Types Of Slow-wave Structures Research Articles

Study on Operation of Oversized Backward Wave Oscillator for Broadband Terahertz Radiation

We studied the operation of an oversized backward wave oscillator driven by an electron beam with energy less than 100 keV for terahertz radiation. Cylindrical slow wave structures (SWSs) with rectangular corrugations and annular electron beam are used to generate broadband terahertz radiation. The starting conditions for intense terahertz radiation are examined by varying the beam parameter and the SWS length. Operation frequencies in the range of 0.26–0.34 THz and 0.31–0.39 THz are obtained using two types of SWSs with different corrugation amplitudes. The obtained maximum output power is at the kilowatt level. Characteristics of the beam instabilities in the terahertz-SWSs are examined by comparison between the experimental and numerical results.

A three-dimensional nonlinear beam–wave interaction theory for common traveling wave tubes

A three-dimensional (3-D) nonlinear theory model of beam–wave interaction for common traveling wave tubes (TWTs) is described. The equation governing the amplitude of electromagnetic wave is derived analogously to Poynting’s theorem. The electron dynamics are treated using the 3-D Lorentz force equations. RF space charge fields are obtained from solutions of the Helmholtz equations. In the model, the RF field profiles for cold structure are represented by the digitized RF field calculated by a finite-element software, HFSS. Because the digitized RF field can be obtained in the same way, the 3-D simulation code can be used to simulate common TWTs, such as helix TWTs, coupled-cavity TWTs, and even the folded waveguide TWTs. Results from the 3-D code are compared with those from 1-D code, experiment and the existing analytical theories for three types of slow wave structures.

Design and RF Characterization of W-band Meander-Line and Folded-Waveguide Slow-Wave Structures for TWTs

Studies on design and RF characterization were carried out for two different types of slow-wave structures (SWS) at W-band frequencies: 1) a meander-line SWS along with step impedance transformer, and 2) a folded-waveguide slow-wave structure along with tapered waveguide coupler. Quasi-TEM analysis was used for the design of these structures and the structures were fabricated using wire-cut and spark-erosion electric discharge machining. Dispersion characteristics and S-parameters of the structures were measured and compared against those obtained from analysis and 3-D electromagnetic simulation using CST-microwave studio.

Analysis of the instability in relativistic traveling wave tube

The relativistic traveling wave tube is an important high power microwave source. The corrugated cylindrical waveguide is usually used as slow wave structure of this device. Starting from wave equation and using boundary conditions, dispersion relation is derived for the corrugated waveguide, in which an intense relativistic electron beam propagates along the axis. Two cases which are shorter period and longer period are discussed in this paper respectively. The small signal gain of the relativistic traveling wave tube is analyzed and some conclusions are drawn. The analysis method presented in this paper can be extended to other types of slow wave structures of relativistic traveling wave tube.

E-plane horn excitation of slow wave structures for obtaining high-density electron cyclotron resonance plasmas

This paper describes a new method of exciting slow wave structures (SWS) for obtaining high-density electron cyclotron resonance plasmas. The electric field component corresponding to the slow wave mode (SWM) of SWS is excited by an E-plane horn antenna. The special features of the microwave transmission line are the stable tuning for a given antenna and no requirement for water cooling on any of the components. Two types of SWS, a helical coil and a slotted line antenna, are studied, and the experiments are carried out in nitrogen and argon. The plasma producing capability is examined for these systems in the region wce,wpe≳wrf, where wce, wpe, and wrf correspond to electron cyclotron, plasma, and microwave frequencies, respectively. A high-density, large-diameter plasma (n0∼5×1011 cm−3; diameter ∼8.0 cm) could be obtained and the plasma could be maintained in the region 1≤wce/wrf≤2.

A traveling-wave maser system for radio astronomy

The design of a traveling-wave maser (TWM) for radio astronomy is discussed with particular reference to the Onsala system, which at present includes eight masers covering most of the frequency range 1-8 GHz (the frequency range in which the telescope is useful). Data are presented on the maser crystals iron- and chromium-doped rutile. A short discussion of different types of slow-wave structures (SWS's) used as maser interaction circuits, and some design criteria are given. We briefly consider the design of the ferrimagnetic isolator. A new method for rapidly retuning the maser to within a frequency band of the order of 100 MHz is introduced. The cryogenic system and the low-noise front-end waveguide are discussed. Also some general conclusions about the TWM bandwidth and a short survey of masers for frequencies above 10 GHz are given. Finally, we discuss which types of radio-astronomical research programs could most benefit from these extremely low-noise amplifiers.

Some New Circuits for High-Power Traveling-Wave Tubes

A discussion of new types of slow-wave structures, in which the coupling between sections is obtained largely by negative mutual inductance, is given in this paper. Since this type of coupling can be used to give "fundamental" amplifier operation with relatively high impedance, the devices are somewhat unusual in the field of high-power traveling-wave tubes. Several structures which make use of this type of coupling are examined in a qualitative manner, and the results of "cold tests" on each model are given. In particular, one device, the so-called "clover-leaf" structure, is investigated in some detail. Curves of impedance, C, and gain at megawatt power levels are included. Some discussion of the practical problems involved in the design of an amplifier using this circuit is presented to serve as a guide for those interested in the construction of high-power traveling-wave tubes.