Search

We proposed an oversized coaxial multi-beam relativistic klystron amplifier (OCMB-RKA) with a new input coupler of lesser complexity giving enhanced input microwave power absorption rate for generating high power millimeter-wave radiation in Ka-band. The high-frequency structure of the OCMB-RKA was designed, fabricated, and cold-tested for results that agreed well with the simulated results. Furthermore, using the 3D particle-in-cell (PIC) code, the beam-wave interaction of the OCMB-RKA was simulated, considering two different materials (stainless steel and copper) making the interaction structure. When a 500 kV, 3 kA electron beam, and a focusing magnetic flux intensity of 1 T were adopted in the PIC simulation, a five-cavity OCMB-RKA yielded the output power of 610 MW at 30.525 GHz with the electronic efficiency of 40.7% and the saturated gain of 55.3 dB. Experimentally, the OCMB-RKA demonstrated its capability of generating high power Ka-band radiation typically of 390 MW power with the pulse width of 27 ns.

A miniaturized, high electronic efficiency, S-band metamaterial extended interaction klystron (MEIK) is proposed. The metamaterial-based extended interaction resonant cavities were designed, fabricated, and tested, the assembled and cold-tested results confirm the feasibility of miniaturization in MEIK. Furthermore, the particle-in-cell (PIC) simulation predicts that, typically, when the beam voltage and current are 30 kV and 3 A, respectively, the focusing magnetic field is 1000 G, a 3-cavity MEIK yields the output power of 56 kW at 2.453 GHz, with the saturated gain of 47 dB and the electronic efficiency of 62%, and, importantly, with the cavity diameter of its interaction structure being ~1/2 of a conventional extended interaction klystron. As a power amplifier, the emerging MEIK with its miniaturization and high electronic efficiency has potential applications such as in future accelerators and microwave heating systems.

A highly efficient and compact metamaterial extended interaction oscillator (MEIO) is characterized and designed. The power exchange function of the multiple-gap extended interaction resonant cavity loading the proposed metamaterial is investigated for the π mode. Furthermore, the cavity diameter of 5-gap MEIO is only 37 mm at S-band. The CST PIC simulations show the peak output power of about 10 MW and the electronic efficiency up to 48% at 2.866 GHz when the beam voltage and current are 130 kV and 80 A, respectively, and the focusing magnetic field is 2000 G. The simulation results suggest that the proposed MEIO has the potential application in the future accelerators as an MW-level high-efficiency, miniaturized microwave source.

A helical slow-wave structure consisting of a metallic helix supported by double-negative metamaterial (DNG-MTM) rods, symmetrically arranged around the helix, in a metal envelope was analyzed, considering the frequency-dependent permeability and the permittivity of the DNG-MTM following Lorentz and Drude models. The analysis was validated against the 3-D electromagnetic simulation using CST Studio and was extended for studying the effects of the DNG-MTM parameters on the dispersion and interaction impedance of the structure. Tunability of the structure over multiple-frequency bands was also demonstrated. The possible means of metal MTM layering of the radial faces of the discrete support rods were suggested in a more realistic structure configuration. The structure exhibited a high value of interaction impedance as compared to its traditional counterpart, promising enhanced device efficiency and miniaturization. The structure has potential applications in backward-wave amplifiers and backward-wave oscillators.

The tape-helix model of analysis of a helix surrounded by a double-negative metamaterial tube in a metal envelope was developed adding a rigor to the earlier analysis that had used the simp...

A simple metamaterial loading scheme for a helical slow-wave structure was proposed in lieu of a conventional metal vane loading. The proposed structure consists of a helix in a metal envelope supported by rectangular dielectric rods each with I-shaped metal-strip epsilon-negative metamaterial printed on both of its radial faces. Our study, based on CST simulation, showed that the proposed simple structure gives controlled dispersion as obtained by the conventional vane-loaded helix with large interaction impedance values even higher than those of the latter.

We proposed a miniaturized S-band extended interaction klystron (EIK) assisted by metamaterial. The interaction structure of the EIK consists of a cylindrical resonant cavity filled with a metamaterial (complementary electric split-ring resonator) array. The study based on CST Eigenmode Solver predicted that the transverse cavity dimension of the proposed metamaterial assisted EIK is 1/3-1/2 times smaller than that of its conventional counterparts, while the device delivers typically 122 kW power, 53.5 dB gain and 43.5% electronic efficiency with an input drive of 0.27 W for typical beam and magnetic field parameters. The proposed metamaterial assisted EIK has potential applications in radar, industrial heating, accelerator, and satellite communications.

The performance of a disc-loaded gyro-traveling wave tube (gyro-TWT), which is optimized a priori by controlling the structure parameters for wide device bandwidths at large gains, is analyzed for studying the sensitivity of the gain and bandwidth of the device to the beam and the magnetic field parameters. Hence, it is predicted that the optimum beam and the magnetic field parameters will result in a much wider bandwidth at a larger gain than that of a smooth-wall gyro-TWT.

