have abundant fuel, easy to concentrate, and therefore relatively cheap, but the equipment to create fusion is very large and expensive (unless those small-scale devices pan out). Anti-particles are much scarcer, and expensive to produce, but release energy without any effort. The trick is controlling the release rate.
Suppose we had a way to mass produce anti-protons. They could be stored in “magnetic and electric bottles”. Controlled expulsion of anti-protons into a neutral plasma would release the energy of annihilation and make a fine exhaust of the remaining plasma. Given a supply of anti-protons and given that the containment is feasible, it seems that creating an anti-matter rocket may be easier than a fusion rocket.
For a novel twist on the use of particle beams to propel a stip via momentum transfer, suppose that an interlaced stream of particles and anti-particles was sent to the ship and combined to annihilate behind the ship like the Orion concept. This would avoid an anti-particle containment failure destroying the ship, and as with beamed propulsion sidestep the limitations of the rocket equation.
A clever idea! I don’t think I’ve run into that one anywhere else. You should write it up!
“…stream of particles and anti-particles was sent to the ship and combined to annihilate behind the ship…”
The second of those particle streams would make a remarkably formidable doomsday weapon. As a means of propulsion, what could possibly go wrong?
Okay, I said that with excessive sarcasm, but I agree with Alex about the extraordinary obstacles to fusion as a means of propulsion. Hence my abstaining from commenting on this and the immediately preceding articles. Wake me up when we have a working, effective and safe fusion reactor right here on Earth. It’ll be far enough in the future that I expect that waking me up will involve resurrection, which is perhaps less probable than controlled fusion.
My favorite science fiction TV of all time is the recent show The Expanse. It’s the closest I have ever seen the domesticated space opera that I cut my teeth on in the 1950s, that is, adapted faithfully as visual narrative. Especially with that verisimilitude that John Campbell and the writers for Astounding evolved in the 1940s, perfected on the pages of books and magazines in the 1950s.
That show paid even better attention to physics and engineering physics than Star Trek did. One small gritch (for me) , the authors of the books and in the show the main propulsion is fusion, thats good. Two hindered years in the future (I think 300 in the books) its advanced fusion propulsion. Still, and someone knew their physics, there is the mass ratio problem. (After all there is a lot of ‘thrust’ gravity used, at low g values, still.) So there is a fusion technology at nearly 100% efficiency, pretty clever. Still, 300 years in the future, the technology of antimatter factories and antimatter propulsion should be mastered. Not an absolute solution to the mass ratio problem but its 300 times more energetic than fusion.
One notes all the travel in The Expanse (excluding the Ring Gate) is in the Solar System. Bob Forward mapped out the antimatter methods in 1984 and I am sure in 300 years technological progress will produce even better approaches.
Antimatter propulsion in science fiction goes back to the 1940s , Heinlein was using it in the 1950s. The Expanse authors knew their engineering physics but seemed to have missed this propulsion method.
Al, I was surprised to learn that Jack Williamson wrote some of the earliest SF stories involving antimatter. I wondered if you had any Williamson anecdotes?
Yes that was Collision Orbit” July 1942. Tho called contraterrene , not used for propulsion.
Oddly seems the term “anti-matter” had been used by Arthur Schuster in 1898, tho I thought his term was anti-atoms.
I saw Jack Williamson twice at a couple of SF cons, but never spoke to him. Gee there is an SF author one does not hear much about these days. Started in Amazing stories in 1928 and published SF in 2006 the year he died, at 98. He adapted to the more sophisticated SF form in the 1940s , a very good writer.
2023 is the 90th anniversary of Dirac’s Nobel prize (shared with Schrödinger). Interesting thing about that is Dirac had combined special relativity with quantum mechanics to get the correct model of the electron. So 1933 was the first year the Swedish Academy recognized Special Relativity. The Dirac Equation also predicted the anti-electron, and actually anti-matter. Einstein never got a Nobel for SR. Even in 1922 when SR had been validated , but it is an odd story.
Hi Alex
If quark nuggets exist, especially the magnetised variety, then doing fusion and making antimatter both become much easier to do.
Very nice to see lots of recipes. But as they say, the proof of the pudding…
If ITER fails, it would be due to the rashness of the international consortium spending billions on an un-proven Tokamak design. So government-leaning people would be very disappointed but other groups working on non-tokamak designs would not be.
