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Direct Functionalization of Nitrogen Heterocycles via Rh-Catalyzed C-H Bond Activation

Description: Nitrogen heterocycles are present in many compounds of enormous practical importance, ranging from pharmaceutical agents and biological probes to electroactive materials. Direct funtionalization of nitrogen heterocycles through C-H bond activation constitutes a powerful means of regioselectively introducing a variety of substituents with diverse functional groups onto the heterocycle scaffold. Working together, our two groups have developed a family of Rh-catalyzed heterocycle alkylation and arylation reactions that are notable for their high level of functional-group compatibility. This Account describes their work in this area, emphasizing the relevant mechanistic insights that enabled synthetic advances and distinguished the resulting transformations from other methods. They initially discovered an intramolecular Rh-catalyzed C-2-alkylation of azoles by alkenyl groups. That reaction provided access to a number of di-, tri-, and tetracyclic azole derivatives. They then developed conditions that exploited microwave heating to expedite these reactions. While investigating the mechanism of this transformation, they discovered that a novel substrate-derived Rh-N-heterocyclic carbene (NHC) complex was involved as an intermediate. They then synthesized analogous Rh-NHC complexes directly by treating precursors to the intermediate [RhCl(PCy{sub 3}){sub 2}] with N-methylbenzimidazole, 3-methyl-3,4-dihydroquinazolein, and 1-methyl-1,4-benzodiazepine-2-one. Extensive kinetic analysis and DFT calculations supported a mechanism for carbene formation in which the catalytically active RhCl(PCy{sub 3}){sub 2} fragment coordinates to the heterocycle before intramolecular activation of the C-H bond occurs. The resulting Rh-H intermediate ultimately tautomerizes to the observed carbene complex. With this mechanistic information and the discovery that acid co-catalysts accelerate the alkylation, they developed conditions that efficiently and intermolecularly alkylate a variety of heterocycles, including azoles, azolines, dihydroquinazolines, pyridines, and quinolines, with a wide range of functionalized olefins. They demonstrated the utility of this methodology in the synthesis of natural products, drug candidates, and other biologically active molecules. In addition, they developed conditions to directly arylate these heterocycles with aryl halides. The initial conditions ...
Date: February 4, 2008
Creator: Lewis, Jared; Bergman, Robert & Ellman, Jonathan
Partner: UNT Libraries Government Documents Department

High intensity production of high and medium charge state uraniumand other heavy ion beams with VENUS

Description: The next generation, superconducting ECR ion source VENUS(Versatile ECR ion source for NUclear Science) started operation with 28GHzmicrowave heating in 2004. Since then it has produced world recordion beam intensities. For example, 2850 e mu A of O6+, 200 e mu A of U33+or U34+, and in respect to high charge state ions, 1 e mu A of Ar18+, 270e mu A of Ar16+, 28 e mu A of Xe35+ and 4.9 e mu A of U47+ have beenproduced. A brief overview of the latest developments leading to theserecord intensities is given and the production of high intensity uraniumbeams is discussed in more detail.
Date: November 15, 2007
Creator: Leitner, Daniela; Galloway, Michelle L.; Loew, Timothy J.; Lyneis, Claude M.; Rodriguez, Ingrid Castro & Todd, Damon S.
Partner: UNT Libraries Government Documents Department


Description: Two high-pressure bioassay vessels failed at the Savannah River Site during a microwave heating process for biosample testing. Improper installation of the thermal shield in the first failure caused the vessel to burst during microwave heating. The second vessel failure is attributed to overpressurization during a test run. Vessel failure appeared to initiate in the mold parting line, the thinnest cross-section of the octagonal vessel. No material flaws were found in the vessel that would impair its structural performance. Content weight should be minimized to reduce operating temperature and pressure. Outer vessel life is dependent on actual temperature exposure. Since thermal aging of the vessels can be detrimental to their performance, it was recommended that the vessels be used for a limited number of cycles to be determined by additional testing.
Date: September 22, 2008
Creator: Vormelker, P
Partner: UNT Libraries Government Documents Department

