9 ms·

A primer to nuclear fusion and First Light Fusion

61 points by gtzi 4y ago

ohiovr 4y ago
"There are three boxes we need to tick, in order to overcome this repulsion I mentioned before and get the nuclei very close. And this is not an easy feat. We need high temperature (think a hundred million degrees), high density (have a lot of these nuclei in a very small space), and keep the nuclei in that small space long enough for them to “react”. " High temperatures are usually used because the nuclei must have a lot of force to counter that of the liked charged partner. The most obvious way to do this is with heating the plasma because individual particles, when they collide head on, can have the combined momentum to plow their way together. But Philo T Farnsworth found a clever way to get them close with electrostatic forces. If it weren't for those darned wires. With millions of degrees that plasma viciously expands. An even more incredible contraction force must be used to keep this together long enough for "interesting results". This is done with inertial confinement like the Hbomb or emulations of it. Magnetic confinement merely slows the expansion, but it must at some point touch the walls. Actually, heat is not wanted. You only need to get the nuclei close enough that they quantum tunnel to each other to relieve their own stress in their environment. 2 Dueterons spread farther than helium3 does. Think of it like phase changes in condensed matter. Except we don't care at all about electrons, simply move them somewhere that the fuel ions wish to congregate at. Fortunately this can be a single point, as charges are concentrated on pointy things, as Faraday found in his experiments. The other side is full of the fuel ions. They don't have to be hot but warming them a little in an environment that is under 770 giga-pascals of pressure might be enough to moderate a nuclear combination process. It isn't hard to create two chambers in a crystal and make them undergo reductions or oxidations to free ions or electrons (tragically this happens with lithium ion batteries all the time). If they are surrounded in an environment that is very hard, very good dielectric strength, ions or electrons can be freed with no where to go. This is known as a meta-stable state and many crystal patterns exhibit this. The best dielectric known is diamond and it's also the hardest and has a ton of other helpful properties. If diamond couldn't do this, then nothing can. A mad genius with money and time would not have to go further than it to rule it out completely. Say my fancy idea doesn't work, if colliding macro projectiles is something useful to the author have they tried something like levitating pyrolytic carbon and propelling it with laser ablation? It could be done in a loop if part of the magnet can de-energize fast enough to allow the tiny block of carbon to escape. The plan they have seems very Wile E. Coyote to me but fun and cool. I hope they succeed.
- thehappypm 4y ago
  Hard to imagine a crystal can hold together atoms that need millions of degrees of temperature to fuse
  - ohiovr 4y ago
    If you had fingers small enough, you could bring together two nuclei at room temperature and they would fuse.
    - drdeca 4y ago
      By “fingers” do you mean “things which can apply precisely controlled forces to individual atoms”, or..? If you have two atoms in a vacuum with one moving directly towards the other at a not very high speed, I’m pretty sure they don’t fuse. There’s a repulsive force, right? Like, the (expectation of) potential energy goes up (up to a certain point) as the centers of their nuclei get closer together (after perhaps getting lower for a bit because maybe they form a bond or something)? So, presumably the “fingers” would have to do enough work to get past this potential energy barrier? (Or at least, make it high enough up this barrier that the probability of tunneling through becomes non-negligible?)
      - dotancohen 4y ago
        I believe that you are correct. In nature, those "fingers" are more often than not hydrogen atoms, and the force acting on them is gravity. 10^30 kilograms of hydrogen, in a stack 600,000 kilometers tall, makes for high enough forces for the hydrogen to fuse.
      - ohiovr 4y ago
        That's basically it. The strength of your fingers are more than enough to overcome the charge of 2 individual nuclei. Perhaps we need a shrink ray..
        drdeca 4y ago
Game_Ender 4y ago
Lots of interesting fusion startups. This group is using a gun type design that reminds of the Fat Man atomic bomb [0]. Except here it's a fusion target hit by high speed slug causing is to rapidly compression and undergo fusion. The key things is that unlike the NIF they have a clear path to power extraction. In production they are planning to use a chamber with circular sheets of falling liquid lithium to capture the fusion neutrons then transfer the heat [1]. Breeding some tritium along the way. 0 - https://en.wikipedia.org/wiki/Gun-type_fission_weapon https://en.wikipedia.org/wiki/Gun-type_fission_weapon 1 - https://firstlightfusion.com/technology/power-plan https://firstlightfusion.com/technology/power-plan
- sbierwagen 4y ago
  Cool idea. Capital costs would certainly be lower than any of the magnetic confinement designs, if it works. The power plant design they show has a 150MWe target power. Will be an interesting engineering challenge scaling it up and keeping all the finicky little parts and seals in the gun working when by design it's connected to a (small) nuclear explosion by a long pipe. If the timing is right you could have a heavy rotating shutter shielding the muzzle from the backblast.
  - pencilguin 4y ago
    They will, fortunately, not need to solve any of those problems, because there won't be any power plant. Instead, they will spend all the investors' money and then go do something else.
