Microwave Cavity Mode Research Articles

Electron cyclotron resonance light source from TE011 mode microwave plasma

An intense ultraviolet and visible radiation source for various applications has been conceptualized, designed, and developed using a TE011 mode microwave cavity filled with plasma immersed in a magnetic field. The radiation intensity emitted from the source, as a function of the magnetic field intensity, approaches maximum at the electron cyclotron resonance. Light intensity increases with pressure inside the Hg+Ar lamp and the microwave power.

Microwave synthesis and sintering of Ba(Mg 1/3Ta 2/3)O 3

Ba(Mg 1/3Ta 2/3)O 3, BMT, was synthesized and sintered by microwave processing at 2.45 GHz. Appropriate amounts of BaCO 3, MgO, and non-stoichiometric Ta 2O 5− x were used as starting materials for the synthesis. BMT was obtained by heating the precursors in a multimode microwave cavity of 2 kW between 900°C and 1300°C for just 20 min. The synthesis was carried out in N 2 atmosphere to prevent the oxidation of Ta 2O 5− x . The perovskite BMT starts forming at 900°C and becomes single phase material at 1300°C. The sintering of BMT was carried out in a single mode microwave cavity for 5 to 30 min at 1400°C to 1600°C without using any sintering aid. A relative density of 97% was obtained in 30 min of microwave sintering at 1600°C. In contrast, it was found that to achieve the same densification, it requires 6 h of soaking at the same temperature in conventional sintering process.

Observation of Nonlinear Coupled Photon-Magnon Oscillations in YIG

Nonequilibrium spin waves excited by the parallel pumping in an yttrium iron garnet placed in a microwave cavity was studied by means of additional weak microwave signal. The response of the probe signal represented a two-hump spectrum just above the threshold of parametric instability. It corresponds to mixed oscillations of photons and magnons and demonstrates that the parametric spin-wave pair behaves as a single-mode oscillator nonlinearly coupled with the electromagnetic mode of microwave cavity. We observed another splitting in the spectrum before the onset of auto-oscillations. It is assumed to indicate that this steady state of parametric system consists of two different parametric spin-wave pairs. Theoretical calculations which consider coupled systems of resonator mode and magnetic sample are found to be in good agreement with the experimental data.

The crystal growth anisotropy of YBa 2Cu 3O 7− δ fabricated by the MTG method in a microwave cavity

The aim of this work is to optimise a microwave melt texture growth process in a vertical travelling solvent zone technique in a single mode microwave cavity to grow large single-domain Y123 samples. Indeed, the large observed thermal gradient (>180°C/cm) in combination with the possibility of translating the sample across the microwave cavity allows this technique to achieve conditions similar to those used in the classical MTG using a vertical furnace. However, the particular heating mechanism, in the microwave case, allows for a novel range of thermal conditions to be accessed, particularly a larger thermal gradient, to grow large Y123 single-domain in novel thermal conditions. In a first effort to optimise this microwave technique, a composition corresponding to a Y211-rich Y123 mixture, doped with cerium dioxide, was sought in order to improve the Y123 domain size. Secondly, the influence of the melt temperature and the bar diameter on the size and orientation of the Y123 quasi-crystals was investigated. The influence of each parameter is discussed with respect to the classical Y123 growth mechanism, and an explanation of the angle, which is observed to be near to 45°, between the ab-plane and the pulling direction is proposed. The Bean critical current density without applied magnetic field, for a cleaved sample at 77 K reaches 50,000 A/cm 2 showing the high quality of the microwave melt processed material.

Grain size, density, and mechanical properties of alumina batch-processed in a single-mode microwave cavity

Four different microwave cavity modes, namely, TM 111, TE 112, TE 113, and TM 013, were used to sinter alumina powder compacts in a batch process using a cylindrical single-mode microwave cavity. The grain size, mass density, hardness, and fracture toughness of the final densified products were examined in terms of (i) the position of the specimen within the microwave casket and (ii) the Cavity mode.

Effect of increasing hygroscopicity on the microwave heating of solid foods

The effect of a progressive increase in the bound strength of moisture in soybeans — a porous hygroscopic solid — during microwave heating is investigated. Thin layers of soybeans were dried with a single mode (TE 10) microwave cavity operating at 2450 MHz. The absorbed microwave power, temperature, and mass loss of the seeds were monitored continuously. Under a constant absorbed microwave power of 0.57 W/g, the temperature of a soybean seed increased rapidly at the initial stages of drying, reached a maximum of about 75 °C in approximately 50 min, and decreased gradually during the latter stages of drying to about 58 °C in 150 min. To maintain a constant drying temperature the absorbed microwave power had to be progressively increased as required. The results indicate that drying increases the average bound strength of the remaining moisture in a hygroscopic material and the energy needed to evaporate a unit mass of moisture increases accordingly. Consequently, progressively higher absorbed microwave powers are needed to maintain the temperature of low moisture solid foods during microwave heating processes that are accompanied by significant moisture loss.

