1,721,047 research outputs found
Heavy-Ion Fusion Targets with 'Diffuse' Spherical Radiation Converter
No full textSpherically symmetric targets for indirect-drive heavy-ion fusion are studied, in which the fusion capsule is enclosed in a low-density thick spherical shell, where the ion beams are stopped and their energy is converted into thermal radiation. The thermal radiation then drives the implosion of the fusion capsule, with mininum hydrodynamic coupling between the energy deposition region and the ablation layer. The conditions for effective hydrodynamic decoupling have been derived. It is found that with the use of heavy ions with energy about or below 8 GeV, the beam-to-fuel energy coupling efficiency can be as large as in foreseen conventional hohlraums. On the other hand, these targets only allow for a low dynamic range of pulse shaping, which results in rather poor entropy shaping and modest fuel gain. Robust targets have been designed, which achieve energy gain G approximate to 30, when driven by shaped pulses of 12.5 MJ of 8.5 GeV Bi ions. Inclusion of a high-density pusher, which increases the fuel compression leads to higher gain at lower beam energy, but two-dimensional simulations demonstrate the extremely violent instability of the fuel-pusher interface
Spherically Symmetric Radiation Converters for Ion Beam Fusion
No full textThick spherical shells, irradiated nearly symmetrically by ion beams, can convert efficiently ion beam energy to thermal radiation, with parameters of relevance to inertial confinement fusion. The evolution of such radiation converters has been studied by means of an analytic model, in turn validated by 1D radiation hydrodynamic simulations. Expressions are derived for the overall conversion efficiency, the heating time and the radiation temperature as a function of the beam and target parameters. Conditions are also derived for the effective hydrodynamic insulation between the converter and the fusion capsule contained inside the converter. For realistic heavy ion beam parameters (e.g. 6-8 GeV Bi beams, with total energy of 10 MJ and power about 700 TW) such converters can achieve an efficiency adequate for fusion applications, but only allow for a modest dynamic range of pulse shaping
Implosion of Reactor Size, Gas Filled, Spherical Shell Targets Driven by Shaped Pressure Pulses
No full textThe implosion of a family of reactor‐size targets for inertial confinement fusion (ICF) is studied analytically and numerically. The targets consist of a deuterium–tritium (D–T) shell filled with D–T vapor and they are imploded by a multistep pressure pulse designed in such a way that the final hot spot is formed mainly from the initially gaseous fuel. The formation of the hot spot is described by means of a relatively simple model, and scaling laws for the quantities that characterize the state of the initially gaseous part of the fuel prior to ignition are derived. The results of the model are compared with one‐dimensional fluid simulations, and good agreement is found. A parametric study of the fuel energy gain is then presented; the dependence of the gain and of the hot spot convergence ratio on the pulse parameters and on the filling gas density is analyzed. It is also shown that a substantial increase in the gain (for a given target and pulse energy) can be achieved by replacing the last step of the pulse with an exponential ramp
Ignition Conditions and Fuel Energy Gain of Spark-Ignited and Volume-Ignited ICF Targets
No full textEvaluation of the Time and Frequency Transfer Capabilities of a network of GNSS receivers located in timing laboratories
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Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
ERS-1 Orbits: The Routine Operation and High Precision Products
No full textThe objective of the paper is to summarise the experience of one year of orbit determination and prediction for the ERS-1 spacecraft: firstly, the results of the operational solutions based on S-band ranging and doppler plus fast delivery altimetry will be discussed, and subsequently, higher precision solutions using data from the global laser ranging network. Steady progress has been achieved in improving the latter, in particular through better solutions for station positions, drag, gravity and tides. The development of this offline capability has strengthened considerably the routine orbit determination, and gives high confidence that the requirements for the latter are being satisfied. The paper attempts to quantify the accuracies which have been reached in the European Space Operations Center solutions, and to answer the question: how far are we still from achieving 10 cm radial accuracy for altimeter satellites at 800 km
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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