A crossed-field multisegment depressed collector for beam-type tubes

The velocity-dependent action of crossed electric and magnetic fields can be used to sort the electrons of the spent beam of a klystron or traveling-wave tube into two or more velocity classes, and to collect each class of electrons at a potential appropriate to its velocity. Secondary electrons produced at the collection surfaces do not return to the interaction space of the tube because of the nonreciprocal action of the crossed fields. An experimental tube permitted two-segment operation with 20 per cent of the beam power dissipated in the collector at small signals. Velocity sorting that permitted operation near this percentage of beam power over a considerable range of RF signal levels was observed. The major limitation was found to be migration of secondary electrons within the collector region from low-potential to high-potential electrodes, and this process prevented the depression of the collector power below 20 per cent of the beam power.     

The Ubitron, a high-power traveling-wave tube based on a periodic beam interaction in unloaded waveguide

The Ubitron is a high-power traveling-wave tube which makes use of the interaction between a magnetically undulated periodic electron beam and the TE01mode in unloaded waveguide. The electron-wave interaction exhibits the same type of first-order axial beam bunching characteristic of the conventional slow-wave traveling-wave tube; hence, it can be used in place of conventional O-type interaction in extended interaction klystrons and electron accelerators, as well as traveling-wave tubes. Experimental results are presented for the simplest physical embodiment of the Ubitron, which consists of an undulated pencil beam in a rectangular waveguide. Two of the unique features of this tube are very broad interaction bandwidth which results from the absence of a dispersive slow-wave circuit, and variable interaction phase velocity--hence, variable saturation power level. Among the physical embodiments of the Ubitron are a number of higher-order mode waveguide and beam configurations. These include plane, coaxial, and circular waveguides, all supporting the TE01mode, interacting with magnetically undulated sheet, hollow and cylindrical beams, respectively. The advantage of these configurations, which have not yet been tested experimentally, is that they provide a very large interaction area for beam placement. This property, plus the fact that the peak interacting field is far from the waveguide walls, makes the Ubitron an interesting prospect for high-power millimeter wave amplification.     

Theory and performance of depressed trochoidal collectors for improving traveling-wave tube efficiency

This paper discusses the theory and performance of depressed trochoidal collectors which are used to improve the efficiency of S-band traveling-wave amplifiers. These crossed-field multistage collectors sort the electrons in the spent beam into velocity classes, and collect each class at an appropriately low potential. The sorting and collecting actions depend on the tendency of electrons to flow to the lower-potential anode in a split-anode cylindrical magnetron. The magnetic field required in the collector region to produce sorting action is evaluated, and the design parameters of the collector structure are determined from an analysis of electron ballistics inside the collector tunnel. In the trochoidal-collector tube, spent electrons are sorted into eight energy levels and collected by eight electrodes biased at different potentials. This tube provides information on the fraction of electrons collected at a voltage equal to, or greater than, the equivalent voltage lost by the electrons in the process of RF interaction, and on the collection voltages required for spent electrons at different levels of RF drive. Complete performance curves for the assembly are included for both an unmodulated beam and an RF driven beam. When the tube produces a power output of 16 watts and a saturated gain of 35 db at 2360 Mc, the collector efficiency is 42 per cent, the over-all efficiency 38 per cent, and the electronic efficiency 16 per cent. These results are achieved without adverse effects on the RF performance as a result of beam instabilities and regenerations caused by space-charge blocking of electron flow or by motion of electrons returning to the helix region.     

Low-noise klystron amplifiers

The principles of low-noise guns have been applied to klystron amplifiers with good corroboration of the theory. In the past, many people thought that klystrons had inherently high noise figures, while others advanced the theory that low-noise guns might be used with klystrons as well as with wave tubes. The development to be described here shows that the former impression is not true and verifies that low-noise klystron amplifiers are possible. The most obvious difference between the guns for low-noise klystron amplifiers and those typical of low-noise traveling-wave tubes is the higher beam current which is required for adequate klystron gain. A byproduct of this higher current is a wide dynamic range. In addition to the development of the electrical parameters, a major effort went into klystron construction techniques somewhat peculiar to low-noise klystron amplifiers. The data taken show that alignment of the low-noise gun electrodes with the drift tube, alignment of the beam with the magnetic field, elimination of the collector's secondary electrons from the beam, and cleanliness of the tube are of primary importance in constructing a low-noise klystron amplifier. Several two-cavity, low-noise klystron amplifiers were built for operation in both S-band and C-band. The typical low-level gain was 11.5 db, and the saturated power output was 180 mw. Several tubes exhibited noise figures below 9 db; the lowest value obtained was 6.7. db.     

