The BLACKBEARD payload aboard the ALEXIS satellite has been making broadband observations in the VHF band of the radio spectrum. Since November of 1993 several hundred unusual signals have been recorded. The peculiar nature of these bursts of radio noise is that they have a duration of approximately 10 µsec, are typically 20 to 40 dB brighter than the average background, and occur in pairs separated by approximately 50 µsec. We have dubbed these emissions TransIonospheric Pulse Pairs, or TIPP events. We do not know what the source of these emissions is, but the dispersion of these signals is consistent with an origin at or near the earth's surface. The satellite field of view and time of day when TIPP events are generally detected are consistent with regions of thunderstorm activity such as south‐central Africa or Indonesia.

The edge plasma of the ZT-40M [Fusion Technol. 8, 1571 (1985)] reversed-field pinch has been studied using a combination of three different plasma probes: a double-swept Langmuir probe, an electrostatic energy analyzer, and a calorimeter–Langmuir probe. The edge plasma has been measured both with and without a movable graphite tile limiter present nearby in the plasma. Without a limiter a fast nonthermal tail of electrons (T≂350 eV) is detected in the edge plasma with nearly unidirectional flow along B and having a density between 2% and 10% of the cold edge plasma (T≂20 eV). The toroidal sense of this fast electron flow is against the force of the applied electric field. A large power flux along B is measured flowing in the same direction as the fast electrons and is apparently carried by the fast electrons. With the limiter present the fast electrons are still detected in the plasma, but are strongly attenuated in the shadow of the limiter. The measured scrape-off lengths for both the fast electrons and the cold plasma indicate cross-field transport at the rate of, or less than, Bohm diffusion. Estimates indicate that the fast electrons could carry the reversed-field pinch current density at the edge and, from the measured transverse diffusion rates, could also account for the electron energy loss channel in ZT-40 M. The long mean-free-path kinetic nature of these fast electrons suggests that a kinetic process, rather than a magnetohydrodynamic process that is based upon a local Ohm’s law formulation, is responsible for their generation.

Edge fluctuations are characterized and their associated transport is determined from Langmuir probe measurements in the ZT-40M reversed field pinch. It is found that the fluctuations have high normalized amplitudes and |ñ|/n = 0.4). There are significant contributions from magnetic perturbations acting on the equilibrium gradients. Compared to the global estimates, the fluctuation driven particle flux is large, whereas the corresponding electron energy flux is not. In the limiter shadow, the equilibrium density and electron temperature scale lengths are shorter and the fluctuation levels are higher. The fluctuation driven particle flux in the limiter shadow is 60% less than that in the plasma edge; most of the reduction is in the low frequency spectral region, which is where global MHD magnetic fluctuations are strongest.

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The different startup modes of a reversed-field pinch (RFP) are examined and compared. The RFP startup is not the same as startup of other toroidal devices such as the tokamak because of the spatial and temporal variations of the toroidal field and the reversed toroidal field in the outer region of the pinch near the wall. In matched mode startup, used in many RFP experiments today, the toroidal flux is held constant during the current rise, with the field reversal occurring before the peak current. This mode, with its short rise time, has a low volt-second (V⋅s) input but requires a high toroidal voltage to reach a specific current in a relatively short time. In a ramped current mode, alow current RFP discharge is ramped to its final peak value. The toroidal flux needed as the current rises is generated by a dynamo action. This slower startup mode can be driven by a lower voltage but requires more V⋅s input than the matched mode. Different startup modes in the ZT-40M experiment at Los Alamos are compared and an analytic expression is given for characterizing the V⋅s contributions. The resistive component of the toroidal loop voltage during the current rise in ramped discharges is found to depend on theta (Θ = Bpol(wall)/Bϕave)- At a theta of ≅ 1.45, the resistive voltage has a minimum and it has been possible to reduce the V⋅s input by as much as 40% in ramp discharges by keeping theta close to this value.