Czeslaw Golkowski

Electron emission from lead–zirconate–titanate ceramics

We report extensive experimental data on electron emission from lead–zirconate–titanate ferroelectric ceramics. A 1–2 MV/m pulse is applied to a gridded ferroelectric cathode and diode currents of up to 120 A/cm2 are measured across an A–K gap of 5×10−2 m, with the anode at 35 kV. Both the current and the anode voltage pulse duration may extend to several microseconds. The measurements extend previously reported data by nearly two orders of magnitude in the diode voltage and by a factor of more than 3 in the diode spacing. Two major regimes of operation were identified. In the first ∼1 μs the ferroelectric cathode controls the electron flow through the diode. Beyond this time plasma effects dominate the current flow. The results are of importance to the development of novel cathodes for high current electron beam generation.

Hydrogen-Peroxide-Enhanced Nonthermal Plasma Effluent for Biomedical Applications

A novel nonthermal plasma dielectric-barrier discharge (DBD) system for decontamination, sterilization, and medical applications has been developed. The discharge is physically removed from the disinfection zone, and plasma-induced free radicals are delivered through an air stream. The physical distance between the discharge and the treatment surface can be up to 3 m, making the technology robust and flexible for applications in the medical clinic. The bactericidal properties of the free-radical effluent are enhanced by hydrogen peroxide additives. We report a 6-log reduction in Staphylococcus aureus and Pseudomonas aeruginosa bacteria strains in under 1 min of exposure in vitro and inactivation of Bacillus atrophaes spores and Escherichia coli biofilms. The concentration of hydrogen peroxide additives is seen to be a key variable in inactivation efficacy, suggesting that active species in our experiment may be different than in other DBD configurations. Precise chemical concentration measurements using direct frequency comb spectroscopy show presence of ozone ( O3), hydrogen peroxide (H2O2), nitrous oxide (N2O), and nitrogen dioxide (NO2). In vivo multiple exposures of mouse skin to the plasma effluent do not yield any adverse effects.

Electron beam generation using a ferroelectric cathode

Data is presented on the production of electron beams from a ferroelectric cathode at voltages of order 0.5 MV and current densities of order 100 A/cm/sup 2/. In comparison with data at lower voltages, the beam current scales as the three-halves-power of the voltage. An interpretation of the voltage dependent scaling, based on the coupling of electrostatic energy from the ferroelectric to the gun, is presented.

Superconducting bearings for high load applications

Abstract Progress in the application of high temperature superconducting ceramic materials to magnetic bearings and the prospects for higher load devices is reviewed. In particular we present experimental evidence from two studies at Cornell. New measurements from a hybrid superconducting bearing show the possibility of peak magnetic pressures of 60 N/cm 2 or higher in the temperature range of 20°–40° K using a wire wound coil of NbSn wire as the source of magnetic field and a melt-quenched processed YBa 2 Cu 3 O 7 bulk superconductor as the other half of the bearing. In a second experiment we demonstrate an 0.85 kg levitated rotor at 28,000 RPM and 5 kJ stored energy. This experiment, conducted at 78°K, demonstrates a six-component discrete-element YBCO bearing with a rare earth ring magnet. Stiffness and spin-decay measurements are reported. These experiments point the way to large rotor levitation of 10–100 kg in the near term nad 1000 kg rotors in the not too distant future.

Remote delivery of hydroxyl radicals via secondary chemistry of a nonthermal plasma effluent

Electron paramagnetic resonance spectroscopy is used to observe hydroxyl radicals produced by an atmospheric pressure nonthermal plasma device at distances greater than 1 m from the discharge. The plasma device is an indirect treatment setup with closed loop airflow and hydrogen peroxide additives that is effective in deactivating bacteria on time scales of seconds. The generation of the detected hydroxyl radicals is shown to occur in secondary chemical processes near the point of delivery of the plasma treated air stream. The production of hydroxyl radicals is correlated with humidity of the air stream and ability to lyse bacterial membranes. The overall mechanisms of bacteria inactivation are found to be a combinatorial effect of effluent species. The results indicate the feasibility of selective plasma induced free radical delivery for biomedical applications even in the case of short‐lived species like the hydroxyl radical. Biotechnol. Bioeng. 2013; 110: 1936–1944.

