Showing papers in "International Journal of Electronics in 1984"
TL;DR: In this paper, the authors report on measurements and calculations on the conversion of circular electric TE0n gyrotron mode compositions (TE01 to TE04) at 28 and 70 GHz to the linearly polarized TE11 mode by means of mode converter systems using periodic waveguide wall perturbations.
Abstract: This work reports on measurements and calculations (coupled mode equations) on the conversion of circular electric TE0n gyrotron mode compositions (TE01 to TE04) at 28 and 70 GHz to the linearly polarized TE11 mode by means of mode converter systems using periodic waveguide wall perturbations. Mode transducers with axisymmetric radius perturbations transform the TE0n gyrotron mode mixture to the more convenient TE01 mode for long-distance transmission through overmoded waveguides. Proper matching of the phase differences between the TE0n modes and of lengths and perturbation amplitudes of the several converter sections is required. A mode converter with constant diameter and periodically perturbed curvature transfers the unpolarized TE01 mode into the TE11 mode which produces an almost linearly polarized millimetre-wave beam needed for efficient electron cyclotron resonance heating (ECRH) of plasmas in thermonuclear fusion devices. The experimentally determined TE0n -to-TE01 conversion efficiency...
145 citations
TL;DR: In this article, the authors present a critical analysis of various electrical properties of MIM devices, with supporting experimental evidence, showing that the emission of electrons through the top electrode becomes most apparent at the onset of the voltage-controlled negative resistance (VCNR) region.
Abstract: Some insulating films of thickness normally between 10 nm and 600 nm in both sandwich and planar configurations (MIM devices) undergo a forming process in which the formed devices acquire a permanently, irreversibly enhanced conductivity, The I(V) characteristics with a region of voltage-controlled negative resistance (VCNR) are influenced by the fabrication methods, electrode metals and ambient conditions such as temperature and pressure. The emission of electrons through the top electrode becomes most apparent at the onset of the VCNR region. Switching and memory phenomena are also observed. In this paper we present a critical analysis of various electrical properties of MIM devices, with supporting experimental evidence.
95 citations
TL;DR: In this paper, a linear theory for a gyrotron backward-wave oscillator (gyro-BWO) is developed, which solves a reduced one-dimensional Maxwell-Vlasov equation in the form of a linear integro-differential equation using the Laplace transformation.
Abstract: A linear theory for a gyrotron backward-wave oscillator (gyro-BWO) is developed. The theory solves a reduced one-dimensional Maxwell-Vlasov equation in the form of a linear integro-differential equation using the Laplace transformation. The relative amplitudes among the waveguide modes and beam modes are completely determined and enable one to calculate gyro-BWO start-oscillation conditions. Using this analysis and including velocity spread effects, a design of a millimetre-wave gyro-BWO has been carried out based on the operating parameters of an existing electron gun. Tunability over a range of 86 GHz to 103 GHz is predicted with output power estimated to be ∼ 1 kW.
81 citations
TL;DR: In this paper, a new cyclotron fast-wave tube named the gyro-peniotron is proposed, which is promising as a highly efficient and powerful source of millimetre or sub-millimetre waves, and reports the analytical results of its operational characteristics using some computer simulations.
Abstract: This paper proposes a new cyclotron fast-wave tube named the ‘gyro-peniotron’, which is promising as a highly efficient and powerful source of millimetre or sub-millimetre waves, and reports the analytical results of its operational characteristics using some computer simulations. The analytical results assuming two operating conditions of ω0;≃ ωc and ω0≃3ωc for the 35 GHz gyro-peniotron in the TE021 cavity mode predict a high efficiency of 63% and a quite high output power of 48 MW at a beam voltage of 80 kV and a magnetic field of 13 kG in the case of ω0≃ωc, and also, an efficiency of 48% and a power of 9 MW at a beam voltage of 60 kV and a magnetic field of 4·425 kG in the ease of ω0≃3ωc
75 citations
TL;DR: In this article, the operating characteristics of a 140 GHz pulsed gyrotron are reported, and a variety of new and highly accurate diagnostic techniques that have been developed to measure the power, frequency and mode content of the output radiation are reviewed.