Design of microwave vitrification systems for radioactive waste

Description: Oak Ridge National Laboratory (ORNL) is involved in the research and development of high-power microwave heating systems for the vitrification of DOE radioactive sludges. Design criteria for a continuous microwave vitrification system capable of processing a surrogate filtercake sludge representative of a typical waste-water treatment operation are discussed. A prototype 915 MHz, 75 kW microwave vitrification system or `microwave melter` is described along with some early experimental results that demonstrate a 4 to 1 volume reduction of a surrogate ORNL filtercake sludge.
Date: April 1, 1996
Creator: White, T.L.; Wilson, C.T.; Schaick, C.R. & Bostick, W.D.
Partner: UNT Libraries Government Documents Department

Intense high-frequency gyrotron-based microwave beams for material processing

Description: Microwave processing of materials has traditionally utilized frequencies in the 0.915 and 2.45 GHz regions. Microwave power sources are readily available at these frequencies but the relatively long wavelengths can present challenges in uniformly heating materials. An additional difficulty is the poor coupling of ceramic based materials to the microwave energy. Los Alamos National Laboratory scientists, working in conjunction with the National Center for Manufacturing Sciences (NCMS), have assembled a high-frequency demonstration processing facility utilizing gyrotron based RF sources. The facility is primarily intended to demonstrate the unique features available at frequencies as high as 84 GHz. The authors can readily provide quasi-optical, 37 GHz beams at continuous wave (CW) power levels in the 10 kW range. They have also provided beams at 84 GHz at 10 kW CW power levels. They are presently preparing a facility to demonstrate the sintering of ceramics at 30 GHz. This paper presents an overview of the present demonstration processing facility and describes some of the features they have available now and will have available in the near future.
Date: March 1, 1997
Creator: Hardek, T.W.; Cooke, W.D.; Katz, J.D.; Perry, W.L. & Rees, D.E.
Partner: UNT Libraries Government Documents Department

Plasma-surface interactions with ICRF antennas and lower hybrid grills in Tore Supra

Description: The edge plasma interactions of the actively cooled radio-frequency heating launchers in Tore Supra- ion-cyclotron range-of-frequencies (ICRF) antennas and lower-hybrid (LH) grills-are studied using infrared video imaging. On the two-strap ICRF antennas, operated in fast-wave electron heating or current drive mode, hot spots with temperatures of 500-900{degrees} C are observed by the end of 2-s power pulses of 2 MW per antenna. The distribution and maximum values of temperature are determined principally by the relative phase of the two antenna straps: dipole (heating) phasing results in significantly less antenna heating than does 90` (current drive) phasing. Transient heat fluxes of 1-20 MW/m{sup 2} are measured on the lateral protection bumpers at ICRF turn-on; these fluxes are primarily a function of plasma and radio frequency (rf) control, and are not simply correlated with the strap phasing or the final surface temperature distributions. The remarkable feature of the lower hybrid edge interaction is the production of beams of heat flux in front of the grills; these beams propagate along the helical magnetic field lines and can deliver fluxes of 5-10 MW/m{sup 2} over areas of several cm{sup 2} to plasma-facing components such as the grill or antenna lateral bumpers. Both the ICRF and LH phenomena appear to result from the acceleration of particles by the near fields of the launchers. Modeling of the heat flux deposition on components and its relation to sputtering processes is presented, and possibilities for controlling these interactions are discussed.
Date: October 1, 1996
Creator: Harris, J.H.; Hutter, T. & Hogan, J.T.
Partner: UNT Libraries Government Documents Department

Studies on the scale-up of the microwave-assisted nitridation and sintering of reaction-bonded silicon nitride