    - Schroedingersat 4y ago
      What's your take on Helion? They're acting exactly like every other scammer on the surface, but the more I dig the more I find evidence of thinking about things like how much quartz will evaporate and get into parts you don't want it to over 10 years. I can't see an overriding reason why it's immensely stupid like all the other schemes out there either.
      - 4y ago
legohead 4y ago
I've asked before but didn't get an answer. If we can achieve stable fusion, what are the plans for getting the power out? The guy in the article said you just do the same thing as coal or any other plant - generate steam. But we're talking about millions of degrees vs a couple thousand. Does it really scale that simply?
- chihuahua 4y ago
  I'm just guessing, but I imagine if you have a way of maintaining something at a temperature of millions of degrees, there's always a way to transfer that heat to some other thing. For example, by moving a gas past the very hot object, thus heating up the gas, and then moving the gas through a more conventional heat exchanger, where you generate steam for a steam turbine. Depending on the speed of the gas, it absorbs energy but isn't necessarily heated to the same temperature of millions of degrees, so it doesn't destroy the heat exchanger. I think this is somewhat similar to how a fission reactor is used to drive a steam turbine in an ordinary nuclear (fission) power plant.
- deleted 4y ago
  [deleted]
- DennisP 4y ago
  Plasma temperature is high but total heat is similar to other power plants. The atoms are moving fast but there aren't many of them. So basically, surround the plasma with a neutron-absorbing coolant and you're good. CFS uses molten FLiBe salt, and some others use a molten mix of lead and lithium. Then you run water pipes through that.
- rolph 4y ago
  there is more than just thermal energy, but so far it all looks like steam generation. if more experimentation reveals the persistence of the fusion reaction during perturberance of magnetic flux, we may be able to couple into the field with static coils.
- XorNot 4y ago
  Deuterium-Tritium fusion produces a neutron each time. Neutrons are not charged and so escape magnetic containment slamming into the reactor wall, transferring heat to it. This is how you get heat out, it's also how you breed more tritium from lithium.
raydiatian 4y ago
One thing I don’t understand about fusion is the mechanics of gain factors. If we can achieve a fusion reactor with a very small gain factor of say 1.01, is that sufficient to kick off an energy revolution, or do we need something more extreme like 10x or 100x? I suppose it boils down to what the “saturation threshold” of nuclear reactors is, where you can’t pump more energy in without breaking the thing. In any case, what are the benchmarks that engineers are shooting for?
- XorNot 4y ago
  Q=10 is believed to be necessary to make it economically viable.
  - raydiatian 4y ago
    Is there any insight into how long a road from 1 to 10 it is?
    - XorNot 4y ago
      So the assumption is that once you exceed 1 with some reactor architecture, you've more or less got it provided you can build a bigger containment vessel. ITER is as large as it is because within reasonable magnetic field strengths, you still need a certain amount of distance to curve the charged particles back towards the centre - and probability means you have a distribution, some but not all will make it. Bigger vacuum vessel, the more particles you can loop back into your reactor. So, if we can provably get over 1, and validate our plasma behaviour models, we can then derive the correct engineering equations to target a specific Q factor when building the production type reactors.
      - xupybd 4y ago
        So we might have to go much bigger than ITER?
        XorNot 4y ago
Temporary_31337 4y ago
Plenty of people have already explained why 99% of the ventures are plain scams. Small nuclear fission reactors are much more practical and already exist. In the extremely unlikely scenario that such a small reactor actually blows up (pretty much impossible by design) it’s an explosion smaller than some traditional bombs and way smaller than Hiroshima. But the only realistic risk is efficient supply chain of fuel and disposal of nuclear waste- again there are risks here but they are outweighed by not polluting the atmosphere with co2. We should use a lot more nuclear energy now, until renewables are more reliable. Renewables also use lots of rare earth metals and generally are resource intensive to build and most components have a pretty short lifespan so for now nuclear is the greener way to produce power.
- elcritch 4y ago
  It makes me wonder how small such systems could go. If you pack the fissile material just so then perhaps you could make the lifetime fairly short (not an RTG). Then could there be an optimal size which would both provide reasonable life while making it infeasible to stockpile enough to make a nuclear weapon? I'm too lazy to even back-of-a-napkin calculation. Though it seems like you'd need either a way to highly compress the fissile material or a really good neutron reflector to reach any sorta criticality. Neither seem likely exist though.
  - joshjob42 4y ago
    Well we know that aqueous homogeneous reactors (AHRs) can be very small; we’ve operated them with < 1 meter diameter cores at powers of >5MWth before. A big plant with 380MWth was estimated to be an approximately 2.5m diameter cylinder and 5m long primary reactor and breeding/shielding blanket, power density ~16kWth/L. https://www.osti.gov/servlets/purl/4123899 https://www.osti.gov/servlets/purl/4123899 Smallest AHRs were ~2 feet or so in diameter and put out ~5kWth, so it’s at least possible that you could deploy them buried in your backyard or something like that.

