Randy D. Curry

A comparison of pulsed and continuous ultraviolet light sources for the decontamination of surfaces

The experimental results on the development of a decontamination process that uses ultraviolet light and chemical photosensitizer for disinfecting surfaces and solutions are reported. Reduction in the microbial viability as a function of applied UV fluence is presented for the inactivation of Bacillus subtilis spores. Results obtained with aqueous solutions and with surfaces indicate that pulsed UV light is more effective than continuous UV light. Nearly three orders of magnitude of enhanced inactivation have been achieved with the photosensitized UV process on surfaces.

Microbial Inactivation in Water Using Pulsed Electric Fields and Magnetic Pulse Compressor Technology

Pulsed electric field (PEF) disinfection is a promising technology for the nonthermal disinfection of water. Magnetic pulse compressors due to their high repetition rates and lifetimes, appear to be a promising alternative to the existing pulse forming circuits used for sterilization applications. The application of these systems for the purification of water has yet to be explored. The use of the short duration electrical pulses from the magnetic pulse compressor for inactivation of spores, bacteria (Escherichia coli) and viruses in drinking water is being investigated at the University of Missouri, Columbia. The test cell designed herein allows flowing tests for pulsewidths of 130-500 ns. The coupling of the magnetic modulator with the test cell and the inactivation protocols that aim at effective inactivation under optimal conditions are discussed. A 4 log reduction was seen for (Escherichia coli) E. coli at field strengths of 110 kV/cm and 70 pps, with a total energy consumption of 40 J/cm3. A comparative study of different parameters, e.g., pulsewidth, electrode gap, frequency, and electric field, which effect the microbial inactivation are also presented

Analysis and Comparison of a Fast Turn-On Series IGBT Stack and High-Voltage-Rated Commercial IGBTS

High-voltage-rated solid-state switches such as insulated-gate bipolar transistors (IGBTs) are commercially available up to 6.5 kV. Such voltage ratings are attractive for pulsed power and high-voltage switch-mode converter applications. However, as the IGBT voltage ratings increase, the rate of current rise and fall are generally reduced. This tradeoff is difficult to avoid as IGBTs must maintain a low resistance in the epitaxial or drift region layer. For high-voltage-rated IGBTs with thick drift regions to support the reverse voltage, the required high carrier concentrations are injected at turn on and removed at turn off, which slows the switching speed. An option for faster switching is to series multiple, lower voltage-rated IGBTs. An IGBT-stack prototype with six, 1200 V rated IGBTs in series has been experimentally tested. The six-series IGBT stack consists of individual, optically isolated, gate drivers and aluminum cooling plates for forced air cooling which results in a compact package. Each IGBT is overvoltage protected by transient voltage suppressors. The turn-on current rise time of the six-series IGBT stack and a single 6.5 kV rated IGBT has been experimentally measured in a pulsed resistive-load, capacitor discharge circuit. The IGBT stack has also been compared to two IGBT modules in series, each rated at 3.3 kV, in a boost circuit application switching at 9 kHz and producing an output of 5 kV. The six-series IGBT stack results in improved turn-on switching speed, and significantly higher power boost converter efficiency due to a reduced current tail during turn off. The experimental test parameters and the results of the comparison tests are discussed in the following paper

The development of photosensitized pulsed and continuous ultraviolet decontamination techniques for surfaces and solutions

The experimental results of a decontamination process that uses an ultraviolet (UV) light and a chemical photosensitizer for disinfecting surfaces and solutions are reported. Reduction in the microbial viability as a function of applied UV fluence and initial photosensitizer concentration is presented for the inactivation of both the vegetative and spore forms of Bacillus subtilis niger. Encouraging results have been obtained with both aqueous solutions and surfaces; and with both continuous and pulsed UV light sources. Extrapolation of the results and an estimate of the process speed and efficiency permit a comparison with other decontamination methods.