Description: Studies using laboratory test samples have shown that microwave heating produces sintered reaction-bonded silicon nitride materials with improved properties. The final challenge for processing this material by microwave heating is the development of a technology for processing larger batch-size quantities of these materials. Initial microwave scale-up experiments were performed using powder compacts of a bucket tappet geometry. In experiments using microwave-transparent boron nitride sample crucibles, temperature gradients within some crucibles led to larger variations in the sample densities than were obtained with the conventionally processed samples. The use of a microwave-suscepter type crucible made of silicon carbide and boron nitride resulted in an improved temperature uniformity and in density variations comparable to those obtained for the control groups.
Date: May 1, 1996
Creator: Kiggans, J.O.: Tiegs, T.N. & Kimrey, H.D.
Partner: UNT Libraries Government Documents Department

Production of high charge state ions with the Advanced Electron Cyclotron Resonance ion source at LBNL

Description: Production of high charge state ions with the Advanced Electron Cyclotron Resonance ion source (AECR) at Lawrence Berkeley National Laboratory (LBNL) has been significantly improved by application of various new techniques. Heating the plasma simultaneously with microwaves of two frequencies (10 and 14 GHz) has increased the production of very high charge state heavy ions. The two-frequency technique provides extra electron cyclotron resonance heating zone as compared to the single-frequency heating and improves the heating of the plasma electrons. Aluminum oxide on the plasma chamber surface improves the production of cold electrons at the chamber surfaces and increases the performance of the AECR. Fully stripped argon ions, {gt} 5 enA, were produced and directly identified by the source charge state analyzing system. High charge state ion beams of bismuth and uranium, such as {sup 209}Bi{sup 51+} and {sup 238}U{sup 53+}, were produced by the source and accelerated by the 88-Inch Cyclotron to energies above 6 MeV/nucleon for the first time. To further increase the production of high charge state ions to support the nuclear science research programs at the 88-Inch Cyclotron, an upgrade is taking place to increase the AECR magnetic field strengths and mirror ratios to improve the plasma confinement. Conceptual design is underway for a 3rd Generation ECR that uses superconducting magnets to reach higher magnetic field strengths and higher mirror ratios, high secondary emission chamber walls to increase the yield of cold electrons at the chamber surfaces and microwaves of multiple frequencies to improve plasma heating.
Date: September 1, 1995
Creator: Xie, Zu Qi & Lyneis, C.M.
Partner: UNT Libraries Government Documents Department

Design of the 3rd generation ECR ion source

Description: Development of the 3rd Generation ECR ion source has progressed from a concept described in the last ECR Ion Source Workshop to the fabrication of a full scale prototype superconducting magnet structure. The prototype consists of three solenoid coils and six race track coils with iron poles forming the sextupole. The design calls for mirror fields of 4 T at injection and 3 T at extraction and for a radial field strength at the wall of 2.4 T. The prototype magnet will be tested this spring in an existing vertical cryostat to determine its operating characteristics including maximum operating values, training characteristics and to study the interaction between the solenoid and sextupole coils. Design of the ECR plasma chamber includes aluminum walls to provide an enhanced source of cold electrons, up to three separate microwave feeds to allow simultaneous heating of the plasma electrons at 10, 14 and 18 GHz or at 6, 10 and 14 GHz. Water cooling of the plasma chamber walls and the injection and extraction plates is planned so that up to 10 kW of microwave power can be used without excessive heating of the chamber components. Experience with the AECR-U at LBNL shows that increasing the magnetic fields and using two frequency heating allows operation at lower neutral pressures and higher microwave power density. Both of these conditions are needed to produce very high charge states from elements with masses greater than xenon and the resulting higher energy, more intense heavy beams from the 88-Inch Cyclotron would provide new research opportunities.
Date: February 1, 1997
Creator: Lyneis, C.M.; Xie, Z.Q. & Taylor, C.E.
Partner: UNT Libraries Government Documents Department

Microwave process control through a traveling wave tube source

Description: A rapid feedback control system was designed to operate with a traveling wave tube for regulating the sintering temperature of tows and tubes in a single mode microwave cavity. The control system regulated the microwave frequency and power absorbed by the sample in order to maintain the sample temperature. Testing with NICALON tows and mullite tubes demonstrated that the control scheme worked well for stationary and slowly moving ({lt}10mm/min) samples, but failed for fast moving samples. Difficulty with measuring sample temperatures was resolved by using a light sensor to measure the emitted light intensity and to relative degree of heating.
Date: April 1, 1996
Creator: Vogt, G.J.; Regan, A.; Rohlev, A. & Curtin, M.
Partner: UNT Libraries Government Documents Department

