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This paper considers the use of a spherical array of sources producing a large fast-transient electromagnetic wave near the center of a sphere. For comparison, a lens type of implosion impulse radiating antenna (IRA) is included as an appendix. This complements the prolate-spheroidal focusing-reflector type of IRA, which has been already appearing in journal papers. Index Terms--Array, electromagnetic implosion, focusing, lens, time domain.

The interaction of the fast cyclotron wave of a linear electron beam guided by a magnetic field with a counter-propagating electromagnetic wave leads to the appearance of a stop-band over a wide range of the magnetic field near its resonance. Suppression of generation in backward wave oscillators and the resonant-cyclotron method of mode selection are based on this effect, termed 'cyclotron absorption.' In this paper, we analyze the possibility of controlling regenerative amplification in such oscillators as a traveling wave tube (TWT) by suppressing parasitic feedback using the guide magnetic field in the region of cyclotron absorption (RCA). Approaching the magnetic field to values that border this region, which contain thresholds of self-excitation, leads to a decrease in suppression of the reflected wave that is responsible for the positive feedback; in other words, this leads to an increase in gain. We illustrate amplification in the RCA using two approaches: the theory of stationary operation of a TWT accounting for the cyclotron resonance of electrons with a reflected wave, and particle-in-cell computer simulations. Index Terms--Cherenkov and cyclotron interactions, cyclotron absorption, cyclotron waves, positive feedback, regenerative amplification, traveling wave tube.

We report on the results of experimental investigations of plasma discharges in air during which red Flashes similar to those arising in the upper layers of atmosphere have been observed. In addition, it was shown that under the influence of acoustic waves in the atmosphere, a response in the form of visible radiation was brought about, and pulsed electromagnetic waves were generated. Index Terms--Acoustic waves, discharge, superluminescence Rydberg levels.

A high-current helicon ion source has been developed for neutron generator application. High-density plasmas with high electron temperatures are generated by launching helicon waves with a half-helical antenna in various magnetic field configurations. Helicon plasmas with high power efficiency are favorable in building ion sources with high current density and high monatomic ion beam fraction that are required for compact neutron generators. A maximum hydrogen beam current of 50 mA is extracted at 34 kV from the helicon plasma source with 1.9-kW RF power at 13.56 MHz. High current densities of 212 mA/[cm.sup.2] and high atomic fractions of up to 94% are achieved with this source. These measured beam parameters are mostly consistent with plasma parameters, except for unusually high monatomic beam fraction, which may be due to the existence of energetic electrons in helicon plasmas. Index Terms--Helicon plasma, ion sources, neutron sources.

The linear and nonlinear theory of a plasma-filled relativistic Cerenkov generator with coaxial slow-wave structure (SWS) is developed. Linear analysis includes the space-charge limiting current, dispersion relations, dispersion curves, and coupling impedance. In nonlinear theory, the electron beam space-charge effect, nonsynchronous interaction, and complex reflection coefficients of the electromagnetic wave at the boundaries of the SWS are taken into account. With the assumption of quasi steady state, the self-consistent equations are numerically calculated using the fourth-order Runga-Kutta method. The effects of the relative phase between inner and outer corrugations, phase and amplitude of the complex reflection coefficient at the boundaries of the SWS, and plasma density on device efficiency are discussed. Efficiencies of up to 37% without plasma and about 50% with plasma density of [n.sub.p] = 3-7 x [10.sup.11] [cm.sup.- 3] are obtained. Index Terms--Cerenkov radiation, coaxial slow-wave structure (SWS), dispersion curves, high-power microwave (HPM), nonlinear theory, plasma fill.

The excitation of nonmonochromatic signals by source current and their longitudinal propagation in an inhomogeneous magnetoplasma is studied. Three types of excitation source current are considered for the study. The inhomogeneity of magneto-ionic medium is taken with respect to the variation in plasma density and strength of the magnetic field. The effect of interparticle collisions on the amplitude of the signal is studied. Properties of the excited signals are discussed in different frequency ranges in terms of charge per unit length of the excitation source and the distance of propagation of the signal. Index Terms--Current source, Laplace transforms, left circularly polarized (LCP) mode, magnetoplasma, right circularly polarized (RCP) mode.

Laser-induced-fluorescence (LIF) measurements, with 1-ms resolution, of the temporal evolution of the argon-ion velocity distribution function in the expansion region of a pulsed helicon plasma show two ion populations 19 cm downstream of the helicon source: a slow population that forms as soon as the 200-ms-long discharge is created and persists for few milliseconds after the RF pulse terminates and a fast population whose LIF signature appears ~28 ms after the RF pulse begins. Index Terms--Electric double layer, helicon plasma, ion beam, ion velocity distribution function, time-resolved laser induced fluorescence.

A highly nonlinear whistler wave packet has been generated in a large laboratory plasma. The wave field exceeds the ambient field, locally reverses its direction and exhibits a topology of a spheromak. It propagates along the ambient magnetic field at a speed that decreases with amplitude. Electrons are strongly energized in the spheromak. Anisotropies create whistler instabilities. The whistler spheromak becomes a propagating source for secondary whistlers, a new phenomenon in magnetic turbulence. Index Terms--Antenna radiation patterns, electromagnetic propagation in plasma media, nonlinear wave propagation, plasma instabilities.

We show images of propagation spectrograms based on spacecraft observations of electromagnetic radiation of lightning strokes. We use multicomponent data of the DEMETER spacecraft, and we match observations of fractional-hop whistler signals with the source lightning strokes in the Mediterranean region. We perform multidimensional analysis of the spacecraft data, and we obtain detailed information on wave polarization characteristics and propagation directions. Index Terms--DEMETER microsatellite, fractional-hop whistlers, ionospheric wave propagation, lightning induced whistlers, multicomponent wave measurements.