Abstract: The operating characteristics of a 140 GHz pulsed gyrotron are reported. Total efficiencies of 36% and output powers of 175 kW have been obtained in single-mode operation. Measurements of power and efficiency have been made for a variety of modes between 120 and 160 GHz, and these results are in good agreement with predictions based on non-linear theory. The best results have been obtained with isolated asymmetric modes, such as the TE4, 2, 1 (127·3 GHz), TE2, 3, 1,(136·7 GHz) and TE3, 3, 1(155·6 GHz). Although mode competition was found to prevent the TE0, 3, 1, mode (139·5 GHz) from reaching the optimum operating conditions, an output power of 138 kW and total efficiency of 29% were achieved with this mode. A variety of new and highly accurate diagnostic techniques that have been developed to measure the power, frequency and mode content of the output radiation are reviewed. In addition, the operating characteristics of both laminar and non-laminar magnetron injection guns are compared. The hig...
66 citations
TL;DR: In this article, it is demonstrated by computer simulations that the increase in beam momentum spread diminishes the gain slightly but reduces the efficiency significantly, the decrease in conversion efficiency arises mainly from the dispersion of the wave reducing the available free energy from the electron beam.
Abstract: Since in a Doppler shift dominated cyclotron maser, the Doppler term is the main contribution to the output frequency, the electron-beam momentum spread plays an important role in determing the gain and efficiency. It is demonstrated by computer simulations that the increase in beam momentum spread diminishes the gain slightly but reduces the efficiency significantly. The decrease in conversion efficiency arises mainly from the dispersion of the wave reducing the available free energy from the electron beam. Further increase in momentum spread eventually changes the saturation mechanism from phase trapping to energy depletion.
61 citations
TL;DR: In this paper, the authors used a harmonic mixer system to measure the bandwidth of individual 1 μs pulses of the gyrotron, to determine the dependence of the operating frequency on the cathode voltage and resonator magnetic field, to detect and identify second-harmonic radiation and to study multimode operation.
Abstract: Accurate measurements of the emission frequency and bandwidth of a pulsed 140 GHz gyrotron have been made using a harmonic mixer system. This system has been used to measure the bandwidth of individual 1 μs pulses of the gyrotron, to determine the dependence of the operating frequency on the cathode voltage and resonator magnetic field, to detect and identify second-harmonic radiation and to study multimode operation. Bandwidths as low as 3 MHz, which is the instrumental limit, have been observed. In addition, frequency pulling has been measured and compared with predictions based on linear and self-consistent non-linear theory. It was found that linear theory is inadequate for describing the frequency characteristics of a gyrotron operating well above the starting current, while self-consistent non-linear theory was in reasonable agreement with the experimental results. The small bandwidths and stable operating frequencies that were measured confirm the viability of the gyrotron as a millimetre ...
47 citations
TL;DR: The first experimental results of a high-power quasi-optical gyrotron are presented in this article, where the cavity was designed to eliminate all mode competition, longitudinal as well as radial.
Abstract: The first experimental results of a high-power quasi-optical gyrotron are presented. The cavity was designed to eliminate all mode competition, longitudinal as well as radial. Powers to 80 kW and efficiencies to 11% were measured with indications that the actual electronic efficiency was at least a factor of 1·5 greater.
47 citations
TL;DR: In this article, the possibility of increase in frequency of millimetre-wave gyrotron operation by transition to higher EC harmonics at a fixed magnetic field by the use of high-selectivity two-resonator cavities is discussed.