Suppression of parasitic self-excitation in Cherenkov amplifiers

A means for removing the parasitic feedback in microwave amplifiers, the main obstacle to achieving a high gain, is described here. The method is based on utilizing the resonant interaction between fast cyclotron waves on an electron beam and the electromagnetic waves that are propagating in the opposite direction. This is an effective method to prevent detrimental self-excitation in amplifiers whose operation is based upon the stimulated Cherenkov radiation of a forward-propagating electron beam in a guiding magnetic field. Conditions for the resonant interaction are provided by proper choice of the guiding magnetic field. At such resonances the counter-propagating waves are in stop-bands and, therefore, cannot propagate. Results of theoretical and experimental investigations of cyclotron absorption of counter-propagating waves in amplifiers are given in the present work. It is shown that the resonant cyclotron interaction leads to a complete suppression of the feedback and that the threshold of self- excitation becomes unachievable even for large reflections. Only a minor decrease in the amplification results in comparison with an ideal amplifier without reflections. It follows from these results that a spatially varying magnetic field can be applied along the axis of the amplifier to expand the zone of the cyclotron absorption and thereby exclude a re-tuning of the self-excitation frequency.

Design of Ferroelectric Diode for High-Current Matched Electron-Beam Generation

An electron gun using a ferroelectric cathode with a two-stage compression system has been designed. The performance of the beam generated by the gun has been investigated by simulation and experiment. When the applied diode voltage is 440 kV, a beam current of 230 A is obtained. The waveform of the beam current follows the diode voltage reasonably well, and their flat top overlaps for about 200 ns. Faraday cup measurement shows that the beam radius is 4.1 mm after second-stage compression, and the axial variation of the beam radius has been minimized.

Initiation of microwave-induced electrical breakdown of high-pressure gases

Measurements of microwave-induced electrical breakdown at 2.45 GHz in Ar, Kr, and Xe have been made in a tunable microwave cavity. The influence of UV illumination on gas breakdown at pressures up to 300 torr, and data on fiber initiator-induced breakdown above atmospheric pressure are presented. A marked decrease in the statistical spread in breakdown was observed with UV illumination, but the maximum pressures at which breakdown occurred with available microwave power, with and without UV illumination, were the same. To initiate breakdown in gases above 1 atm, a conducting fiber was used to enhance the applied macroscopic electric field at the fiber tip. Using 8-/spl mu/m diameter SiC fibers coated with 0.2-/spl mu/m-thick Pt, breakdown was obtained with pulses as short as 0.25 ms in the pressure range 1-3 atm for Ar, Kr, and Xe. The required microwave electric field at 2280 torr with one fiber was less than that at 200 torr without a fiber. The increase of the breakdown field with pressure was much slower than linear. The effect of fiber length, diameter, orientation, and conductivity, and of the number of fibers, on the required breakdown electric field, and fiber initiation in Cl/sub 2/ mixture gases, were also investigated.

Abstract 138: Treating Infected Wounds in the Era of Antibiotic Resistance

PURPOSE: We recently described a bioinspired material composed of nanoparticulate mineralized collagen glycosaminoglycan (MC-GAG) that induces efficient osteogenic differentiation of human mesenchymal stem cells (hMSCs) without the addition of exogenous growth factors, thereby suggestive of a promising, growth factorfree, materials-based method for clinically utilizable bone regeneration. We have previously reported that MC-GAG scaffolds autogenously induce BMP receptor signaling via the canonical (Smad1/5) pathway. However, the necessary and sufficient components of this mechanism remain unknown. Our current study evaluates the contribution of the non-canonical (MAP kinase) pathway in MC-GAG induced osteogenesis.

Chemical dosimetry of an indirect exposure non-thermal plasma device

Summary form only given. Interest in the use of non-thermal plasmas in the biomedical setting is rapidly growing. Potential applications of such devices range from instrument sterilization to clinical therapy. One of the largest hurdles to the implementation of nonthermal plasmas, specifically in regard to patient exposure, is the relatively poor understanding of the chemical processes taking place. Recent research has focused intensely on the dynamic chemical cocktail associated with specific discharge configurations. Our group recently detailed the ability to control chemical species created by our device through modifying operating parameters, namely humidity1. Specifically, we demonstrated our devices capability to deliver the short-lived hydroxyl radical to treatment sites at a distance of over a meter from the plasma discharge. This recent development of our remote design allows for potential user-defined specificity in both concentration and flavor of chemical exposure to the treatment environment. Introduction of non-thermal plasma devices to the clinical setting, specifically in the United States, will inevitably require a certain degree of therapeutic control. We report on the in vitro “plasma dosimetry” related to the application of our device. Control of the device effluents chemical makeup allows for parameterization of treatment-related variables like the ratio of inactivation or DNA oxidation between prokaryotic and eukaryotic species. Building on previous work using electron spin resonance spectroscopy to enumerate free radicals delivered to our treatment site, we demonstrate the potential for a therapeutic window of operation. Such regulation provides the potential to tune non-thermal plasma based devices with regard to the contamination or infection being treated.