8 ms·

Forgive my ignorance; what with all the effort made to isolate the exceedingly hot plasma from connecting with any surface, what are the plans to extract the he

Forgive my ignorance; what with all the effort made to isolate the exceedingly hot plasma from connecting with any surface, what are the plans to extract the heat in order to generate power?

amelius 4y ago
Since the plasma runs hotter than the Sun, and the magnetic field cannot confine photons, my guess is that the hull will become insanely hot, and you could use it to drive a steam engine.
- dleslie 4y ago
  Ah interesting, so then the coolant for the shielding is also the means to power a generator.
pfdietz 4y ago
This would be for DT fusion, so most of the energy would come out as neutrons. And it would face the same showstoppingly bad volumetric power density as tokamaks, because of limits on that energy flow through the surface of the reactor.
- sidkshatriya 4y ago
  > And it would face the same showstoppingly bad volumetric power density as tokamaks, because of limits on that energy flow through the surface of the reactor. I do think it is worth persevering though. The future of energy is Solar/Wind but Fusion should not be ignored. It is one of Nature's fundamental processes. Mastering fusion could turn out to be useful in ways we cannot possibly fathom at the moment right now.
  - GordonS 4y ago
    I agree. If we were able to eventually miniaturise fusion reactors, they would be incredible for space flight. Back on Earth, if they could be made safe enough, maybe we could even use them to run container ships?
    - sidkshatriya 4y ago
      With all the fast neutrons emanating from a fusion reactor (and the heavy confinement that it requires) I don't think a container ship would be a safe enough environment (threat of disaster at sea, constantly jostling which might affect plasma stability etc.). But yes, there is a potential for a lot of space applications and other things we haven't thought of yet.
      - ClumsyPilot 4y ago
        what kindof disaster could be relevant in this context? If the ship sinks, the minor radioctivity of a shutdown reactor will not be relevany Technically, container ships are enormous and can use ballast water for shielding. I can't judge the ecobomics ofcourse
        sidkshatriya 4y ago
        Well fusion reactors are likely to cost a huge amount of money when they do become operational. No point having them sinking in a storm. Probably just safer to charge a huge battery and put it on a ship (if you don’t want to use fossil fuels). Avoids a lot of unfoseen commercial risk. Even though you could use water for shielding, the metal container and other things that hold the reactor would be highly radioactive and brittle due to continuous neutron bombardment. You wouldn’t want that to be lost at sea spewing radiation (even though the reactor itself would shutdown automatically).
        GordonS 4y ago
        > Probably just safer to charge a huge battery and put it on a ship Large container ships burn through 16 tons of bunker oil per hour, and each journey can last up to 3 weeks - any idea what size of battery such a ship would need? I have no clue how to calculate that), but I'm guessing it would be completely impractical, even if we made huge strides in battery energy density.
        4y ago
  - Galaxeblaffer 4y ago
    We already have the perfect way to create heat and the science around it has been long solved and understood. Solar and wind won't save us and fusion certainly won't. It amazes me how solar and wind dreamers all seem to like fusion but fission is just super evil.
    - pfdietz 4y ago
      Why won't solar and wind save us? There are many bogus reasons people give for that (IMO incorrect) opinion; I'm wondering which one you're going to come up with.
      - Galaxeblaffer 4y ago
        I'm not coming up with anything, but the first and glaring problem is that we can't store the energy created in any meaningful capacity. Sure we have some ideas like power2x but that doesn't really help for grid scale storage covering periods of several days where no power is created due to the weather. So imo the biggest problem is that it's just not a reliable source of energy. Here in Denmark we've spent billions on wind and we have nothing to show for it our energy is almost as dirty as when we started and the biggest reason for that is that we now use gas and biomass instead of coal. I could go on, but what it all comes down to is that we already have the perfect source of energy with nuclear fission, we can easily connect it to existing grids and it even works for district heating further decreasing our reliance on gas and fossil fuels.
