Hydromagnetic waves and the trapped radiation: 1. Breakdown of the adiabatic invariance

The magnetic moment of a charged particle traveling through a hydromagnetic wave does not remain constant. The motion through small, static, transverse perturbations of a uniform magnetic field is calculated. The changes of the magnetic moment are not random. They depend strongly on the number of wavelengths traversed by the particle during one Larmor period and on the pitch angle of the gyration. For sinusoidal waves a resonant decrease of the nioment may oocur when the particle traverses 0.5 wavelength per Larmor period. For sufficiently peaked waves the moment generally decreases if the particle traverses less than about 0.3 wavelength per Larmor period. (auth)