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DT burns at the lowest temperatures but what it releases is horribly nasty: a 14 MeV neutron that takes a solid meter of metal to fully shield.
This means your magnets are further from the last-closed flux surface of the plasma, demanding more current to operate
Tritium isn't something that's easily obtainable either - the number one engineering challenge for fusion companies is engineering a Tritium-Breeding Blanket, something that can let high-energy neutrons combine with Li6 to produce more tritium.
This means circulating liquid lithium, an extremely reactive and corrosive material, at 600 degrees Celsius through metal pipes on the inside of a cryogenic containment vessel that keeps the superconducting magnets cold.
This is an engineering nightmare
CFS is developing the SPARC reactor, a compact tokamak, but the open secret is this device will likely just fry its own magnets after a limited time of use - there isn't enough neutron shielding to protect against these DT high energy neutrons
A far nicer fuel is deuterium-deuterium: it releases a much friendlier ~4 MeV proton or 3.3 MeV neutron that doesn't require nearly as much shielding, and, its extremely abundant.
About one in every 6420 hydrogen atoms is deuterium. The issue: needs a much higher temp to burn
The hard part with getting higher temperatures is you start losing energy faster and faster due to radiation emitted by electrons, meaning at higher temps you need a higher density of fusion power to overcome these losses.
This has been the long-march towards Q infinity
This is because all magnetic confinement fusion approaches - tokamaks, stellarators, etc - all have a thermalized plasma meaning the electrons and ions are equal temperature. Brehmstrahlung radiation power goes like 1/m^(3/2), so electrons emit a lot more power than ions
This means you don't want an arbitrarily hot plasma - past a certain point you're losing far more energy from electrons emitting light than you're releasing from ions fusing.
But what if you only heat up the ions? This is the secret of Electrostatic Inertial Confinement (IEC)
IEC means using electric fields to accelerate ions to high speeds and they fuse when colliding together.
It's considerably simpler than creating a thermalized plasma with equivalent ion temperature, so much so that it comes in at high school science-fair tech level
There are longstanding issues with IEC - the high voltage grids get bombarded and eroded by particles, collisions between particles thermalize the velocity distribution, and electrons still end up emitting bremstrahlung losses
A particular issue is reaching the space-charge limit of plasma density: you can't just arbitrarily pack ions into a confined volume since they electrostatically repel each other. Magnetic confinement plasmas are electrically neutral or quasi-neutral which allows higher density
To achieve higher plasma densities and thus higher fusion power production, electrostatic devices need to introduce electrons that circulate with ions to overcome this space charge limit. But then collisions will act to thermalize the plasma - and you're back to square 1
They key to achieving electrostatic inertial confinement is to inject the ion beam into the electrical potential well with a high enough energy such that the beam ions dominate over the thermal or Maxwellian distributed ions
Keeping losses low and ion temperature high
Achieving this high ion temperature without heating up the electrons unlocks the holy grail of fusion fuel types: proton-boron-11.
Here's why pB11 is by far the best fusion fuel you could hope for if you can get the ions hot enough:
First off, Boron-11 is the most abundant isotope Boron which makes up a significant fraction of the Earth's crust. A single mine in California produces 30% of the worlds borates supply in a town called, yep, Boron.
Second is the products are 3MeV charged helium nuclei. Far less shielding than those 14 MeV neutrons and because they're charged, you can capture their energy directly by electrostatic or magnetic fields. 70%-80% efficient versus 40% efficient for a thermal cycle
Third is power density: pB11 can produce 1kW of output for 11 months, 165x the amount of power released by an equivalent amount of uranium in a fission reactor.
This is the heart of my contrarian take: by far the most funded approaches in fusion have the least viable chance of ever producing an economical energy source because they can only burn thermalized plasmas producing neutrons that are a nightmare to engineer around
In contrast to this conventional view, pB11 is by far the best fusion fuel but you can only burn it in an electrostatic confinement device that combines beam-driven ions with electric potential trap.