        pfdietz 4y ago
        Ok, the "can't store energy" canard. No, we can, in multiple ways. Batteries of many different flavors, pumped hydro, storing as thermal energy (via resistive heaters or heat pump cycles), hydrogen (electrolyzers have crashed in price) and other e-fuels. Costs of these are declining rapidly as demand picks up and the scent of trillion dollar markets entices a wide range of enterprises and investors. Storage has not been much of a thing before because we were still burning fossil fuels and could just turn those up and down instead. But that doesn't mean storage wouldn't work. In Denmark now e-fuels will be much cheaper than the fossil fuels (well, except maybe coal) you are now using. You're temporarily stuck in a rough spot right now, but the way out is via renewables + storage, and you'll be saving money doing it.
sidkshatriya 4y ago
From what I've understood from previous discussions (don't know much about plasma physics though): It is a multistep challenge. Step 1: Figure out how to get a self-sustaining fusion reaction. Step 2: figure out how to extract the energy in a useful, safe, non-destructive (to the reactor) way. Doing Step 1 alone is very difficult so the've postponed Step 2 to the future. I may be wrong though.
- onlyrealcuzzo 4y ago
  I would imagine since, combined, we're spending tens of billions of dollars on Fusion research - someone must have some ideas for step 2, right?!
  - kortex 4y ago
    We have some ideas, of course. The rough idea is: surround the reactor with a lithium blanket. This gets bombarded with neutrons, breeding fuel and heating the lithium, which transfers its heat to coolant to spin turbines. The devil is in all the engineering details, like: how do we make alloys to deal with neutron bombardment/hydrogen embrittlement, what's the optimal geometry to capture flux while being serviceable, etc. Much of that work can and is researched in parallel, but there will be inevitable integration hell that has a burning fusion reactor core as a prerequisite.
    - TedDoesntTalk 4y ago
      What is done with the “spent” lithium blanket? Is it radioactive waste?
      - esteth 4y ago
        It depends on how it’s engineered. The lithium itself wouldn’t be “radioactive waste” but the vessel for the lithium would likely be.
  - pfdietz 4y ago
    There are currently major unsolved problems with step 2. https://cpb-us-w2.wpmucdn.com/research.seas.ucla.edu/dist/d/39/files/2022/06/Final-FINAL-CIMTEC-2022-copy-Perugia-Italy-6-29-2022.pdf https://cpb-us-w2.wpmucdn.com/research.seas.ucla.edu/dist/d/...
trebligdivad 4y ago
I'm not sure, but there's a thing called the 'Divertor' in some designs, it's said to be for removing inpurities, but some things talk about it being used for removing heat as well: https://www.iter.org/mach/Divertor https://www.iter.org/mach/Divertor
- trebligdivad 4y ago
  oh, and the other thing is some of the walls they talk about having 'blankets' that absorb the neutrons and ... somehow get the heat out; one of them is 'flibe' which is a lithium salt: https://www.tandfonline.com/doi/full/10.1080/00295450.2019.1691400 https://www.tandfonline.com/doi/full/10.1080/00295450.2019.1...
- willis936 4y ago
  I was going to make a comment about divertors. W7-X has 10 strike points and an island divertor. It's pretty wild physics.
Maken 4y ago
Because no known material can withstand direct contact with the plasma. Even with the air gap the walls require a cooling system, and therefore a continuous hot stream of fluid will be generated like in any other thermal power plant. However, at the stage fusion research is, the main problem is figuring how to create a device to keep the plasma fluid stable for long periods of time. As far as I know, none of the existing prototypes aims to be a functional electricity generator.
- exitheone 4y ago
  Is this not false? The plasma is so incredibly thin that it would cool down immediately the moment it touches the walls. Afaik the heat generated here is mostly due to neutron bombardment and not because of the plasma.
  - ncmncm 4y ago
    The plasma had better not touch the wall, becuase then no plasma. But the wall would be heated by the neutrons hammering it. Nobody has identified a material to make this wall out of. It has not even been worked on in decades.
Someone 4y ago
