J. E. Rowe

Experimental Investigation of the Low‐Voltage Arc in Noble Gases

An experimental investigation of the low‐voltage arc mode of the hot‐cathode discharge has been carried out in a diode utilizing planar electrode geometry. The investigation consisted predominantly of Langmuir‐probe measurements of the discharge in a neon atmosphere. Measurements were also obtained in argon, xenon, and hydrogen and hydrogen‐neon and argon‐neon mixtures. The probes were of planar, guard‐ringed geometry. The volt‐ampere characteristic of the hot‐cathode discharge in the Torr range of gas pressure was investigated to further define the low‐voltage arc. For ample electron emission at the cathode there are two stable high‐current, low‐voltage discharge modes that occur in the noble gases; these are termed the low‐voltage arc and the ball‐of‐fire modes of the hot‐cathode discharge. No low‐voltage discharge modes were obtained in hydrogen. The steady‐state characteristics obtained for the low‐voltage arc indicated peak plasma potentials of approximately 14, 6, and 4.5 V for neon, argon, and xeno...

Emission of Microwave Noise Radiation From InSb

Low‐field 10‐GHz noise radiation and attendant rf current oscillations are generated in 10‐mm‐long specimens of n‐type InSb at 77°K. Using a special experimental arrangement, both the azimuthal and the polar orientation of the applied magnetic field can be varied and the spatial distribution of the radiation along the length of the InSb specimen can also be measured. Two distinct modes of low‐field radiation are found in InSb specimens. One mode of radiation (B∥ mode) prevails when the magnetic field is aligned parallel to the direction of current flow and the other mode of radiation (B∥ mode) prevails when the magnetic field is aligned transverse to the direction of current flow. The B⊥ mode of radiation is investigated in considerable detail and it is determined that a reproducible anisotropic radiation pattern of twofold periodicity is obtained when a transverse magnetic field is rotated in the azimuthal plane around the InSb specimen. A computer analysis using a theory which incorporates an acoustoele...

Noise Transformation and Cyclotron Waves in Crossed Fields

A transmission‐line analog is developed for crossed‐field space‐charge flows from the simultaneous solution of Maxwells equations, the Lorentz force equation, and the continuity equation. A thin one‐dimensional injected beam is assumed. The resulting fifth‐degree secular equation is solved for several values of ωc/ωp. The five system waves consist of a pair of hybrid waves, a pair of near‐cyclotron waves and a near‐synchronous wave. The results indicate that noise transformers may be based on an equivalent piecewise uniform transmission line.

Monte Carlo Simulation of the Low‐Voltage Arc Mode in Plasma Diodes

A statistical simulation of the low‐voltage arc mode of plasma diodes is carried out on a large‐scale digital computer to ascertain the importance of various thermalization and transport mechanisms. The computer experiment is two‐dimensional and utilizes Monte Carlo techniques to study the low‐voltage arc in neon at p=2 Torr, current=4 A, and diode spacing=2.37 cm. Results on the potential distribution, electron‐density distribution, and electron‐energy density function are presented and discussed. The theoretical results are correlated with experimental results.

ENHANCEMENT OF PLASMA DENSITY IN AN ARC DISCHARGE.

The amplification or generation of coherent signals by electron‐beam—plasma interactions requires the creation of a high‐density stable plasma. A plasma density of approximately 1015 particles/cm3 is required to produce a plasma resonance frequency of 300 Gc/sec. The density in an arc‐discharge plasma has been increased using mechanical and magnetic constriction methods with the result that np=7.5×1014 particles/cm3 is realized at a discharge current of 4 A in argon. Double Langmuir probe measurements on density and temperature in the plasma are presented and interpreted for zero and finite magnetic‐field conditions.

Acoustoelectric Effects in Indium Antimonide

The acoustoelectric interaction in InSb is developed and investigated on the basis of a hydrodynamical theory. Comparison of numerical results obtained from this theory with the corresponding numerical results from more detailed microscopic theories reveals that the essential features of the microscopic theories are also present in the simpler hydrodynamical theory. In particular, the hydrodynamical theory accounts for the existence of two distinct modes of acoustic domain formation and for the reduction of peak acoustic gain at low values of magnetic field. Valuable insight into the physical basis of the acoustoelectric effect is obtained and it is shown that in the limit of large electron drift velocities and small transverse magnetic field strengths, the Mode I‐type acoustoelectric interaction arises from a drift‐enhanced quenching of electron diffusion effects. Moreover it is found that the frequency of maximum acoustoelectric gain, as given by the hydrodynamical theory of the present paper, does not ...

Experimental Characteristics of Crossed‐Field Space‐Charge Flows

An experimental method is described for determining the characteristics of space‐charge flow in crossed electric and magnetic fields. A beam‐intercepting system, which consists of a movable grid of wires biased at appropriate potentials, is inserted across the space‐charge flow. The currents intercepted by the wires provide a description of the beam profile at each cross section of the electron beam. Evaluation of the data indicated that in no case did the beam assume a scalloped configuration. In general, it was found that the entire beam undulates in a serpentine manner and has variable thickness throughout the region of interest. The experimental undulation is observed to be in good agreement with the theoretical cycloidal wavelength for electron motion in a crossed‐field environment. Calculations of space‐charge density indicate that the average value is generally between 0.5 and 1.5 times the Brillouin space‐charge density in each case.

Energy Mismatch and Cutoff Waves in a Two‐Dimensional Space‐Charge Flow

A general treatment of the input boundary value problem for two‐dimensional space‐charge flow is developed using a theory of electrostatics (Thomsons) which notes that in an electrostatic problem the electric field distribution is such that the electrostatic‐field energy is a minimum. This principle is used to determine the average energy density mismatch and the starting conditions for finite thickness beams in M‐type backward‐wave oscillators. It is shown that the mismatch is greatest for strong space‐charge fields, high‐circuit attenuation, and signal frequencies below the cyclotron frequency. The starting length and beam velocity are greater as calculated by the variational procedure than obtained by the approximate method. Under certain conditions the average energy density mismatch is greater than 20% of the electrostatic field energy in the absence of the beam.

New carrier‐heated electron‐hole instability in semiconductor plasmas

A study of the quasistatic hybrid mode in high‐electron‐mobility semiconductor plasmas subject to perpendicular static electric and magnetic fields shows that when carrier‐heating effects are fully taken into account an entirely new mode arises as a result of the carrier heating. This mode has properties suitable for readily generating the two‐stream instability and the interaction of this mode with hole‐cyclotron harmonics is much stronger than that of any unheated mode.

Focusing of a relativistic electron flow.

The trajectory differential equation governing the motion of relativistic electrons is derived in terms of the scalar and vector potentials of the system using the principle of least action. The conservation of energy and momentum are used to develop the paraxial‐ray differential equation describing the beam radius of a laminar‐flow relativistic electron beam. The focusing of the electron beam in drift and accelerating regions has been examined and the conditions for perfect balancing and nonspreading of a laminar‐flow drifting beam are also derived. It is shown that the equilibrium condition for Brillouin flow is that 2ωL2−ωp2[1 − (uz/c)2]=01 where ωL is the Larmor precession frequency and ωp the electron‐plasma frequency. uz and c denote, respectively, the axial beam velocity and the speed of light in vacuum. The variation of the normalized ripple amplitude and the scallop wavelength of a drifting beam is discussed. The profile of a beam accelerated in a uniform longitudinal electrostatic field is also ...