Increasing Microwave Power Research Articles

Thermal Stability of Hydrogen in Silicon Nitride Films Prepared by ECR Plasma CVD method

Infrared (IR) absorption measurements, hydrogen evolution experiments and ESR measurements have been carried out in order to study the thermal stability of hydrogen, bond configuration and defect structure in silicon nitride films (SiN) prepared by an ECR plasma CVD method and in part by a conventional plasma CVD method. It is shown that the SiN films deposited at high microwave powers in which the bond configuration of N-H is predominant are thermally very stable, even after annealing at 900 °C in a dry N2 atmosphere. The IR spectra scarcely vary before and after the annealing. The hydrogen evolution from SiN films was found to be highly dependent upon the deposition conditions and deposition methods. The amount of hydrogen evolved after experiments up to 900 °C becomes less as the microwave power increases. The temperature at which hydrogen evolution starts to take place for SiN films deposited by the ECR plasma CVD method is generally higher than that for the P-CVD method, except for ECR SiN films deposited at high gas pressure. ESR measurements revealed that the hydrogen concentration in SiN films has little influence on the spin density.

Radiation effects in hydrolysed CaF 2, SrF 2 and BaF 2

Radiation damage of CaF 2, SrF 2 and BaF 2 crystals after thermal treatments in air at high temperatures (above 700°C) has been studied and compared with that of “as grown” samples. An enhancement of the V k -centres' production efficiency was found in the three compounds under LNT X-irradition. Interstitial atomic hydrogen (H o i) and OH −-interstitial fluorine complexes were also found in SrF 2, and BaF 2 but not in CaF 2, irradiated at LNT. RT irradiation produces H o i in CaF 2 and H o i, OH −-interstitial complexes and substitutional hydrogen ions (H − s) in SrF 2 and BaF 2. A different behaviour of the EPR signal of the H o i centres created at RT and LNT was observed at increased microwave power.

The Josephson Effect in Ceramic Bridge at Liquid Nitrogen Temperature

Bridge junction can be made by cutting a bulk ceramic superconductor into the right sizes. Using this sort of bridge, both dc and ac Josephson effects are confirmed in liquid nitrogen . We have observed microwave induced steps at either nhf/2e or 2nhf/2e where n is an integral, as well as the oscillation of critical supercurrent with the increase of microwave power or externally applied magnetic field.

Power-shifted microwave resonances of a hot cavity filled with a surface-ionized alkali-metal plasma: Theory and experiment

A new kind of thermal plasma device has been constructed consisting of an indirectly heated 2100 K X-band microwave cavity. The cavity is filled with a surface ionized K or Cs plasma with densities of from 1\ifmmode\times\else\texttimes\fi{}${10}^{16}$ to 1\ifmmode\times\else\texttimes\fi{}${10}^{17}$ ${\mathrm{m}}^{\mathrm{\ensuremath{-}}3}$. As a first experiment, the frequency of the ${\mathrm{TM}}_{010}$ mode has been measured as a function of microwave power absorbed by the cavity. The measurements are carried out under conditions where instabilities are not observed in the plasma. The resonant frequency is found to decrease as the microwave power increases. Two theories are developed to explain the frequency shifts, one depending on the ponderomotive force, the other on high-frequency resistive electron heating. Frequency shifts predicted by the ponderomotive force theory are substantially smaller than the observed shifts. The data are in reasonable agreement with the resistive-electron-heating theory if it is assumed that the work function of the microwave cavity wall is decreased by alkali-metal-atom coverage.

