Magnetocentrifugal acceleration of plasma in a nonaxisymmetric magnetosphere

Moscow Engineering Physics Institute, Kashirskoje Shosse 31, Moscow 115409, Russia e-mail: bogoval@axpk40.mephi.ru

Received: 28 January 2000
Accepted: 3 November 2000

Abstract

Violation of the axial symmetry of a magnetic field essentially modifies the physics of the plasma outflow in the magnetosphere of rotating objects. In comparison to the axisymmetric outflow, two new effects appear: more efficient magnetocentrifugal acceleration of the plasma along particular field lines and generation of MHD waves. Here, we use an ideal MHD approximation to study the dynamics of a cold wind in the nonaxisymmetric magnetosphere. We obtain a self-consistent analytical solution of the problem of cold plasma outflow from a slowly rotating star with a slightly nonaxisymmetric magnetic field using perturbation theory. In the axisymmetric (monopole-like) magnetic field, the first term in the expansion of the terminating energy of the plasma in powers of Ω is proportional to , where Ω is the angular velocity of the central source. Violation of the axial symmetry of the magnetic field crucially changes this dependence. The first correction to the energy of the plasma becomes proportional to Ω. Efficient magnetocentrifugal acceleration occurs along the field lines curved initially in the direction of the rotation. I argue that all the necessary conditions for the efficient magnetocentrifugal acceleration of the plasma exist in the radio pulsar magnetosphere. We calculated the first correction of the rotational losses due to the generation of the MHD waves and analysed the plasma acceleration by these waves.