Abstract: In experiments aimed at the development of gyrotrons for electron-cyclotron (EC) plasma heating, output power of 2 MW at a wavelength of 3 mm was attained. The possibility of increase in frequency of millimetre-wave gyrotron operation by transition to higher EC harmonics at a fixed magnetic field by the use of high-selectivity two-resonator cavities is discussed. Outputs of over 100 kW were generated at the second and third harmonics of EC frequency. The results of calculation of pulsed magnetic systems, capable of providing the operation of near millimetre-wave long-pulsed gyrotrons, are given. The principles of increase in efficiency of gyrotrons by means of a depressed two-stage collector of electrons are discussed.
46 citations
TL;DR: In this article, a physical interpretation of beam modes in typical vacuum tubes is proposed showing that each beam mode leads to three different beam mode lines in gyrotron-typc devices, two of which are peniotron (resonant) interactions, the third one being n synchronous (gyrotron) interaction.
Abstract: A physical interpretation of beam modes in typical vacuum tubes is proposed showing that each beam mode leads to three different beam mode lines in gyrotron-typc devices, two of which are peniotron (resonant) interactions, the third one being n. synchronous (gyrotron) interaction. Using the definition as given in this paper, it is shown that both peniotron and gyrotron interactions generally coexist in gyrotron-type devices, hut, that either one or the other predominates. The coupling terms entering the small-signal dispersion relationship of gyrotrons is shown to implicitly contain the three different interactions. By placing the guiding centre of thc beam electrons in gyrotron beams at a proper location, the gyrotron interaction can become negligibly small as compared to peniotron interactions (Js−m(x) = 0).
35 citations
TL;DR: In this article, an analytical theory is developed that permits one to analyse the influence of the transverse inhomogeneity of the interaction space on the efficiency of gyrotrons with various resonators.
Abstract: An analytical theory is developed that permits one to analyse the influence of the transverse inhomogeneity of the interaction space on the efficiency of gyrotrons with various resonators. A number of different gyrotrons including the quasi-optical one are considered. The results obtained make it possible, in particular, to estimate the efficiency of quasi-optical gyrotrons for different values of the electron beam radius and the ellipticity of the resonator mirrors.
TL;DR: In this article, a survey of gyrotron-oscillator cavity designs with enhanced mode stability properties is described, including complex and Fabry-Perot cavities, and a 60 GHz TE01/TE02 gyroron has already resulted in power greater than 200 kW CW.
Abstract: We survey work in the U.S.A. High average power gyrotrons (1 MW at 100-150GHz) are required for ECRH of magnetic fusion plasmas. Even though gyrotrons have superior mode stability compared with other tubes, they must be so grossly overmoded to handle 1 MW CW that mode control does become an issue. Studies of gyrotron-oscillator cavity designs with enhanced mode stability properties are described, including complex and Fabry-Perot cavities. In the complex cavity concept, two cavities each operating in a different mode are strongly coupled. Exploitation of this concept in a 60 GHz TE01/TE02 gyrotron has already resulted in power greater than 200 kW CW. Designs of TE03/TE04 and TE03/TE06 gyrotrons which promise to extend performance are discussed. A 115 GHz gyrotron using a Fabry-Perot cavity has been successfully demonstrated at power levels above 50 kW and prospects of extending performance are considered. Study of high peak power gyrotrons is stimulated by the perceived requirement for 300 MW RF ...
TL;DR: In this paper, the authors used a Green's function approach to treat scattering from underground tunnels, which leads to an integral equation for the unknown surface current J(ř) of the conducting cylinder, and an effective truncation algorithm was employed to evaluate these coefficients and the scattered field.
Abstract: Using a Green's function approach, similar to that used to treat scattering from underground tunnels, the problem is considered of electromagnetic scattering from conducting wires buried in the earth. The method leads to an integral equation for the unknown surface current J(ř) of the conducting cylinder. The expansion of J(ř) in terms of surface cylindrical wavefunctions and substitution in the integral equation results in an infinite set of linear equations for the unknown expansion coefficients. An effective truncation algorithm has been employed to evaluate these coefficients and, afterwards, the scattered field. Numerical results for the far-field region of the buried scatterer are plotted and some useful conclusions based on them are discussed.
