Experimental results are presented which show that r.f. power at frequencies near the lower hybrid frequency couples resonantly into a standing whistler wave. For an input power flux of less than 5 W densities above 10" cm-3 with close to 100% ionization have been achieved. Measured density, temperatures and wave fields are presented and are used as input parameters for a theoretical model.

A simple two‐dimensional model of the magnetosphere‐ionosphere system is discussed in which a localized electromotive force applied across a magnetic field line at t=0 is shown to propagate along the magnetic field with the Alfvén velocity. The perpendicular electric field is assumed to reverse direction across the field line. Since the perpendicular electric field is limited in space, the propagation involves parallel electric fields whose magnitude depends on the characteristic scale length of the applied emf and the local plasma parameters. The electric field pulse associated with the ‘shock’ front is reflected at the ionosphere and propagates back to the source region. The finite Pedersen conductivity in the ionosphere damps the wave, and a steady state current system is established in the order of several hours. The parallel electric field can accelerate ions and electrons.

An electric double-layer is generated near the open end of a high-density low pressure helicon sustained radio frequency (13.56 MHz) plasma source which expands into a diffusion chamber. Ion energy distribution functions measured with a retarding field energy analyzer placed in the diffusion chamber with its aperture facing the double-layer show the presence of a low energy peak (∼29 V) around the local plasma potential and a high energy peak (∼47 V) corresponding to a supersonic ion beam (∼2.1cs). At an axial distance 12 cm downstream of the double-layer, the beam density is 14% of the local density at that position and the ion energy gain is approximately 70% of the potential drop of the double-layer. The ion beam is observed from the center out to a radius corresponding to that of the plasma source tube (−6.8 cm⩽r⩽+6.8 cm) and is not greatly affected by the expanding magnetic field. A depression in the total ion flux just downstream of the double-layer—previously measured on the main z-axis of the reactor—is also present across the chamber diameter. Evidence of an electron beam near the closed end of the source tube, generated via “backwards” acceleration through the double-layer, has been observed on a Langmuir probe trace.

The axial force imparted from a magnetically expanding current-free plasma is directly measured for three different experimental configurations and compared with a two-dimensional fluid theory. The force component solely resulting from the expanding field is directly measured and identified as an axial force produced by the azimuthal current due to an electron diamagnetic drift and the radial component of the magnetic field. The experimentally measured forces are well described by the theory.

We compute the flux of positive ions exiting a low-pressure, planar, electronegative discharge as a function of the negative ion concentration and temperature. The positive ions are modelled as a cold, collisionless fluid, while both the electron and negative ion densities obey Boltzmann relations. For the plasma approximation, the plasma edge potential is double-valued when the negative ions are sufficiently cold. When strict charge neutrality is relaxed, spatial space-charge oscillations are observed at the edge of the plasma when the flux associated with the low (in absolute value) potential solution is less than that of the high potential solution. However, the flux is always well defined and varies continuously with the negative ion concentration. We demonstrate that the correct solution for the plasma approximation is that having the greater flux.

Experimental measurements taken in a large magnetoplasma show that a simple double half-turn antenna will excite mϭ1 helicon waves with wavelengths from 10-60 cm. Increased ionization in the center of the downstream plasma is measured when the axial wavelength of the helicon wave becomes less than the characteristic length of the system, typically 50-100 cm. A sharp maximum in the plasma density downstream from the source is measured for a magnetic field of 50 G, where the helicon wave phase velocity is about 3ϫ10 8 cm s Ϫ1 . Transport of energy away from the source to the downstream region must occur to create the hot electrons needed for the increased ionization. A simple model shows that electrons in a Maxwellian distribution most likely to ionize for these experimental conditions also have a velocity of around 3ϫ10 8 cm s Ϫ1 . This strong correlation suggests that the helicon wave is trapping electrons in the Maxwellian distribution with velocities somewhat slower than the wave and accelerating them into a quasibeam with velocity somewhat faster than the wave. The nonlinear increase in central density downstream as the power is increased for helicon waves with phase velocities close to the optimum electron velocity for ionization lends support to this idea.

Vector-rf-B-field measurements in the near-field of a helicon plasma source taken throughout the volume of the source are reported. Three distinct modes of operation of the helicon plasma source, capacitive, inductive, and helicon-wave, are identified by the structure of the plasma-wave-fields. Results are reported for a double-half-turn antenna, which is believed to be the first reporting for such an antenna structure in application to helicon-wave plasma sources. Comparison is made to a double-saddle-coil antenna which also demonstrates the distinct inductive and helicon-wave modes.

With nonperturbative laser-induced fluorescence measurements of ion flow, we confirm numerical simulations of spontaneous electric double-layer (DL) formation in a current-free expanding plasma. Measurements in two different experiments confirm that the DL is localized to the region of rapidly diverging magnetic field. The measurements indicate that the trapped ion population is a single Maxwellian, that the spatial gradient of the energy of ions accelerated through the DL matches the magnetic field gradient, and that DL formation is triggered when the ion-neutral collisional mean-free path exceeds the magnetic field gradient scale length.