Theoretically, energy generated by antimatter might be sufficient to make more antimatter. This would solve the problem of carrying a dangerous amount of antimatter on a ship.
One site says that one ounce of antimatter equates to 1.22 megatons, which is comparable to a single modern day H-bomb.
There are a number of small-scale fusion projects that claim they can commercialize fusion energy long before ITER. As time goes by, I am not reading of any successful milestones being met. If another decade goes by without results, we might conclude that these ideas were wrong.
AFAIK, the only proof of net energy generation has been shown by the NIF experiment. The experiments have not been reliably reproducible. Whether the approach can be made commercially viable by continuously sending a stream of the pellets into the device to fuse and the energy collected is unknown.
As the saying goes, it is a lot easier to collect the energy from the stable fusion reactor 150 million kilometers overhead. And clearly, that is exactly what a K2 civilization would do.
This firm has been on the fringe of fusion energy development for a many years… but they keyed in on Hydrogen – Boron reaction early on. Hope they or a similar firm finds a successful approach.
@MLosh. The LPPFusion website reads like an investment scam. Their board appears to have no relevant experts to guide the science and technology – this should be a red flag for any high technology R&D. The technology is not explained at all, especially how their technology overcomes the extremely high temperatures needed with p-B11. There are media puff pieces and the background science is like filler for the unscientific public. As of now, they are not even remotely near demonstrating anything relevant to fusing p-B11.
I hope you haven’t invested any capital in this technology.
Alex: Oh no, I’m just interested in p-B fusion. I agree they seem somewhat scamy. Either they don’t have the right engineering staff to scale things appropriately in a reasonable timeframe or this overall approach is very challenging and may be no better than tokamak and ICF.
Forgot link:
https://www.lppfusion.com/moving-toward-symmetry-and-hydrogen-boron-tests/
Interesting approach, best of luck! A great link from your site also, relevant to the discussion in February on the article High Redshift Caution:
https://www.nytimes.com/2023/09/02/opinion/cosmology-crisis-webb-telescope.html
“the rashness of the international consortium spending billions on an un-proven Tokamak design”
This seems a bit unfair? In the sense that there are nothing but ‘un-proven’ designs, as far as I know, and wasn’t that the case when the project was conceptualized?
It’s true that new directions are being tried, though. It’s an odd project in the sense that there are so many ‘sciency’ questions raised (resultant products, for instance, arising from radiating the outer shells) that might have been solved in smaller ways. Still, how should success be measured here? We all want it to produce cheap power, but we will also benefit from the sense that fundamental science is being tested.
I’m but an interested citizen, though.
Heck! I imagine that some other fusion solution, totally unimagined and coming out of left field would delight the researchers as much as it would me.
This why I think a fission implosion drive would be better either via Winterberg’s concepts or an adapted firstlight fusion concept. I wondering if we could crowd fund a simulation run using their numerical integrator program using a fissile material or combo. Impact fusion opens a door to fusion and or fission drives IMO due to the simplicity of the design and it would not be a lot of fissile material.
https://firstlightfusion.com/assets/documents/JDP_IFSA_2019.pdf
If ITER succeeds I doubt it will have much benefit for fusion propulsion as I understand it since the whole idea behind ITER is that it has to be big to work. If small scale Tokamaks had a chance of working they would be doing that instead. ITER should make net energy from fusion and if it fails I suspect the failure mode would more likely be an explosion due to failure of the cooling of the magnets. I heard that would be a very large explosion. However, I am more optimistic about companies such as Helion Energy making practical fusion for the grid than any derivative of ITER.
I would have thought a fusion rocket engine would be easier than energy production. The fusion need not be continuous nor contained, just enough to fuse and be allowed to exhaust. It could even just be pulses. Containment is less difficult as the vacuum is freely available, so the containment just needs to protect the superconducting coils.
If laser implosion was used, like at the NIF, the D/T pellets could be fused behind the vehicle, just directed by magnetic fields to create the thrust vector. This obviates the need for magnetic compression but does require very powerful laser pulses. Could beamed power provide the needed power, if only to jumpstart the engine?
Clearly, this is a very tough nut to crack. I cannot get excited until I see validated experimental results that fusion is occurring and that it could generate enough energy to be self-sustaining as the R&D matures. At least this isn’t as speculative as reactionless drives or even cold fusion.