Inner Surface Of Cavity Research Articles

Template-based fluoroethylenepropylene ferroelectrets with enhanced thermal stability of piezoelectricity

In ferroelectrets, the piezoelectricity stems from the charges of both polarities trapped on the inner surfaces of the cavities in the material, so that its thermal stability is defined by the stability of the respective charges. In the present work, a template-based lamination technique has been employed to fabricate tubular-channel ferroelectrets from fluoroethylenepropylene (FEP) films. It has been shown that the piezoelectricity in FEP ferroelectrets decays at relatively low temperatures due to the inherently lower thermal stability of the positive charge. In order to improve charge trapping, we have treated both FEP films and inner surfaces of the ferroelectret cavities with titanium-tetrachloride vapor, using the atomic-layer-deposition technique. Using surface-potential-decay measurements on FEP films, we have found that the charge-decay curves shift by more than 100 °C to the higher temperatures as a result of the surface treatment. Direct measurements of piezoelectric d33 coefficients as a function of temperature have shown that the piezoelectric stability is likewise improved with the d33-decay curves shifted by 60 °C to the right. The improvement of electret/ferroelectret properties can be attributed to the formation of the deeper traps on the chemically modified FEP surface. SEM micrographs and EDS analysis reveal island-like structures with titanium- and oxygen-containing species that can be responsible for the deeper trapping of the electret charges.

In-situ plasma cleaning to decrease the field emission effect of half-wave superconducting radio-frequency cavities

The in-situ plasma cleaning technique using the chemical reactive oxygen plasma to remove the hydrocarbon contaminants, the outmost layer of the inner surface of the HWR cavity, has been explored at Institute of Modern Physics, CAS. For the purpose of cleaning the HWR cavity in the cryomodule by plasma, an offline apparatus for the plasma discharge study was set up, which duplicates the assembly of the cavity inside the cryomodule. Plasma ignition procedures were investigated. And the plasma parameters such as free electron number density, electron temperature and dissociated oxygen atom intensity were diagnosed by optical emission spectra to optimize the operation conditions for plasma in-situ cleaning of the HWR cavity. To evaluate the efficiency of the plasma in-situ cleaning of the HWR cavity, the related experiments were carried out on the vertical test stand. The results show that the hydrocarbon contaminants on the inner surface of the cavity were removed, and the maximal available accelerating gradient of the cavity was improved by 29% due to the mitigation of field emission inside the cavity after plasma cleaning. Details of these experimental results and observations are discussed in this article.

(Invited) Study on Electro-Polishing of Nb Surface By Periodic Reverse Current Method with Sodium Hydroxide Solution for Particle Accelerator Application

Superconducting Radio-Frequency (SRF) cavities are used to accelerate particles in particle accelerators. In this application, the cavity is made of niobium (Nb) material and the inner surface of cavity should be polished so as to obtain the high performance of particle accelerator. The Electro-Polishing (EP) process is one of the best methods to polish the inner-surface of Nb cavity where the electrolyte is the mixture of sulfuric and hydrofluoric acids. However, this EP electrolyte is very dangerous in the operation and thus the operators need rigorous protection. Furthermore, all parts of instrument for the EP process must be made of high density polyethylene or fluorocarbon resin because the corrosion of metal occurs by hydrofluoric acid. These are the reasons why the cost of EP process becomes very expensive. In addition, the EP process produces sulfur compound on the Nb surface as a by-product. This sulfur compound can be the sources of field-emission on the inner surface of cavity and degrades the accelerating performance. In this article, we report a novel EP method using periodic reverse current and sodium hydroxide solution. The reaction produces no sulfur content and the instrument is less expensive because it is made of usual plastic material. As the result of experiments with Nb-coupon samples, we found that the surface roughness is equivalent to the conventional EP method. And some experiments with a Nb single-cell cavity will be reported.

A study on photothermal waves in an unbounded semiconductor medium with cylindrical cavity

The theory of coupled plasma, thermal, and elastic waves was used to investigate the wave propagation on semiconductor material with cylindrical cavity during photo-thermoelastic process. An unbounded material, elastic semiconductor containing a cylindrical cavity with isotropic and homogeneous thermal and elastic properties has been considered. The inner surface of cavity is constrained, and the carrier density is photogenerated by an exponentially decaying pulse boundary heat flux. The eigenvalue approach, together with Laplace transform techniques, was used to obtain the analytical solutions. Numerical computations have been done for a silicon-like semiconductor material, and the results are presented graphically to estimate the effect of the coupling between the plasma, thermal, and elastic waves. The graphical results indicate that the thermal activation coupling parameter is an important phenomenon and has a great effect on the distribution of field quantities.

Deposition of Poly(Ethylene Oxide)‐Like Plasma Polymers on Inner Surfaces of Cavities by Means of Atmospheric‐Pressure SDBD‐Based Jet

The jet of reactive effluents produced by surface dielectric barrier discharge was used to deposit PEO‐like plasma polymers from di(ethylene) glycol vinyl ether. The jet was confined within the hollow space of either circular cross‐section with substrate placed perpendicular to the jet, or rectangular cross‐section with the walls used as substrates. The best 67% retention of the ethers was obtained for the circular channel, whereas it was only 50% for the rectangular channel. In the latter case, deposition at longer distances was possible. In both cases, the deposition started with the formation of islands that grew, coalesced and eventually built up a continuous coating.

