4 ms·

Dumb question, but is the basic idea that you need to harvest more heat energy from the plasma than is needed to maintain the magnetic field? Also, very dumb q

by ilaksh 2y ago

Dumb question, but is the basic idea that you need to harvest more heat energy from the plasma than is needed to maintain the magnetic field? Also, very dumb question but the plasma means that fusion is actually occuring, right? And does anyone know how this one collects the heat and converts it into electricity or whatever? Or any other fusion device, how does it actually collect or output energy from the fusion. And how much do they make, and how far off is that from matching the input power? Maybe it was some protons escaping from the plasma and hearing something external or something.

virtue3 2y ago
I dont believe magnetic containment would contain heat, so just run a liquid through the reactor and use it to heat up water to make steam and drive a turbine. Nuclear plants do this.
- ilaksh 2y ago
  Well it's a torus right? So you put a turbine in the middle? I don't think I've heard that explanation before. Or maybe it can go in the outside. I guess it's like, you need a huge amount of electricity to make the magnetic field strong enough, right? So the question is, how do you collect enough heat without melting key components?
  - baq 2y ago
    No unless you want your turbine to be neutron activated. (You don't.) You would pump water through the reactor and use a heat exchanger to a secondary water loop which powers the turbine. Maybe you can do without the secondary loop altogether, not sure; this ITER document suggests only one loop, but it's super vague: https://www.iter.org/sci/MakingitWork https://www.iter.org/sci/MakingitWork
    - lazide 2y ago
      No one has figured out how to actually do this yet. Which is why it is vague. The radiation levels and difficulty maintaining the magnetic confinement make this essentially impossible right now. Another reason why fusion is always 50 years away. It’s really hard (outside of a nuclear bomb or star, anyway).
mnau 2y ago
> the plasma means that fusion is actually occuring No. Plasma simply means a specific state of a matter. E.g. the fluorescent lamps (the long tubular lights that flicker on start) have a plasma inside when it produces light
- ilaksh 2y ago
  Your reply implies that in this specific case there is no fusion. I know that plasma can occur without it, but this discussion is about the specific machine.
  - jfengel 2y ago
    In the case of this machine it implies that they got plasma by fusion. Which means the fusion is working. It's a milestone, albeit one of many.
    - johnbcoughlin 2y ago
      You don't ever create plasma via fusion, fusion occurs in plasma that has reached a certain temperature and density threshold.
  - marcosdumay 2y ago
    You make the plasma before any fusion can happen. Just there being plasma there means nothing, you inject it on the machine already that way.
__MatrixMan__ 2y ago
1. Yes, sorta, but it's more than just the magnetic field. You're also heating the fuel, so you have to offset that too. Plus there are pumps which circulate coolant to carry heat away from the plasma and towards a turbine, so you have to offset their power. Probably a few other things as well. 2. I don't think plasma == fusion. You can get plasma just by heating a gas beyond a certain point. Plasma cutters, for instance, operate on super heated air, no fusion anywhere nearby. 3. I think the wall of the reaction chamber heats up because they're being bombarded by radiation. Most of the radiation incident on the reaction chamber walls is infrared, radiated from the hot plasma, but there are also more exotic things like stray neutrons also crash into the sides of the thing. These cause the metal to deteriorate over time (and become somewhat hazardous), but they also they impart additional heat energy. So you have to have two cooling systems, one to keep the magnets actually cold so they they remain superconducting, and another to keep the housing below the point where it melts. It's this second one that let's you pull heat away from the hot metal donut that is a tokomak and use it to make electricity. Between the magnet coolant and the chamber coolant and the reacting plasma you have some of the steepest thermal gradients anywhere in the known universe.
- ilaksh 2y ago
  Thanks..right I know about plasma in general, I just assumed in this case it was caused by the fusion. Maybe not. But they have fusion right? Just not recovering any/enough energy to make up for power requirements.
  - SeanAnderson 2y ago
    The article is light on details. It doesn't mention an operating temperature or Q factor. I would hazard to guess that no - they did not achieve fusion. They achieved plasma which is a precursor to fusion. Controlled plasma, at a high enough temperature, is an environment in which fusion can occur. All this article says is they created controlled plasma. Crucially, they did so with high temperature magnets which is fairly novel. https://en.wikipedia.org/wiki/Fusion_energy_gain_factor https://en.wikipedia.org/wiki/Fusion_energy_gain_factor You might also be interested in reading this. Q factor is what's used to discuss whether a fusion device is generating net positive energy.
pfdietz 2y ago