Electrostatic electron beam couplers

Electrostatic electron beam couplers can be used in conjunction with a parametric amplifier to produce low-noise electron beam amplification. The characteristics and design of both traveling-wave and resonant couplers are considered. The latter are broader-band and shorter than the traveling-wave version; however, the traveling-wave coupler does not require critical load adjustment and is electrically tunable. An important advantage of the electrostatic fast-wave coupler over the magnetic version considered by Cuccia is the elimination of the magnetic field.     

Efficiency improvement of the traveling-wave interaction process

Experimental evidence that conventionally designed, uniform-period traveling-wave amplifiers are potentially highly efficient devices is presented. Experiments with a traveling-wave re-entrant cavity tube and with a two-helix tube show that substantial improvement is possible when the RF energy of the so-called beam of a saturated traveling-wave tube is used. Tests reported here on the two-helix tube realized efficiencies greater than 43 percent.     

Investigating the characteristics of an M-type traveling-wave tube in the presence of multifrequency interaction

The model of interaction between an electron beam and electromagnetic waves with complex spectra is described. The correct application of the numerical implementation of the proposed model is investigated and numerical results are presented. Simultaneous amplification of several components of a complex electromagnetic signal in an M-type traveling-wave tube is considered and analyzed.     

An Equivalent Circuit for the "Centipede" Waveguide

An equivalent circuit is presented for the "centipede" coupled-cavity waveguide. The "centipede" waveguide, which is typical of the class of slow-wave structures suitable for use in a wide-band high-power traveling-wave tube, has two pass bands which may interact strongly with a small-diameter electron beam. The equivalent circuit is able to represent both of these pass bands. A detailed comparison with an S-band "centipede" waveguide shows that the equivalent circuit can represent the dispersion, interaction, and loss characteristics of the waveguide within a few percent.     

Traveling-wave tube gain fluctuations with frequency

Periodic traveling-wave tube gain fluctuations with frequency are described in terms of fundamental tube parameters and readily measurable quantities using the simplified one-wave theory of Pierce. An analysis of the feedback existing in a traveling-wave amplifier due to mismatches in the discontinuity regions is presented. Thus, the form, periodicity, and magnitude of these fluctuations and their dependence upon the beam voltage are quantitatively determined. The microwave structure is analyzed from a network point of view and the circuit parameters are defined with mismatches in the lumped center attenuator and at the ends of the slow-wave transmission line. The gain fluctuations are related to the cold circuit parameters and standing wave measurements. Pertinent experimental data, indicating the correlation of gain fluctuations to vswr variations, are included, in addition to an elementary discussion of the distortion effects possible due to such periodic gain variations in a traveling-wave tube.     

A Simple Closed-form Formula for Backward-Wave Start-Oscillation Condition for Millimeter-Wave Helix TWTs

An accurate and simple closed-form formula, for backward-wave start-oscillation condition for a millimeter-wave helix traveling-wave tube amplifier was developed, using an artificial neural network (ANN) algorithm. The analysis considers the effects of circuit loss and also the variation of electron beam diameter corresponding to beam filling. The formula is simple and amenable to easy computation, even using a scientific calculator, and without resorting to exhaustive numerical iterative search followed in conventional analyses and, at the same time, without sacrificing the accuracy in results. The formula was validated against published results, and excellent accuracy was observed. The analysis has been further used for inferring some physical interpretations on the effects of beam-filling factor and circuit loss on the start-oscillation condition of a typical millimeter-wave helix traveling-wave tube.     

An investigation of the magnetic transverse waves on an electron beam

An electron beam in the presence of an axial magnetic field supports four transverse waves; two cyclotron waves, and two synchronous waves. A general coupling theory is developed from an electronic equation and a circuit equation to describe how these waves can be coupled to traveling-wave circuits. The polarization and power flow characteristics of the waves are derived. The theory is applied to. the bifilar helix, a circuit which can couple selectively to each of the four modes. A bifilar helix traveling-wave tube was used to investigate experimentally the four beam modes and provide a quantitative check of the coupling theory.     

