By using Clebsch representations for all necessary vector fields, an action principle for a compressible, inviscid, one-component magneto-fluid, undergoing isentropic motion in an electromagnetic field, is given.
lntroductionThere are many papers regarding the derivation of the equations ofmagnetofluid dynamics from an action principle. One of the first and most important problems arising in such derivations is the construction of a Lagrangian density, suitable for the considered magnetofluid model.Regardless of the particular tases which are under discussion, there exist certain rules (or procedures) used in the derivation of the set of equations describing the behaviour of the magnetofluid system. One of tbese rules says that the electromagnetic field E, Bis expressed in terms ofeither the well-known potentials A, 9 [e.g. [1][2][3][4][5][6][7] or the so called "generalized antipotentials" [8]. On the other hand, the fluid velocity field vis usually represented in terms of a set of Clebsch potentials, and an interaction termas well. Both electromagnetic and Clebsch potentials are taken as variational parameters. But we should mention that this procedure is not compulsory: the Clebsch representation of the velocity field can be obtained asa result of the variation.The main purpose of the present paper is to give a variational principle for an inviscid, conducting fluid, and show that the representation of all vector fields in terms of Clebsch potentials is not only a possible, but also a useful method in the Lagrangian approach of magnetofluid dynamics.
Construction of the Lagrangian densityLet our model of magnetofluid be an inviscid, one-component, compressible fluid, which undergoes isentropic motion in the electromagnetic field E, B. Ifwe denote by p and pe the mass and charge densities, and suppose that the particle number density Acta Physica Hungarica 54, 1983