Results 1 - 10 of 19865
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[en] A self-consistent model of the L to H transition is derived from coupled nonlinear envelope equations for the fluctuation level, radial electric field shear, Er' and pressure gradient, triangledown Pi. These equations exhibit a bifurcation between dual L-mode and H-mode fixed points. They show that the L to H transition has similar characteristics to a phase transition of the second kind for which the order parameter is Er'. The transition occurs when the turbulence drive is large enough to overcome the damping of the E x B flow. This leads to a power threshold condition for the transition Pcrit ∼ (μnT)edge aRLs
[en] This paper presents a model of the divertor region. The model is based on the two-point approach described by Galambos and Peng but has been enhanced to include the key processes of remote radiative cooling, neutral recycling, particle convection, ash effects, and the effects of divertor geometry and plate material. Neutral particle effects are represented using a wedge-shaped section of plasma overlying the divertor plate and a slab attenuation model. The results of benchmarking against four other divertor models demonstrate the applicability of the proposed model. System sensitivities to key parameters are discussed and several general observations regarding divertor design are presented
[en] Funding for fusion energy R ampersand D by the Federal government is an important investment in the development of an attractive and possibly essential new energy source for this country and the world in the middle of the next century and beyond. This funding also sustains an important field of scientific research - plasma science - in which the United States is the world leader and which has generated a panoply of insights and techniques widely applicable in other fields of science and in industry. And U.S. funding has been crucial to a productive, equitable, and durable international collaboration in fusion science and technology that represents the most important instance of international scientific cooperation in history as well as the best hope for timely commercialization of fusion at this time because the development costs are too high and the potential economic returns too distant. But funding fusion is a bargain for society as a whole. However, in light of present congressional funding climates the authors are suggesting a program which falls far short of what US DOE is proposing, but provides monies to keep the program alive, and to retain limited participation in the international program which currently is aimed at the construction of ITER. This limited funding will severly strain the program as it exists domestically at present, will limit industrial participation, will stretch the reasonable date for an operating demonstation fusion reactor, but will maintain the basic stucture of a domestic fusion research program
[en] The continued progress of inertial-confinement fusion (ICF) is dependent on the diagnosis of the dense fusion plasma. The current information obtainable from ICF implosions is limited to average density-radius product (/sub rho/R) and temperature. Although some initial success has been made in cold targets using x-ray backlighting, the analysis of the target implosions with respect to stability, preheat, and shock-wave propagation in the fuel has not been possible. The understanding of these crucial issues is vital for the achievement of high fuel compression ratios and ultimately high fusion energy gain. The detailed study of ICF implosions becomes feasible with the use of simple analytic models. The ability to analyze fusion-product spectra is greatly enhanced, making time-dependent and localized measurements of the target during implosion possible. In this thesis, implosion models are developed for both exploding pusher and ablative experiments, including the modeling of the global target temperature and density evolution and the localized behavior of shock waves and Rayleigh-Taylor instabilities. Using these models, the analysis of fusion-product spectra can yield a wealth of accurate implosion information
[en] The performance of the NIF baseline design has been modeled in two transverse dimensions using the Fourier optics code PROP92 and the nonlinear harmonic conversion code THG4DO1. The results obtained are in good agreement with those of the ID versions of these codes which were used during the design optimization, yielding good confidence that a near- optimal design has been chosen. We project that this design is able to fulfill NIF's three major mission specifications without component damage. Further modeling, including the effects of air- path turbulence, quasi-static thermal deformations, SSD, and sensitivity to misalignment and component tolerances is ongoing
[en] It is shown that when a magnetic field is used to support neutral atoms against the gravitational force mg, the total curvature of the field magnitude B must be larger than m2g2/(2μ2B), where μ is the magnetic moment of the atoms. This limits the minimum confinement strength obtainable for a trapped atomic gas. It is also conjectured that the curvature must be larger than twice this value for a magnetic potential that varies in only one or two dimensions, such as an atomic waveguide
[en] A necessary condition for igniting indirectly driven inertial confinement fusion spherical capsules on the National Ignition Facility (NIF) is controlling drive flux asymmetry to the 1% level time-integrated over the pulse and with <10%/ns swings during the pulse [J. D. Lindl, P. Amendt, R. L. Berger et al., Phys. Plasmas 11, 339 (2003)]. While drive symmetry during the first 2 ns of the pulse can be inferred by using the re-emission pattern from a surrogate high Z sphere and symmetry during the last 5 ns inferred from the shape of fully imploded capsules, the midportion (≅2-10 ns) has been shown to be amenable to detection by the in-flight shape of x-ray backlit thin-shell capsules. In this paper, we present sensitivity studies conducted on the University of Rochester's OMEGA laser [J. Soures, R. L. McCrory, C. P. Verdon et al., Phys. Plasmas 3, 2108 (1996)] of the thin-shell symmetry measurement technique at near NIF-scale for two candidate capsule ablator materials: Ge-doped CH and Cu-doped Be. These experiments use both point and area backlighting to cast 4.7 keV radiographs of thin 1.4 mm initial-diameter Ge-doped CH and Cu-doped Be shells when converged by a factor of ≅0.5 in radius. Distortions in the position of the transmission limb of the shells resulting from drive asymmetries are measured to an accuracy of a few micrometers, meeting requirements. The promising results to date allow us to compare measured and predicted distortions and by inference drive asymmetries for the first four asymmetry modes as a function of hohlraum illumination conditions.
[en] This paper reviews the status of direct-drive inertial confinement fusion (ICF) research at the University of Rochester's Laboratory for Laser Energetics (LLE). LLE's goal is to demonstrate direct-drive ignition on the National Ignition Facility (NIF) by 2014. Baseline 'all-DT' NIF direct-drive ignition target designs have been developed that have a predicted gain of 45 (1-D) at a NIF drive energy of ∼1.6 MJ. Significantly higher gains are calculated for targets that include a DT-wicked foam ablator. This paper also reviews the results of both warm fuel and initial cryogenic-fuel spherical target implosion experiments carried out on the OMEGA UV laser. The results of these experiments and design calculations increase confidence that the NIF direct-drive ICF ignition goal will be achieved.
[en] The VAX Professional Workstation (VPW) is a collection of programs and procedures designed to provide an integrated work-station environment for the staff at KMS Fusion's research laboratories. During the past year numerous capabilities have been added to VPW, including support for VT125/VT240/4014 graphic workstations, editing windows, and additional desk utilities. Graphics workstation support allows users to create, edit, and modify graph data files, enter the data via a graphic tablet, create simple plots with DATATRIEVE or DECgraph on ReGIS terminals, or elaborate plots with TEKGRAPH on ReGIS or Tektronix terminals. Users may assign display error bars to the data and interactively plot it in a variety of ways. Users also can create and display viewgraphs. Hard copy output for a large network of office terminals is obtained by multiplexing each terminal's video output into a recently developed video multiplexer front ending a single channel video hard copy unit
[en] Of the United States' two major research and development programs pursuing the goal of fusion energy production, the magnetic confinement fusion energy (MFE) program was removed from security classification restrictions in 1958, whereas the inertial confinement fusion (ICF) program remains classified in part, with concomitant barriers to information flow and scientific cooperation both internationally and intranationally. This report attempts to put the question of ICF classification in perspective, and to review and remark upon especially to an appeal by Ray Kidder for ICF declassification. 16 refs