On some properties of the Landau kinetic equation

We discuss some general properties of the Landau kinetic equation. In particular, the difference between the ”true” Landau equation, which formally follows from classical mechanics, and the ”generalized” Landau equation, which is just an interesting mathematical object, is stressed. We show how to approximate solutions to the Landau equation by the Wild sums. It is the so-called quasi-Maxwellian approximation related to Monte Carlo methods. This approximation can be also useful for mathematical problems. A model equation which can be reduced to a local nonlinear parabolic equation is also constructed in connection with existence of the strong solution to the initial value problem. A self-similar asymptotic solution to the Landau equation for large v and t is discussed in detail. The solution, earlier confirmed by numerical experiments, describes a formation of Maxwellian tails for a wide class of initial data concentrated in the thermal domain. It is shown that the corresponding rate of relaxation (fractional exponential function) is in exact agreement with recent mathematically rigorous estimates. A.V. Bobylev Keldysh Institute for Applied Mathematics, RAS, Moscow, Russian Federation Tel.: +7-499-9781314 Fax: +7-499-9720737 E-mail: [email protected] I.M. Gamba ICES, University of Texas at Austin, Austin, Texas, USA Tel.: +1-512-4713312 Fax: +1-512-4718694 E-mail: [email protected] I.F. Potapenko Keldysh Institute for Applied Mathematics, RAS, Moscow, Russian Federation Tel.: +7-499-9781314 Fax: +7-499-9720737 E-mail: [email protected]