3,369 Matching Results

Search Results

Advanced search parameters have been applied.

Duals for SU(N) SUSY Gauge Theories with an Antisymmetric Tensor: Five Easy Flavors

Description: I consider N = 1 supersymmetric SU(N{sub c}) gauge theories with matter fields consisting of one antisymmetric representation, five flavors, and enough antifundamental representations to cancel the gauge anomaly. Previous analyses are extended to the case of even N{sub c} with no superpotential. Using holomorphy I show that the theory has an interacting infrared fixed point for sufficiently large N{sub c}. These theories are interesting due to the fact that in going from five to four flavors the theory goes from a non-trivial infrared fixed point to confinement, in contradistinction to SUSY QCD, but in analogy to the behavior expected in non-SUSY QCD.
Date: December 16, 1997
Creator: Terning, John
Partner: UNT Libraries Government Documents Department

Computational modeling of magentically driven liner-on-plasma fusion experiments

Description: Magnetized Target Fusion (MTF) is an approach to controlled fusion which potentially avoids the difficulties of the traditional magnetic and inertial confinement approaches. It appears possible to investigate the critical issues for MTF at low cost, relative to traditional fusion programs, utilizing pulsed power drivers much less expensive than ICF drivers, and plasma configurations much less expensive than those needed for full magnetic confinement. Computational and experimental research into MTF is proceeding at Los Alamos, VNIIEF, and other laboratories.
Date: December 31, 1996
Creator: Sheehey, P.T.; Faehl, R.J.; Kirkpatrick, R.C. & Lindemuth, I.R.
Partner: UNT Libraries Government Documents Department

Quantum confinement, carrier dynamics and interfacial processes in nanostructured direct/indirect-gap semiconductor-glass composites

Description: The behavior of semiconductor clusters precipitated in an insulated matrix was investigated. Semiconductor compositions of CdTe, Si and Ge were studies and the insulating matrix was amorphous SiO2. As a function of size, quantum confinement effects were observed in all three composite systems. However significant differences were observed between the direct-gap column 2-6 semiconductors and the indirect-gap column 4 semiconductors. As observed by others, the direct-gap 2-6 semiconductors showed a distinct saturation in the energy-gap blue shift with decreasing size. Theoretical studies using a 20-band k dot p calculation of the electronic and valence bands for a 3-dimensionally confined CdTe semiconductor showed that mixing of the conduction band states leads to a flattening of the central valley. This increases the electron mass drastically and saturates the size dependent blue shift in the bandgap. In contrast, the blue shift in the Si and Ge nanocrystals showed no sign of saturation and increased drastically with decreasing size. In fact, Si and Ge crystals were formed with blue shift values that moved the bandgap to the near UV region. We examined the absorption curves to determine whether the bandgap was direct or indirect in the quantum dots. The results are that the absorption shows an indirect gap for all but the smallest Si crystals and an indirect gap for all Ge crystals. Raman studies showed negligible size dependence due to a lack of phonon confinement in the matrix embedded clusters. Exciton saturation and recovery times were found to be very short (of the order of 400fs) and are the fastest reported for any quantum dot system. Work to examine the type of confinement obtained in a matrix that consists of a transparent conductor is under way. Studies of the photoinduced absorption change in GeSe glasses showed a significant effect of photodarkening, regardless of ...
Date: August 13, 2002
Creator: Simmons, Joseph H.
Partner: UNT Libraries Government Documents Department

The Dependence of H-mode Energy Confinement and Transport on Collisionality in NSTX