Reducing deuterium-tritium ice roughness by electrical heating of the saturated vapor

Description: High gain targets for inertial confinement fusion (ICF) contain a layer of deuterium-tritium (DT) ice which surrounds a volume of DT gas in thermal equilibrium with the solid. The roughness of the cryogenic fuel layer inside of ICF targets is one of the sources of imperfections which cause implosions to deviate from perfect one dimensional performance. Experiments at Lawrence Livermore National Laboratory have shown that applying a heat flux across the inner surface of a hydrogen layer such as that inside an ICF target reduces the intrinsic roughness of the surface. We have developed a technique to generate this heat flux by applying and electric field to the DT vapor in the center of these shells. This vapor has a small but significant conductivity due to ionization caused by beta decay of tritium in the vapor and the solid. We describe here experiments using a 1.15 GHz cavity to apply an electric field to frozen DT inside of a sapphire test cell. The cell and cavity geometry allows visual observation of the frozen layers.
Date: June 14, 1996
Creator: Mapoles, E.R.; Sater, J.D.; Monsler, E. & Pipes, J.
Partner: UNT Libraries Government Documents Department

Phase 2 microwave concrete decontamination results

Description: The authors report on the results of the second phase of a four-phase program at Oak Ridge National Laboratory to develop a system to decontaminate concrete using microwave energy. The microwave energy is directed at the concrete surface through the use of an optimized wave guide antenna, or applicator, and this energy rapidly heats the free water present in the interstitial spaces of the concrete matrix. The resulting steam pressure causes the surface to burst in much the same way popcorn pops in a home microwave oven. Each steam explosion removes several square centimeters of concrete surface that are collected by a highly integrated wave guide and vacuum system. The authors call this process the microwave concrete decontamination, or MCD, process. In the first phase of the program the principle of microwaves concrete removal concrete surfaces was demonstrated. In these experiments, concrete slabs were placed on a translator and moved beneath a stationary microwave system. The second phase demonstrated the ability to mobilize the technology to remove the surfaces from concrete floors. Area and volume concrete removal rates of 10.4 cm{sup 2}/s and 4.9 cm{sup 3}/S, respectively, at 18 GHz were demonstrated. These rates are more than double those obtained in Phase 1 of the program. Deeper contamination can be removed by using a longer residence time under the applicator to create multiple explosions in the same area or by taking multiple passes over previously removed areas. Both techniques have been successfully demonstrated. Small test sections of painted and oil-soaked concrete have also been removed in a single pass. Concrete with embedded metal anchors on the surface has also been removed, although with some increased variability of removal depth. Microwave leakage should not pose any operational hazard to personnel, since the observed leakage was much less than the regulatory standard.
Date: April 1, 1995
Creator: White, T.L.; Foster, D. Jr.; Wilson, C.T. & Schaich, C.R.
Partner: UNT Libraries Government Documents Department

Soil sample preparation using microwave digestion for uranium analysis

Description: A new sample preparation procedure has been developed for digestion of soil samples for uranium analysis. The technique employs a microwave oven digestion system to digest the sample and to prepare it for separation chemistry and analysis. The method significantly reduces the volume of acids used, eliminates a large fraction of acid vapor emissions, and speeds up the analysis time. The samples are analyzed by four separate techniques: Gamma Spectrometry, Alpha Spectroscopy using the open digestion method, Kinetic Phosphorescence Analysis (KPA) using open digestion, and KPA by Microwave digestion technique. The results for various analytical methods are compared and used to confirm the validity of the new procedure. The details of the preparation technique along with its benefits are discussed.
Date: April 5, 2000
Partner: UNT Libraries Government Documents Department

