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1.
The discrepancies between measured and calculated small-signal space-charge wavelengths are discussed. It is shown that conventional methods of calculation are inadequate, causing errors up to 40 percent in a typical case. It is demonstrated that these errors cannot be explained by beam scalloping action, and that they are most severe when a high-perveance beam is used at low voltages with a high magnetic field under conditions of low interception. Although these effects would not be noticed in klystrons with relatively short drift lengths, they may in many cases explain the critical variation of gain and efficiency with magnetic field. A more accurate method of calculating space-charge wavelengths is developed, and the effectiveness of this method is demonstrated by a comparison with measurements.  相似文献   

2.
Use of the dc transit time as a new spatial variable and the use of RS beam current multiplied by the dc beam velocity as a new space-charge wave variable simplify the form of the equations for space-charge waves on one-dimensional accelerated electron streams. Using the simplified equations, RF impedance functions are found for electron diodes. Nyquist analysis is used to investigate the stability of diodes for varying current densities, voltages, and external loadings. The results of a number of past authors' studies of impedance, oscillations, and instabilities are correlated and treated from a unified point of view. The methods developed here are an alternative to the Llewellyn-Peterson technique, utilizing solutions of ordinary differential equations rather than integral equations.  相似文献   

3.
The propagation of slow electrokinetic waves on finite electron beams which fill a conducting tunnel is discussed for modes of axial symmetry. In addition to the familiar space-charge modes, a pair of modes exists which are related to the vortex frequency (omega_{upsilon} = omega_{c} - 2theta_{0}). The finite magnetic field introduces a coupling between these modes. A set of four orthogonal modes can be derived by the use of matrix transformations, thus eliminating the necessity of solving a complicated characteristic equation. For infinitely high magnetic fields, the two additional modes disappear and the four modes reduce to the fast and slow space-charge waves.  相似文献   

4.
Methods of enhancing transmission of ribbon-shaped electron beams undergoing circular motion in azimuthally periodic cylindrical electrostatic lenses are treated. Lens forces add to the naturally occurring curvature focusing to achieve this increase in beam transmission. Three basic configurations, differing only in the method of applying lens voltages, are treated: symmetrical focusing, deflection focusing, and asymmetric focusing (including inner and outer electrode segmentation). Expressions for beam perveance and rippling are derived from the paraxial-ray equation for thin electron ribbons advancing along a two-dimensional curved optical axis. The stiffness of azimuthally periodic electrostatically focused electron ribbons (i.e., the immunity of the beam to transverse disturbing forces) also receives attention. Mathematical extensions of the analysis to ribbon beams undergoing helical motion are discussed, and numerical results applicable to selected values of lens parameters are presented. Experimental results for an azimuthally periodic lens, constructed to test the analysis, are discussed in light of the theory developed.  相似文献   

5.
The approximate phase characteristics of the space-charge waves in bounded plasmas are developed assuming the charge density to be statistically distributed. The influence which the correlation function of the charge distribution has on the phase characteristics is also found.  相似文献   

6.
Noise along periodic-electrostatically focused electron beams have been measured. The noise variation is periodic with the wavelength of the reduced plasma frequency. It is concluded that electrostatic focusing exhibits similar noise properties as magnetic focusing.  相似文献   

7.
A double-cathode tube is working in the space-charge region. A small-signal theory for such a tube, including transit-time effects, yields the result that two space-charge waves are traveling inwards from each of the cathodes.  相似文献   

8.
Space-charge waves in a two-dimensional negative-mobility medium are described by a relatively simple and easy-touse expression for the complex propagation constant. Attention is focused on the dominant mode in the most important limit of low growth rate. Diffusion is included in the analysis. Whereas most previous workers imposed a stiff lateral-motion constraint at the surfaces of the drifting electron stream, we allow the electrons to move freely in the transverse direction at the lateral boundaries of the stream. This free-surface assumption corresponds to the partially depleted condition which prevails in many experiments. It has the effect of reducing diffusion damping and hence enhancing the growth of space-charge waves at high frequencies. The enhanced high-frequency growth rate makes the free-surface theory agree better with experimental data on thin-layer reflection and traveling-wave amplifiers than the stiff-surface theory does. Our results are cast in a form which allows heterogeneous dielectric media to be characterized by a single "effective dielectric constant." Dielectric configurations considered include symmetrical and unsymmetrical combinations of simple dielectric media, multilayered dielectric media, and simple or multilayered dielectric media with metal backing.  相似文献   

