Laboratory observations of ion cyclotron waves associated with a double layer in an inhomogeneous magnetic field

Abstract

Observations of coherent electrostatic ion cyclotron (EIC) waves associated with a strong, magnetized double layer are presented. The double layers are produced in a weakly ionized argon plasma by applying a positive potential to an electrode plate located in the diverging magnetic field region of a cylindrical plasma column. Ionization within the electrode sheath is essential to the formation of these double layers. The resulting V‐shaped potential structures have extended parallel, oblique and perpendicular (to B) electric field components. The frequency of the ion cyclotron instability is dependent upon the magnetic field strength at the position of the parallel potential structure. The properties of EIC waves in the presence of the double layer are discussed in relation to the possible excitation mechanisms (field‐aligned currents, ion and electron beams, and perpendicular E fields).

Time-resolved measurements of double layer evolution in expanding plasma

“…45͒ or with DLs created in divergent magnetic fields. 44 However, to the best of our knowledge, complete collapse of a DL correlated with the appearance of intense electrostatic instabilities has not been reported previously in a laboratory experiment. These results suggest that creation of strong DLs in expanding plasmas for plasma propulsion 48,49 may be self-limited through instability growth and also demonstrate a mechanism for the collapse of naturally occurring DLs.…”

“…43 Experimentally, ion cyclotron instabilities have been observed in TP device DL experiments in an inhomogeneous magnetic field. 44 For these waves, their axial propagation rules out drift waves as the source of the instabilities. The short parallel wavelength and multiharmonic excitation are inconsistent with the characteristics of the ionization instability observed in other DL experiments.…”

Anomalous transport in discrete arcs and simulation of double layers in a model auroral circuit

“…Other important consequences of the model are also in accord with satellite and rocket observations of DA's and laboratory DL experiments. These include: (1) the density in a DA is substantially depleted relative to the ambient density (Benson and Calvert, 1979;Alport et al, 1986); and (2) concomitant with the depletion of the arc is that the current is diverted to the flanks, so that the highest current density is at the edges (Bruning, 1983;Burke, 1984).…”

V-Shaped dc Potential Structure Caused by Current-Driven Electrostatic Ion-Cyclotron Instability

“…However, the steady state theory cannot answer the question how shock is created. Although many laboratory experiments [12,13] and numerical simulations [14,15] concerned with a V-shaped potential structure or an ion-cyclotron instability have been performed, noone succeeded in demonstrating that currentdriven electrostatic ion-cyclotron instability creates a Vshaped potential structure.With these situations in mind, we investigate development of a current-driven electrostatic ion-cyclotron instability and resulting dc potential structure with special attention on two-dimensional structure by means of a sophisticated particle simulation model.In our previous particle simulation [16], we observed a clear wave front pattern accompanied by the ion-cyclotron instability. In that simulation we used a periodic boundary condition for both particles and fields, namely, particles going out one boundary periodically enter the system from the other boundary.…”

“…However, the steady state theory cannot answer the question how shock is created. Although many laboratory experiments [12,13] and numerical simulations [14,15] concerned with a V-shaped potential structure or an ion-cyclotron instability have been performed, noone succeeded in demonstrating that currentdriven electrostatic ion-cyclotron instability creates a Vshaped potential structure.…”