Mirowave annealing of silicon nitride materials

Description: Dense silicon nitride-based ceramics were microwave annealed to determine if microwave heating offers advantages over conventional heating for the enhancement of the high temperature creep resistance. Gas pressure sintered silicon nitride (GPS-SN) and sintered reaction-bonded silicon nitride (SRBSN) were heated in microwave or graphite element furnaces at 1150{degrees}C and 1600{degrees}C. Annealed materials were characterized for the room and high temperature flexural strengths, room temperature fracture toughness values, and high temperature creep properties. In addition, SEM analyses were performed to study grain growth and other microstructural changes. The results of this study showed that both types of furnace anneals at 1150{degrees}C lowered the room temperature strength and toughness values of both SRBSN and GPS-SN materials; however, the anneal treatments at 1600{degrees}C had little effect on the room temperature properties. Both the SRBSN and GPS-SN control and annealed samples had reduced high temperature fast fracture strengths, when compared to the room temperature strengths. Creep tests at 1200{degrees}C indicated that both the SRBSN and the GPS-SN materials that were annealed by microwave heating at I 150{degrees}C for 20 h showed enhanced creep resistance, when compared to unheated controls and conventionally heated materials. No qualitative differences were seen in the microstructures of the SRBSN and the GPS-SN materials which could account for the differences in the creep properties of the annealed materials. Additional experimental work is in progress to further understand the mechanisms for the enhanced creep properties of silicon nitride materials annealed by microwave heating.
Date: August 1, 1997
Creator: Kiggans, J.O. Jr.; Montgomery, F.C. & Tiegs, T.N.
Partner: UNT Libraries Government Documents Department

Recent progress in ceramic joining

Description: Both fundamental and practical aspects of ceramic joining are understood well enough for many, if not most, applications requiring moderate strengths at room temperature. This paper argues that the two greatest needs in ceramic joining are for techniques to join buried interfaces by selective heating, and methods for joining ceramics for use at temperatures of 800 to 1,200 C. Heating with microwave radiation or with high-energy electron beams has been used to join buried ceramic interfaces, for example SiC to SiC. Joints with varying levels of strength at temperatures of 600 to 1,000 C have been made using four techniques: (1) transient liquid phase bonding; (2) joining with refractory braze alloys; (3) joining with refractory glass compositions; and (4) joining using preceramic polymers. Joint strengths as high as 550 MPa at 1,000 C have been reported for silicon nitride-silicon nitride bonds tested in four-point flexure.
Date: September 1, 1998
Creator: Loehman, R.E.
Partner: UNT Libraries Government Documents Department

Quasi-optical gyrotron materials processing at Los Alamos

Description: Los Alamos has recently obtained and installed quasi-optical gyrotrons of 37 and 84 GHz with power outputs up to 35 kW. A quasi-optical gyrotron is unique in that the output is a Gaussian beam which can be focused and manipulated using mirrors. The Gaussian beam output is ideally suited for one and two dimensional materials processing applications such as joining and surface treatment. Working with the National Center for Manufacturing Sciences (NCMS) we have formed a consortium of companies to investigate several materials processing applications.
Date: May 1, 1995
Creator: Katz, J.D. & Rees, D.E.
Partner: UNT Libraries Government Documents Department

Adhesive bonding via exposure to microwave radition and resulting mechanical evaluation

Description: Adhesive bonding/joining through microwave radiation curing has been evaluated as an alternative processing technology. This technique significantly reduces the required curing time for the adhesive while maintaining equivalent physical characteristics as the adhesive material is polymerized (crosslinked). This results in an improvement in the economics of the process. Testing of samples cured via microwave radiation for evaluation of mechanical properties indicated that the obtained values from the single lap-shear test are in the range of the conventionally cured samples. In general, the ultimate tensile strength, {sigma}{sub B}, for the microwave processed samples subjected to this single lap-shear test was slightly higher than for conventionally cured samples. This technology shows promise for being applicable to a wide range of high volume, consumer goods industries, where plastics and polymer composites will be processed.
Date: April 1, 1996
Creator: Paulauskas, F.L.; Warren, C.D. & Meek, T.T.
Partner: UNT Libraries Government Documents Department

