Large signal behavior of high power traveling-wave amplifiers

The results of an experimental investigation on the large signal behavior of a kilowatt power level helix type traveling-wave amplifier tube are presented. Operation with and without attenuators was investigated using a movable electromagnetic probe to measure power level along the tube. Quite different effects of drive power and beam voltage on the saturation level were found for operation with and without attenuators. The maximum power level is lower for attenuator operation. Also, power levels do not continue to increase with increasing beam voltage and drive power. In contrast, attenuator-less operation produces the highest efficiency, and the power levels continue to rise with increasing beam voltage and drive power. Conversion efficiencies as high as 25 per cent are obtained with an attenuator and as high as 40 per cent without an attenuator. Efficiency calculations based on small-signal theory can be made to agree reasonably well with the experimental attenuator-less operation efficiencies by assuming an appropriate ratio of the ac component of beam current to the dc component of beam current, i/I0.     

Dynamic defocusing of electron beams in high-power helical traveling-wave tubes with length-dependent dispersion

Dynamic defocusing in a wideband helical traveling-wave tube (TWT) with an output power of 1.5–2.0 kW in the continuous-operation mode is analyzed. The TWT contains fragments with normal and anomalous dispersion of the phase velocity. It is demonstrated that the TWT output characteristics can be improved and the TWT stability against self-excitation on the backward wave can be increased with the use of appropriate values of parameters of the electron-optical system that forms a converging axially symmetric beam focused by a periodic permanent-magnet focusing system.     

Triode electron injection systems for hollow beams

Novel electron guns, in which a conical hollow electron beam is projected at a large angle to the axis into a coaxial deflection region, were tested. The guns have a triode structure so that the perveance can be varied easily. The strong deflection increases the effective perveance of the beam and makes the trajectories insensitive to current variations. In the form of a device with the gun at a large radius and projecting the beam inward, the electron paths are sensitive to scattering in the gun. The inverted gun, projecting the beam outward, is relatively free from this difficulty. The systems generally behave as expected, and should be quite useful for initiating variable-current hollow electron beams in various available focusing arrangements.     

Simulation of electron-optical forming systems with highly compressed electron beams

A method of synthesis is developed, equations are derived, and the results are obtained via this method for the simulation of systems that form high-intensity electron beams with a high compression. The relatively high compression of a beam is realized owing to both a faster (in comparison with a variation in the accompanying magnetic field) increase in the axial component of the magnetic field at a certain plane in the gun region and to selection of the length of the region in the gun where the potential increases. Electron-optical systems with beams whose structure is substantially affected by electron thermal velocities are considered. Relationships that allow determination of the initial parameters of the beam and the focusing magnetic field during the synthesis of such systems are presented.     

Heating of solid targets by electron beams

The heating of a solid material by a high-energy electron beam is discussed. The two-dimensional transient nonlinear heat equation has been solved by the finite element method, considering both the penetration of the beam into the target and its finite size. The importance of the temperature dependences of each of the material properties on melt time have been established. Results are presented for the time needed for the first melting of the target for Cu, AI, Si, GaAs, impinged by beams having energies and parameters covering a wide range of values. Also the regimes of validity of the one-dimensional heat equation are discussed.     

Regrowth of heavy-ion implantation damage by electron beams

Electron transparent Si, Ge and GaP samples were implanted with 50 keV Xe⁺ ions to a dose around 10¹¹ ions/cm². At this implantation condition, each heavy ion created a small, spatially isolated amorphous zone. Following the ion implantation, the samples were irradiated with electrons having energies from 25 to 300 keV at temperatures 90 and 300 K. At each electron energy, transmission electron microscopy (TEM) images of a selected sample area were taken in regular time intervals to record the evolution of the implant damage. At all electron irradiation conditions it was observed that the amorphous zones shrunk with increasing electron dose and some of them eventually disappeared. The most interesting result is the observation that regrowth occurs below the displacement threshold and, moreover, regrowth rate increases when decreasing electron energy below ∼100, ∼125 and ∼200 keV, for Si, GaP and Ge, respectively. These results are discussed in terms of possible mechanisms stimulating regrowth.     

Measurement of transverse velocity in electron beams emitted from axisymmetric electrode systems

Some general relations are derived for the transverse momentum and angular velocity of electrons and their guiding centres in axisymmetric systems with a radial electric field. Two methods are described for measurement of the transverse velocity of electrons ejected from a coaxial electrode system. The first method uses observations of the magnetic fields at which the outermost and innermost electrons are intercepted by an anode; a modified form of the trajectory equations of Kino and Taylor is then used to estimate the behaviour of the electron beam under operating conditions. The second method deduces the transverse velocity of electrons at any axial position at which the radial electric field is small, from observation of the maximum magnetic field which permits current to reach the collector. The potential depression and axial velocity for the desired operating conditions can also be deduced.     

