The collective gyration of a heavy ion cloud in a magnetized plasma

Abstract

In both the ionospheric barium injection experiments CRIT I and CRIT II, a long-duration oscillation was seen with a frequency close to the gyro frequency of barium and a time duration of about one second. A model for the phenomenon which was proposed for the CRIT I experiment is here compared to the results from CRIT 1I which made a much more complete set of measurements. The model follows the motion of a low -0 ion cloud through a larger ambient plasma. The internal field of the model is close to antiparallel to the injection direction v i but slightly tilted towards the self-polarization direction Ep = -v ixB. As the ions move across the magnetic field, the space charge is continuously neutralized by magnetic-field aligned electron currents from the ambient ionosphere, drawn by the divergent: in the perpendicular electric field.These currents give a perturbation of the magnetic field relatec to the electric field perturbation by AEIAB = VA . The model predictions agree quite well with the observed vector directions, field strengths, and decay times of the electric and magnetic fields in CRIT II. The possibility to extend the model to the active region, where the ions are produced in this type of self-ionizing injection experiments, is discussed.

Momentum and Energy Transfer in an Ionospheric Critical Ionization Velocity Experiment

“…The rate of change of the barium ion velocity is found from dvn, +/dt = iGy X B,~b~/mn, nn, . This gives the time constant for ion energy loss r~", = W/(dW/dt) = 0.01 s in burst 1, using parameters from [3]. This is definitely significant, since it is comparable to the time duration of the active region in burst 1.…”

“…parallel current component is expected already in the absence of CI I/' for an injected heavy ion cloud [2]. The current density can be directly estimated from the density increase measured inside the beam by the main payload as i Gx = nba + &pa, perp e. Using estimates of nba from [3], this gives io = 0.6 -1.3 mA/m in burst 1 and iG = 0.13 -0.22 mA/m in burst 2. For burst 2, these iG values agree we11 with the iG components in Fig.…”