Betsy Ancker-Johnson

Bio: Betsy Ancker-Johnson is an academic researcher from Washington University in St. Louis. The author has contributed to research in topics: Pinch & Plasma. The author has an hindex of 6, co-authored 8 publications receiving 86 citations.

Properties of Injected Plasmas in Indium Antimonide

Abstract: Plasmas composed of injected electron-hole pairs in p-type indium antimonide were studied. The injection times were measured and pinching of the plasma was observed. The current-voltage curves show a steep rise at voltages well below those required for brenl;down, indicating a large increase in carrier density before breakdown. The Hall voltage measured as a function of current changed sign from that expected for hole transport to that expected for electron transport. Negative resistances were observed in the plasma in the presence of transverse magnetic fields. Longitudinal magnetic fields decreased the plasma density, probably because of an increased radial diffusion of the plasma to the surface. Coherent oscillations were observed on top of the pinch both with and without longitudinal fields, and their dependence on current and magnetic field is described. (auth)

Thermal Pinching in Electron-Hole Plasma

Abstract: A different kind of current pinching than the familiar Bennett pinch effect has been observed in the electron-hole plasma formed in InSb. The new type of pinching is controlled by temperature rather than pressure. It is initiated by the Bennett pinch effect but dominates conduction immediately after the onset of pinching. The necessary critical condition for the onset of this thermal pinch is that the power into the pinch channel less the heat conduction loss be greater than zero. The radii of eight pinch channels have been measured and found to be an order of magnitude smaller than previously thought (\ensuremath{\sim}2\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}3}$ cm). The density within the pinches exceeds ${10}^{18}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ and the plasma becomes hot enough to cause melting of the lattice within the channel (M.P.=808\ifmmode^\circ\else\textdegree\fi{}K).

Some Observations of Growing Oscillations in Electron-Hole Plasma

Abstract: Highly reproducible growing oscillations have been observed in electron- hole plasma produced by injection from current contacts into single-crystal p- type indium antimonide at 77 deg K. Two types of growing oscillations have been observed in different samples. In one type, the frequency is current controlled; in the other, the frequency is independent of current. Both occur in the absence of an applied magnetic field. The observed behavior of these oscillations is presented and discussed. (H.D.R.)

Hysteresis in Stability Conditions of Electron-Hole Plasma

Abstract: The investigation of the hysteresis occurring in the threshold conditions for the helical instability oscillations in electron-hole plasma has been extended. The hysteresis in electric field strength $E$ can exceed 45 V/cm and 50% of the applied $E$ at threshold. By determining the stability-instability boundary in the $p$-type InSb as a function of the parallel (or antiparallel) electric and magnetic field strengths and also the plasma density, the magnetic field induced by the formation of the helical density perturbation is deduced. Resulting displaced loop $B\ensuremath{-}H$ curves are presented. The magnitude of the induction enhancement ${B}_{\mathrm{hys}}$ can be as large as 165 Oe and 55% of the applied $B$ at threshold. The extent of applied magnetic field (or electric field strength) over which the loops can occur is limited at the high magnetic field end (typically \ensuremath{\le}600 G) by vanishingly small plasma density and at the other end (\ensuremath{\ge}280 G) by the occurrence of magnetic pinching. The loops are largest at the low magnetic field end. The range of loop energy, defined as the product of ${E}_{\mathrm{hys}}$ and ${B}_{\mathrm{hys}}$, increases with decreasing plasma cross-sectional area until saturation occurs at a plasma radius of \ensuremath{\sim}3\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}2}$ cm. The full range from largest to smallest loop in any one sample is achieved by a relatively small variation in the "input energies," i.e., the product of the magnetic and electric field strengths at threshold.

Some Plasma Effects in Semiconductors

Abstract: This is a review of some selected plasma effects in semiconductors, principally InSb at 77° K. The production of nonequilibrium electronhole plasmas by electrical injection and impact ionization is described including some instabilities which attend the latter process. Some new results on the pinch effect obtained by diagnosis with a 10.6 ? CW laser are shown. Observations of the manifestation of another instability, namely gigahertz radiation, not requiring an applied magnetic field are presented. A magnetic field is required to produce some instabilities in plasmas, among these are the helical instability. A bistable element resulting from an inherent hysteresis in the threshold conditions of this instability is described. Discontinuous changes in the plasma conductance can be produced by a magnetic field and the relation of this effect to high intensity microwave emission is outlined. Finally, some preliminary results on plasma decay are presented.

Volume-controlled current injection in insulators

Abstract: Current injection in insulators provides a valuable technique for obtaining such information about defect states in insulators as their density, their energetic location in the forbidden gap, and their cross sections for capture of free electrons and holes. It also enables determination of free carrier drift mobilities. The physical principles underlying one-carrier space-charge-limited current injection, both steady-state and transient, and steady-state, two-carrier, largely neutralized current injection are discussed. Experimental verifications of the different types of current injection are also discussed briefly.

Plasmas in Solids

Abstract: Publisher Summary This chapter examines the behavior of solids when they contain a collection of charges that satisfies the definition of plasma It is concerned primarily with metals, semimetals, and semiconductors The properties of a gaseous discharge containing gaseous plasma have been the subject of intensive study for many years During the past forty of these, the relevance of the plasma character to the observed behavior has become well established The study of plasma effects in solids has been much more recent, with much of the significant progress coming during the past decade It is thus natural that the plasma theory developed with gases in mind has led the way in the understanding of effects in solids What is striking is that the progress of experimental work on plasmas in solids has been very rapid This can be ascribed to the well-developed state of the plasma theory and to the ready availability of pure materials As a result, in some areas more precise tests of theory have been possible than in the case of gaseous plasmas, where the control over the experimental conditions is always difficult It thus appears that the study of plasmas in solids should prove fruitful both in providing well-controlled tests of plasma theory and in giving further knowledge of the properties of solids