Microwave Process Control Through A Traveling Wave Tube Source

AbstractA rapid feedback control system was designed to operate with a traveling wave tube amplifier for regulating the sintering temperature of tows and tubes in a single mode microwave cavity. The control system regulated the microwave frequency and power absorbed by the sample in order to maintain the sample temperature. Testing with NICALON tows and mullite tubes demonstrated that the control scheme worked well for stationary and slowly moving (<10mi/min) samples, but failed for fast moving samples. Difficulty with measuring sample temperatures was resolved by using a light sensor to measure the emitted light intensity and to gauge the relative degree of heating. This work was supported by the Department of Energy, Office of Industrial Technologies, Advanced Industrial Materials Program.

Self-pulsing behaviour in a mesomaser

The dynamics of a mesoscopic system of two-level Rydberg atoms, in resonant interaction with a microwave cavity mode and a coherent injected signal, is described in terms of Maxwell-Bloch equations with atomic propagation. When the system operates as an absorber, atomic cooperation can induce multistability as well as temporal instability and self-pulsing, quite differently from standard absorptive optical bistability. The self-pulsing behaviour is discussed in detail. At the instability boundaries the numerically calculated values of the oscillation frequency turn out to be in excellent agreement with those predicted by the linear stability analysis.

Microwave heating: A new process for texturing the high Tc superconductor YBa 2Cu 3O 7−δ

Microwave heating appears as a very promising method that can be applied to the melt texture growth (MTG) process for the texturing of the high Tc superconductor “YBaCuO”. In the new MMTG (Microwave Melt Teture Growth) process, the conventional furnace is replaced by a single mode microwave cavity and the “123” sample is placed orthogonally to the electrical field. A high termal gradient acting as a texturing strength is produced, that allows well textured domains to be developed. One of the advantages of this technique will be the texture formation of long samples by a translation of the bars in the microwave cavity.

The study of a 2.45 GHz plasma source as a plasma generator for the SCECR electron cyclotron resonance ion source

The 2.45 GHz plasma source is a multicusp electron cyclotron resonance source with a tuned single mode microwave cavity. This is a bright plasma source with a well characterized operating mode and plasma parameters [A. K. Srivastava, et al., Rev. Sci. Instrum. 63, 2556 (1992); A. K. Srivastava and J. Asmussen, J. Vac. Sci. Technol. A 11, 1307 (1993)]. The superconducting electron cyclotron resonance (SCECR) is a fully superconducting, hexapole stabilized tandem mirror ion source with a multimode microwave cavity. It is a high charge state ion source with extensive beam diagnostics [T. A. Antaya, Nucl. Instrum. Methods B 40/41, 1024 (1989)]. The coupling of these two sources permits a number of fundamental studies important to both classes of ion sources. The 2.4 GHz plasma source will be used to study the effects of ion or electron (or both) density enhancement on the charge state distribution, total extracted current, and ion energy distributions of the SCECR. The SCECR in turn will be used as a test stand to measure directly the ion distribution and beam characteristics of the 2.45 GHz plasma source. The first results with this hybrid ion source will be presented at this conference.

Mechanical characteristics of hybrid multilayer green Tape™ ceramics sintered in a 2.45 GHz single mode microwave cavity

Research indicates that microwave energy offers many advantages over conventional heating methods. These advantages generally can be divided into two categories. One of them is the reduction in processing time and temperature, and the second one is the fabrication of materials with unique and/or superior properties. Microwave energy appears to be especially advantageous for the processing of many types of ceramics requiring high thermal process temperatures. This is connected with the increased coupling efficiency of ceramics at high temperatures with the microwave energy, the more uniform volumetric heating, and increased densification rates at lower processing temperatures. This paper describes microwave sintering of a commercial alumina-based product, Green Tape[sup TM] Dielectric 851AT (DuPont), that is designed for use as a material for hybrid integrated multilayer structures in the production of hybrid integrated circuits, as well as for some unconventional applications (ion optics, sensors, etc) (4,5). This study compares mechanical properties of conventionally and microwave sintered Green Tape[sup TM] 851AT hybrid multilayer structures.

