Microcavity plasma devices show promise for controlled plasma chemistry. However, these devices are typically made through processes that are difficult to scale up. We present the design and characterization of a microchannel system suitable for the study of microplasmas. The channel was created with a micro-mill CNC machine that allows for quick device manufacturing. The channel is characterized using scanning electron microscopy and profilometry. Finally, we use recently published models of flow in a microchannel with bends to elucidate pressure conditions throughout the channel. Future work will encompass characterization of plasma conditions. (C) 2015 Published by Elsevier B.V.

Summary form only given. The ability to generate steady atmospheric pressure microdischarges has become feasible as micro-manufacturing technologies have continued to improve. At present, there are a small number of developing technologies surrounding microplasmas, perhaps most prominently as a low-profile light source. Other potential applications of such research include the cost-effective remediation of various gaseous waste streams (e.g., CO2), and the reformation of hydrogen gas from common sources such as methane (CH4) and ammonia (NH3). The reaction kinetics in a microplasma channel can be controlled to some extent through electric field strength and frequency, reactant gas flow rate, and the geometry of the channel itself. The microchannel for this work is fabricated on a MACOR™ ceramic surface using micro-machining technology available at the Univ. of Illinois at Urbana Champaignt, which has the advantage of being easily machinable, unlike alumina, while still bearing the high dielectric constant required. Microchannels for this device are 80 micrometers deep and 150 micrometers wide, and range from simple straight channels to highly complex shapes and paths. The recessed microchannels are covered by a glass microscope slide cover with a thin indium tin oxide (ITO) coating, allowing voltage to be put across the channel while simultaneously permitting spectroscopic measurements. In the experimental setup for this work, power is applied across the microchannel using a variable autotransformer and a high-voltage transformer. The latter is capable of producing ~5.7 kVpp at 20 kHz. Residence time can be varied by changing intake gas flow rate, and also by changing the electric field strengths within the channel. Positive pressure from a feedstock gas is applied into a mass flow controller that feeds into the microchannel; the exhaust of the microchannel is evacuated using a mechanical vacuum pump. Three iterations of reactors were built and tested to iteratively improve on design. Initial experiments consisted of inert gases followed by more complex diatomic and polyatomic gases. Plasma properties are measured by observing the intensity of its light with a spectrometer. Plasma properties of primary interest in this experiment are: species residence time, electron density, electron temperature, ion temperature, and ionization fraction. These quantities can be determined through the use of spectroscopic line ratio measurements in addition to some simple chemical reaction modeling.

The superior strength and stiffness of carbon nanotubes (CNTs) make them attractive for many structural applications. Although the strength and stiffness of CNTs are extremely high, fibres of aligned CNTs have been found to date to be far weaker than the constituent CNTs. The intermolecular interactions between the CNTs in the fibres are governed by weak van der Waals forces, resulting in slippage between CNTs which occurs at tensions well below the breaking strength of the CNTs. Both theoretical and experimental studies show that by introducing chemical bonds between the CNTs increases load transfer and prevents the CNTs from slipping.

The principal objective of this work is to implement a new material development paradigm using atomistic simulations to guide the molecular design of materials. Traditional empirical macroscopic material development studies omit the fundamental insight needed to understand material behavior at the atomic and molecular levels where material response begins. The new paradigm relies heavily on a tight integration between simulation and experimental efforts to design and process new materials with nanometer-scale precision. Exploiting nanotechnology requires atomic-molecular-level material design and the ability to process these materials with atomic-molecular-level precision. Processing materials with nanoscale precision poses formidable theoretical, computational, and experimental challenges to developing advanced materials. High performance computers and advanced physics-based simulations can complement experimental efforts to design, test, synthesize, and analyze novel materials and innovative structural designs. This method can be applied to a wide range of material designs. As a proof of concept, we began our work on the design of novel carbon nanotube-based materials. The mechanical properties of carbon nanotubes such as low-density, high-stiffness, and exceptional strength make them ideal candidates for reinforcement material in a wide range of high performance composites. Molecular dynamics simulations are used to predict the tensile response of fibers composed of aligned carbon nanotubes with intermolecular bonds of interstitial carbon atoms. The effects of bond density and carbon nanotube length distribution on fiber strength and stiffness are investigated. Results indicate that including cross link atoms between the carbon nanotubes in the strands significantly increases the load transfer between the carbon nanotubes and prevents them from slipping. This increases the elastic modulus and yield strength of the fibers by an order-of-magnitude. Carbon nanotube-based materials appear poised to affect civil and military engineering significantly over the next two decades by providing materials with an order-of- magnitude improvement in strength-to-weight and stiffness-to-weight ratios over existing materials.