9.
A theoretical investigation of the validity of Langmuir's expression for the limiting current density in a focused electron beam when space-charge forces are significant was carried out by computing the performance of a series of simple electron tubes, each consisting of a Pierce gun coupled by a thin lens to an equipotential drift space. The analyses show that, while the cathode current density and the peak current density in the spot are related, they are not directly proportional as stated in Langmuir's expression which, therefore, does not give an accurate prediction of the current density that can be obtained in the spot. The dimensions of the tubes were chosen such that this conclusion is also valid in the case of television picture tubes. It is also shown that thermal velocities have only a minor influence on the lens strengths required to focus beams, and that the focused spots havea Gaussian distribution of current density even though the emission density in a Pierce gun is uniform.  相似文献   

10.
A symmetry property is deduced for an electron beam modulated and demodulated by gaps of cavities. This property results from a combination of the theory of space-charge wave propagation in an accelerated beam and of the theory of gaps. It states that in a region bounded by two cavities, the power detected by the second cavity is unaltered by an interchange of potentials on the two cavities, provided the widths of the gaps are small. Experimental results are given for both linear and nonlinear acceleration and deceleration regions. In all cases, this property is found to be true. Most of the experimental results are also tested vs theoretical solutions of the electronic equation for regions of acceleration. The reduction factor is included in the theory.  相似文献   

11.
12.
Submicrometer focused ion beams have been used both for the maskless ion implantation of p-channel depletion-mode Si MOSFET's and for the gate lithography of n-channel enhancement-mode Si MOSFET's. B-Pt and Au-Si liquid-metal-alloy ion sources were utilized in a single-lens focusing column for the implantation and lithography steps, respectively. An 800-Å-thick Al stopping layer was used at the target to separate the lighter ions from the heavier ion species in the beams. Reasonable dc electrical characteristics were measured for the chosen device process parameters.  相似文献   

13.
The non-local nature of impact ionization is modelled using lucky-drift theory with the assumption that the relevant electric field is the average field, but that the relevant drift velocity is that associated with the local field. The carrier density relevant for impact ionization is also taken to be non-local. The model is applied to the case of a thin film insulator with Fowler-Nordheim injections of electrons at the cathode. For clarity's sake we avoid considering the excitation of holes and limit attention to the ionization of a set of occupied deep-level states present in high concentration. We show that the non-local nature of the ionization process reduces the local field markedly, resulting in a pile-up of free electrons to maintain current continuity in the rest of the film. This is contrasted to the prediction of local-impact-ionization theory, in which the field is reduced merely to that necessary to sustain a small level of ionization. Under certain circumstances space-charge striations are produced analogous to the situation in gas discharge, and for some film thicknesses a NDR occurs.  相似文献   

14.
A linearly focused acoustic beam is investigated to be introduced into acoustic microscopy for characterising materials in the nonscanning version. The new acoustic beam enables us to detect acoustic anisotropies of materials to be measured successfully. For forming the acoustic beam, an acoustic sapphire lens with a cylindrical concave surface of 1.0 mm in radius is made and the acoustic field distributions are investigated at 200 MHz.  相似文献   

15.
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.  相似文献   

16.
Direct measurements were made of the electron-beam noise parameters using a modified Currie-type gun. The noise parameters were measured as a function of the electric field in the vicinity of the cathode. The S parameter was found to be strongly influenced by this field in the Currie-type gun, but the parameterpi/sis relatively unaffected.  相似文献   

17.
概述了聚焦离子束直接写入、离子研磨、离子注入及离子沉积技术。介绍了利用聚焦离子束技术在镀金硅片上研磨出的图案及制作出的各种纳米结构。聚焦离子束诱导沉积技术为将在各种科学工程领域应用的多种微结构的实现提供了可能,如聚焦离子束真空封装技术,它可被用来真空封装MEMS器件。  相似文献   

18.
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.  相似文献   

19.
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.  相似文献   

20.
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.  相似文献   

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