Conservation principles in multivelocity electron flow

This paper considers the extension of Poynting's theorem to an electron gas with a continuous distribution of velocities. In particular, an extension of the concept of "kinetic potential" is attempted, since this concept has proved itself very useful in the investigation of single-velocity flow. It is found that in three dimensions the electrokinetic-flow vector cannot be expressed as the product of the convection-current density and a single scalar quantity of the dimension potential. In one-dimensional applications, however, this circumstance is immaterial. Another difficulty is encountered when a small perturbation component on a steady state is considered. The nonlinear Bolzmann transport equation gives a linear equation between the first-order perturbations, but the nonlinearity makes possible a conversion of part of the perturbation power flow to dc power flow. In other words, the power flow associated with a single-frequency perturbation is not necessarily conserved in multivelocity flow, even in the absence of an ac Poynting vector. In the case of space-charge-limited flow in an electron gun, the consequence is that the cooling of an electron stream by adiabatic expansion can proceed beyond the potential minimum and very low noise temperatures are attainable in principle if the accelerating field is maintained small over an appreciable length of the electron gun.     

A method of reducing the effects of anode aperture in high-perveance convergent electron guns

A new theoretical method of designing convergent electron guns of high perveance for use in microwave tubes is presented here. A differential equation which represents electron trajectories in a convergent electron stream has been deduced under certain approximations. Electron trajectories in an electron stream and boundary values along its boundary were numerically calculated by solving the differential equation by means of an electronic computer. Boundary values on the virtual anode surface under space-charge-limited conditions were used as the initial values for the calculations. Focusing electrodes were determined to satisfy the boundary conditions on the stream boundary. The design procedure is also shown. The electron guns designed by this method are somewhat different in structure from the conventional ones which are usually designed experimentally rather than theoretically. In these new electron guns, nearly uniform current densities will be obtained over the whole cathode area, while in conventional convergent guns of high perveance, electron emission density near the center of the cathodes is usually reduced due to the influence of the anode aperture. Laminar flow will be obtained at points near the minimum stream diameter also in guns designed by this method. Digital computer experiments were performed and the results proved this hypothesis to be reasonable. An electron gun of 1.72 × 10^-6perveance and area convergence ratio of 70:1 is shown as an example.     

A Barkhausen-Kurz oscillator at centimeter wavelengths

This paper describes a new device for the generation of high-frequency oscillations in the centimeter wavelength region with high efficiency and low starting currents. The tube is fundamentally a Barkhausen-Kurz oscillator [1] utilizing a resonant cavity and a magnetically focused electron beam, but with no accelerating grids. The important features of this tube are the use of a parabolic potential distribution to utilize multiple transit electron motion, and the use of the magnetic field to control coupling between the electron stream and the resonator field and to reduce to negligible value the current intercepted at the resonator gap. A preliminary theory of the electronic energy interchange of this oscillator is provided, and the background theory of the oscillator design is discussed. Both X-band and K-band tubes have been tested. In the X-band tube, a maximum output power of 1.8 watts and a maximum efficiency of 13.5 per cent were obtained. At K band, the maximum power output was 430 milliwatts, and the maximum efficiency was 12.2 per cent. Starting currents belaw 0.1 ma have been observed at X band.     

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.     

Focus reflex modulation of electron guns

High resolution and low drive features have been successfully combined in a new type of electron gun for cathode-ray tubes. The gun has a spot-defining aperture of 0.007 inch upon which emission from a large cathode area is concentrated by a retarding electron lens. This unit modulates the beam by electron reflection, while focusing it upon the aperture ("Focus Reflex Modulation"). Immediately ahead of the aperture, a modulated virtual cathode is formed with an emission capability of over four amperes per square centimeter. A1000-microa beam with a 6° divergence is controlled by a signal of 12 volts centered at ground potential. Highlight brigntness of 250 foot lamberts was read at 17,500 volts, while more than 500 lines were resolved on a television test pattern. In more recent forms of the FRM gun,1600 microa are measured in the screen return, out of1800-microa cathode current. This is 88 per cent over-all transmission, using the same defining aperture (0.007 inch). 18 volts of drive signal will completely modulate the above current.     

G波段行波管电子枪设计与实验

设计了用于G波段行波管的聚焦极调制皮尔斯电子枪,电子注电压20 kV,电流50.9 mA,注腰半径0.056 mm,射程10.3 mm。利用热-结构耦合分析和电子注轨迹仿真方法,分析了热形变对电子枪性能造成的显著影响。为了消除电子枪热形变的影响,设计了装配模具进行补偿,并得到了实验验证。该电子枪已用于多种G波段行波管,解决了关键部件技术问题。     

Experimental investigation of large-signal traveling-wave magnetron theory

Experiments conducted on a beam-type backward-wave amplifier which closely approximates the theoretical thin-beam model used in the large-signal analysis of Sedin have resulted in gain and phase shift characteristics which are in good quantitative agreement with the adiabatic portion of both the Sedin and Gandhi-Rowe theories. Efficiencies approaching the theoretically-predicted maximum have been observed. By driving the amplifier to very large signal levels a conversion efficiency for power available from the initial potential energy of the beam of 63 per cent was obtained with a corresponding value of 45 per cent for the total electronic efficiency. An important feature of this experimental amplifier is the electron gun design which is based on a theory by Kino. That this gun is capable of producing a well-confined, rectilinear-flow thin beam is demonstrated by visual observations of the beam thickness which indicate thatomega_{c}/omega_{p}is as low as 1.17, a value close to that for a laminar-flow Brillouin beam (omega_{c} = omega_{p}).     