> Dumb question, but is the basic idea that you need to harvest more heat energy from the plasma than is needed to maintain the magnetic field? No, since creating and maintaining the magnetic field in principle consumes no energy. All the energy put into a superconducting magnet (1/2 L I^2) can be recovered. What is needed from a physics point of view is for fusion energy production to comfortably exceed the energy put into the plasma. And there's also a whole host of engineering and economic issues beyond that. Energy is recovered from DT fusion by stopping the neutrons in a blanket, converting their energy to heat, and taking that heat away in a fluid.
- deleted 2y ago
  [deleted]
magicalhippo 2y ago
> plasma means that fusion is actually occuring, rigth? As mentioned plasma is just another state of matter[1], where a significant portion of the electrons and ions a separate rather than combined as atoms. Fusion happens when you overcome the electrostatic repulsion of nuclei, bringing them close enough together so they can fuse[2]. Typically, in reactors like this, that means you confine (compress) a sufficient amount of material ("fuel") to a small volume and heat it up sufficiently. Both are needed to make it possible for the nuclei to come close enough to fuse. The heat required is so great the material will turn into a plasma. > And does anyone know how this one collects the heat and converts it into electricity or whatever? This depends somewhat on reactor design, including fuel used. However they're all fancy steam generators in the end, so not unlike a traditional nuclear power plant in that regard. From what I know, typically the "surplus heat" of a fusion reactor comes in the form of energetic neutron radiation[3]. This radiation is ionizing and as such shielding is required, and this shielding will heat up as it slows down those energetic neutrons. In the ARC reactor[4] for example, a liquid shielding "blanket" surrounds the fusion chamber. As the neutrons heats up the liquid, the liquid gets pumped through a heat exchanger to produce steam to run a steam turbine. edit: I found this talk[5] from one of the folks behind ARC to be very illuminating in how fusion power works and the challenges involved. It's from 2017, but the basics haven't changed. [1]: https://en.wikipedia.org/wiki/Plasma_(physics) https://en.wikipedia.org/wiki/Plasma_(physics) [2]: https://en.wikipedia.org/wiki/Nuclear_fusion#Requirements https://en.wikipedia.org/wiki/Nuclear_fusion#Requirements [3]: https://en.wikipedia.org/wiki/Neutron_radiation https://en.wikipedia.org/wiki/Neutron_radiation [4]: https://en.wikipedia.org/wiki/ARC_fusion_reactor https://en.wikipedia.org/wiki/ARC_fusion_reactor [5]: https://www.youtube.com/watch?v=L0KuAx1COEk https://www.youtube.com/watch?v=L0KuAx1COEk
willis936 2y ago
Great questions. The difference between energy harvested and the energy necessary to maintain confinement is the difference in denominators of Qscientific and Qengineering. Q is power out / power in. Qscientific is a figure of merit used to know close to a burning plasma a machine is (how many fusion reactions it can do vs. how many it would need to do to be a working reactor). Qengineering is power put on the grid / parasitic power needed to keep the machine running. Every electrical power source has an analogous concept (keep the lights on, fuel pumped, inverters operating, etc.) There are some noisy non-experts who claim that focusing on Qplasma is deceitful, but it's akin to complaining that engineers are focusing on engine efficiency instead of car efficiency before the engineers have finished making the engine. At the end of the day the scale of parasitic loads scales much less than the power output of a reactor, so the reactor size chosen will be at the economic minimum between "bigger machine is more expensive to make" and "smaller machine produces less power / lower Qengineering / other difficult scaling law things like neutron bombardment on plasma facing components (maintenance schedule)". https://x.com/JB_Fusion/status/1506964692627034118 https://x.com/JB_Fusion/status/1506964692627034118 Yes, to have a real measure of Q you need to be doing fusion. In many research cases not a lot of fusion is happening and the neutrons are not actively being measured. What is typically done is to measure plasma performance metrics with protium or deuterium then say what the Q would have been if they used deuterium-tritium based on known plasma-performance to Q conversions (Lawson criterion). https://en.wikipedia.org/wiki/Lawson_criterion https://en.wikipedia.org/wiki/Lawson_criterion https://x.com/swurzel/status/1534556521744457731 https://x.com/swurzel/status/1534556521744457731 Heat collection is done via neutrons. In D-T fusion 80% of the energy is released as a 14.1 MeV (17% speed of light, like a bat out of hell). The remaining 20% of energy is an acceleration of a He4 nucleus (fused byproduct). This He4 nucleus is a charged particle, so it stays in magnetic confinement and imparts its energy on fuel via collisions, helping to self sustain the reaction. The neutron has no charge so it flys straight out of the machine. You can model this as a small ring on the innermost core of the donut shooting neutrons in all directions. So you wrap a neutron-absorbing blanket around the vacuum vessel to slow these neutrons down via collision and heat up coolant in the blanket. You run this coolant through a heat exchanger to make pressurized steam to spin a turbine to... you get the idea. https://en.wikipedia.org/w/index.php?title=Deuterium%E2%80%93tritium_fusion&diffonly=true https://en.wikipedia.org/w/index.php?title=Deuterium%E2%80%9...

