Electrically charged iron and aluminum particles having diameters of a few microns have been contained in a confined region of space by means of alternating and static electric fields. The theory is essentially that of alternating gradient focusing; here the motion is governed by Mathieu's equation. Under certain circumstances when many particles are confined the three dimensional focusing force and the Coulomb repulsion results in a "crystaline" array which can be "melted" and reformed.

By electrostatic methods, μ-diam spheres of iron have been accelerated to hypervelocities. Techniques have been developed to give single impacts in vacuum of measured incident velocity, mass, and position.

We report the successful generation and detection of ELF waves in the frequency range of 6-76 Hz by polar electrojet modification using the High-Power Auroral Stimulation (HIPAS) HF Heater Facility near Fairbanks, Alaska. Magnetic field amplitudes of-1 pT and vertical electric field amplitudes of---0.2 mV have been observed at a receiving site 35 km from the HIPAS site. The wave amplitude does not depend strongly on the ELF frequency, however, the amplitude is closely related to the level of electrojet activity inferred from magnetometer chain data and from ionosonde measurements. The 1-MW HF heater is modulated at low ELF frequencies using an "array dephasing" technique where the eight-element antenna array is alternately phased for peak vertical gain and dephased for a spread pattern at the ELF rate. This method can be employed at any modulation frequency without concern for transmitter power supply resonances. Measurements of the wave amplitude are made by conventional analog lock-in techniques and by continuously digitizing the waveform output of the wideband magnetic search coils and the electric field detector. With the digitized waveform, digital postprocessing can be used to extract the low-level coherent signal from the Schumann resonance noise background using a software lock-in routine.Paper number 90RS00041. 0048-6604/90/90RS-00041 $08.00 ionosphere and magnetosphere and into the oceans and the Earth's crust. Previous ELF measurementsat the HIPAS facility were concentrated in the range of 1-5 kHz [Ferraro and Li, this issue]. An extensive data set has been collected in this band, and a wide variety of parametric variations have been investigated.

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High-beta, hot-electron plasmas have been produced by electron-cyclotron heating in the SM-1 axisymmetric mirror using closely-spaced multiple frequencies. The relativistic electrons produce annular distributions (ELMO rings) with as much as ten times more stored energy than with single-frequency heating. While larger frequency separations (Δf/f∼0.1) provide some control of the ring size, the dominant effects are associated with an improvement in heating efficiency which persists to very small frequency separations (Δf/f∼10−3). Details of the reconstruction of the ring distribution (both in steady state and during build-up), the influence of multiple frequency heating on fluctuations, axial electron losses, and a scaling of these effects with power are presented.