Enhanced electron emission has been observed from lead zirconate-titanate (PZT) surfaces into which arrays of microcavities have been fabricated by nanopowder blasting. Arrays of microcavities, each having an elliptical cross-sectional geometry with major and minor axis lengths of 800 and 600 mm, respectively, and depths adjustable from 40 to 300 mm, exhibit a pronounced dependence of the emitter electron current on microcavity depth. For electric field strengths at the emitter surface of similar to 5-12 V/mu m, the RMS current density generated by an array of 250 mu m-deep microcavities with a packing density of 214+/-2 cm(-2) ranges from similar to 3 mA cm(-2) to beyond 8 mA cm(-2), or more than a factor of five larger than that produced from a planar PZT surface.

Edge Localized Modes (ELMs) represent a significant disruption to current and future fusion reactors. Of concern in a device such as the International Thermonuclear Experimental Reactor (ITER) is that ELMs could be the limiting factor for successful operation. ITER ELMs are predicted to impart between 1 10 MJ/m 2 onto the surface of the diverter and first wall of the reactor. This could lead to significant erosion of the diverters and possible melting. The ELM simulating plasma gun (ESP-gun) currently being operated at UIUC is intended to produce plasmas similar to those found in ELM events from TOKAMAKS. The PFN is connected to the conical theta pinch to produce high temperature, high density plasmas similar to ELM events. These plasmas are intended to reproduce the plasma conditions and potential material damage in an ELM event from a large scale fusion experiment such as NSTX or ITER. A Triple Langmuir Probe (TLP) has been used to diagnosis and measure the quality of the plasmas produced by the ESP-gun. To date, electron densities of 1(10) 17 /m 3 and greater with electron temperatures greater than 100 eV in the target area have been measured. Additionally a fast, IR measurement is used during the simulated ELM event to determine target heating and estimate the energy flux on the target due to the plasma load

Summary form only given. Helicon plasmas continue to be useful as a hot, dense source with low magnetic field requirements. Since the implementation of helicon waves in a low pressure gas by Boswell, there have been multiple advances in this field. To date, no single theory has completely explained the coupling mechanism of the waves to the plasma, although Trivelpiece-Gould (TG) modes remain a strong candidate. The concept of an inverted geometry helicon antenna is proposed here, comprised of a standard helicon antenna, covered by a dielectric, and placed within the vacuum chamber. RF energy that is normally radiated outward from the antenna will now also couple to the plasma, for additional heating and better efficiency. An internal antenna is also not constrained to the minimum radius of the vacuum chamber, thus antennas can be made smaller to determine what, if any, critical radius exists for plasma excitation. Smaller antennas also mean more tightly wound magnetic field coils that can deliver the same field for less current. The primary antenna type to be used is a Nagoya type III, although others are used for various experiments. With such an arrangement, it is now possible to make measurements of the plasma at an arbitrarily close distance to the antenna. This setup is in contrast to conventional antennas which surround a dielectric cylinder where the plasma, as well as the diagnostics are housed. To characterize the plasma, an RF-compensated Langmuir probe is employed to make measurements in both radial and axial directions. The radial measurements extend beyond the antenna region for comparison with conventional helicon plasma sources. To explore the method of wave-plasma coupling, mobile B-dot and J-dot probes measure the field shape in the plasma region as well as very close to the antenna itself. In addition to the above diagnostics, optical emission spectroscopy is used to observe visual changes in plasma intensity for mode jumps, as well as to measure line ratios