by ilaksh 2y ago

virtue3 2y ago

I dont believe magnetic containment would contain heat, so just run a liquid through the reactor and use it to heat up water to make steam and drive a turbine. Nuclear plants do this.

ilaksh 2y ago
Well it's a torus right? So you put a turbine in the middle? I don't think I've heard that explanation before. Or maybe it can go in the outside. I guess it's like, you need a huge amount of electricity to make the magnetic field strong enough, right? So the question is, how do you collect enough heat without melting key components?
- baq 2y ago
  No unless you want your turbine to be neutron activated. (You don't.) You would pump water through the reactor and use a heat exchanger to a secondary water loop which powers the turbine. Maybe you can do without the secondary loop altogether, not sure; this ITER document suggests only one loop, but it's super vague: https://www.iter.org/sci/MakingitWork https://www.iter.org/sci/MakingitWork
  - lazide 2y ago
    No one has figured out how to actually do this yet. Which is why it is vague. The radiation levels and difficulty maintaining the magnetic confinement make this essentially impossible right now. Another reason why fusion is always 50 years away. It’s really hard (outside of a nuclear bomb or star, anyway).

mnau 2y ago

> the plasma means that fusion is actually occuring No. Plasma simply means a specific state of a matter. E.g. the fluorescent lamps (the long tubular lights that flicker on start) have a plasma inside when it produces light

ilaksh 2y ago
Your reply implies that in this specific case there is no fusion. I know that plasma can occur without it, but this discussion is about the specific machine.
- jfengel 2y ago
  In the case of this machine it implies that they got plasma by fusion. Which means the fusion is working. It's a milestone, albeit one of many.
  - johnbcoughlin 2y ago
    You don't ever create plasma via fusion, fusion occurs in plasma that has reached a certain temperature and density threshold.
- marcosdumay 2y ago
  You make the plasma before any fusion can happen. Just there being plasma there means nothing, you inject it on the machine already that way.

__MatrixMan__ 2y ago

1. Yes, sorta, but it's more than just the magnetic field. You're also heating the fuel, so you have to offset that too. Plus there are pumps which circulate coolant to carry heat away from the plasma and towards a turbine, so you have to offset their power. Probably a few other things as well. 2. I don't think plasma == fusion. You can get plasma just by heating a gas beyond a certain point. Plasma cutters, for instance, operate on super heated air, no fusion anywhere nearby. 3. I think the wall of the reaction chamber heats up because they're being bombarded by radiation. Most of the radiation incident on the reaction chamber walls is infrared, radiated from the hot plasma, but there are also more exotic things like stray neutrons also crash into the sides of the thing. These cause the metal to deteriorate over time (and become somewhat hazardous), but they also they impart additional heat energy. So you have to have two cooling systems, one to keep the magnets actually cold so they they remain superconducting, and another to keep the housing below the point where it melts. It's this second one that let's you pull heat away from the hot metal donut that is a tokomak and use it to make electricity. Between the magnet coolant and the chamber coolant and the reacting plasma you have some of the steepest thermal gradients anywhere in the known universe.

ilaksh 2y ago
Thanks..right I know about plasma in general, I just assumed in this case it was caused by the fusion. Maybe not. But they have fusion right? Just not recovering any/enough energy to make up for power requirements.
- SeanAnderson 2y ago
  The article is light on details. It doesn't mention an operating temperature or Q factor. I would hazard to guess that no - they did not achieve fusion. They achieved plasma which is a precursor to fusion. Controlled plasma, at a high enough temperature, is an environment in which fusion can occur. All this article says is they created controlled plasma. Crucially, they did so with high temperature magnets which is fairly novel. https://en.wikipedia.org/wiki/Fusion_energy_gain_factor https://en.wikipedia.org/wiki/Fusion_energy_gain_factor You might also be interested in reading this. Q factor is what's used to discuss whether a fusion device is generating net positive energy.

pfdietz 2y ago

> Dumb question, but is the basic idea that you need to harvest more heat energy from the plasma than is needed to maintain the magnetic field? No, since creating and maintaining the magnetic field in principle consumes no energy. All the energy put into a superconducting magnet (1/2 L I^2) can be recovered. What is needed from a physics point of view is for fusion energy production to comfortably exceed the energy put into the plasma. And there's also a whole host of engineering and economic issues beyond that. Energy is recovered from DT fusion by stopping the neutrons in a blanket, converting their energy to heat, and taking that heat away in a fluid.

