Average Electric Field Strength Research Articles

Magnetospheric electric field measurements with balloons

Two balloons have been flown from Fort Churchill, Canada, in August 1968 to measure horizontal and vertical electric fields. It is shown theoretically and experimentally that horizontal upper atmospheric electric fields are generally equal to one-second, several hundred kilometer averages of the horizontal ionospheric electric field. Analyses of thirty-five hours of data obtained during quiet and active periods yield the following conclusions. The average equatorial electric field strength was 0.6 mv/m during a quiet period and 1.0 mv/m during an active period. During magnetic bays, ground-based magnetometers principally measured Hall currents whose variations depended on conductivity changes as much or more than on electric field variations. For a period of about 30 minutes before the onset of a negative bay near local midnight, the ionospheric electric field pointed westward, indicating radially inward flow in the equatorial plane. This result is interpreted in terms of a model of the magnetospheric substorm in which bays are triggered deep within the magnetosphere by an instability associated with a radial plasma density gradient established by convective flow. The average electric field in the dayside ionosphere was about an order of magnitude smaller than that at night, suggesting that the dayside magnetosphere tended to corotate with the earth. Equipotential contours of the electric field in the equatorial plane are constructed based on this and other hypotheses.

Gigahertz Radiation from Magnetic-Field-Free Electron-Hole Plasmas

This work shows that gigahertz radiation is emitted from electron-hole plasmas in $p\ensuremath{-}\mathrm{I}\mathrm{n}\mathrm{S}\mathrm{b}$ at 77\ifmmode^\circ\else\textdegree\fi{}K whose only external influence is an applied voltage. In order to satisfy the conditions for radiation, the plasma must have a conductance which falls within a limited range. The appropriate plasma conductances require unusually high average electric field strengths $E$ with attendant low average current densities $J$ near threshold, or large $J$ above threshold. The area of the $J\ensuremath{-}E$ plane associated with radiation is accessible only with plasmas produced in high-quality InSb. More conductance conditions necessary for radiation become accessible by applying a staircase voltage function instead of the usual square wave, because plasma is accumulated from step to step. Some properties of the radiation are described, such as its extreme sensitivity to plasma conductance, its decay characteristics, and a possible correlation between radiation amplitude and current level. The radiation observed at current levels which are far above its current threshold occurs during plasma pinching with two orders of magnitude more plasma current flowing than flows near threshold, namely \ensuremath{\sim}2 A instead of \ensuremath{\sim}20 mA. A further extension of accessible conductance conditions that are suitable for producing radiation, particularly an extension to higher electric field strengths at low current densities, is obtained by application of magnetic field strengths of a few hundred gauss. Many data obtained by fulfilling the necessary condition for radiation, namely, the appropriate range of plasma conductance, are summarized. Evidence that this is not a sufficient condition when the plasma conductance is "tuned" by means of a magnetic field is discussed.

Pulse-height Defects in Semiconductor Detectors for Fission Fragments

Measurements have been done of the response of surface-barrier detectors to fission fragments as a function of the bias voltage applied to the detectors. It is found that the reciprocal of pulse height decreases linearly with decrease of the reciprocal of average electric field strength within the depletion region. In accordance with such saturation characteristics, the pulse height defect for fission fragments is shown to decrease approximately linearly with decrease of the reciprocal of the electric field. By extrapolation of the linear relation to the infinite field strength, the pulse height defect for each group of light and heavy fragments is separated into field-dependent and field-independent components. The defect obtained at a finite field strength is a few MeV greater for heavy fragments than for light ones, and this difference comes mainly from the field-independent component. The field-independent defect seems to be smaller than the ionization defect in gas. Possible causes of the pulse height defect are discussed.

Multiplication Phenomenon for Fission Fragment Response in Semiconductor Detectors

A multiplication phenomenon caused by fission fragments has been observed in 300 Ω-cm gold surface barrier detectors when operated at bias voltages greater than 100 V. This phenomenon occurs only for fission fragments that penetrate beyond some threshold depth for multiplication, and the threshold depth is found to decrease with increasing bias voltage. However, the effect could also be due to the surface properties of the detector making the depth correlation fortuitous. An analysis in terms of a threshold depth indicates that the multiplication may be due to a hole rather than an electron effect. No multiplication was observed for alpha particles with the same electric fields. P-n diffused junction detectors operated at similar average electric field strengths did not show any multiplication effects.

Response of Semiconductor Detectors to Fission Fragments

Measurements with a Cf252 spontaneous fission source have shown that semiconductor detectors exhibit a pulse-height defect for fission fragments, and that this defect is greater for the low-energy, heavy-mass group than for the high-energy, light-mass group. It has also been shown that the defect decreases with increasing bias voltage or average electric field strength within the depletion region. However, for a given electric field strength, the defect was found to be approximately independent of the type and resistivity of the detector. These results are consistent with the hypothesis that the pulse-height defect arises from an inability to collect all of the hole-electron pairs in the dense plasma produced by an energetic fission fragment.