Can Negative Temperatures Bring Us Closer to Fusion as a Viable Power Source?

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Discussion Overview

The discussion centers on the concept of negative temperatures and their potential implications for achieving nuclear fusion as a viable power source. Participants explore the theoretical aspects of negative temperatures, their relationship to entropy, and the conditions necessary for fusion, including high-energy states and temperature requirements.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants suggest that negative temperatures, being "hotter than hot," could theoretically bring fusion closer to reality due to the high energy associated with such states.
  • Others argue that negative temperatures arise in systems with limited high-energy states and do not apply to fusion plasma, which has a near-infinite number of states available.
  • It is noted that fusion requires high-energy thermal motion, which cannot be constrained to a negative temperature system.
  • Some participants propose that a system with an upper bound might fuse at negative temperatures and low entropy, questioning the relationship between energy and entropy in fusion processes.
  • A participant emphasizes that fusion occurs when particles collide at high speeds, which cannot be limited by an upper bound, thus negating the possibility of applying negative temperatures to fusion.
  • Concerns are raised about the confusion in the discussion, with calls for clarification on the repeated questions regarding the relationship between negative temperatures and fusion.
  • A participant with experience in fusion research states that while fusion temperatures can be achieved in the lab, negative temperatures do not contribute to maintaining a favorable power balance for fusion.

Areas of Agreement / Disagreement

Participants generally disagree on the applicability of negative temperatures to fusion, with multiple competing views presented. The discussion remains unresolved regarding the potential implications of negative temperatures for fusion as a power source.

Contextual Notes

Limitations include the dependence on specific definitions of temperature and entropy, as well as the unresolved nature of how negative temperatures might interact with the conditions necessary for fusion.

John d Marano
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I was reading about negative temperature here http://www.nature.com/news/quantum-gas-goes-below-absolute-zero-1.12146 and how the state is "hotter than hot" and thought of fusion.Since you need very high temperatures for fusion does the discovery on negative temperatures bring fusion as a power source closer to reality? I know my thinking is simplistic but I thought I'd give it a shot!
Regards,
JDM
 
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No, negative temperature is a result of a system that has a limit on the number of high-energy states available. These are very specialized circumstances and the temperature becomes negative because of the relationship between energy and entropy. It doesn't have any bearing on fusion.
 
Drakkith said:
No, negative temperature is a result of a system that has a limit on the number of high-energy states available. These are very specialized circumstances and the temperature becomes negative because of the relationship between energy and entropy. It doesn't have any bearing on fusion.
Fusion isn't economical because "Currently, here on Earth the amount of energy you'd need to put into produce that kind of heat or pressure is much, much higher than what you get out in usable energy" [ http://www.popularmechanics.com/sci...ration/why-dont-we-have-fusion-power-15480435 ] but "a negative temperature is not colder than absolute zero, but rather it is hotter than infinite temperature" [ http://en.wikipedia.org/wiki/Negative_temperature ] hotter than infinity seems like it should be enough to achieve fusion economically!
 
Negative temperatures don't apply to fusion plasma since there are a near-infinite number of states available for the plasma. In other words, we can keep inputting energy into the plasma and the entropy keeps increasing. To reach negative temperatures, the entropy would need to decrease while the energy increases.
 
Drakkith said:
Negative temperatures don't apply to fusion plasma since there are a near-infinite number of states available for the plasma. In other words, we can keep inputting energy into the plasma and the entropy keeps increasing. To reach negative temperatures, the entropy would need to decrease while the energy increases.
Normally fusion occurs at high temperatures but "You need a lower bound for the energy in order to get positive temperatures and an upper bound in order to get negative temperatures" [ http://www.quantum-munich.de/research/negative-absolute-temperature/ ]. We know a typical system with a lower bound fuses at high temperature and high entropy might a system with upper bound fuse at negative temperatures and low entropy?
 
No, fusion occurs because the particles slam into each other at high speeds. This high-energy thermal motion cannot have an upper bound put on it, so it can't be made into a negative temperature system.
 
John, you have asked the same question three times. Are you going to keep asking it until someone tells you "yes"? Drakkith has explained why it is not three times. If you would like him/us to elaborate on the answer, please explain what parts are confusing you. But don't just start from the top again.
 
Vanadium 50 said:
John, you have asked the same question three times. Are you going to keep asking it until someone tells you "yes"? Drakkith has explained why it is not three times. If you would like him/us to elaborate on the answer, please explain what parts are confusing you. But don't just start from the top again.
I feel like I'm not explaining myself; couldn't there be a point of such high energy and so little entropy that the atoms have no place else to go but will smush together?
 
And the answer is still no.
 
  • #10
lol; you're funny
 
  • #11
Perhaps this might serve as an introduction.

 
  • #12
John d Marano said:
I feel like I'm not explaining myself; couldn't there be a point of such high energy and so little entropy that the atoms have no place else to go but will smush together?

No, because in order to "smush" together and fuse, they must be traveling at a high velocity. Velocity is a type of state that has no upper limit. You can just keep inputting energy all you want and you'll never hit a boundary. The states that negative temps apply to are things like the spin of atoms, which have only up or down. If we look at a system of 100 atoms in an electric/magnetic field, we could excite the atoms in this system to an up spin to increase their energy. But at a certain point the number of atoms in a high energy state (spin up) becomes equal to the number of atoms in a low energy state. If we continue to add energy we begin to run out of high energy states and the entropy decreases instead of increasing. This is the point where negative temperatures come into play.

Note that systems where negative temperatures can be used are typically very close to absolute zero in a "traditional" view of the word temperature. We have to cool them off first and then set up this very sensitive system of up/down states. In the example above, the thermal motion of the atoms even at room temperature would wreak havoc on our system, flipping spins randomly and exciting atoms and their electrons to other states that we didn't have before.
 
  • #13
I'm working in fusion. We have no problem reaching fusion temperatures (~150MK) in the lab. The problem is keeping the power balance favorable. Negative temperatures won't help with this. In fact, if you get too hot, the fusion rate starts to decrease.
 

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