TL;DR: In this article, the results of a study of second-harmonic emission from a gyrotron designed for high-power highfrequency operation at the fundamental of the cyclotron frequency are presented.
Abstract: The results of a study of second-harmonic emission from a gyrotron designed for high-power high-frequency operation at the fundamental of the cyclotron frequency are presented. Stable, very narrow bandwidth second-harmonic cavity emission from 209 GHz to 302 GHz has been observed. An output power of 25 kW and efficiency of 6·5% in the TE11, 2, 1, mode at 241 GHz is reported; this represents the highest power obtained to date from a high-frequency (> 100 GHz) harmonic gyrotron. These experiments have been carried out in a cavity for which the mode density is very high; the cavity diameter is approximately six free-space wavelengths for emission at the second harmonic. Mode competition between fundamental and second-harmonic modes is discussed. It is also shown that, in general, gyrotrons designed for high-power low-Q operation in overmoded cavities at the fundamental will also have high efficiencies and strong emission in second-harmonic modes. Prospects for high-frequency harmonic gyrotrons for p...
TL;DR: In this article, a Varian 60 GHz gyrotron designed specifically to generate microwaves in a single output mode has been operated at power levels up to 200 kW CW using mode-specific directional couplers.
Abstract: For the first time, a Varian 60 GHz gyrotron designed specifically to generate microwaves in a single output mode has been operated at power levels up to 200 kW CW. Using mode-specific directional couplers, measurements of the output mode content indicated that greater than 95% of the microwave output was in the desired TE02 mode with only small percentages in the neighbouring TE01 and TE03 circular electric modes. High output-mode purity is required for the efficient utilization of gyrotrons as high-power microwave sources for electron cyclotron resonance heating (ECRH) in magnetic fusion plasmas.
TL;DR: In this article, the authors report on the most recent results obtained with this gyrotron and discuss the cavity resonances that occur in this split cavity design, and present a detailed analysis of the cavity properties of the split cavity.
Abstract: The tunable millimetre-submillimetre wave source, Gyrotron III, incorporates a split cavity which permits mechanical fine tuning so that any frequency in the range 100-325 GHz becomes accessible. This paper reports on the most recent results obtained with this gyrotron and discusses the cavity resonances that occur in this split cavity design.
TL;DR: The recent advances in the experimental techniques are outlined in this paper, and the data at radio frequencies and for microwaves are reviewed.
Abstract: Electrical properties of biological substances and tissues are important for the understanding of biophysical interaction mechanisms as relevant to evaluation of potential health hazards. The knowledge of the tissue permittivity is also essential in developing effective electromagnetically-induced hyperthermia. The recent advances in the experimental techniques are outlined in this paper, and the data at radio frequencies and for microwaves are reviewed
TL;DR: In this paper, the influence of the resonator geometry on the design of quasi-optical gyrotrons is presented, and the effect of the actual electromagnetic field profile on the electronic efficiency is calculated for several cases.
Abstract: The influence of the resonator geometry on the design of quasi-optical gyrotrons is presented. Basic equations and relevant properties of quasi-optical resonators are reviewed. Since confocal resonators radiate an equal amount of power from each mirror, non-confocal resonators have to be used in order to maximize the output-coupling on one side. Technical constraints on ohmic power losses and mirror diameter are discussed. Using numerical solutions of the quasi-optical resonator equations, the influence of the actual electromagnetic field profile on the electronic efficiency is calculated for several cases.
TL;DR: Peniotron-gyrotron interactions in gyrotrons II. The dispersion relation contains terms describing their interplay, but the radial displacements of the beam require modifications to the stabilizing terms.