Electron-beam defocusing due to high-intensity RF fields

The electric fields associated with a "slow" electro-magnetic wave propagating along an electron beam will modulate this beam; the axial component of field will produce the usual "bunching," while the radial component will cause periodic perturbations in the radius of such an electron beam. This paper presents the results of analytical and experimental studies in an attempt to explain certain features of this defocusing effect of intense RF fields on the beam in a traveling-wave tube. In particular the effect of cathode flux on the RF defocusing of a beam in Brillouin flow is treated.     

Modeling a subterahertz traveling-wave tube with a slow-wave structure of the double grating type and a sheet electron beam

A traveling-wave tube of the millimeter range belonging to the short-wavelength region with a sheet electron beam and a slow-wave structure of the double grating type is studied. Its dispersion characteristics and coupling impedances for various spatial harmonics are calculated. The issues of design of the electron-optical system are discussed. The focusing of a sheet electron beam with a high current density by a uniform magnetic field is modeled.     

Effects of intermodulation, AM-PM conversion, and additive noise in multicarrier TWT systems

The intermodulation due to the traveling-wave tube (TWT) is analyzed for the case where arbitrarily modulated carriers and Gaussian noise are amplified through the TWT. Both AM-PM conversion effects and nonlinear amplification in the TWT are considered. The possibility of reducing intermodulation for system improvement is also discussed.     

The effect of various design parameters on the performance of medium-power traveling-wave tubes

In the design of traveling-wave tubes, the effect of changing such design parameters as beam current, frequency, or helix diameter is usually not immediately obvious. This paper makes the effect of some major design parameters more apparent by introducing certain approximations. Within the limits of the approximations, the gain-helix radius product is shown to depend only on beam perveance and a geometry-determined factor F. For a given geometry (defined as the ratios of all radial dimensions),CandQCare derived fromgamma aand beam perveance. Thus, universal graphs for gain per unit length,CandQC, are evolved. By keepinggamma a, beam perveance and tube geometry invariable, the RF behavior of traveling-wave tubes can be preserved. Consequently, scaling equations for traveling-wave tubes can be derived, and are presented in this paper.     

Computer simulation of ion trapping and detrapping in a PPM focusedtraveling wave tube

This paper presents results from a time-dependent, electrostatic electron gun simulation code, simulating ion trapping and detrapping in a traveling wave tube (TWT) focused by periodic permanent magnets (PPM). The simulations described indicate that ion loss is primarily radial through the beam tunnel walls, rather than axial through the gun or collector. The electrostatic potential well formed by the electron beam is constantly being filled by ionization of a background neutral gas. This effect constitutes the primary ion loss mechanism. Filling of the potential well is made possible by loss of the low energy electrons produced by ionization (secondary electrons) through periodic nulls in the magnetic field     

An investigation into density-wave propagation within high-temperature superconducting plasmas for use in creating traveling-wave devices

This paper theoretically investigates a novel application of high-temperature superconductors where the superconductor serves as the active component in a microwave or millimeter traveling-wave amplifier. A guided electromagnetic wave interacts with a dc superconducting electron current to set up charge-density gradients within the superconducting electron "plasma." The electromagnetic wave gradually extracts energy from the superconducting electrons by traveling in phase synchronism with these charge gradients. The interaction mechanism is similar to that of a conventional traveling-wave tube amplifier or oscillator. We have modeled the wave behavior of superconducting electrons using the London equations and a two-fluid approach. Our model includes dissipation within the superconductor, and it shows that traveling-wave devices may be possible using high-quality thin-film superconductors in which dissipation is kept low.     

耦合腔行波管大信号注波互作用研究与设计

行波管中注波互作用的特点是电子的速度调制、群聚及其与高频场的能量转换等过程沿整个慢波结构连续且同时进行,这是行波管可以在很宽频带内得到大输出功率的原因。在研究冷腔特性的基础上,使用三维PIC粒子模拟软件定量分析了耦合腔行波管的大信号注波互作用过程,完成了X波段连续波行波管的设计。设计参数:工作频率7.18.5GHz,带宽18%,最大输出功率3kW。     

A Traveling-Wave Electron Deflection System

Several types of traveling-wave electron deflection structures that can be used in microwave oscillographs are described and compared. An interaction structure consisting of a folded wire over a plane is considered in detail, both theoretically and experimentally. A general analysis of the interaction of electrons with sinusoidally varying transverse electric fields is presented and is applied to traveling-wave deflection systems. This analysis gives quantitative information about the interdependence of deflection and drift space lengths, beam velocities, frequencies and phase velocities along the structure. Limitations on the design and performance of traveling-wave deflection systems can be determined from this analysis.