Edge Localized Modes (ELMs) continue to be an obstacle in magnetic confinement fusion. The simulation of such ELM events using a conical theta pinch serves as a means to explore methods to manage these events in future experiments. For the purposes of pre-ionization before the pinch, a 100-200 W helicon source, (at pressures between 5-100 mTorr, in either hydrogen or argon) is employed. Plasma pinching is the result of pulsed current through a single turn conical copper coil from discharge of high voltage capacitors. Direction of current flow around the coil and hence the magnetic field direction from pinching, as compared to the steady state magnetic field, is such that the system lends itself to a field reversed configuration (FRC). Axial magnetic field measurements during the theta pinch at the location of the coil as well as at a target downstream are accomplished using a B-dot probe array. Steady state magnetic field topology was configured in order to optimize the transfer of the pinched plasma from the pinch coil to the target, as well as to simulate tokamak-level magnetic field strengths. Thermal heating of a small target by the RF and pinched plasmas as a means of measuring plasma energy deposition augments data taken using other diagnostics. This heating is observed using an RF-compensated in-situ thermocouple probe attached to the target assembly. Power and energy densities are estimated. RF power and capacitor discharge voltage are varied to illustrate target heating parameters. Optical spectroscopy is used for atomic line spectra measurements. The results of these experiments with the imposed conditions are discussed

TEAM — Edge Localized Modes (ELMs) pose a significant problem to current and future fusion reactors. One concern in a device such as ITER is that ELMs may be the limiting factor for successful operation. ITER ELMs are predicted to impart between 1 – 10 MJ/m 2 onto the divertor surface and first wall of the reactor. This may lead to significant erosion of the divertors and possible melting. The ELM Simulating Plasma gun (ESP-gun) in operation at UIUC is intended to produce plasmas similar to those found in TOKAMAK ELM events. ESP-gun operates with several small pulse forming networks (PFN) that are sequentially triggered to produce a ringing, under-damped current waveform with peak currents in excess of 50 kA. Each PFN is connected to the conical theta pinch to produce high T e , high n e plasmas similar to ELM events. A Triple Langmuir Probe (TLP) diagnoses and measures the quality of the plasmas produced by the ESP-gun. To date, an n e of 1(10) 19 /m 3 and greater with a T e greater than 50 eV in the target area have been measured. From these measurements, plasma energies can be calculated. Axial magnetic field measurements during the theta pinch at the location of the coil and at a downstream target are accomplished.

Experimental evidence for the mechanisms of bubble mobility in irradiated UO2 is reviewed. Examination of the bubble distribution in irradiated material shows that significant directed bubble motion does not occur. This result is confirmed by calculation, and it is also predicted that Brownian movement is an unimportant mode of release for burn-ups of practical interest. A description is made of the theory of transport of gas to the grain boundaries involving the irradiation re-solution of intra- and inter-granular bubbles.

In order to calculate the rate of escape of vacancies at the surfaces of a thin foil specimen prepared from a quenched sample of an aluminium-5 wt. % magnesium alloy, Eikum and Thomas, in a recent paper, used a mobility energy deduced from a plot of rate of loop growth versus reciprocal temperature. It is shown that diffusion parameters derived from such Arrhenius plots are not usually meaningful unless extreme precautions are taken. It is reconfirmed that the observed growth of prismatic loops in the aluminium alloy is only possible if the foil surfaces are sealed by an oxide film. Other evidence for the oxide film effect is reviewed and discussed.

Previous workers have found that, on heating thin foils made from quenched samples of a dilute aluminium alloy in the electron microscope, vacancy loops can grow at temperatures as high as 385°c. It is demonstrated that this cannot be due, as was supposed, to the release of vacancies from vacancy-solute aggregates. It is suggested that the enhanced vacancy lifetime within the foils is a consequence of an impervious oxide film which prevents the escape of vacancies at the surfaces of the foils. A similar explanation was used to account for the present authors' observations of the growth of vacancy loops in foils prepared from quenched specimens of pure magnesium and zinc. The implications of this oxide film effect are discussed in relation to other physical processes, in particular to the low temperature ageing of dilute aluminium alloys.

It has been shown that dislocation loops can be nucleated and grown in thin foils made from quenched specimens of magnesium and zinc. Observations are presented which indicate that the surfaces of the thin foils are sealed with an oxide film. Freely diffusing vacancies can only escape from the foil where this oxide film has become locally ruptured, exposing the metal surface. The loops are usually faulted, with b = R = 1/6 <2023>. Occasionally unfaulted loops, with b = <0001>, are observed. An analysis of the kinetics of climb of the faulted loops provides estimates of the stacking fault energy (corresponding to a single violation of the next-nearest-neighbour stacking sequence). These values are, for magnesium, 280 ± 100 erg/ cm 2 and, for zinc, 300 ± 150 erg/cm 2 . Factors influencing the climb rate are discussed.

