Gravitationsdrift

Gravitationsdrift, or gravitational drift, is a drift motion of charged particles in a magnetized plasma produced by a constant external gravitational force. For a particle of mass m and charge q in a magnetic field B and a gravitational acceleration g, the drift velocity is v_g = (m g × B) / (q B^2). This expression describes the average, steady motion of the guiding center of the particle, neglecting collisions and other forces.

The drift is perpendicular to both gravity and the magnetic field; its magnitude depends on the particle’s mass-to-charge ratio and on the orientation of g relative to B. When gravity is perpendicular to B, the magnitude simplifies to |v_g| = m g /(q B). Electrons and ions experience opposite drifts due to their opposite charges, and heavier species (larger m/q) drift more strongly for a given B and g. In practice, gravitational drift is often small for light electrons in typical laboratory or planetary magnetic fields but can become relevant for heavy ions or charged dust.

Gravitational drift has applications in space and astrophysical plasmas, including ionospheres, accretion disks, and dusty plasmas, where gravity can contribute to vertical stratification and subtle charge separation. However, in many environments it is subdominant compared with other drifts such as E×B, grad-B, or curvature drifts, and with pressure-gradient effects. Realistic plasmas may require considering nonuniform fields, collisions, and additional forces that modify or compete with the simple drift formula.