Non-fusion applications of RF and microwave technology

Description: The processing of materials using rf and/or microwave power is a broad area that has grown significantly in the past few years. The authors have applied rf and microwave technology in the areas of ceramic sintering, plasma processing, and waste processing. The sintering of ceramics in the frequency range of 50 MHz-28 GHz has lead to unique material characteristics compared to materials that have been sintered conventionally. It has been demonstrated that sintering can be achieved in a variety of materials, including alumina, zirconia, silicon carbide, and boron carbide. In the area of plasma processing, progress has been made in the development and understanding of high density plasma sources, including inductively coupled plasma (ICP) sources. The effects of processing conditions on the ion energy distribution at the substrate surface (a critical processing issue) have been determined for a variety of process gases. The relationship between modeling and experiment is being established. Microwave technology has also been applied to the treatment of radioactive and chemical waste. The application of microwaves to the removal of contaminated concrete has been demonstrated. Details of these programs and other potential application areas are discussed.
Date: December 1, 1995
Creator: Caughman, J.B.O.; Baity, F.W.; Bigelow, T.S.; Gardner, W.L.; Hoffman, D.J.; Forrester, S.C. et al.
Partner: UNT Libraries Government Documents Department

Kinetics of the carbon monoxide oxidation reaction under microwave heating

Description: 915 MHz microwave heating has been used to drive the CO oxidation reaction over Pd/Al{sub 2}O{sub 3} with out significantly affecting the reaction kinetics. As compared to an identical conventionally heated system, the activation energy, pre-exponential factor, and reaction order with respect to CO were unchanged. Temperature was measured using a thermocouple extrapolation technique. Microwave-induced thermal gradients were found to play a significant role in kinetic observations. The authors chose the CO oxidation reaction over a supported metal catalyst because the reaction kinetics are well known, and because of the diverse dielectric properties of the various elements in the system: CO is a polar molecule, O{sub 2} and CO{sub 2} are non-polar, Al{sub 2}O{sub 3} is a dielectric, and Pt and Pd are conductors.
Date: June 1, 1996
Creator: Perry, W.L.; Katz, J.D.; Rees, D.; Paffett, M.T. & Datye, A.
Partner: UNT Libraries Government Documents Department

Enhancement of thermal stability in microwave applicators by mismatching and detuning

Description: Many microwave applicator systems experiencing thermal runaway can be stabilized by mismatching and/or detuning the system. The stability of the systems is discussed qualitatively and a conservative guide for adjusting microwave applicators for enhanced stability is described.
Date: July 1996
Creator: Nelson, E. M.
Partner: UNT Libraries Government Documents Department

The utilization of microwave heating for the fabrication of sintered reaction-bonded silicon nitride

Description: The results of studies in which microwave heating was used to fabricate sintered reaction-bonded silicon nitride (SRBSN) are reviewed. These results are compared to parallel studies where conventional heating was used for the fabrication of these materials. Microwave fabrication of SRBSN involves a single heating cycle, whereas conventional processing requires two separate furnace runs and sample packaging steps. SRBSN containing high levels of sintering aids which were fabricated by microwave heating showed improved strength and toughness, as compared to those materials fabricated using a conventional resistance-heated furnace. An analysis of the microstructures of the microwave fabricated materials showed enhanced acicular grain growth as compared to conventionally heated material. Results are presented on studies involving the scale-up of the microwave fabrication process.
Date: December 31, 1995
Creator: Kiggans, J.O.; Tiegs, T.N.; Lin, H.T. & Holcombe, C.E.
Partner: UNT Libraries Government Documents Department

