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Name:  Krishna B.
Status: student
Age: 13
Location: N/A
Country: N/A
Date: 2000-2001


Question:
The core temperature in the sun is 12 million Kelvin which is enough for a successful fusion reaction to orrour. Yet on earth to creat a fusion reaction we have to get to temperatures of 100 million Kelvin. Why can we not creat a controlled thermo fusion reaction at 12 million Kelvin?


Replies:
We cannot create the density that exists at the center of a star and also get to 12 million Kelvins. For efficient fusion, you need to get the product of the density and the pressure up very high for a short time. So far, we are better at temperature than at density.

Tim Mooney


Yes, a controlled, self-sustaining fusion reaction occurs in the sun. However, it is extremely slow. Think about it - the sun has been going at it for billions of years. If we tried to run a fusion reaction here on earth with such a low rate of conversion we would not get enough energy out of it to be worthwhile. Per its mass, the energy output of the sun actually is not very high. The human body beats it by a lot.

So we try to initiate fusion reactions here on earth at much higher temperatures so that the reaction may proceed at a useful rate.

Richard Barrans


Assuming your temperatures are correct. I do not happen to know those numbers off the top of my head -- the big difference is that the pressure at the core of the sun is much greater than what can be obtained in a terrestrial lab, so it is reasonable that a higher temperature would be required. I suspect that there are astrophysical data available to quantify this but I do not have it at hand.

Vince Calder



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