Transport of noise fluctuations in convergent flow crossed-field electron guns

The transport of noise fluctuations in convergent flow or so-called Kino-type crossed-field electron guns is investigated in terms of a two-dimensional computer simulation of the gun by the well-known Monte Carlo method for studying stochastic processes. The exact electrode configurations are simulated in the computer memory. After sufficient time has elapsed for the electron flow to achieve a steady-state condition 2000 additional time intervals are computed and then a statistical analysis is made of the fluctuation quantities. Six emission spots are considered on a finite-width cathode. The analysis is facilitated by the development of a rapid method for the solution of Poisson's equation (two-dimensional). Of particular interest in the results is the improved laminarity of the flow in the KG-M gun and the fact that there is significant space-charge smoothing throughout the gun region in both Kino-type guns. Of greater significance and as yet not explainable is the fact that Ψ versus ωct has local peaks when the space-charge density, which is spatially varying, passes through the Brillouin value (ω_{p}-ω_{c}for this condition). This knowledge could be profitably used in deciding on the location of the gun exit plane. The fact that the laminarity of the flow is sensitive to slight changes in the electric field near the cathode indicates that an absolute evaluation of the noise performance of KG-A and KG-M guns is difficult and may only be obtained through appropriate experiments.     

Aperture lens formula corrected for space charge in the electron stream

The aperture lens formula of Davisson and Calbick is rederived to include the effect of space charge forces. The correction is applied to a parallel flow Pierce gun, leading to the focal length reduction as a function of perveance, e.g., 30 per cent reduction at perveance 3 × 10^-6.     

The DEMATRON—A new crossed-field amplifier

A nonreentrant beam, distributed-emission, crossed-field, forward-wave amplifier, the DEMATRON, is described. The difficulties encountered by early experimenters in achieving gain in excess of 6 db in nonreentrant, crossed-field amplifiers are overcome in the DEMATRON by use of either an electron velocity taper or circuit velocity taper. A crossed-field amplifier design theory is given which is based on the use of equivalent magnetrons, and which takes into account the need for velocity compensation. In practice, electron velocity compensation is accomplished by either changing the sole-anode spacing, or by varying the dc magnetic field or a combination of both. Experiments with the DEMATRON have yielded gains in excess of 10 db over a 15 per cent bandwidth. Power levels between 300 and 500 kw have been achieved at an operating voltage of 25 kv. The design theory has been experimentally shown to be quite satisfactory in the large-signal, saturated gain region of operation, However, the lack of adequate small-signal theory has thus far prevented full optimization of the velocity compensation.     

A method to from a rectilinear electron beam with small pulsations for free electron masers

When a solid electron beam is formed by a two-electrode axially-symmetrical gun immersed in uniform axial magnetic field, the anode aperture, cutting off the near-axis part of the beam acts as an electrostatic lens and causes unwanted pulsations of the beam. Initial oscillations of electrons are especially unfavorable for free-electron masers (FEMs), in which they lead to a too large spread in the oscillating and, correspondingly, in the translational velocities of the particles. A method for compensation of the parasitic action of the anode aperture by means of a small correcting coil and formation of an electron beam with minimum pulsations is suggested in this paper. Results of estimations and numerical simulations demonstrating the effectiveness of the method when using it in an electron-optical system of a millimeter wavelengths cyclotron autoresonance maser (CARM) are discussed.     

场致发射阵列阴极电子枪的设计及模拟研究

讨论了微波管用电子枪的一般参数和要求，对于在微波管中应用场发射阵列阴极电子枪的情况作了分析，表明其中存在的主要问题是电子注散焦。通过比较场发射电子注聚焦的几种方法，利用传统电子枪整体聚焦的思想，初步设计了一个场发射阵列阴极电子枪模型，它包括场致发射阵列阴极，一个Whelnelt电极，一个聚焦电极和一个阳极。通过利用Mafia软件对电子注轨迹的模拟计算，对电子枪的聚焦部分进行了改进。     