Description: Understanding the dependence of confi nement on collisionality in tokamaks is important for the design of next-step devices, which will operate at collisionalities at least one order of magnitude lower than in present generation. A wide range of collisionality has been obtained in the National Spherical Torus Experiment (NSTX) by employing two different wall conditioning techniques, one with boronization and between-shot helium glow discharge conditioning (HeGDC+B), and one using lithium evaporation (Li EVAP). Previous studies of HeGDC+B plasmas indicated a strong and favorable dependence of normalized con nement on collisionality. Discharges with lithium conditioning discussed in the present study gen- erally achieved lower collisionality, extending the accessible range of collisionality by almost an order of unity. While the confinement dependences on dimensional, engineering variables of the HeGDC+B and Li EVAP datasets differed, collisionality was found to unify the trends, with the lower collisionality lithium conditioned discharges extending the trend of increasing normalized confi nement time with decreasing collisionality when other dimension less variables were held as fi xed as possible. This increase of confi nement with decreasing collisionality was driven by a large reduction in electron transport in the outer region of the plasma. This result is consistent with gyrokinetic calculations that show microtearing and Electron Temperature Gradient modes to be more stable for the lower collisionality discharges. Ion transport, near neoclassical at high collisionality, became more anomalous at lower collisionality, possibly due to the growth of hybrid TEM/KBM modes in the outer regions of the plasma.
Date: November 27, 2012
Creator: S.M.. Kaye, S. Gerhardt, W. Guttenfelder, R. Maingi, R.E. Bell, A. Diallo, B.P. LeBlanc and M. Podesta
Partner: UNT Libraries Government Documents Department

STATUS OF THE LBL/LLL DEVELOPMENT PROGRAM

Description: The status and near-term goals of the LBL/LLL neutral-beam-development program are described. The emphasis in this paper is on the technology of systems based on the acceleration and neutralization of positive ions; this approach will be used in the near term, probably through 1985 at least. For more efficient injection, part of our plan is to develop a negative-ion approach suitable for 200- to 400-kV injectors on confinement experiments in the 1985-90 period. However, the negative-ion based program is still very much in the research phase, and it is difficult to project how it will phase into fusion reactor fueling experiments.
Date: November 1, 1977
Creator: Berkner, K.H.; Berkner, K.H.; Ehlers, K.W.; Pyle, R.V. & Hooper Jr., E.B.
Partner: UNT Libraries Government Documents Department

Ignition and burn in inertially confined magnetized fuel

Description: At the third International Conference on Emerging Nuclear Energy Systems, we presented computational results which suggested that breakeven'' experiments in inertial confinement fusion (ICF) may be possible with existing driver technology. We recently used the ICF simulation code LASNEX to calculate the performance of an idealized magnetized fuel target. The parameter space in which magnetized fuel operates is remote from that of both conventional'' ICF and magnetic confinement fusion devices. In particular, the plasma has a very high {beta} and is wall confined, not magnetically confined. The role of the field is to reduce the electron thermal conductivity and to partially trap the DT alphas. The plasma is contained in a pusher which is imploded to compress and adiabatically heat the plasma from an initial condition of preheat and pre-magnetization to the conditions necessary for fusion ignition. The initial density must be quite low by ICF standards in order to insure that the electron thermal conductivity is suppressed and to minimize the generation of radiation from the plasma. Because the energy loss terms are effectively suppressed, the implosion may proceed at a relatively slow rate of about 1 to 3 cm/{mu}s. Also, the need for low density fuel dictates a much larger target, so that magnetized fuel can use drivers with much lower power and power density. Therefore, magnetized fuel allows the use of efficient drivers that are not suitable for laser or particle beam fusion due to insufficient focus or too long pulse length. The ignition and burn of magnetized fuel involves very different dominant physical processes than does conventional'' ICF. The fusion time scale becomes comparable to the hydrodynamic time scale, but other processes that limit the burn in unmagnetized fuel are of no consequence. The idealized low gain magnetized fuel target presented here is large and requires ...
Date: January 1, 1991
Creator: Kirkpatrick, R.C. & Lindemuth, I.R.
Partner: UNT Libraries Government Documents Department