There's only one company pursuing this: by
Their Orbitron device is the only approach in the entire commercial fusion industry I'm aware of that's able to produce a compact power supply capable of burning pB11 in the future, starting in the 100kW class and scaling up from there.
The compact size and power rating of the Orbitron means they can iterate far more quickly than magnetic confinement devices like tokamaks - where the entry cost to build first-of-a-kind plant starts at $400m and easily goes into the several $ billion
Direct energy capture from beam-driven pB11 in a compact size and insane fuel density opens up entirely new classes of vehicles - like a flying car that just ionizes the atmosphere with an electric jet thruster
Electric arc jets normally require prohibitively large and expensive power supplies in order to operate, meaning traditional liquid fueled jets always beat them out.
Not if you have an Orbitron though. As much power as you need with fuel to give you months of flying time
By that point you've basically re-created the Mr. Fusion Home Reactor and are ready to mount an Orbitron class generator on the back of your DeLorean
The most contrarian but long term correct bet in fusion is . Compact, IEC, burning pb11.
Flying DeLoreans LFG
Can you not do electrostatic inertial confinement with Deuterieum-Deuterium and get the same advantage that you would have with pB11 by not producing high energy neutrons. Why do you argue that pB11 is significantly better there?
DD reactions produce 2.5 MeV neutrons half the time and the other half 3MeV protons. I'd argue neutrons in general are a bad fusion product because they'll always require thick shielding and a thermal heat exchanger mechanism, which is much lower efficiency than direct energy
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Great thread, can't wait for my pB11 flying car!
Can we have another thread on He3 fusion? Is it even better long-term, or is it fantasy because fuel is unobtainable?
I think the fuel is hard to obtain unfortunately. People say they'll mine the moon for it. Maybe thats convenient if the reactor is on the moon.
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Interesting analysis.
I'm not certain if you're correct, but you definitely know more on this subject than I do
You’re leaving off another sick benefit: it burns rock down into helium.
Airship maximalists rejoice, this will make helium free!
Good thread. That’s right: DT has higher radiation concerns with the 14MeV neutrons and tritium is hard to get. The joke in the community is you need a fission reactor to power your fusion reaction for tritium production. pB11 on paper is great but is very hard. Fusion is hard.
But of course DT fuel is being prioritised to get ‘there’ first. They all know alternative fusion fuels likely more efficient in the long run, but it’s not worth anything unless you can pay for it by delivering first.
I thought Tri-Alpha Energy was also pursuing pB11, but haven’t kept up with them.
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These issues are addressed from another perspective in my book on fusion -
Dude did you just google all of these? If so its opening my eyes to some things
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Great post on revealing the true engineering challenges fusion has. Thank you!
Sad to see so much capital being wasted on bad ideas, like watching VC’s invest crypto funding cosmos app chains.
Nice thread Andrew, when I hear the word contrarian I think of Thiel. So I’m guessing some of this, is from Thiel’s school of thought. To this end I think the another contrarian thought is fission works good enough, and is the likely a 50 year bet worth pursuing
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Where's the technology at the heart of in these variants and if they overlap, how are the problems you raise being solved? Or not?
Fascinating. I know about 100 times more about fusion than I did before! I like the cross-section graphs.
What do you think about Lawrenceville Plasma Fusion’s pinch device? They tell a nice story.
Is there a plasma containment system at the intersection of the electrostatic wind? And the sliver/ring/hexagon where a planets magnetic field density is highest?
x.com/PlanetaryShow/
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Can plasma be kept from touching
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John Davis
@redneckbwana
Replying to @DMontesG
How do we know it is not fusion being ignited at the corners of the hexagon where magnetic flux is most intense? Combined w/ southward facing CME?
youtube.com/watch?v=iUooYd
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Great thread, and plug for . Love the project they're working on. Was the case for D-T fusion always that you can achieve fusion reactions at lower temperatures? Demonstrate tractability and then move on to better fuels? What prevents p-B11 from being exploited
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If they’re breeding tritium, it’s not worst case. You need to input deuterium but that’s relatively cheap.
p-B11 is better technologically but may not be superior economically if getting there requires significant additional reactor performance.
