Possible fusion power plants of the future

[hagar]

Question about fusion power sources. An article I just read stated that they would be safe as if anything went wrong they would just stop working. Is this correct ? If so than why do stars continue to burn and seem (to me at least) to be self feeding.

Respectfully,
Pat Hagar

 

[Astronuc]

An article I just read stated that they would be safe as if anything went wrong they would just stop working. Is this correct ?

If the plasma reaches the first wall, it loses heat rapidly, i.e., it is quenched and the fusion process would cease. The plasma density is on the order of 10¹⁴ particles/cm³.

If so than why do stars continue to burn and seem (to me at least) to be self feeding.

Think of the size of stars compared to the Sun or our planet, and then think about the size of a power plant compared to the plant. Stars are orders of magnitude greater in size and mass compared to a power plant [understatement].

The plasma density, temperatures and pressures are much, much greater than we could ever achieve in a terrestrial tokamak.

https://en.wikipedia.org/wiki/Solar_core
http://solarscience.msfc.nasa.gov/interior.shtml
https://fusedweb.llnl.gov/CPEP/Chart_Pages/5.Plasmas/SunLayers.html

The sun has been around for about 4.5 billion years, so it's remarkably stable. Occasional CMEs blow off a very small fraction of a percentage of solar mass.

If you're standing on the photosphere of the sun -- the "surface", the gravitational strength of the sun will be about 27.9 times that of the Earth, if you were standing on the surface of the Earth. In metric units, on Earth, the acceleration due to gravity is 9.81 meters/sec^2, so on the Sun, that would be 273.7 meters/sec^2.

Ref: https://van.physics.illinois.edu/qa/listing.php?id=1063

 

[Simon Bridge]

This would be "safe" by comparison with nuclear fission plants.

 

[mfb]

The plasma density, temperatures and pressures are much, much greater than we could ever achieve in a terrestrial tokamak.

The temperature in tokamaks (if they do fusion) is higher than in the core of sun, roughly a factor of 7.We don't have gravitational pressure, if anything goes wrong and the plasma containment gets lost. fusion stops immediately. In the worst case, some parts of the reactor wall will melt. Bad for the reactor, but not dangerous for anyone.

 

[hagar]

The temperature in tokamaks (if they do fusion) is higher than in the core of sun, roughly a factor of 7.

Fascinating, I had no idea of this.

Than size,density and gravity controlling pressure and temperature would be the limiting factors.
Thanks to all for the responses and links.

Respectfully,
Pat Hagar

 

[mfb]

There is no relevant gravity in the plasma on Earth. Pressure is maintained by the magnetic field.

 

[hagar]

There is no relevant gravity in the plasma on Earth. Pressure is maintained by the magnetic field.

I thank you for the correction. My comment was not stated correctly. I meant the gravity of the sun maintains the pressure and temperature.

Respectfully,
Pat Hagar

 

[Astronuc]

The temperature in tokamaks (if they do fusion) is higher than in the core of sun, roughly a factor of 7.

Thanks for the correction. I had switched the numbers.

Than size,density and gravity controlling pressure and temperature would be the limiting factors.

As mfb mentioned Earth's gravity is relatively weak. The pressure is determined by the plasma density and temperature (P = nkT), and it is counter balanced by the magnetic field, which is limited by what field the superconducting magnets can provide. The temperature is determined by the energy balance in the plasma, with the goal that energy generated by fusion would greatly exceed the loses from the plasma.

 

[hagar]

Thanks for the correction. I had switched the numbers.As mfb mentioned Earth's gravity is relatively weak. The pressure is determined by the plasma density and temperature (P = nkT), and it is counter balanced by the magnetic field, which is limited by what field the superconducting magnets can provide. The temperature is determined by the energy balance in the plasma, with the goal that energy generated by fusion would greatly exceed the loses from the plasma.

Thank you for the correction, it seems I did it again. I was referring to the suns fusion process and not to a local power plant.

Respectfully,
Pat Hagar