Forward- and backward-wave interaction analyses of a plasma-filled helix traveling-wave tube are developed following the Eulerian hydrodynamic approach and taking into account the effects of the following three factors: 1) the thermal velocity of plasma electrons; 2) collisions between the plasma electrons; and 3) the finite diameter of the electron beam and its proximity to a metallic boundary. The electron beam is treated as a moving charged fluid, and the plasma is treated as a stationary quasineutral fluid. The coupled circuit and the electronic equations are developed, and a Pierce-type hot (beam-present) dispersion relation is obtained, which is then interpreted for the forward-wave gain-frequency response and for the backward-wave oscillation criterion of the device. In the absence of the slow-wave structure, the dispersion relation reduces to that of a beam-plasma amplifier, whereas in the absence of the plasma, the dispersion relation passes on to that of a conventional vacuum traveling-wave tube. The analysis is further validated with an existing forward-wave interaction analysis of a plasma-assisted helix traveling-wave tube that treats the beam-wave interaction in the device as a boundary-value problem by considering the beam-plasma system as a propagating medium of an equivalent relative permittivity tensor. Interestingly, similar to a beam-plasma amplifier, a plasma-filled TWT supports no backward-wave oscillation in the reactive-plasma convective instability.

Simple closed-form formulas for the estimation of the π-mode stopband and the stopband attenuation in an azimuthally asymmetric helical slow-wave structure (SWS) are developed, following the coupled-mode analysis of multiple reflections. The formulas are simple and amenable to easy computation, and also allow the use of the dispersion characteristics of the structure obtainable from any standard electromagnetic modeling, thereby accruing the accuracy of 3-D electromagnetic analysis. The analysis is benchmarked against published results with close agreement. Based on the analysis, SWS configurations that would reduce the deleterious effects of asymmetry and also would improve TWT efficiency are suggested.

A simple equivalent circuit analysis of the ring-bar slow-wave structure of a traveling-wave tube is developed, using the coupled transmission-line approach, for the dispersion and interaction-impedance characteristics of the structure. The effects of the ring and the bar widths of the structure are included in the analysis. The analysis is validated, with respect to 1) an X-band structure, against both measurement and simulation, as well as 2) a Q-band structure, against simulation.

The concept of broadbanding of a helical slow-wave structure using ldquomultidispersionrdquo phase velocity taper has been analytically explored, following Pierce's small-signal analysis in order to form a physical basis behind this approach. Furthermore, large-signal analysis has been used to make out the efficacy of the physical basis arrived at from the small-signal analysis. Useful inferences are also drawn on the flattening of gain- and power-frequency responses and the reduction of second-harmonic content, using multidispersion phase velocity taper.

A helix supported by a double-negative metamaterial in a metal envelope was analyzed in the sheath-helix model to explore its potential as the slow-wave structure of high efficiency backward-wave devices. The transmission line equivalent distributed line parameters of the structure were interpreted for the dispersion relation of the structure. The ratio of the envelope-to-helix radii was found to control the dispersion characteristics and hence the frequency range of backward wave interaction, a critical value of the ratio of radii corresponding to the existence of a non-propagating, leaky wave.

Small-signal analysis of a plasma-filled helix traveling-wave tube was developed following Eulerian hydrodynamic approach. The electron beam was treated as a moving charged fluid and the plasma a stationary quasi-neutral fluid. The coupled circuit and electronic equation was developed and a Pierce-type hot dispersion relation obtained, which was then interpreted for the gain-frequency response of the device. The analysis was validated against an existing approach that treats the interaction as a boundary value problem by considering the beam-plasma system as a propagating medium of an equivalent relative permittivity tensor.

Attenuator-coated helix-support rods in a helical slow-wave structure were modeled by considering them to be made up of lossy dielectric material having equivalent bulk conductivity. The same conductivity values were used in 3D HFSS modeling of the helical slow-wave structure having the helix supported by three such support rods inside a metal envelope, and the attenuation constant of the structure was found. The proposed approach was used to characterize the attenuation constants in the sever region of a typical X-Ku band slow-wave structure and benchmarked against measurement.

This paper presents a simple self consistent large-signal formulation for computation of saturated gain, power and saturation length of a gyro-TWT. A computer code has been developed in C++ language. The computed results were found to be matching with the reported results obtained from other formulation. Using this code, a gyro-TWT interaction structure has been designed at 35 GHz with beam voltage of 50 kV.

1. In cats anaesthetized with chloralose, repeated injections of 20 μg ouabain were made either into the cerebral ventricles, or into the ventromedial nucleus of the hypothalamus (VMH), or intravenously whilst the electrocardiogram, arterial blood pressure and respiration were recorded. 2. The injections produced cardiac arrhythmias preceded by sinus bradycardia, variable changes in arterial blood pressure and respiratory depression. Death occurred either from ventricular fibrillation or from cardiac arrest. 3. The arrhythmias which occurred after the injections into the cerebral ventricles were not peripheral effects produced after absorption of the ouabain into the blood stream, because with intravenous injections larger amounts were required to produce the arrhythmias and to cause death than with intraventricular injections. The arrhythmias which resulted in death were due to an action on the VMH. With microinjections of ouabain into this region of the brain death occurred earlier and after smaller doses than after intraventricular injections. 4. While sinus bradycardia was abolished by bilateral vagotomy other cardiac arrhythmias were prevented by acute cardiac sympathectomy and cervical cord transection. Thus both the sympathetic and parasympathetic nervous systems appear to be involved in the production of these arrhythmias. 5. Since some of the cardiac arrhythmias obtained with ouabain in anaesthetized cats resemble the cardiotoxic effects seen in clinical practice during treatment with digitalis glycosides it is concluded that these effects, too, are, at least in part, central in origin, caused by an action on the VMH and mediated mainly via the sympathetic nervous system.