4 ms·

>The plasma heats up, but how do you turn that into useful electrical energy? I appreciate that many people are commenting 'you couple the plasma to a working

>The plasma heats up, but how do you turn that into useful electrical energy? I appreciate that many people are commenting 'you couple the plasma to a working fluid', but I think the original comment was more along the line of how you couple a confined plasma to a working fluid. By definition the plasma is in a hard vacuum, magnetically bottled. What, then, is the coupling method? Thermal photons escaping confinement? I genuinely have no idea myself, but would really like to know.

pfdietz 6y ago
80% of the energy from DT fusion comes out as neutrons, which enter a blanket and deposit energy there by collisions and nuclear interactions.
- Baeocystin 6y ago
  Thank you! Do you know how far along are we in understanding how to build an effective blanket that can withstand the neutron flux while maintaining its physical integrity?
  - pfdietz 6y ago
    It's not a solved problem (since really testing a wall design requires a working high power source of fusion neutrons), and it's not clear it can be solved in a sufficiently practical way. Indeed, the ability of the first wall to withstand the energy flowing through it will likely cause DT fusion reactors to have low volumetric power density, with sad effects on their economics.
    - Baeocystin 6y ago
      Thanks again for the reply.
  - DennisP 6y ago
    SPARC's approach is for the blanket to be a molten salt, and also function as a coolant. That will surround an inner wall which gets replaced annually. They tested joints in the REBCO superconductors, so the reactor can be opened up on hinges.
- jnxx 6y ago
  > which enter a blanket So, what is that blanket made of? It needs to be a material which: - can withstand high temperatures and radiation - does not becomes radioactive itself - facilitates production of Tritium by breeding - operates in very high magnetic fields, which means high forces No such material is known so far. It is a bit like some engineer from 1700 said: "Well, you could just build a more efficient and compact and light steam engine, and connect it to a machine which has flapping wings, and then you have a transport vehicle which can carry people across the Atlantic ocean at supersonic speed, and at little cost."
  - tuatoru 6y ago
    Not such a bad analogy, as the blanket will get hot, and the heat will be used to turn water into steam, which will power generating plant. Just like in the 18th and 19th centuries. It would have had to have been an unusually well informed and far-sighted engineer though, as Savery's engines first worked in 1698 and the first for-sale commercial engine, Newcomen's, wouldn't happen until 1712. And they were incredibly inefficient: 0.01% to 0.1%.
isoprophlex 6y ago
You're right, I was curious about capturing the fusion products in some way and still being able to extract useful energy. I looked up the effects of neutron radiation on materials[]. Sounds like a hell of an engineering challenge to come up with a robust way of getting that energy out! Radiation damage to materials occurs as a result of the interaction of a [neutron] with a lattice atom in the material. The collision causes a massive transfer of kinetic energy to the lattice atom, which is displaced from its lattice site, becoming what is known as the primary knock-on atom (PKA). [...] The magnitude of the damage is such that a single 1 MeV neutron creating a PKA in an iron lattice produces approximately 1,100 Frenkel pairs. [] https://en.m.wikipedia.org/wiki/Neutron_radiation https://en.m.wikipedia.org/wiki/Neutron_radiation
- jnxx 6y ago
  > https://en.wikipedia.org/wiki/Monju_Nuclear_Power_Plant https://en.wikipedia.org/wiki/Monju_Nuclear_Power_Plant Yep. And anything touched by the neutron flux would become radioactive if it captures neutrons. For example steel, normal steel contains carbon, carbon captures neutrons, so the steel becomes radioactive, and also brittle. And then you need wiring and insulation and coolant and pumps and all that.

pfdietz 6y ago

80% of the energy from DT fusion comes out as neutrons, which enter a blanket and deposit energy there by collisions and nuclear interactions.

Baeocystin 6y ago
Thank you! Do you know how far along are we in understanding how to build an effective blanket that can withstand the neutron flux while maintaining its physical integrity?
- pfdietz 6y ago
  It's not a solved problem (since really testing a wall design requires a working high power source of fusion neutrons), and it's not clear it can be solved in a sufficiently practical way. Indeed, the ability of the first wall to withstand the energy flowing through it will likely cause DT fusion reactors to have low volumetric power density, with sad effects on their economics.
  - Baeocystin 6y ago
    Thanks again for the reply.
- DennisP 6y ago
  SPARC's approach is for the blanket to be a molten salt, and also function as a coolant. That will surround an inner wall which gets replaced annually. They tested joints in the REBCO superconductors, so the reactor can be opened up on hinges.
jnxx 6y ago
> which enter a blanket So, what is that blanket made of? It needs to be a material which: - can withstand high temperatures and radiation - does not becomes radioactive itself - facilitates production of Tritium by breeding - operates in very high magnetic fields, which means high forces No such material is known so far. It is a bit like some engineer from 1700 said: "Well, you could just build a more efficient and compact and light steam engine, and connect it to a machine which has flapping wings, and then you have a transport vehicle which can carry people across the Atlantic ocean at supersonic speed, and at little cost."
- tuatoru 6y ago
  Not such a bad analogy, as the blanket will get hot, and the heat will be used to turn water into steam, which will power generating plant. Just like in the 18th and 19th centuries. It would have had to have been an unusually well informed and far-sighted engineer though, as Savery's engines first worked in 1698 and the first for-sale commercial engine, Newcomen's, wouldn't happen until 1712. And they were incredibly inefficient: 0.01% to 0.1%.

isoprophlex 6y ago

You're right, I was curious about capturing the fusion products in some way and still being able to extract useful energy. I looked up the effects of neutron radiation on materials[]. Sounds like a hell of an engineering challenge to come up with a robust way of getting that energy out! Radiation damage to materials occurs as a result of the interaction of a [neutron] with a lattice atom in the material. The collision causes a massive transfer of kinetic energy to the lattice atom, which is displaced from its lattice site, becoming what is known as the primary knock-on atom (PKA). [...] The magnitude of the damage is such that a single 1 MeV neutron creating a PKA in an iron lattice produces approximately 1,100 Frenkel pairs. [] https://en.m.wikipedia.org/wiki/Neutron_radiation https://en.m.wikipedia.org/wiki/Neutron_radiation

jnxx 6y ago
> https://en.wikipedia.org/wiki/Monju_Nuclear_Power_Plant https://en.wikipedia.org/wiki/Monju_Nuclear_Power_Plant Yep. And anything touched by the neutron flux would become radioactive if it captures neutrons. For example steel, normal steel contains carbon, carbon captures neutrons, so the steel becomes radioactive, and also brittle. And then you need wiring and insulation and coolant and pumps and all that.