Breaking of the first adiabatic invariants of charged particles in time-dependent magnetic fields: Computer simulations and theory
- Space Plasma Physics Group, Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (USA)
- Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242 (USA)
The mechanics of the first adiabatic invariant {mu} of nonrelativistic charged particles in time-dependent magnetic inductions {ital B}({ital t}) are studied by means of computer simulations and analytic theory. Linear-ramp magnetic-induction profiles {ital B}={ital B}{sub 0}+({Delta}{ital B}/{Delta}{ital t}){ital t} are utilized, as well as hyperbolic-tangent ramps and sine half-wave ramps. The change in {mu} that results from an induction change {Delta}{ital B} that occurs over a time {Delta}{ital t} is quantified for all values of {Delta}{ital B} and {Delta}{ital t}, as well as for all values of the particle position. It is found that the cases fall into two categories with very different {mu} behavior: cases in which the change in the magnetic induction occurs over a time {Delta}{ital t} that is {ital exactly} equal to an integer number of gyroperiods (textbook case) or cases in which the change in the induction occurs over a time {Delta}{ital t} that is not equal to an integer number of gyroperiods (more general case). In both categories {mu} is an adiabatic invariant, although the conservation of {mu} is much poorer in the latter category. It is pointed out that, in addition to the well-known constraints on {Delta}{ital B} and {Delta}{ital t}, there is a constraint on the particle's initial position in the magnetic field if the change in the adiabatic invariant is to be kept small.
- OSTI ID:
- 5589055
- Journal Information:
- Physical Review, A; (USA), Vol. 43:10; ISSN 1050-2947
- Country of Publication:
- United States
- Language:
- English
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