Can Small Fusion Cells Overcome Low Confinement Time Challenges?

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Discussion Overview

The discussion centers on the feasibility of creating small fusion cells and the challenges associated with low confinement times in fusion reactions. Participants explore theoretical aspects of fusion technology, particularly in relation to scaling down existing models like tokamaks.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions the definition of "small" and "fusion cell," noting that while small particle accelerators can induce fusion, their efficiency is insufficient for power generation.
  • Another participant proposes a hypothetical scenario of a small tokamak scaled down by a factor of 1:1000, questioning whether it would retain efficiency.
  • A participant asserts that scaling a tokamak in such a manner is not feasible, citing the need to increase the magnetic field strength significantly, which they claim is impossible.
  • In response, another participant expresses confusion about the necessity of scaling the magnetic field, suggesting that if plasma pressure and Beta remain constant, the magnetic field should not change.
  • Another participant explains that the relationship between plasma size and the Larmor radius would necessitate adjustments to the magnetic field or temperature to maintain fusion conditions.
  • A further inquiry is made about the implications of keeping the Larmor radius constant while reducing the size of the plasma vessel.
  • It is noted that reducing the size while maintaining the Larmor radius would facilitate particle escape, potentially leading to rapid loss of plasma confinement.

Areas of Agreement / Disagreement

Participants exhibit disagreement regarding the implications of scaling tokamaks and the necessary adjustments to magnetic fields and plasma conditions. The discussion remains unresolved with multiple competing views on the feasibility of small fusion cells.

Contextual Notes

Participants express varying assumptions about the relationships between plasma size, magnetic fields, and confinement times, which may affect their conclusions. The discussion does not resolve these assumptions or the mathematical relationships involved.

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Can a small fusion cell be created? If no, is it due to low confinement time it would have or something else?

Thank you.
 
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What is "small", and what is a "fusion cell"?
It is easy to induce fusion with a small particle accelerator. The efficiency is not high enough to use this for a power plant, but that was not part of the question.
The short timescale of energy loss in small objects is certainly an issue in some (not all) fusion concepts.
 
Say I have built a small tokamak of 1:1000 scale factor to ITER, assuming somehow I shrinked it without losing any function. Would it have one thousandth efficiency?
 
You cannot scale a tokamak like that.
As an example, you would have to scale the magnetic field up by a factor of 1000, and that alone is completely impossible.
 
I don't understand why field should scale up. If the plasma pressure and Beta remain the same, magnetic field should also not change.
 
The size of the plasma relative to the Larmor radius would change if you do not adjust the field (or the temperature, but then you can completely forget fusion).
 
What happens when the larmor radius stays the same and we reduce the size?
 
It gets easier for particles to escape, as that radius depends how much their position orthogonal to the magnetic field varies. In the extreme case, your plasma vessel is smaller than the radius, then the particles will hit the wall within microseconds.
 

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