Field-reversed configuration (FRC) experiments

Description: FRCs with equilibrium separatrix radii up to 0.18 m have been formed and studied in FRX-C/LSM. For best formation conditions at low fill pressure, the particle confinement exceeds the predictions of LHD transport calculations by up to a factor of two; however, the inferred flux confinement is more anomalous than in smaller FRCs. Higher bias field produces axial shocks and degradation in confinement, while higher fill pressure results in gross fluting during formation. FRCs have been formed in TRX with s from 2 to 6. These relatively collisional FRCs exhibit flux lifetimes of 10 {yields} 20 kinetic growth times for the internal tilt mode. The coaxial slow source has produced annular FRCs in a coaxial coil geometry on slow time scales using low voltages. 16 refs., 4 figs., 1 tab.
Date: January 1, 1988
Creator: Siemon, R.E.; Chrien, R.E.; Hugrass, W.N.; Okada, S.; Rej, D.J.; Taggart, D.P. et al.
Partner: UNT Libraries Government Documents Department

Advances in ICF power reactor design

Description: Fifteen ICF power reactor design studies published since 1980 are reviewed to illuminate the design trends they represent. There is a clear, continuing trend toward making ICF reactors inherently safer and environmentally benign. Since this trend accentuates inherent advantages of ICF reactors, we expect it to be further emphasized in the future. An emphasis on economic competitiveness appears to be a somewhat newer trend. Lower cost of electricity, smaller initial size (and capital cost), and more affordable development paths are three of the issues being addressed with new studies.
Date: April 17, 1985
Creator: Hogan, W.J. & Kulcinski, G.L.
Partner: UNT Libraries Government Documents Department

Transport of intense ion beams. [HIBALL II]

Description: The maximum transportable current for an ion beam is determined by considerations of focal strength, space charge equilibrium and stability, structural practically and emittance. These factors are described within the context of a heavy ion driver for Inertial Confinement Fusion. Recent supporting results from particle-in-cell simulations and transport experiments will be described.
Date: June 1, 1986
Creator: Lee, E.P.
Partner: UNT Libraries Government Documents Department

Confinement Studies of Auxiliary Heated NSTX Plasmas

Description: The confinement of auxiliary heated NSTX discharges is discussed. The energy confinement time in plasmas with either L-mode or H-mode edges is enhanced over the values given by the ITER97L and ITER98Pby(2) scalings, being up to 2-3 times L-mode and 1.5 times H-mode. TRANSP calculations based on the kinetic profile measurements reproduce the magnetics-based determination of stored energy and the measured neutron production rate. Power balance calculations reveal that, in a high power neutral beam heated H-mode discharge, the ion thermal transport is near neoclassical levels, and well below the electron thermal transport, which is the main loss channel. Perturbative impurity injection techniques indicate the particle diffusivity to be slightly above the neoclassical level in discharges with L-mode edge. High-harmonic fast-wave (HHFW) bulk electron heating is described and thermal transport is discussed. Thermal ion transport is found to be above neoclassical level, but thermal electron transport remains the main loss mechanism. Evidences of an electron thermal internal transport barrier obtained with HHFW heating are presented. A description of H-mode discharges obtained during HHFW heating is presented.
Date: May 6, 2003
Creator: LeBlanc, B.P.; Bell, M.G.; Bell, R.E.; Bitter, M.L.; Bourdelle, C.; Gates, D.A. et al.
Partner: UNT Libraries Government Documents Department

Development of a General Shocked-Materials-Response Description for Simulations

Description: This report outlines broad modeling issues pertaining to polymeric materials behavior under detonation conditions. Models applicable system wide are necessary to cope with the broad range of polymers and complex composite forms that can appear in Laboratory weapons systems. Nine major topics are discussed to span the breadth of materials, forms, and physical phenomena encountered when shocking polymers and foams over wide ranges of temperatures, pressures, shock strengths, confinement conditions, and geometries. The recommendations for directions of more intensive investigation consider physical fidelity, computational complexity, and application over widely varying physical conditions of temperature, pressure, and shock strength.
Date: July 1, 2000
Creator: Valone, Steven M.
Partner: UNT Libraries Government Documents Department

Femtosecond chirp-free studies of energy relaxation in semiconductor quantum dots: Search for a phonon bottleneck