A novel intrinsic multimode fiber-optic sensor for the detection or monitoring of microwave power

A graded-index silica multimode fiber with an acrylate primary coating has been shown to act as an intrinsic sensor of microwave power. When under the influence of a microwave field, the fiber absorbs a small fraction of microwave energy and this alters the propagation condition for transmitted laser light (632.8 nm). This alteration is manifested in the speckle pattern which is projected, after transmission, from the cut end of the fiber, and is recorded either by an optical detector or by visual observation. The rate of change of the speckle pattern is the important feature. The sensitivity of the effect increases as the microwave power increases, as the fiber length increases, and when the fiber is coated with conducting silver paint. Microwave powers, transmitted at 2.45 GHz in a rectangular waveguide is in the range 0.07-700 W were detected with an accuracy of better than 2 dB. These power levels correspond to electric field levels of 2.8 \times 10^{2} V . m-1and 2.8 \times 10^{4} V . m-1at the position of the fiber. The results are briefly compared with recent similar observations using a silica single-mode fiber as the sensor and an interferometer as detector. Discussions relate to use of the speckle pattern for detection and to possible applications.

Evolution of low-density Thomson scattering on ELMO Bumpy Torus

The ELMO Bumpy Torus (EBT) confines a low-density, steady-state, microwave-driven plasma. On the basis of favorable initial diagnostic results, major machine upgrades—increases in microwave power and magnetic field—were initiated, and the feasibility of Thomson scattering was considered. From the time of the first laser measurements, in which a two-point spectrum was integrated during 30 or more Q-switched pulses, the Thomson scattering system has evolved into a reliable diagnostic tool that is able to obtain scans along 20 cm of the plasma diameter and to determine the central electron temperature at densities as low as 2×1011 cm−3. Based on a 25-J ruby laser and a seven-channel polychrometer, the present system (1) reveals a bulk plasma with Te=20–100 eV and ne=5–10×1011 cm−3 and (2) indicates a suprathermal tail consistent with x-ray measurements. With up to 200 kW of microwave power inside the machine, major problems to overcome were radiation damage to optical materials (≤3000 R/h) and plasma coating of windows and dumps.

Electron confinement studies on the EBT-S Bumpy Torus Experiment using soft x-ray techniques

Soft x-ray bremsstrahlung measurements have been performed on the ELMO Bumpy Torus (EBT-S) plasma to determine the electron temperature Te and electron density density ne using a calibrated Si(Li) detector over a wide range of operating conditions. The purpose of this paper is to outline the necessary assumptions and essential x-ray techniques that are inherent in soft x-ray measurements in order to investigate the electron heating and confinement properties of EBT-S. In addition, by utilizing the electron density as determined by the soft x-ray measurements, the previous EBT-S confinement analyses have been extended. The steady-state plasma of EBT-S is heated by microwaves using a continuous wave (cw) gyrotron that can operate up to power levels of 200 kW. From the soft x-ray measurements, both the electron temperature and density are found to increase at higher microwave power levels. For operation at microwave power levels of 200 kW, Te approaches 1 keV while ne approaches 1.2×1012 cm−3. In general, confinement properties are found to improve with increased microwave power. The data are compared with neoclassical transport scaling and the electron transport is found to be collisionless (ν/Ω<1) as well as neoclassical.

Magnetic interactions in milk xanthine oxidase.

The relaxation behavior of the EPR signals of MoV, FAD semiquinone, and the reduced Fe/S I center was measured in the presence and absence of other paramagnetic centers in milk xanthine oxidase. Specific pairs of prosthetic groups were rendered paramagnetic by poising the native enzyme or its desulfo glycol inhibited derivative at appropriate potentials and pH values. Magnetic interactions were found between the following species: Mo--Fe/S I (100-fold increase in microwave power required to saturate the MoV EPR signal at 103 K when Fe/S I is reduced as opposed to oxidized), FAD--Fe/S I and FAD--Fe/S II (70-fold increase in power required to saturate the FADH.EPR signal at 173 K when either Fe/S center is reduced), and Fe/S I--Fe/S II (2.5-fold increase in power to saturate the reduced Fe/S I EPR signal at 20 K when Fe/S II is reduced). The Mo--Fe/S I interaction was also detected as a reduced Fe/S I induced splitting of the MoV EPR spectrum at 30 K. No splittings of the FADH. or Fe/S center spectra were detected. No magnetic interactions were found between FAD and Mo or between Mo and Fe/S II. These results, together with those of Coffman & Buettner [Coffman, R. E., & Buettner, G. R. (1979) J. Phys. Chem. 83, 2392-2400], were used to estimate the following approximate distances between the electron carrying prosthetic groups of milk xamthine oxidase: Mo--Fe/S I, 11 +/- 3 A; Fe/S I-Fe/S II, 15 +/- 4 A; FAD-Fe/S I, 16 +/- 4 A; FAD-Fe/S II, 16 +/- 4 A. A model for the arrangement of these groups within the xanthine oxidase molecule is suggested.