deleted 2y ago
[deleted]

magicalhippo 2y ago

> plasma means that fusion is actually occuring, rigth? As mentioned plasma is just another state of matter[1], where a significant portion of the electrons and ions a separate rather than combined as atoms. Fusion happens when you overcome the electrostatic repulsion of nuclei, bringing them close enough together so they can fuse[2]. Typically, in reactors like this, that means you confine (compress) a sufficient amount of material ("fuel") to a small volume and heat it up sufficiently. Both are needed to make it possible for the nuclei to come close enough to fuse. The heat required is so great the material will turn into a plasma. > And does anyone know how this one collects the heat and converts it into electricity or whatever? This depends somewhat on reactor design, including fuel used. However they're all fancy steam generators in the end, so not unlike a traditional nuclear power plant in that regard. From what I know, typically the "surplus heat" of a fusion reactor comes in the form of energetic neutron radiation[3]. This radiation is ionizing and as such shielding is required, and this shielding will heat up as it slows down those energetic neutrons. In the ARC reactor[4] for example, a liquid shielding "blanket" surrounds the fusion chamber. As the neutrons heats up the liquid, the liquid gets pumped through a heat exchanger to produce steam to run a steam turbine. edit: I found this talk[5] from one of the folks behind ARC to be very illuminating in how fusion power works and the challenges involved. It's from 2017, but the basics haven't changed. [1]: https://en.wikipedia.org/wiki/Plasma_(physics) https://en.wikipedia.org/wiki/Plasma_(physics) [2]: https://en.wikipedia.org/wiki/Nuclear_fusion#Requirements https://en.wikipedia.org/wiki/Nuclear_fusion#Requirements [3]: https://en.wikipedia.org/wiki/Neutron_radiation https://en.wikipedia.org/wiki/Neutron_radiation [4]: https://en.wikipedia.org/wiki/ARC_fusion_reactor https://en.wikipedia.org/wiki/ARC_fusion_reactor [5]: https://www.youtube.com/watch?v=L0KuAx1COEk https://www.youtube.com/watch?v=L0KuAx1COEk

willis936 2y ago

Great questions. The difference between energy harvested and the energy necessary to maintain confinement is the difference in denominators of Qscientific and Qengineering. Q is power out / power in. Qscientific is a figure of merit used to know close to a burning plasma a machine is (how many fusion reactions it can do vs. how many it would need to do to be a working reactor). Qengineering is power put on the grid / parasitic power needed to keep the machine running. Every electrical power source has an analogous concept (keep the lights on, fuel pumped, inverters operating, etc.) There are some noisy non-experts who claim that focusing on Qplasma is deceitful, but it's akin to complaining that engineers are focusing on engine efficiency instead of car efficiency before the engineers have finished making the engine. At the end of the day the scale of parasitic loads scales much less than the power output of a reactor, so the reactor size chosen will be at the economic minimum between "bigger machine is more expensive to make" and "smaller machine produces less power / lower Qengineering / other difficult scaling law things like neutron bombardment on plasma facing components (maintenance schedule)". https://x.com/JB_Fusion/status/1506964692627034118 https://x.com/JB_Fusion/status/1506964692627034118 Yes, to have a real measure of Q you need to be doing fusion. In many research cases not a lot of fusion is happening and the neutrons are not actively being measured. What is typically done is to measure plasma performance metrics with protium or deuterium then say what the Q would have been if they used deuterium-tritium based on known plasma-performance to Q conversions (Lawson criterion). https://en.wikipedia.org/wiki/Lawson_criterion https://en.wikipedia.org/wiki/Lawson_criterion https://x.com/swurzel/status/1534556521744457731 https://x.com/swurzel/status/1534556521744457731 Heat collection is done via neutrons. In D-T fusion 80% of the energy is released as a 14.1 MeV (17% speed of light, like a bat out of hell). The remaining 20% of energy is an acceleration of a He4 nucleus (fused byproduct). This He4 nucleus is a charged particle, so it stays in magnetic confinement and imparts its energy on fuel via collisions, helping to self sustain the reaction. The neutron has no charge so it flys straight out of the machine. You can model this as a small ring on the innermost core of the donut shooting neutrons in all directions. So you wrap a neutron-absorbing blanket around the vacuum vessel to slow these neutrons down via collision and heat up coolant in the blanket. You run this coolant through a heat exchanger to make pressurized steam to spin a turbine to... you get the idea. https://en.wikipedia.org/w/index.php?title=Deuterium%E2%80%93tritium_fusion&diffonly=true https://en.wikipedia.org/w/index.php?title=Deuterium%E2%80%9...