Evaluation of nanocrystalline materials, amorphous metal alloys, and ferrites for magnetic pulse compression applications

A magnetic pulse compressor test stand was developed to evaluate the switching and loss properties of magnetic core materials that included ferrite and several alloys of nickel-iron, Metglas, and the nanocrystalline material Vitroperm. The test stand generated 1−cos(ωt) voltage pulses across the core under evaluation to simulate the magnetic excitation encountered in pulse compressors. Pulse amplitude and repetition rate were user controlled in order to vary the initial time to saturation while keeping magnetic core temperature constant. Switching losses were calculated directly as ∫(νi)dt, and an advanced figure of merit was utilized to compare test results. The test stand, data acquisition and analysis, and test results are discussed.

Comparison of pulsed and CW ultraviolet light sources to inactivate bacterial spores on surfaces

The University of Missouri-Columbia is optimizing photosensitized UV processes for the decontamination of surfaces. The biological inactivation results obtained with high-power pulsed xenon flashlamps are compared to those of a continuous-wave medium-pressure mercury-argon lamp. The inactivation mechanisms associated with pulsed and continuous-wave multispectral light sources, which are used synergistically with a hydrogen peroxide photosensitizer, are discussed. Typically, the process yields more than six logs reduction of Bacillus subtilis spores on various surfaces.

Design, modeling, and verification of a high-pressure liquid dielectric switch for directed energy applications

A high-power liquid dielectric switch is being developed to satisfy the requirements for future directed energy applications. A flowing, high-pressure liquid dielectric was chosen for the design of a megavolt class switch operating at 100 pps. This paper reports on the design philosophy, modeling, and experimental results of a full size, single-shot prototype 250-300 kV concept validation test (CVT) switch which can transfer kilojoules per pulse. Analysis of design criteria and scaling for a compact, 100-pps, kilojoule, high-voltage switch are presented. Optimization studies indicate that a pressure range of 6.9-13.8 MPa (1000-2000 psi) appears to be ideally suited to a flowing dielectric rep-rate switch.

Development of a terawatt test stand at the University of Missouri for fast, multichannel switching analysis

The University of Missouri Terawatt Test Stand (MUTTS) began assembly in January 2003. Construction of MUTTS is progressing rapidly with the design and development of its high energy Marx bank. The Marx bank consists of 32, 100 kV, 0.7 /spl mu/F capacitors switched by 16 Physics International T508 spark gaps. The Marx is switched into two parallel 7 nF, intermediate storage capacitors, which are fired into a dummy load through a fast multi-channeling output switch. The Marx stores 100 kJ and can deliver a voltage of 2 MV at 500 kA into a 4 /spl Omega/ load delivering 1 TW to the load. Initial testing will be of a multichanneling 2 MV output switch, which scales nicely to a 6 MV switch design for future very high energy machines at Sandia National Laboratories. The output switch is to reliably multichannel, or close with many parallel arc channels. The goal is to adapt an existing multichanneling switch to create a multichanneling output switch with significant operational advantages, including lower inductance, compared to existing multichannel switches. The target switch inductance is 100 nH or less. The facility and tank were assembled from January to June 2003, with testing to begin in July 2003. Simulations of the test stand and specifications of the output switch will be presented. Electrode configurations and switch augmentations that will facilitate a reliable multi-channeling switch will be introduced. Details describing the development of the MUTTS facility will be included.

The status of PCB radiation chemistry research; prospects for waste treatment in nonpolar solvents and soils

This paper presents a review of PCB radiolysis in oil, polar and nonpolar solvents and soil. The origins of PCB radiolysis research in alkaline isopropanol are discussed, and contrasted with radiolysis in neutral isopropanol and nonpolar solutions. Micellar solution chemistry is presented. Additionally, new applications of soil PCB radiolysis will be discussed and the effect of soil on the chemistry shown. The applicability of the extraction of PCBs from soil followed by the floatation of the solvent and subsequent radiolysis of the PCB in the floatant are reported, along with radiolysis of PCB in soil matrices.

Experimental study of the multichanneling self-break section of the rimfire switch

Many accelerators at Sandia National Laboratories utilize the Rimfire gas switch for high-voltage, high-power switching. In addition, there are many multichannel closing switches used in pulsed power applications. This paper presents a study of the multichanneling section of the Rimfire switch. The electrical effects of multichanneling and a method to force multichanneling are presented. In addition, an objective curve fitting method is utilized to deduce switch inductance from the measured data.