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Consider you have a plasma, and then you use a laser to heat it so that the part of the plasma that the laser went through is heated to 150 million degrees. The rest of the plasma temperature is not altered drastically. I was wonder if a maxwellian boltzmann distribution will appear. Since, the particles have extremely high kinetic energies, almost all collisions will result in fusion. For a plasma to resort to the maxwell boltzmann distribution, elastic collisions need to take place. But since, in this case almost all collisions result in fusion, do elastic collisions even happen? I know that helium would be produced and then it will resort to the distribution, but that is not what I am interested in. Do elastic collisions even happen if a part of the plasma is almost instantaneously heated or If a high energy particle beam hit the dense plasma?

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  • $\begingroup$ Coulomb collisions are elastic and those certainly occur. If you have really high energies, then there will be bremsstrahlung radiation and I am not sure whether that would be treated as elastic or inelastic... $\endgroup$ – honeste_vivere Mar 12 '17 at 17:06
  • $\begingroup$ But why do elastic collisions happen? Do they happen because of the particle that didn't fuse? Since, the probability of fusion is kind of small (0.00048) from the Gamows factor? $\endgroup$ – Chandrahas Mar 13 '17 at 9:19
  • $\begingroup$ Can the particles get close such that they can participate in elastic collisions but not fuse? $\endgroup$ – Chandrahas Mar 13 '17 at 9:21
  • $\begingroup$ How close are the particles supposed to get for a coulomb collision to take place? $\endgroup$ – Chandrahas Mar 13 '17 at 9:22
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    $\begingroup$ Yep, look up the Spitzer-Härm collision rate to get an approximation based upon 90 degree deflections. There are more accurate estimates that take into account small-angle collisions but that gets rather complicated very quickly. $\endgroup$ – honeste_vivere Mar 14 '17 at 15:46
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There is one major misunderstanding in your question: even if you heat up the plasma to very high temperatures, elastic collisions are still more likely to occur than fusion reactions.

For more details on how the collision cross section scales as compared to the fusion cross section, check my answer on one of your other questions (this answer is also related).

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