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High energy density systems are quite hard to develop an intuition for. While average kinetic energy is one way to think about temperature, think about it instead in terms of the Maxwellian particle distribution [1]. In this sense, the Maxwellian is a parameter of this distribution, and as it increases, the location of the distribution changes. A high temperature corresponds to, in this hypothetical system, more particles with higher velocities in the system. (This technically only applies to certain systems in which the assumptions hold. For example, in systems in which other degrees of freedom matter, such as vibration/rotation of molecules, the interpretation is harder. At high temperatures, these degrees of freedom are destroyed, though others, like ionization, can matter significantly.) Of course, these systems are highly collisional, in the sense that each particle will probably go only a short distance before Coulomb scattering off another particle. So the particles are not really vibrating; the energy is in translational motion, but in the mean, there is no real directionality to it, so the particles won't typically stream out of the plasma. This can be readily understood in the context of achieving controlled fusion. Nuclei are positively charged, and therefore exert forces that tend to repel them away from other nuclei. The nuclear scale, at which nuclear reactions must occur, is very small, and the 1/r* Coulomb potential is quite large at those distances. As a result, it is to be expected that an individual fusion reaction should only occur when the kinetic energy of an incoming nucleus is sufficiently strong to overcome the Coulomb barrier. (Practically, quantum mechanics effectively reduces the barrier through tunneling, but nevertheless it is quite high.) As a result, you need a sufficiently large number of nuclei with high speed to have an appreciable fusion rate, i.e. your temperature must be high enough. (Hence, "thermonuclear" fusion.) This has to be contrasted with your confinement quality, in the sense that you have to keep your fuel at that temperature and at a sufficient density (so that your collision rate is high enough) long enough for fusion burn to consume an appreciable fraction of your fuel. In context, the temperature seems a simpler quantity to discuss rather than the pressure. It is easier to conceive of this pressure as a momentum flux, and in stars, gravitational confinement demands that the plasma pressure balance the crushing momentum flux of the weight of the star. Such static pressures are simply outside of our ability to intuit, and result in quite counterintuitive properties of matter. [1] https://en.wikipedia.org/wiki/Maxwell-Boltzmann_distribution *edit: inverse square is the force, the potential goes as 1/r... update for clarity. |