61 points by gtzi 4y ago

"There are three boxes we need to tick, in order to overcome this repulsion I mentioned before and get the nuclei very close. And this is not an easy feat. We need high temperature (think a hundred million degrees), high density (have a lot of these nuclei in a very small space), and keep the nuclei in that small space long enough for them to “react”. " High temperatures are usually used because the nuclei must have a lot of force to counter that of the liked charged partner. The most obvious way to do this is with heating the plasma because individual particles, when they collide head on, can have the combined momentum to plow their way together. But Philo T Farnsworth found a clever way to get them close with electrostatic forces. If it weren't for those darned wires. With millions of degrees that plasma viciously expands. An even more incredible contraction force must be used to keep this together long enough for "interesting results". This is done with inertial confinement like the Hbomb or emulations of it. Magnetic confinement merely slows the expansion, but it must at some point touch the walls. Actually, heat is not wanted. You only need to get the nuclei close enough that they quantum tunnel to each other to relieve their own stress in their environment. 2 Dueterons spread farther than helium3 does. Think of it like phase changes in condensed matter. Except we don't care at all about electrons, simply move them somewhere that the fuel ions wish to congregate at. Fortunately this can be a single point, as charges are concentrated on pointy things, as Faraday found in his experiments. The other side is full of the fuel ions. They don't have to be hot but warming them a little in an environment that is under 770 giga-pascals of pressure might be enough to moderate a nuclear combination process. It isn't hard to create two chambers in a crystal and make them undergo reductions or oxidations to free ions or electrons (tragically this happens with lithium ion batteries all the time). If they are surrounded in an environment that is very hard, very good dielectric strength, ions or electrons can be freed with no where to go. This is known as a meta-stable state and many crystal patterns exhibit this. The best dielectric known is diamond and it's also the hardest and has a ton of other helpful properties. If diamond couldn't do this, then nothing can. A mad genius with money and time would not have to go further than it to rule it out completely. Say my fancy idea doesn't work, if colliding macro projectiles is something useful to the author have they tried something like levitating pyrolytic carbon and propelling it with laser ablation? It could be done in a loop if part of the magnet can de-energize fast enough to allow the tiny block of carbon to escape. The plan they have seems very Wile E. Coyote to me but fun and cool. I hope they succeed.