The design and performance of grid-controlled, high-perveance electron guns

The focusing electrode and a probe projecting through the cathode serve as control electrodes for the current from a convergent-beam electron gun. The principal advantage of this type of "grid" is that there is no interception of the high-current-density beam by the probe-grid. This paper presents the design procedure and experimental results for typical probe-gridded guns. The design procedure is used to obtain the desired perveance, beam diameter, and approximate laminar electron flow. The probe geometry that results in a minimum beam distortion is discussed. The range of values of amplification factor obtainable and the influence of probe geometry on this factor are discussed. The magnetic field required for focusing the beam from a probe-gridded gun is compared with that required for perfect laminar flow and for focusing the beam from a nongridded gun of similar design. An electrolytic tank in conjunction with an analog computer was used to plot electron trajectories, with the effect of space charge included, for the probe-gridded gun and a similar nongridded gun. A comparison of the electron optics of the gridded and nongridded gun is made. Electrical breakdown and beam current during the interpulse time are problems considered. Methods used to minimize electrical breakdown and interpulse beam current are presented. Several models of probe-gridded guns were constructed. The measured characteristics of these guns demonstrate that the advantages of grid control can be obtained with only a minor effect on gun perveance and beam focusing.     

A gun and focusing system for crossed-field traveling-wave tubes

A problem encountered in the design of crossed-field traveling-wave tubes (particularly M-type amplifiers or backward-wave oscillators) is a limitation on current due to the restricted cathode size in the usual gun systems. The scheme considered here incorporates into a crossed-field device the techniques commonly used in O-type devices for designing converging Pierce-type strip-beam guns, which can increase the effective cathode area by perhaps ten times. A design procedure is presented for getting a well-formed beam from such a gun, which is magnetically shielded, through a fringing crossed-field region into the uniform-field region of interaction. An analysis of electron flow through the fringing-field region, including the effect of space charge, is presented. A trajectory equation, solved on a digital computer, yields trajectories for the beam and design curves for various values of the important parameters. The results show the scheme to be feasible. Results are also presented from tests on an experimental, demountable tube used to test the focusing scheme. About 90 to 95 per cent of the current entering the crossed-field region could be focused to the collector, and the system behaved generally as the design predicted. An evaluation of the experimental data showed the scheme to be useful.     

Focusing of an Electron Beam from a Low-noise Gun with Different Magnet Systems†* Part IV. Trajectories of the Outermost Electron in a Beam Focused by a Periodic Permanent Magnet

This paper deals with the traces described by the outermost electron in a beam produced by a magnetically immersed electron gun and focused by a periodic permanent magnet in the drift region. The beam profiles have been computed by use of a fast computer for three types of magnetic flux density distribution in the transition interval between the gun and the drift regions.

In the first series of solutions, the uniform magnetic field over the gun region connects directly "with the rising part of the sinusoidally varying magnetic field. With the period of the alternating flux held constant, proper and improper flux densities in the gun and helix regions produce, respectively, acceptable or runaway electron beams. In the second series of computations, a compensating field in the form of a dent is introduced over the intervening space between the gun and drift regions. Variations are made in the magnitude of the gun field and the amplitude and period of the alternating field. Satisfactory profiles are obtained when these parameters have optimum values; incompatibility between high flux densities and large period of the magnets is indicated by the ever-growing beam ripples. In the third series, beam profiles are computed for the cases when optimum spatial period of the magnet is used and the magnitudes of flux densities in the gun, transition, and helix regions are altered. Very high gun fields are not conducive to producing good electron transmission, while judicious choice of compensating field leads to smooth beams even with comparatively low flux densities in both the gun and helix regions.

There are other modes of flux distribution over the gun and the transition regions which also provide both good electron transmission and noise performance, but these are not considered here.     

The design and performance of a magnetron-injection gun

The space-charge flow solutions described by Kino and others in connection with the crossed-field carcinotron gun can be generalized to form the basis of a magnetron-injection gun design suitable for the production of hollow electron beams. In the first part of the paper this generalization is described. From the resulting flow it is possible to determine by an approximate method the electrodes to produce a gun of desired perveance with nearly uniform current density at the cathode. This technique has been used to design guns having ratios of cathode length to a diameter considerably greater than unity. The close agreement between the results obtained on several experimental guns and the theoretical predictions is described, along with the effect of departures from the prescribed fields given by the design method.     

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.     

TEM场发射枪通信控制技术研究

研究了200kV场发射枪透射电子显微镜（TEM）场发射枪的通信控制原理。上位机PLC采用ModBus协议与下位机200kV场发射枪通信控制板通信,下位机场发射枪通信控制板与电子枪被控对象采用三务总线形式的I^2C协议,基于两种不同协议之间的通信控制,设计了两种协议之间的转换控制模块,实现了上位机PLC和下位机200kV场发射枪电源之间的数据可靠通信,给出了对200kV场发射枪透射电子显微镜场发射枪电源通信控制的软硬件设计。     

基于Spindt冷阴极的行波管电子枪设计

针对X波段小型化Spindt冷阴极螺旋线行波管进行了电子枪设计.基于皮尔斯型电子枪结构,联合PPM高频聚焦系统,以电子注聚焦特性为优化目标,采用CST粒子工作室对电子枪结构和工作参数进行了优化设计,获得了 30 mA工作电流下电子注填充比为0.68的良好电子注聚焦.在此电子枪结构和高频结构下,分析了特定电流下电子注聚焦...     

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.