Hi, I'm wondering why charged particles stay trapped in a magnetic. Assume the magnetic bottle is oriented in the x-direction. Then a particle will keep oscillating in the x-direction while making circle movements in the y- and z-direction. But why does it oscillate in the x-direction? Since the magnetic force does no work on a particle because it is always directed perpendicular to the velocity, the kinetic force of the particle stays constant. When oscillating, there must be some point where the speed in the x-direction is zero, which means that the kinetic energy must change. How is that possible? I suppose the magnetic force alone can't be responsible for the oscillation? Thank you.