https://www.iter.org/sci/MakingitWork https://www.iter.org/sci/MakingitWork: “The helium nucleus carries an electric charge which will be subject to the magnetic fields of the tokamak and remain confined within the plasma, contributing to its continued heating. However, approximately 80 percent of the energy produced is carried away from the plasma by the neutron which has no electrical charge and is therefore unaffected by magnetic fields. The neutrons will be absorbed by the surrounding walls of the tokamak, where their kinetic energy will be transferred to the walls as heat. In ITER, this heat will be captured by cooling water circulating in the vessel walls and eventually dispersed through cooling towers. In the type of fusion power plant envisaged for the second half of this century, the heat will be used to produce steam and—by way of turbines and alternators—electricity.” That’s about ITER, but the two devices do not differ in this.
- dathinab 4y ago
  Makes me wonder if given the increasing value of water this has to change a bit (for reactors not close to shore). I.e. instead of letting the steam escape into the air after going through a turbine using some mechanism to passively cool/condense it "somehow", reusing _all_ coolant water, only having closed loop(s) (the "inner" cooling loop is often closed anyway for various reasons transferring the heat to an outer loop before its used for anything).
  - ncmncm 4y ago
    There is no expectation that the steam would be released. That would be terribly wasteful, and it is not done in existing plants, whether coal or nuke-fired.
baking 4y ago
For Deuterium-Tritium reactions, the easiest to achieve, 80% of the energy is contained in neutrons which pass through the first wall and must be captured in a blanket. The rest of the energy could be carried to the first wall by photons, called radiative cooling, but you can also use divertors that allow the fusion products to escape the plasma carrying away some of the heat. I think in a stellarator you will need divertors to remove the fusion products because of the continuous operation.
ak217 4y ago
By capturing neutrons (which, not being charged, escape the magnetic confinement continuously as the reaction goes on) with a moderator blanket which is then cooled with water/steam. How to keep the blanket from quickly degrading and becoming nuclear waste seems to be an open problem (not too different from what goes on in fission reactors though) https://en.wikipedia.org/wiki/Fusion_power#Energy_capture https://en.wikipedia.org/wiki/Fusion_power#Energy_capture
- warinukraine 4y ago
- Tuna-Fish 4y ago
  > How to keep the blanket from quickly degrading and becoming nuclear waste seems to be an open problem Not really. Most reactors plan to also use the neutrons to breed the tritium fuel for the reactor, so the blanket would consist of liquid metallic lithium. The only products from neutrons reacting with lithium nucleii (either 6 or 7) are He-4 and tritium. The open problem is how to safely maintain the reactor-facing wall of the lithium blanket. It gets bombarded by a lot of neutrons, yet needs to contain the hot lithium. It helps that the lithium can be unpressurized, but it's still a problem, because molten metallic lithium is not fun to have leak into anywhere. The plan of the ARC guys appears to be to design the reactor so that the lithium vessel is easy to remove and swap for a new one, and just use steel for the vessel. The downside of this is that it's going to result in a lot of low-activity waste -- actually probably quite a bit more than what fission plants produce. There are other approaches, including using a material that doesn't really get activated by neutrons, and which is maintained above it's annealing temperature so embrittlement caused by dislocations is repaired as it happens. The downside of this is that materials above their annealing temperatures can be kind of soft.
  - imglorp 4y ago
    It looks like all the isotopes of LI are very short lived. Is the problem some of the daughters, or perhaps the Fe and C in the steel that are the problem? https://www.thoughtco.com/lithium-isotopes-radioactive-decay-half-life-608238 https://www.thoughtco.com/lithium-isotopes-radioactive-decay...
mpweiher 4y ago
From the fine article: "Over the past 3 years, W7-X’s creators stripped it down and replaced all the interior walls and fittings with water-cooled versions, ..." I am guessing that the water used to cool the interior walls will get hot in the process...