Abstract: Using the concept of beam modes and beam mode lines described in the preceding paper, it is shown that, the classical small-signal dispersion relation of gyrotrons derived in 1980 by Chu et al. contains terms which describe the relative interplay of peniotron and gyrotron interactions in gyrotron-type devices. However, due to the radial displacements of the beam (electrons which appear to have been neglected by Chu el al.), the stabilizing terms must be modified. When the location R0 of the guiding centres is such that J8-m(x) disappears, no s-harmonic gyrotron interaction can occur, leaving peniotron interaction as the only possible type of interaction.
TL;DR: In this article, a quasi-optical cavity of special configuration suitable for use in a high-power gyrotron operating at short millimetre and submillimetre wavelength has been developed.
Abstract: A quasi-optical cavity of special configuration suitable for use in a high-power gyrotron operating at short millimetre and submillimetre wavelength has been developed. A gyrotron using this new type of cavity is under development. Both the linear and non-linear analyses are worked out. Digital calculation predicts efficiency of 37% at V 0 = 50 kV.
TL;DR: In this paper, the periodic space charge field generated by two interfering light beams is calculated for a general set of parameters using a linearization method, and the results are shown to be similar to ours.
Abstract: The periodic space charge field generated by two interfering light beams is calculated for a general set of parameters using a linearization method.
TL;DR: The DC conductivity of semiconducting vanadium germanate glasses of compositions in the range of 40-70mol(%) V2O5 has been measured in the temperature region 300-530 K as discussed by the authors.
Abstract: The DC conductivity of semiconducting vanadium germanate glasses of compositions in the range of 40-70 mol(%)V2O5has been measured in the temperature region 300-530 K. Measurements have been made on unannealed samples and some samples annealed at 300°C. Annealing the samples at temperatures of about 300°C causes the appearance of a crystalline phase resulting in an increase of conductivity. The crystalline temperature has been estimated from the conductivity data for unannealed samples. These seem to be in reasonable agreement with the corresponding results found in the literature.
TL;DR: In this paper, the authors present a new model of the gyrotron interaction mechanism and suggest that many current models are both inadequate and misleading, and show that five different energy transfer mechanisms can be recognized, three of them acting in the transverse and two in the axial direction.
Abstract: The main object of the paper is to present a new model of the gyrotron interaction mechanism and to suggest that many current models are both inadequate and misleading. The model is based on the concept of a filamentary/tubular ‘beamlet’ and its interaction with an electromagnetic field set up in a waveguide. It is shown that, contrary to the currently accepted view, five different energy transfer mechanisms can be recognized, three of them acting in the transverse and two in the axial direction. Four of the five mechanisms act in pairs, the two members of each pair opposing each other; one mechanism is due to the relativistic variation of electron mass and the other to the magnetic component of the RF field. It is also shown that when a gyrotron is operating near the cutoff frequency of a TE mode the effects due to the relativity variation of electron mass predominate, the amplification process then being at its maximum. A detailed and critical discussion of the existing literature is included, ...
TL;DR: In this article, a high-harmonic gyro-klystron amplifier with high-order cylindrical-cavity TE modes has been proposed, achieving gain in excess of 20 dB at the fifth and sixth harmonics of the cyclotron frequency.
Abstract: Experimental results of a high-harmonic gyro-klystron amplifier are presented along with small-signal theory and large-signal simulation data. In this device, axis-encircling electrons interact synchronously with high-order azimuthal cylindrical-cavity TE modes. Gain in excess of 20 dB has been achieved at the fifth and sixth harmonics of the cyclotron frequency. The requisite high-energy beam is provided by a gyro-resonant RF accelerator. Harmonic operation together with RF acceleration potentially constitute a compact high-power high-frequency amplifier.
TL;DR: In this article, the authors examined the interaction between a relativistically rotating electron layer and electromagnetic fields with exp (jωt − Γz − jsθ) variation, and the linearized relativistic Lorentz force equation was used to evaluate the RF displacement due to harmonic fields.