IT has been suggested many times that the hardening of iron and steel on irradiation may result from the interaction of glide dislocations with dispersed clusters of point defects. Two observations of such clusters using the technique of transmission electron microscopy have been reported in the literature1,2. The work reported in this communication was undertaken to determine the crystallography of dislocation loops observed in pure iron.

physica status solidi (b)Volume 9, Issue 3 p. K181-K184 Short Note The Stacking Fault Energy of Zinc and Magnesium J. E. Harris, J. E. Harris Berkeley Nuclear Laboratories, Berkeley, GloucesterSearch for more papers by this authorB. C. Masters, B. C. Masters Berkeley Nuclear Laboratories, Berkeley, GloucesterSearch for more papers by this author J. E. Harris, J. E. Harris Berkeley Nuclear Laboratories, Berkeley, GloucesterSearch for more papers by this authorB. C. Masters, B. C. Masters Berkeley Nuclear Laboratories, Berkeley, GloucesterSearch for more papers by this author First published: 1965 https://doi.org/10.1002/pssb.19650090335Citations: 16AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onEmailFacebookTwitterLinkedInRedditWechat References 1 A. Berghezan, A. Fourdeux, and S. Amelinckx, Acta metall. 9, 464 (1961). 2 P. B. Price, Electron Microscopy and Strength of Crystals, Interscience, New York 1963 (p. 41). 3 J. E. Dorn and J. B. Mitchell, paper presented at the Second International Symposium on Materials, Berkeley, California, June 1964; Univ. Calif. Rep. No. UCRL-11418. 4 A. Seeger, Defects in Crystalline Solids, Physical Society, London 1955 (p. 328). 5 P. R. Thornton and P. B. Hirsch, Phil. Mag. 3, 738 (1958). 6 J. W. Edington and R. E. Smallman, to be published. 7 J. Friedel, Dislocations, Pergamon, London 1964. 8 P. H. Miller and F. R. Banks, Phys. Rev. 61, 648 (1942). 9 H. B. Huntington, G. A. Shirn, and E. S. Wajda, Phys. Rev. 87, 211 (1952). 10 G. A. Shirn, E. S. Wajda, and H. B. Huntington, Acta metall. 1, 513 (1953). 11 T. Liu and H. G. Drickamer, J. chem. Phys. 22, 314 (1954). 12 F. E. Jaumot and R. L. Smith, Trans. AIME 206, 137 (1956). 13 I. A. Naskidashvili and V. M. Dolidze, Akad. Nauk Gruz. SSR 18, 671 (1957). 14 P. G. Shewmon, Trans. AIME 206, 918 (1956). Citing Literature Volume9, Issue31965Pages K181-K184 ReferencesRelatedInformation

The experimental results of I indicate that the dislocation velocity is limited by a thermally activated process, and the parameters of the appropriate rate equation are evaluated. At very low temperatures, the stress derivative of the free energy of activation (the 'activation volume’) is only a few atomic volumes. It is very difficult to explain the magnitude of the low-temperature stress or that of the activation volume if direct dislocation—impurity interactions are responsible for most of the resistance to motion, and it is concluded that there is probably a significant lattice interaction (a ‘Peierls-Nabarro force’). The results are compared with the predictions of recent models for the overcoming of the Peierls barrier by the production of double kinks in straight dislocation lines.

Measurements of the tensile yield stress and of the temperature and strain-rate sensitivity of the flow stress are reported for single crystals of niobium and for polycrystalline speci­mens of niobium, vanadium and tantalum over the temperature range 4.2 to 373°K. The temperature dependences of yield and flow stresses are nearly identical, and the results show that the high yield stresses at low temperatures are attributable mainly to a frictional force opposing the motion of free dislocations. The yield stress is very dependent on the purity of the metal, and the temperature and strain rate sensitivities vary slightly with purity, especially at higher temperatures. At very low temperatures, the stress needed to cause macroscopic deformation at a strain rate of 10 -4 s -1 is ca . 1% of the shear modulus in all specimens examined. The relation of the results to the interpretation of the para­meters in the Hall-Petch equation for the variation of yield stress with grain size is briefly discussed.