Forgive my ignorance; what with all the effort made to isolate the exceedingly hot plasma from connecting with any surface, what are the plans to extract the heat in order to generate power?

amelius 4y ago

Since the plasma runs hotter than the Sun, and the magnetic field cannot confine photons, my guess is that the hull will become insanely hot, and you could use it to drive a steam engine.

dleslie 4y ago
Ah interesting, so then the coolant for the shielding is also the means to power a generator.

pfdietz 4y ago

This would be for DT fusion, so most of the energy would come out as neutrons. And it would face the same showstoppingly bad volumetric power density as tokamaks, because of limits on that energy flow through the surface of the reactor.

sidkshatriya 4y ago
> And it would face the same showstoppingly bad volumetric power density as tokamaks, because of limits on that energy flow through the surface of the reactor. I do think it is worth persevering though. The future of energy is Solar/Wind but Fusion should not be ignored. It is one of Nature's fundamental processes. Mastering fusion could turn out to be useful in ways we cannot possibly fathom at the moment right now.
- GordonS 4y ago
  I agree. If we were able to eventually miniaturise fusion reactors, they would be incredible for space flight. Back on Earth, if they could be made safe enough, maybe we could even use them to run container ships?
  - sidkshatriya 4y ago
    With all the fast neutrons emanating from a fusion reactor (and the heavy confinement that it requires) I don't think a container ship would be a safe enough environment (threat of disaster at sea, constantly jostling which might affect plasma stability etc.). But yes, there is a potential for a lot of space applications and other things we haven't thought of yet.
    - ClumsyPilot 4y ago
      what kindof disaster could be relevant in this context? If the ship sinks, the minor radioctivity of a shutdown reactor will not be relevany Technically, container ships are enormous and can use ballast water for shielding. I can't judge the ecobomics ofcourse
      - sidkshatriya 4y ago
        Well fusion reactors are likely to cost a huge amount of money when they do become operational. No point having them sinking in a storm. Probably just safer to charge a huge battery and put it on a ship (if you don’t want to use fossil fuels). Avoids a lot of unfoseen commercial risk. Even though you could use water for shielding, the metal container and other things that hold the reactor would be highly radioactive and brittle due to continuous neutron bombardment. You wouldn’t want that to be lost at sea spewing radiation (even though the reactor itself would shutdown automatically).
        GordonS 4y ago
        > Probably just safer to charge a huge battery and put it on a ship Large container ships burn through 16 tons of bunker oil per hour, and each journey can last up to 3 weeks - any idea what size of battery such a ship would need? I have no clue how to calculate that), but I'm guessing it would be completely impractical, even if we made huge strides in battery energy density.
        4y ago
- Galaxeblaffer 4y ago
  We already have the perfect way to create heat and the science around it has been long solved and understood. Solar and wind won't save us and fusion certainly won't. It amazes me how solar and wind dreamers all seem to like fusion but fission is just super evil.
  - pfdietz 4y ago
    Why won't solar and wind save us? There are many bogus reasons people give for that (IMO incorrect) opinion; I'm wondering which one you're going to come up with.
    - Galaxeblaffer 4y ago
      I'm not coming up with anything, but the first and glaring problem is that we can't store the energy created in any meaningful capacity. Sure we have some ideas like power2x but that doesn't really help for grid scale storage covering periods of several days where no power is created due to the weather. So imo the biggest problem is that it's just not a reliable source of energy. Here in Denmark we've spent billions on wind and we have nothing to show for it our energy is almost as dirty as when we started and the biggest reason for that is that we now use gas and biomass instead of coal. I could go on, but what it all comes down to is that we already have the perfect source of energy with nuclear fission, we can easily connect it to existing grids and it even works for district heating further decreasing our reliance on gas and fossil fuels.
      - pfdietz 4y ago
        Ok, the "can't store energy" canard. No, we can, in multiple ways. Batteries of many different flavors, pumped hydro, storing as thermal energy (via resistive heaters or heat pump cycles), hydrogen (electrolyzers have crashed in price) and other e-fuels. Costs of these are declining rapidly as demand picks up and the scent of trillion dollar markets entices a wide range of enterprises and investors. Storage has not been much of a thing before because we were still burning fossil fuels and could just turn those up and down instead. But that doesn't mean storage wouldn't work. In Denmark now e-fuels will be much cheaper than the fossil fuels (well, except maybe coal) you are now using. You're temporarily stuck in a rough spot right now, but the way out is via renewables + storage, and you'll be saving money doing it.