Abstract: Several authors have assumed the existence of the (s + 1), s and (s − 1) harmonic interactions in the electron beam immersed in an axial magnetic field (Dohler et al. 1982, Ono et al. 1983). This paper examines the interaction between a relativistically rotating electron layer and electromagnetic fields with exp (jωt − Γz − jsθ) variation. The linearized relativistic Lorentz force equation is used to evaluate the RF displacement due to harmonic fields. It can be shown from this analysis that in the non-relativistic case, the beam waves are one at the (s + 1), one at the (s − 1) and two at the s harmonic of the cyclotron frequency. These modes may be identified as the fast (s + 1) and slow (s − 1) peniotron modes. This result is consistent with existing theories. The gyrotron interaction is observed as a result of energy exchange between the forward circuit wave and two beam waves at the s harmonic; it is a three-wave interaction. Whereas the fast (slow) peniotron interaction is observed as a resu...
TL;DR: A novel active-R synthesis baaed on the single-pole rolloff characteristics of operational amplifiers is described, and it is shown by experiments that the inductance simulator presents reliable high frequency performance.
Abstract: A novel active-R synthesis baaed on the single-pole rolloff characteristics of operational amplifiers is described. Various types of driving-point impedance, such as an inductance, frequency-dependent negative-resistance and frequency-dependent negative-inductance are systematically derived by the suitable choice of the amplifier transfer function. It is shown by experiments that the inductance simulator presents reliable high frequency performance.
TL;DR: It is shown that, even when the model is successful in accurately representing the image properties in the data domain, significant differences still exist between measured and predicted transform domain properties and, therefore, that such modelling although widely employed, is at best only an approximate guide to the efficient coding of transform coefficients.
Abstract: The success of a transform image coding scheme is dependent on a determination of the statistical properties of the data (measured either in the input or the transform domain) in order to ensure efficient allocation of coding capacity (bits) to significant coefficients, and in this regard simple parametric models have often been employed. In this paper the justification for such an approach is examined, using three widely differing test sources, and spectral responses and transform domain coefficient variances are determined both by direct measurement and via simple covariance models. It is shown that, even when the model is successful in accurately representing the image properties in the data domain, significant differences still exist between measured and predicted transform domain properties and, therefore, that such modelling although widely employed, is at best only an approximate guide to the efficient coding of transform coefficients.
TL;DR: In this article, a CdS-Pr6O11 thin film transistor fabricated by a multiple pump-down fabrication procedure is reported. The transistor characteristics are presented. Various transistor parameters are obtained from the characteristics.
Abstract: A CdS-Pr6O11 thin film transistor fabricated by a multiple pump-down fabrication procedure is reported in this paper. The transistor characteristics are presented. Various transistor parameters are obtained from the characteristics
TL;DR: In this article, a new kind of ECRM with a multi-mirror quasi-optical cavity is proposed and analyzed, and the analytical solutions of the cavity fields have been found and the experimental results are in satisfactory agreement with theory.
Abstract: A new kind of ECRM with a multi-mirror quasi-optical cavity is proposed and analysed. The new type of cavity used in this ECRM is studied in the first part of this paper. It is shown that this cavity is free from mode concentration and has a structure suitable for developing high-power short-millimetre and submillimetre ECRM. The analytical solutions of the cavity fields have been found and the experimental results are in satisfactory agreement with theory. The non-linear numerical analysis of this new ECRM is given in the second part of this paper. Employing the above-mentioned cavity and a hollow electron beam with large radius, this ECRM can operate even at the submillimetre waveband effectively and possesses great potential for increased output power. This ECRM is easy to manufacture because of its lack of stringent requirements on the electron beam and its simple construction.
TL;DR: In this paper, general expressions for the fields produced by an arbitrarily variable charge and current distribution are derived in the time domain, and the results are compared with those obtained by Fourier analysis.
Abstract: In this paper, general expressions for the fields produced by an arbitrarily variable charge and current distribution are derived in the time domain. The results are compared with those obtained by Fourier analysis. Starting from these results, the non-sinusoidal fields produced by the basic large-current radiator when fed by different excitation currents, are analysed