With pB11 you are trading off an engineering nightmare for a physics nightmare. No one wants neutrons, but so far they have been deemed the lesser nightmare.
Wait, I looked up Avalanch and the specs on their device say its deuterium tritium fusion. What's up?
Power density. If you take a DT plasma and replace it with any other fuel, the total power output will go down by a factor of >50 (due to the lower cross-section). Even if this allows you to eliminate the blanket and make the plasma bigger, you still won't recover a factor of 50.
I followed EMC2 for a long time: they were early proponents for inertial confinement and P-B11 fusion. Dr. Park hasn't published anything in ages. Does anyone know if they found a fatal flaw with polywell or did the money just run out?
I dont know much about this dataset/graph but in general if I was looking for big energy I'd look here
Well written thread, thanks Andrew! The holy grail of fusion is indeed a concept in which confinement time scales positively with temperature. As you note, no closed-field system can show this scaling, but FRCs and magnetic mirrors can. Think TAE, Realta, and Terra Fusion.
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This seems really interesting but I’m too tired rn. I’m going to share anyways and if someone likes it tomorrow I will remember to read.
Here's the standard approach:
youtu.be/L0KuAx1COEk
But in my opinion, most fusion research is venture-capital-funded vapourware. It's irrelevant to climate change and too expensive and too hard for widespread adoption.
This was very illluminating. Nicely put together at the right level of details 
proton-Boron was totally new idea to me.
proton-Boron was totally new idea to me.
Good to see this brought up again - obviously been quite a lot of research into this over many years - what do you think the odds are of making it within 10 years?
porque las startups puede que lleguen a la fusión pero esto no signifique que es comercialmente viable y escalable.
I think a large chunk of the funding going to “fight” global warming & climate change could be better served if invested in solving fusion energy
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There’s a new version of this post
If the most compact design happens to also be the most promising, this feels almost too good to be true!
Exceptional thread as always! What is the crux challenge with pB11 approaches that still needs to be solved ?
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also avoid most of the problems you cite, and have a chance of commercially viable generation in a reasonable timeframe.
They're not going to be powering flying cars, though.
This is catnip for high functioning ADHDers
Great thread.
Been following this field for 40 years, even had a colleague who did student placement at JET.
I’d have thought Musk would be all over fusion;solve that & you really do change humanity for ever.
Great thread.
Been following this field for 40 years, even had a colleague who did student placement at JET.
I’d have thought Musk would be all over fusion;solve that & you really do change humanity for ever.
Look at LPPFusion. They are already testing with PB11 fuel with Prof Eric Lerner. Have detected fusion by products after test shots.
All I want to see is one of those projects using liquid metals for plasma facing components
I feel much better prepared for my next dinner party debate about fusion. These fools are going to get totally owned in front of their wives and girlfriends. Game, Set, Match
What about his position? What about commercial application? (civil customer) 
Helion energy says that with D-He-3 they create 2.45MeV neutrons.
Poor Andrew, he will be long dead before any of these companies succeeds in giving positive energy to the reactor, by this I mean comparing the total energy provided vs the total energy produced
Or just like…don’t burn fuel at all. Use the energy already there..? Hot fusion will never get you where you want to go.
He3 has a somewhat surprising area of plausibility from around 20 to 70KeV
this is what Helion is targeting
Polaris may get to 10-20KeV in next month or few
Terrific read, aneutronic fusion definitely the way to go. Always slightly bemused by the 'get to the moon so we can harvest He3' crowd.
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Here's the spiciest detail from the new o1 system card:
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OpenAI
@OpenAI
Replying to @OpenAI
The updated OpenAI o1 system card builds on prior safety work, detailing robustness evals, red teaming insights, and safety improvements using Instruction Hierarchy. It maintains a "medium" risk rating based on testing with an expanded suite of evaluations, reflecting it is safe
Here is a fun o1 test. I gave it this XKCD comic & the prompt: "make this a reality. i need a gui and clear instructions since i can't code. that means you need to give me full working software"
It took less than 15 minutes, and it didn't get caught in any of the usual LLM loops