Effects of quasiparticle redistribution on the surface impedance of superconductors

Calculations of surface impedance of a thin film superconductor indicate a significant decrease, with increasing microwave power, due to quasiparticle redistribution. An expression for the microwave-to-film coupling is derived. The distribution function is solved self-consistently to avoid a singularity.

Thermoluminescence and microwave induced thermoluminescence fading of rare-earth-doped barium titanate ceramics

Abstract The effect of microwave exposure on thermoluminescence (TL) of rare-earth-Uoped BaTiO3 ceramic phosphors was investigated as a method for microwave dosimetry. Following exposure to 60Co gamma radiation, phosphors exhibited a TL glow curve with two peaks. The low temperature glow peak faded rapidly, but the high temperature glow peak was relatively stable with more than 50% of the initial response remaining after 48 h. The phosphors were linear in TL response over an exposure range of 103 to 105 R. Within-batch variation in TL response was insignificant for all phosphors except BaTiO3 :Ce. Readouts from three batches of BaTiO3) :Dy showed reproducible glow curve structure but significant differences in glow curve area. All phosphors except BaTiO3, :Nd showed statistically significant TL fading following exposure to 100 mW/cm2 or more of microwaves. Fading increased with increasing microwave power density. Results of these studies show that rare-earth-doped BaTiO3 ceramics can potentially be utiliz...

Microwave alteration of the blood-brain barrier system of rats

Rats were exposed to 1.3 gHz microwave energy to assess the uptake of several neutral polar substances in certain areas of the brain. A quantitative, radioactive isotope method, which uses an internal standard, was employed to measure the loss of test substances to brain tissue. Single, 20 min exposure, to either pulsed or continuous wave (CW) microwave energy induced an increase in the uptake of d-mannitol at average power densities of less than 3.0 mW/sq. cm. The permeability change was greatest in the medulla, followed, in decreasing order, by the cerebellum and hypothalamus, with small or negligible changes in the hippocampus and cortex. Permeability increases were observed for mannitol and inulin but not for dextran. Increased permeability was observed both immediately and 4 h after exposure, but not 24 h after exposure. After an initial rise, the permeability of cerebral vessels to saccharides decreased with increasing microwave power. Differences in the level of uptake occurred between CW energy and pulsed energy of the same average power. Microwaves of the same average power but different pulse characteristics also produced different uptake levels. Our findings suggest that microwaves induce a temporary change in the permeability for small molecular weight saccharides in the blood-brain barrier system of rats.

Microwave-enhanced critical currents in superconducting Al strips with local injection of electrons

In contrast to previously reported results the critical current in superconducting Al strips under microwave irradiation is shown to reach a maximum value before decreasing continuously to zero with increasing microwave power. The influence of local injection of electrons through a Schottky barrier on this phenomenon is investigated.

Electron paramagnetic resonance of the tungsten derivative of rat liver sulfite oxidase.

Sulfite oxidase purified from livers of tungsten-treated rats has been used for EPR studies of tungsten substituted at the molybdenum site of the enzyme in a fraction of the molecules. The EPR signal of W(V) in sulfite oxidase is quite similar to that of Mo(V) in its line shape and in its sensitivity to the presence of anions such as phosphate and fluoride. Hyperfine interaction with a dissociable proton is also observed in both signals. The pH-dependent alteration in line shape exhibited by the Mo(V) EPR signal of the rat liver enzyme. Incomplete reduction of the tungsten center at pH 9 is indicated by attenuated signal intensity at this pH. The W(V) signal has g values lower than those of the Mo(V) signal, has a much broader resonance envelope, and is much less readily saturated by increasing microwave power. Kinetic studies on the reduction of the heme and tungsten centers of sulfite oxidase have shown that reduction of de-molybdo forms of sulfite oxidase by sulfite is catalyzed by the residual traces of native molybdenum-containing molecules. Reduction is accomplished by electron transfer involving intermolecular heme-heme interaction. The W(V) signal is generated only after all the heme centers are reduced. The rate and extent of heme reduction at pH 9 are the same as at pH 7. Studies on the reoxidation of W(V) and reduced heme by O2 and by cytochrome c suggest that the cytochrome b5 of sulfite oxidase is the site of electron transfer to cytochrome c, whereas oxidase activity is the property of the molybdenum center. It appears that the tungsten center in sulfite oxidase is incapable of oxidizing sulfite.