Application of microwave solidification technology to radioactive waste

Description: The EPA has declared vitrification to be the Best Available Demonstrated Technology (BDAT) for High Level Radioactive Waste (40 CFR 268.42). Vitrification has been chosen as the method of choice for treating a number of radioactive residues and wastes in the DOE complex. Vitrification offers advantages of waste volume reduction, the ability to handle changing waste forms, and a stable, nonleachable final waste form. Microwave heating is a superior method for vitrification of radioactive wastes. Advantages of microwave heating include: (1) direct waste heating, eliminates need for electrodes, refractories and other consumables; (2) ``in-can`` processing allows for treatment of the material in its final container, (3) a mechanically simple system where the microwaves are generated away from the treatment area and transmitted to the treatment applicator by a wave guide, thus minimizing worker exposure to radiation; (4) easier equipment maintenance; and (5) a high degree of public acceptance.
Date: September 28, 1995
Creator: Harris, M.; Sprenger, G.; Roushey, B.; Fenner, G. & Nieweg, R.
Partner: UNT Libraries Government Documents Department

Technical and Engineering Feasibility Study of the Vitrification of Plutonium-Bearing Sludges at the Krasnoyarsk Mining and Chemical Combine by Means of Microwave Heating

Description: This engineering feasibility study compared three possible technical options and their economic viability of processing plutonium-bearing sludges containing 0.6 MT of weapons-grade Pu accumulated at the Mining and Chemical Combine (MCC) at Krasnoyarsk. In Option 1, the baseline, the sludges are processed by extraction and purification of plutonium for storage using existing technologies, and the non-soluble radioactive residues generated in these processes undergo subsequent solidification by cementation. Options 2 and 3 involve the direct immobilization of plutonium-bearing sludges into a solid matrix (without any Pu extraction) using a microwave solidification process in a metal crucible to produce a glass, which is boron-silicate in Option 2 and phosphate glass in Option 3. In all three options, the solid radioactive waste end products will be placed in storage for eventual geologic disposal. Immobilization of residual plutonium into glass-like matrices provides both safer storage over the lifetime of the radionuclides and greater security against unauthorized access to stored materials than does the extraction and concentration of PuO{sub 2}, supporting our efforts toward non-proliferation of fissile materials. Although immobilization in boron-silicate glass appears now to be marginally preferable compared to the phosphate glass option, a number of technical issues remain to be assessed by further study to determine the preferable immobilization option.
Date: March 3, 2000
Creator: Revenko, Y.A.; Kudinov, K.G.; Tretyakov, A.A.; Vassilyev, A.V.; Borisov, G.B.; Nazarov, A.V. et al.
Partner: UNT Libraries Government Documents Department

Commissioning of the long-pulse fast wave current drive antennas for DIII-D

Description: Two new four-element fast wave current drive antennas have been installed on DIII-D. These antennas are designed for 10-s pulses at 2 MW each in the frequency range of 30 to 120 MHz. Each element comprises two poloidal segments fed in parallel in order to optimize plasma coupling at the upper end of the frequency range. The antennas are mounted on opposite sides of the vacuum vessel, in ports designated 0{degrees} and 180{degrees} after their toroidal angle. Each antenna array is fed by a single transmitter. The power is first split two ways by means of a 3-dB hybrid coupler, then each of these lines feeds a resonant loop connecting a pair of array elements. The power transfer during asymmetric phasing is shunted between resonant loops by a decoupler. The resonant loops are fitted with line stretchers so that multiple frequencies of operation are possible without reconfiguring the transmission line. Commissioning of these antennas has been underway since June 1994. Several deficiencies in the transmission line system were uncovered during initial vacuum conditioning, including problems with the transmission line insulators and with the drive rods for the variable elements. The former was solved by replacing the original alumina insulators, and the latter has been avoided during operation to date by positioning the tuners to avoid high voltage appearing on the drive rods. A modified design for the drive rods will be implemented before RF operations resume operation June 1995. New transmitters were procured from ABB for the new antennas and were installed in parallel with the antenna installation. During initial vacuum conditioning of the antenna in the 180{degree} port a fast digital oscilloscope was used to try to pinpoint the location of arcing by a time-of-flight technique and to develop an understanding of the typical arc signature in the system.
Date: September 1, 1995
Creator: Baity, F.W.; Barber, G.C.; Goulding, R.H.; Hoffman, D.J.; DeGrassie, J.S.; Pinsker, R.I. et al.
Partner: UNT Libraries Government Documents Department