sidkshatriya 4y ago

From what I've understood from previous discussions (don't know much about plasma physics though): It is a multistep challenge. Step 1: Figure out how to get a self-sustaining fusion reaction. Step 2: figure out how to extract the energy in a useful, safe, non-destructive (to the reactor) way. Doing Step 1 alone is very difficult so the've postponed Step 2 to the future. I may be wrong though.

onlyrealcuzzo 4y ago
I would imagine since, combined, we're spending tens of billions of dollars on Fusion research - someone must have some ideas for step 2, right?!
- kortex 4y ago
  We have some ideas, of course. The rough idea is: surround the reactor with a lithium blanket. This gets bombarded with neutrons, breeding fuel and heating the lithium, which transfers its heat to coolant to spin turbines. The devil is in all the engineering details, like: how do we make alloys to deal with neutron bombardment/hydrogen embrittlement, what's the optimal geometry to capture flux while being serviceable, etc. Much of that work can and is researched in parallel, but there will be inevitable integration hell that has a burning fusion reactor core as a prerequisite.
  - TedDoesntTalk 4y ago
    What is done with the “spent” lithium blanket? Is it radioactive waste?
    - esteth 4y ago
      It depends on how it’s engineered. The lithium itself wouldn’t be “radioactive waste” but the vessel for the lithium would likely be.
- pfdietz 4y ago
  There are currently major unsolved problems with step 2. https://cpb-us-w2.wpmucdn.com/research.seas.ucla.edu/dist/d/39/files/2022/06/Final-FINAL-CIMTEC-2022-copy-Perugia-Italy-6-29-2022.pdf https://cpb-us-w2.wpmucdn.com/research.seas.ucla.edu/dist/d/...

trebligdivad 4y ago

I'm not sure, but there's a thing called the 'Divertor' in some designs, it's said to be for removing inpurities, but some things talk about it being used for removing heat as well: https://www.iter.org/mach/Divertor https://www.iter.org/mach/Divertor

trebligdivad 4y ago
oh, and the other thing is some of the walls they talk about having 'blankets' that absorb the neutrons and ... somehow get the heat out; one of them is 'flibe' which is a lithium salt: https://www.tandfonline.com/doi/full/10.1080/00295450.2019.1691400 https://www.tandfonline.com/doi/full/10.1080/00295450.2019.1...
willis936 4y ago
I was going to make a comment about divertors. W7-X has 10 strike points and an island divertor. It's pretty wild physics.

Maken 4y ago

Because no known material can withstand direct contact with the plasma. Even with the air gap the walls require a cooling system, and therefore a continuous hot stream of fluid will be generated like in any other thermal power plant. However, at the stage fusion research is, the main problem is figuring how to create a device to keep the plasma fluid stable for long periods of time. As far as I know, none of the existing prototypes aims to be a functional electricity generator.

exitheone 4y ago
Is this not false? The plasma is so incredibly thin that it would cool down immediately the moment it touches the walls. Afaik the heat generated here is mostly due to neutron bombardment and not because of the plasma.
- ncmncm 4y ago
  The plasma had better not touch the wall, becuase then no plasma. But the wall would be heated by the neutrons hammering it. Nobody has identified a material to make this wall out of. It has not even been worked on in decades.