thehappypm 4y ago
Hard to imagine a crystal can hold together atoms that need millions of degrees of temperature to fuse
- ohiovr 4y ago
  If you had fingers small enough, you could bring together two nuclei at room temperature and they would fuse.
  - drdeca 4y ago
    By “fingers” do you mean “things which can apply precisely controlled forces to individual atoms”, or..? If you have two atoms in a vacuum with one moving directly towards the other at a not very high speed, I’m pretty sure they don’t fuse. There’s a repulsive force, right? Like, the (expectation of) potential energy goes up (up to a certain point) as the centers of their nuclei get closer together (after perhaps getting lower for a bit because maybe they form a bond or something)? So, presumably the “fingers” would have to do enough work to get past this potential energy barrier? (Or at least, make it high enough up this barrier that the probability of tunneling through becomes non-negligible?)
    - dotancohen 4y ago
      I believe that you are correct. In nature, those "fingers" are more often than not hydrogen atoms, and the force acting on them is gravity. 10^30 kilograms of hydrogen, in a stack 600,000 kilometers tall, makes for high enough forces for the hydrogen to fuse.
    - ohiovr 4y ago
      That's basically it. The strength of your fingers are more than enough to overcome the charge of 2 individual nuclei. Perhaps we need a shrink ray..
      - drdeca 4y ago

Game_Ender 4y ago

Lots of interesting fusion startups. This group is using a gun type design that reminds of the Fat Man atomic bomb [0]. Except here it's a fusion target hit by high speed slug causing is to rapidly compression and undergo fusion. The key things is that unlike the NIF they have a clear path to power extraction. In production they are planning to use a chamber with circular sheets of falling liquid lithium to capture the fusion neutrons then transfer the heat [1]. Breeding some tritium along the way. 0 - https://en.wikipedia.org/wiki/Gun-type_fission_weapon https://en.wikipedia.org/wiki/Gun-type_fission_weapon 1 - https://firstlightfusion.com/technology/power-plan https://firstlightfusion.com/technology/power-plan

sbierwagen 4y ago
Cool idea. Capital costs would certainly be lower than any of the magnetic confinement designs, if it works. The power plant design they show has a 150MWe target power. Will be an interesting engineering challenge scaling it up and keeping all the finicky little parts and seals in the gun working when by design it's connected to a (small) nuclear explosion by a long pipe. If the timing is right you could have a heavy rotating shutter shielding the muzzle from the backblast.
- pencilguin 4y ago
  They will, fortunately, not need to solve any of those problems, because there won't be any power plant. Instead, they will spend all the investors' money and then go do something else.
  - Schroedingersat 4y ago
    What's your take on Helion? They're acting exactly like every other scammer on the surface, but the more I dig the more I find evidence of thinking about things like how much quartz will evaporate and get into parts you don't want it to over 10 years. I can't see an overriding reason why it's immensely stupid like all the other schemes out there either.
    - 4y ago

legohead 4y ago

I've asked before but didn't get an answer. If we can achieve stable fusion, what are the plans for getting the power out? The guy in the article said you just do the same thing as coal or any other plant - generate steam. But we're talking about millions of degrees vs a couple thousand. Does it really scale that simply?

