Gyrocenter-gauge kinetic theory

Gyrocenter-gauge kinetic theory is developed as an extension of the existin g gyrokinetic theories. In essence, the formalism introduced here is a kine tic description of magnetized plasmas in the gyrocenter coordinates which i s fully equivalent to the Vlasov-Maxwell system in the particle coordinates . In particular, provided the gyroradius is smaller than the scale-length o f the magnetic field, it can treat high-frequency range as well as the usua l low-frequency range normally associated with gyrokinetic approaches. A si gnificant advantage of this formalism is that it enables the direct particl e-in-cell simulations of compressional Alfven waves for magnetohydrodynamic (MHD) applications and of rf (radio frequency) waves relevant to plasma he ating in space and laboratory plasmas. The gyrocenter-gauge kinetic suscept ibility for arbitrary wavelength and arbitrary frequency electromagnetic pe rturbations in a homogeneous magnetized plasma is shown to recover exactly the classical result obtained by integrating the Vlasov-Maxwell system in t he particle coordinates. This demonstrates that all the waves supported by the Vlasov-Maxwell system can be studied using the gyrocenter-gauge kinetic model in the gyrocenter coordinates. This theoretical approach is so named to distinguish it from the existing gyrokinetic theory, which has been suc cessfully developed and applied to many important low-frequency and long pa rallel wavelength problems, where the conventional meaning of "gyrokinetic" has been standardized. Besides the usual gyrokinetic distribution function , the gyrocenter-gauge kinetic theory emphasizes as well the gyrocenter-gau ge distribution function, which sometimes contains all the physics of the p roblems being studied, and whose importance has not been realized previousl y. The gyrocenter-gauge distribution function enters Maxwell's equations th rough the pull-back transformation of the gyrocenter transformation, which depends on the perturbed fields. The efficacy of the gyrocenter-gauge kinet ic approach is largely due to the fact that it directly decouples particle' s gyromotion from its gyrocenter motion in the gyrocenter coordinates. As i n the case of kinetic theories using guiding center coordinates, obtaining solutions for this kinetic system involves only following particles along t heir gyrocenter orbits. However, an added advantage here is that unlike the guiding center formalism, the gyrocenter coordinates used in this theory i nvolves both the equilibrium and the perturbed components of the electromag netic field. In terms of solving the kinetic system using particle simulati on methods, the gyrocenter-gauge kinetic approach enables the reduction of computational complexity without the loss of important physical content. (C ) 2000 American Institute of Physics. [S1070-664X(00)00511-5].