Thermodynamics of two-dimensional plasmas or discrete line vortex fluids
The equilibrium properties of a two-dimensional plasma are examined theoretically within the framework of the random-phase approximation. The guiding-center case is of most interest because of the formal equivalence to two-dimensional discrete-line vortex fluids and because of the formal admissibility of negative temperatures. Using a judicious treatment of the periodic boundary conditions, extensive thermodynamics for nonnegative temperatures and a new value for the energy at which the temperature becomes negative are found. An explicit form for the structure function is derived and compared with the result of a Monte Carlo calculation. Good agreement is found for the negative-temperature-threshold prediction and for the general shape of the structure function. An equilibrium energy spectrum is calculated, which for positive temperatures, is the Debye-Hueckel result; for negative temperatures, it predicts an enhanced excitation of the lowest mode, corresponding to macroscopic charge separation.