chihuahua 4y ago
I'm just guessing, but I imagine if you have a way of maintaining something at a temperature of millions of degrees, there's always a way to transfer that heat to some other thing. For example, by moving a gas past the very hot object, thus heating up the gas, and then moving the gas through a more conventional heat exchanger, where you generate steam for a steam turbine. Depending on the speed of the gas, it absorbs energy but isn't necessarily heated to the same temperature of millions of degrees, so it doesn't destroy the heat exchanger. I think this is somewhat similar to how a fission reactor is used to drive a steam turbine in an ordinary nuclear (fission) power plant.
deleted 4y ago
[deleted]
DennisP 4y ago
Plasma temperature is high but total heat is similar to other power plants. The atoms are moving fast but there aren't many of them. So basically, surround the plasma with a neutron-absorbing coolant and you're good. CFS uses molten FLiBe salt, and some others use a molten mix of lead and lithium. Then you run water pipes through that.
rolph 4y ago
there is more than just thermal energy, but so far it all looks like steam generation. if more experimentation reveals the persistence of the fusion reaction during perturberance of magnetic flux, we may be able to couple into the field with static coils.
XorNot 4y ago
Deuterium-Tritium fusion produces a neutron each time. Neutrons are not charged and so escape magnetic containment slamming into the reactor wall, transferring heat to it. This is how you get heat out, it's also how you breed more tritium from lithium.

raydiatian 4y ago

One thing I don’t understand about fusion is the mechanics of gain factors. If we can achieve a fusion reactor with a very small gain factor of say 1.01, is that sufficient to kick off an energy revolution, or do we need something more extreme like 10x or 100x? I suppose it boils down to what the “saturation threshold” of nuclear reactors is, where you can’t pump more energy in without breaking the thing. In any case, what are the benchmarks that engineers are shooting for?

XorNot 4y ago
Q=10 is believed to be necessary to make it economically viable.
- raydiatian 4y ago
  Is there any insight into how long a road from 1 to 10 it is?
  - XorNot 4y ago
    So the assumption is that once you exceed 1 with some reactor architecture, you've more or less got it provided you can build a bigger containment vessel. ITER is as large as it is because within reasonable magnetic field strengths, you still need a certain amount of distance to curve the charged particles back towards the centre - and probability means you have a distribution, some but not all will make it. Bigger vacuum vessel, the more particles you can loop back into your reactor. So, if we can provably get over 1, and validate our plasma behaviour models, we can then derive the correct engineering equations to target a specific Q factor when building the production type reactors.
    - xupybd 4y ago
      So we might have to go much bigger than ITER?
      - XorNot 4y ago

Temporary_31337 4y ago

Plenty of people have already explained why 99% of the ventures are plain scams. Small nuclear fission reactors are much more practical and already exist. In the extremely unlikely scenario that such a small reactor actually blows up (pretty much impossible by design) it’s an explosion smaller than some traditional bombs and way smaller than Hiroshima. But the only realistic risk is efficient supply chain of fuel and disposal of nuclear waste- again there are risks here but they are outweighed by not polluting the atmosphere with co2. We should use a lot more nuclear energy now, until renewables are more reliable. Renewables also use lots of rare earth metals and generally are resource intensive to build and most components have a pretty short lifespan so for now nuclear is the greener way to produce power.

elcritch 4y ago
It makes me wonder how small such systems could go. If you pack the fissile material just so then perhaps you could make the lifetime fairly short (not an RTG). Then could there be an optimal size which would both provide reasonable life while making it infeasible to stockpile enough to make a nuclear weapon? I'm too lazy to even back-of-a-napkin calculation. Though it seems like you'd need either a way to highly compress the fissile material or a really good neutron reflector to reach any sorta criticality. Neither seem likely exist though.
- joshjob42 4y ago
  Well we know that aqueous homogeneous reactors (AHRs) can be very small; we’ve operated them with < 1 meter diameter cores at powers of >5MWth before. A big plant with 380MWth was estimated to be an approximately 2.5m diameter cylinder and 5m long primary reactor and breeding/shielding blanket, power density ~16kWth/L. https://www.osti.gov/servlets/purl/4123899 https://www.osti.gov/servlets/purl/4123899 Smallest AHRs were ~2 feet or so in diameter and put out ~5kWth, so it’s at least possible that you could deploy them buried in your backyard or something like that.