Influence of radiation damping on the threshold of auto-oscillations in YIG under parallel pumping

Nonlinear magnon relaxation above the threshold of magnon instability is influenced by radiation damping as well as internal processes of magnon-magnon and magnon-phonon damping. Parametrically excited magnon pair disappears with creating a microwave cavity photon whose damping is given by a quality factor Q. Influence of microwave cavity mode damping on the instability and auto-oscillations of magnons is discussed on the basis of the S-theory.

Dependence of the frequency shift of the optical-microwave double resonance signal in the Cs D/sub 2/ line on the pumping frequency and power of a GaAs semiconductor laser

The OMDR (optical-microwave double resonance) effect in the Cs D/sub 2/ line was studied for realizing a gas-cell-type Cs atomic frequency standard. A glass cell containing Cs with buffer gases (Ar/N/sub 2/=1.26, total pressure=39 torr) was placed in a TE/sub 012/ mode microwave cavity at a temperature of 45 degrees C and was pumped using a GaAs semiconductor laser frequency locked to an external interferometer tuned to the 6P/sub 3/2/ (F=2,3,4) from 6S/sub 1/2/(F=3) transition. The OMDR signal appearing at the resonance to the F=4 from 3 hyperfine transition of the 6S/sub 1/2/ state shifted with detuning of the laser frequency and with change of the laser and microwave powers. The dependence of the shift on these variables around an optimum operating condition was obtained as, Delta nu /sub MW/(Hz)=-(0.31+or-0.02) (1+(0.44+or-0.15) ( Delta P/sub L//P/sub L/)) Delta nu /sub L/ (MHz)-10( Delta V/sub MW//V/sub MW/). >

Blackbody radiation from a single-mode source: A demonstration

Blackbody radiation emitted or absorbed by a single microwave cavity mode is detected and the signal displayed on an oscilloscope using a relatively straightforward technique.

A Microwave Method for Measurement of Fiber Orientation in Paper*

A microwave method for the measurement of fiber orientation in paper is described. The method uses a dual mode microwave cavity where the modes have equal resonant frequencies and mutually perpendicular electric fields. The paper is inserted through the cavity so that the electric fields of both modes are in the plane of the paper. If the orientation of the fibres in the paper is not random the resonant frequencies will differ due to the dielectric anisotropy of the paper. This difference is measured and can be calibrated to give the amount of fiber orientation. Moisture and thickness variations in paper can cause calibration errors. However, if the variations are within certain limits, these errors can be eliminated by a suitable selection of the resonator bandwidths.

Microwave surface resistance of superconducting Mo0.75Re0.25

A Mo0.75Re0.25 alloy endplate was tested on a Nb TE011 mode microwave cavity resonant at 11.2 GHz. An upper bound for the surface resistance of 2.8 μΩ and a lower bound of 102 G for the microwave magnetic breakdown field were established for the alloy plate. Comparison of these results to current requirements for a superconducting linear accelerator demonstrated the potential feasibility of this alloy as a practical alternative to Nb and Pb for accelerator applications. This is the first alloy shown to be a potential alternative to Nb and Pb and arguments are presented which indicate possible practical advantages of Mo0.75Re0.25 over Nb and Pb.

Design of a Multimode Cavity for a Parametric Amplifier

A triple mode microwave cavity has been designed and constructed for use in a negative resistance parametric amplifier. It is simultaneously resonant at the signal frequency of 3300 Mc/s., idler fr...

Spectrum Analysis of Spin-Echo Signals in Iron-Doped Rutile

X-band electron spin echoes have been obtained at 4.2°K in iron-doped rutile. The frequency spectrum of these echoes was observed on a conventional spectrum analyzer and compared to the spectrum of the input pulses. Not only is it possible for the echo frequency response to be a good replica of the input pulse response, but there is no observed distortion of the echo response vs delay time over the time interval investigated (5–50 μsec). This latter result of no frequency distortion versus delay time for the time interval investigated is in agreement with the fact that the spectral diffusion time constant (as measured by the three-pulse stimulated echo technique) was found to be no less than one millisecond. It is shown, however, that for two identical input pulses the turning angle can be no greater than 120° if good spectral reproducibility is desired. Echoes were also observed simultaneously at two different frequencies within the same resonance line and the same microwave cavity mode with no distorting effect of one echo upon the other; and at two different frequencies in different resonance lines and two different microwave cavity modes.

Beam forming with microwave cavity modes

Beam forming with microwave cavity modes