Diamond single micro-crystals and graphitic micro-balls’ formation in plasmoids under atmospheric pressure

Plasmoids are produced in the argon filamentary discharge. By going through hydrocarbon gas, the plasmoids collect carbon material. These plasmoids produce diamond single micro-crystals upon contact on the inner surface of cavity in air atmosphere. When the plasmoid’s contact point on the substrate is in inert atmosphere, they deposit their material as micro-balls with a graphite core. The dimension and nature of the micro-materials deposited by the plasmoids are analysed using scanning electron microscopy and Raman microspectroscopy. The compressive residual stress in the deposited micro-diamonds varies in the range −7 to −21 GPa.

Plasma production by means of discharge in a spherical cavity

The work is devoted to the study of plasma, appearing as a result of cumulation of shock wave with form close to spherical. The shock wave was obtained by triggering of fast discharge (dI/dt about 1012 A/s) on inner surface of cavity, made from insulator. Spherical cavity with radius 4.5 mm was filled with Ar at 80 Pa. Inductive storage with semiconductive opening switch was used as a current driver. Spherical plasma with diameter about 1 mm, emitting in vacuum ultraviolet (vuv), was detected by means of pinhole measurements with time gated microchannel plate camera, starting about 50 ns from the beginning of the discharge. vuv spectra have shown the presence spectral lines of ArV–ArVIII ions, which gives the estimation of electron temperature as 30 eV. The plasma ball reveals no instabilities, keeps its characteristics and emits vuv radiation during 300 ns. After 600 ns from the beginning of the discharge plasma emits a flux of electrons with energies about 1 keV with temporal structure about 100 ns.

ChemInform Abstract: Characterization of Ferroelectric SrBi2Ta2O9 Thin Films Prepared from Alkoxide Solutions.

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Characterization of Ferroelectric SrBi2Ta2 O 9 Thin Films Prepared from Alkoxide Solutions

thin films prepared by chemical liquid deposition using alkoxide precursor solutions, followed by annealing at various temperatures, were characterized with a focus on the correlation between composition, microstructure, and ferroelectric properties. P-E hysteresis loops of the films exhibited well‐defined shapes at temperatures above 700°C, and the leakage current decreased with increasing annealing temperature, except for a film annealed at 4750°C. The crystal growth proceeded and ferroelectric properties of the films improved with increasing annealing temperature, whereas a large leakage current was observed for the film annealed at 750°C. Quantitative X‐ray photoelectron specroscopic analysis and high‐resolution transmission electron microscopic observation indicated the presence of a substantial amount of metallic bismuth in all films, predominantly in microcrystallite regions and on film surfaces, including the inner surface of cavities. The atomic fraction of metallic bismuth increased upon slight argon etching; however, the total bismuth content was significantly reduced. The metallic bismuth was amorphous and detected as vibrating spherical particles measuring approximately 5 nm under electron irradiation. The discontinuity in morphology, such as cavities at the interface between large single‐crystal grains and microcrystallite regions, was most remarkable in the film annealed at 750°C. The condensation of metallic bismuth at the cavities is believed to increase the leakage current when the path formed by cavities penetrates through the film. © 1999 The Electrochemical Society. All rights reserved.

Studies on Root-Breaking in Certain Crop Plants Caused by the Formation of IcicIe-Layer in the Ground and on Protection Methods against Them : 3. Formation of Ground-Cavity and Its Relation to the Plant Roots

When we observe the profile of frozen soil, we find frequently a cavity formed underneath the root system of a plant. Its profile shows a lenticular shape generally, but sometimes it shows a different one. Under the ridge of rye, cavities are often connected each other and make a long hole like a tunnel along the ridge. Cavities can be found under any kind of crops-rye, wheat, barley, rape, hairy vetch, red clover and orchardgrass, and even under the stubble of plants-maize, millets, soybeans and weeds. The plant roots are found cut by such a cavity formed underneath them. The condition of the cavity varies with the development of the root system. The more vigorous the growth the deeper is the place of its formation under the same kind of plant. When the plant has very poorly developed root system, its roots are cut directly by the icicle layer without forming cavities. Therefore, the formation of cavity is much related to the field practice of crop cultivation. On the inner surface of cavity there are ice crystals, which may be considered as sublimates of vapor from unbrozen part of the soil. The mechanism of cavity formation will be explalined as follows. In the process of icicle-layer formation, it develops spreading horizontally beneath the frozen layer in the soil; but at the parts straightly below the plants, the icicle formation is avoided by the dense distribution of plant roots. With the thickening development of the icicle-layer the frozen surface soil layer is heaved as a whole, and the plant bodies grasp in the latter with their roots are pushed upwards, remaining cavities beneath it, and thus the roots distributed there are stretched and broken finallly (Fig. 2).