Someone 4y ago

https://www.iter.org/sci/MakingitWork https://www.iter.org/sci/MakingitWork: “The helium nucleus carries an electric charge which will be subject to the magnetic fields of the tokamak and remain confined within the plasma, contributing to its continued heating. However, approximately 80 percent of the energy produced is carried away from the plasma by the neutron which has no electrical charge and is therefore unaffected by magnetic fields. The neutrons will be absorbed by the surrounding walls of the tokamak, where their kinetic energy will be transferred to the walls as heat. In ITER, this heat will be captured by cooling water circulating in the vessel walls and eventually dispersed through cooling towers. In the type of fusion power plant envisaged for the second half of this century, the heat will be used to produce steam and—by way of turbines and alternators—electricity.” That’s about ITER, but the two devices do not differ in this.

dathinab 4y ago
Makes me wonder if given the increasing value of water this has to change a bit (for reactors not close to shore). I.e. instead of letting the steam escape into the air after going through a turbine using some mechanism to passively cool/condense it "somehow", reusing _all_ coolant water, only having closed loop(s) (the "inner" cooling loop is often closed anyway for various reasons transferring the heat to an outer loop before its used for anything).
- ncmncm 4y ago
  There is no expectation that the steam would be released. That would be terribly wasteful, and it is not done in existing plants, whether coal or nuke-fired.

baking 4y ago

For Deuterium-Tritium reactions, the easiest to achieve, 80% of the energy is contained in neutrons which pass through the first wall and must be captured in a blanket. The rest of the energy could be carried to the first wall by photons, called radiative cooling, but you can also use divertors that allow the fusion products to escape the plasma carrying away some of the heat. I think in a stellarator you will need divertors to remove the fusion products because of the continuous operation.

ak217 4y ago

By capturing neutrons (which, not being charged, escape the magnetic confinement continuously as the reaction goes on) with a moderator blanket which is then cooled with water/steam. How to keep the blanket from quickly degrading and becoming nuclear waste seems to be an open problem (not too different from what goes on in fission reactors though) https://en.wikipedia.org/wiki/Fusion_power#Energy_capture https://en.wikipedia.org/wiki/Fusion_power#Energy_capture

warinukraine 4y ago
Tuna-Fish 4y ago
> How to keep the blanket from quickly degrading and becoming nuclear waste seems to be an open problem Not really. Most reactors plan to also use the neutrons to breed the tritium fuel for the reactor, so the blanket would consist of liquid metallic lithium. The only products from neutrons reacting with lithium nucleii (either 6 or 7) are He-4 and tritium. The open problem is how to safely maintain the reactor-facing wall of the lithium blanket. It gets bombarded by a lot of neutrons, yet needs to contain the hot lithium. It helps that the lithium can be unpressurized, but it's still a problem, because molten metallic lithium is not fun to have leak into anywhere. The plan of the ARC guys appears to be to design the reactor so that the lithium vessel is easy to remove and swap for a new one, and just use steel for the vessel. The downside of this is that it's going to result in a lot of low-activity waste -- actually probably quite a bit more than what fission plants produce. There are other approaches, including using a material that doesn't really get activated by neutrons, and which is maintained above it's annealing temperature so embrittlement caused by dislocations is repaired as it happens. The downside of this is that materials above their annealing temperatures can be kind of soft.
- imglorp 4y ago
  It looks like all the isotopes of LI are very short lived. Is the problem some of the daughters, or perhaps the Fe and C in the steel that are the problem? https://www.thoughtco.com/lithium-isotopes-radioactive-decay-half-life-608238 https://www.thoughtco.com/lithium-isotopes-radioactive-decay...

mpweiher 4y ago

From the fine article: "Over the past 3 years, W7-X’s creators stripped it down and replaced all the interior walls and fittings with water-cooled versions, ..." I am guessing that the water used to cool the interior walls will get hot in the process...