Simulation and properties of transitions to traveling-wave deflection systems

This paper is related to the super-wideband slow-wave structures, especially to the deflection systems for traveling-wave cathode-ray tubes (CRTs). Transitions to the helical deflection system of the super-wideband traveling-wave CRT are considered. The model of the circuit, containing the deflection system, is composed. As a result of analysis of the model, operation and properties of the transitions are revealed. Opportunities to improve the dynamic characteristics of the traveling-wave CRTs are considered.     

Tailoring electron vortex beams with customizable intensity patterns by electron diffraction holography

An electron vortex beam(EVB) carrying orbital angular momentum(OAM) plays a key role in a series of fundamental scientific researches, such as chiral energy-loss spectroscopy and magnetic dichroism spectroscopy. So far, almost all the experimentally created EVBs manifest isotropic doughnut intensity patterns. Here, based on the correlation between local divergence angle of electron beam and phase gradient along azimuthal direction, we show that free electrons can be tailored to EVBs with customi...     

Microwave deflection of electron beams

When an electron beam interacts with a time-varying electric field, it is usual to ignore the effect of the induced magnetic field. It is shown that this may cause errors at microwave frequencies even for slow electrons. The particular case of electrons traversing a microwave cavity is examined in detail.     

Transistor fabrication using diffusion barriers produced by electron beams

Diffusion barriers produced directly by electron-beam-initiated chemical reactions have been used to fabricate planar bipolar transistors without the use of normal oxidation or etching processes. Electrical characteristics of the transistors are comparable with conventional devices.     

Applications of traveling-wave laser amplifiers in subcarriermultiplexed lightwave systems

Describes applications of traveling-wave laser amplifiers (TWLAs) in subcarrier-multiplexed distribution systems for both frequency-modulated (FM) and amplitude-modulated vestigial-sideband (AM-VSB) video signal distribution. The characteristics of a 1300-nm facet-angled and antireflection-coated TWLA are described. Analytical carrier-to-noise ratio (CNR) characterizations of subcarrier-multiplexed systems employing TWLAs are given. Experimental results of using TWLAs in multichannel FM and AM-VSB video signal systems are described. The potential optical-reflection problems associated with the residual reflectivities of optical fiber connectors and splices while using TWLAs are briefly described     

Formation of Brillouin-type toroidal electron beams

A solution to the problem of formation of toroidal cuts from classic 1D Brillouin flows (solid, hollow, and electrostatic beams) and a 2D Brillouin flow in a nonuniform magnetic field is presented.     

RF defocusing of ion-focused electron beams

Ion-focusing of electron beams in high-power linear-beam microwave tubes is considered, and a qualitative discussion of the defocusing mechanism of an externally applied RF power is presented. The primary mechanism of beam breakup is the space-charge force of bunched electrons which limits the use of ion-focusing in high-power tubes.     

Electrodynamics of rotating relativistic electron beams

On the basis of the Minkowski formulation, this paper discusses the basic laws governing the small-signal fields propagated along an electron beam which is rotating around its axis with constant angular frequency of rotation and drifting in the axial direction at constant relativistic velocity. In the first preliminary section are described the dc conditions for getting a stable relativistic electron beam in the presence of neutralizing ions with arbitrary number density and externally applied static magnetic field. Then, after a brief discussion of the ac-field equations, the constitutive relations for small-signal fields are obtained in both the laboratory frame, which is assumed to be an inertial frame, and the rest frame of the electron beam, which is not an inertial but a rotating frame. The rotating relativistic electron beam is found to be a nonuniformly moving dispersive medium or, more specifically, an inhomogeneous bianisotropic medium with space and time dispersion. With the use of the constitutive relations derived above, the following sections consider the energy and momentum for the small-signal fields, and their conservation relations, together with their transformation laws between the laboratory frame and the rest frame of the electron beam. Our discussion includes, as the special cases, all the important cases of an ion-neutralized or axially confined beam and the Brillouin beam.     

Breakup of hollow cylindrical electron beams

The experimental breakup of a hollow electron beam focused by a longitudinal magnetic field into a discrete set of vortex filaments is described. Agreement with the theory of J. R. Pierce is satisfactory. The theory is extended to include the cases of Harris flow and hollow beams focused by a negative center conductor and a magnetic field. It is predicted that growing waves are possible in Harris flow beams. General considerations of energy and momentum conservation support the detailed analysis.     

Reduction of photoresist standing-wave effects by post-exposure bake

A process is described for reducing the residual effects of standing waves upon exposed and developed lines in positive photoresist films.