ChemInform Abstract: PROTON HYPERFINE STRUCTURE IN THE ELECTRON SPIN RESONANCE SPECTRUM OF THE ACETONITRILE DIMER RADICAL ANION

The e.s.r. spectrum of (CH3CN)–2· has been observed in a γ-irradiated single crystal of acetonitrile at 77 K. At a crystal orientation for which the spectra from magnetically distinguishable sites coalesce, the spectrum consists of a well-resolved hyperfine structure arising from a 14N quintet of 1H septets, typical coupling constants being A(14N)= 0.85 mT and A(1H)= 0.21 mT. This spectrum saturates readily with increasing microwave power and is photobleachable by red light, these effects paralleling those observed for the 14N quintet spectrum of (CD3CN)–2·. The lack of spectral resolution at other orientations is attributable to interference by site splitting and to a decrease in the proton coupling as the nitrogen coupling increases to its maximum value in the rotation plane. Confirmation of the latter observation has been obtained by similar studies on CH2DCN and CHD2CN. Both the magnitude of the proton coupling and its relationship to the nitrogen coupling are shown to be consistent with information on the structure and spin density distribution derived from studies of the dimer radical anion in deuterated acetonitriles.

Proton hyperfine structure in the electron spin resonance spectrum of the acetonitrile dimer radical anion

The e.s.r. spectrum of (CH3CN)–2· has been observed in a γ-irradiated single crystal of acetonitrile at 77 K. At a crystal orientation for which the spectra from magnetically distinguishable sites coalesce, the spectrum consists of a well-resolved hyperfine structure arising from a 14N quintet of 1H septets, typical coupling constants being A(14N)= 0.85 mT and A(1H)= 0.21 mT. This spectrum saturates readily with increasing microwave power and is photobleachable by red light, these effects paralleling those observed for the 14N quintet spectrum of (CD3CN)–2·. The lack of spectral resolution at other orientations is attributable to interference by site splitting and to a decrease in the proton coupling as the nitrogen coupling increases to its maximum value in the rotation plane. Confirmation of the latter observation has been obtained by similar studies on CH2DCN and CHD2CN. Both the magnitude of the proton coupling and its relationship to the nitrogen coupling are shown to be consistent with information on the structure and spin density distribution derived from studies of the dimer radical anion in deuterated acetonitriles.

Electron spin resonance of gamma‐irradiated cellulose

AbstractIrradiation of purified cellulose with cobalt‐60 gamma rays in vacuo produces moderate yields of radicals detectable by electron spin resonance. The ESR spectrum is asymmetric, with five partially resolved peaks occupying a total region of about 50 gauss wide and a spectroscopic splitting factor near g = 2. The peaks show differing saturation behavior with increasing microwave power. Differences of crystallinity have no obvious effect on the yield or nature of the radical ESR spectrum. The presence of about 8% water during irradiation decreases the yield greatly and modifies the hyperfine structure. For dry cellulose the initial G value for radicals is near 2.8 radicals per 100 e.v. absorbed, but the concentration levels off at doses a little over 6 × 1020 e.v./g. Despite the early falling‐off in yield, the radicals in stored irradiated specimens do not decay appreciably in several days. Even upon contact with air the decay is quite slow. Thermal decay is imperfectly second‐order, fairly rapid above 120°C., and indicates several radicals of differing lifetimes.