Description: Contrary to the predictions of phonon bottleneck theories, we observe very fast subpicosecond energy relaxation in strongly confined semiconductor nanocrystals with electron level spacing as large as 20 LO phonon energies.
Date: August 1, 1997
Creator: Klimov, V. & McBranch, D.
Partner: UNT Libraries Government Documents Department

Inertial confinement fusion reactor systems

Description: A variety of reactor cavity concepts, drivers, and energy conversion mechanisms are being considered to realize commercial applications of ICF. Presented in this paper are: (1) a review of reactor concepts with estimates of practically achievable pulse repetition rates; (2) a survey of drivers with estimates of the requirements on reactor conditions imposed by beam propagation characteristics; and (3) an assessment of compatible driver-reactor combinations.
Date: January 1, 1980
Creator: Frank, T.G.; Bohachevsky, I.O. & Pendergrass, J.H.
Partner: UNT Libraries Government Documents Department

High-temperature plasma physics

Description: Both magnetic and inertial confinement research are entering the plasma parameter range of fusion reactor interest. This paper reviews the individual and common technical problems of these two approaches to the generation of thermonuclear plasmas, and describes some related applications of high-temperature plasma physics.
Date: March 1, 1988
Creator: Furth, H.P.
Partner: UNT Libraries Government Documents Department

INERTIAL FUSION DRIVEN BY INTENSE HEAVY-ION BEAMS

Description: Intense heavy-ion beams have long been considered a promising driver option for inertial-fusion energy production. This paper briefly compares inertial confinement fusion (ICF) to the more-familiar magnetic-confinement approach and presents some advantages of using beams of heavy ions to drive ICF instead of lasers. Key design choices in heavy-ion fusion (HIF) facilities are discussed, particularly the type of accelerator. We then review experiments carried out at Lawrence Berkeley National Laboratory (LBNL) over the past thirty years to understand various aspects of HIF driver physics. A brief review follows of present HIF research in the US and abroad, focusing on a new facility, NDCX-II, being built at LBNL to study the physics of warm dense matter heated by ions, as well as aspects of HIF target physics. Future research directions are briefly summarized.
Date: March 31, 2011
Creator: Sharp, W. M.; Friedman, A.; Grote, D. P.; Barnard, J. J.; Cohen, R. H.; Dorf, M. A. et al.
Partner: UNT Libraries Government Documents Department

Alpha Channeling in Mirror Machines

Description: Because of their engineering simplicity, high-β, and steady-state operation, mirror machines and related open-trap machines such as gas dynamic traps, are an attractive concept for achieving controlled nuclear fusion. In these open-trap machines, the confinement occurs by means of magnetic mirroring, without the magnetic field lines closing upon themselves within the region of particle confinement. Unfortunately, these concepts have not achieved to date very spectacular laboratory results, and their reactor prospects are dimmed by the prospect of a low Q-factor, the ratio of fusion power produced to auxiliary power. Nonetheless, because of its engineering promise, over the years numerous improvements have been proposed to enhance the reactor prospects of mirror fusion, such as tandem designs, end-plugging, and electric potential barriers.
Date: October 19, 2005
Creator: Fisch, N. J.
Partner: UNT Libraries Government Documents Department

Reliability Estimation for Double Containment Piping

Description: Double walled or double containment piping is considered for use in the ITER international project and other next-generation fusion device designs to provide an extra barrier for tritium gas and other radioactive materials. The extra barrier improves confinement of these materials and enhances safety of the facility. This paper describes some of the design challenges in designing double containment piping systems. There is also a brief review of a few operating experiences of double walled piping used with hazardous chemicals in different industries. This paper recommends approaches for the reliability analyst to use to quantify leakage from a double containment piping system in conceptual and more advanced designs. The paper also cites quantitative data that can be used to support such reliability analyses.
Date: August 1, 2012
Creator: Cadwallader, L. & Pinna, T.
Partner: UNT Libraries Government Documents Department