Nonresonant interaction of heavy ions with electromagnetic ion cyclotron waves
Abstract
The motion of a heavy ion in the presence of an intense ultralowfrequency electromagnetic wave propagating along the dc magnetic field is analyzed. Starting from the basic equations of motion and from their associated two invariants, the heavy ion velocityspace trajectories are drawn. It is shown that after a certain time, particles whose initial phase angles are randomly distributed tend to bunch together, provided that the wave intensity, b_{1} is sufficiently large. The maximum perpendicular velocity v_{a} which the particle reaches during the bunching process can be a fraction of the Alfvén velocity. When the wave frequency f is smaller than the heavy ion gyrofrequency, F, v_{a} is maximum for waves with frequencies slightly smaller than F. When the wave frequency is larger than the cutoff frequency f_{co}, f_{a} is a continuously decreasing function of f. In both cases, v_{a} is proportional to b_{1}/Ff when b_{1} is small and/or Ff is large, and it is proportional to (b_{1}/f)^{1/3} when b_{1} is larger and/or Ff is small. The process is nonresonant in the sense that it is efficient however small is the heavy ion initial parallel velocity. A parameter study is done which gives the process efficiency for different wave or particle characteristics. Approximate analytical expressions are given, and they are compared with the results of numerical computations. The importance of these results for the interpretation of the recently observed acceleration of He^{+} ions in conjunction with the occurrence of largeamplitude ion cyclotron waves in the equatorial magnetosphere is discussed.
 Publication:

Journal of Geophysical Research
 Pub Date:
 November 1985
 DOI:
 10.1029/JA090iA11p10945
 Bibcode:
 1985JGR....9010945B
 Keywords:

 Equatorial Atmosphere;
 Heavy Ions;
 Ion Cyclotron Radiation;
 Particle Acceleration;
 PlasmaElectromagnetic Interaction;
 Distribution Functions;
 Earth Magnetosphere;
 Helium Ions;
 Particle Trajectories;
 Geophysics