An experimental and simulation study of warm dense carbon foams at ambient density(ne∼10^(21) cm^(−3))is presented.This study of isochorically heated foams is motivated by their potential application in carbon-atmosp...An experimental and simulation study of warm dense carbon foams at ambient density(ne∼10^(21) cm^(−3))is presented.This study of isochorically heated foams is motivated by their potential application in carbon-atmosphere white-dwarf envelopes,where there are modeling uncertainties due to the equation of state.The foams are heated on an approximately picosecond time scale with a laser-accelerated proton beam.The cooling and expansion of the heated foams can be modeled with appropriately initialized radiation-hydrodynamics codes;xRAGE code is used in this work.The primary experimental diagnostic is the streaked optical pyrometer,which images a narrow band of radiation from the rear surface of the heated material.Presented are xRAGE modeling results for both solid aluminum targets and carbonized resorcinol-formaldehyde foam targets,showing that the foam appears to cool slowly on the pyrometer because of partial transparency.So that simulations of cooling foam are processed properly,it is necessary to account for finite optical depth in the photosphere calculation,and the methods for performing that calculation are presented in depth.展开更多
Experiments on the National Ignition Facility show that multi-dimensional effects currently dominate the implosion performance. Low mode implosion symmetry and hydrodynamic instabilities seeded by capsule mounting fea...Experiments on the National Ignition Facility show that multi-dimensional effects currently dominate the implosion performance. Low mode implosion symmetry and hydrodynamic instabilities seeded by capsule mounting features appear to be two key limiting factors for implosion performance. One reason these factors have a large impact on the performance of inertial confinement fusion implosions is the high convergence required to achieve high fusion gains.To tackle these problems, a predictable implosion platform is needed meaning experiments must trade-off high gain for performance. LANL has adopted three main approaches to develop a one-dimensional(1D) implosion platform where 1D means measured yield over the 1D clean calculation. A high adiabat, low convergence platform is being developed using beryllium capsules enabling larger case-to-capsule ratios to improve symmetry. The second approach is liquid fuel layers using wetted foam targets. With liquid fuel layers, the implosion convergence can be controlled via the initial vapor pressure set by the target fielding temperature. The last method is double shell targets. For double shells, the smaller inner shell houses the DT fuel and the convergence of this cavity is relatively small compared to hot spot ignition. However,double shell targets have a different set of trade-off versus advantages. Details for each of these approaches are described.展开更多
基金This work was supported by NNSA cooperative Agreement Grant No.DE-NA0002008the DARPA PULSE program(No.12-63-PULSE-FP014)+2 种基金the Air Force Office of Scientific Research(Grant No.FA9550-14-1-0045)This work was performed under the auspices of the U.S.Department of Energy by the Triad National Security,LLC(Contract No.89233218CNA000001)Los Alamos National Laboratory and was supported by the LANL Office of Experimental Sciences programs.Simulations were run on the LANL Institutional Computing Clusters.
文摘An experimental and simulation study of warm dense carbon foams at ambient density(ne∼10^(21) cm^(−3))is presented.This study of isochorically heated foams is motivated by their potential application in carbon-atmosphere white-dwarf envelopes,where there are modeling uncertainties due to the equation of state.The foams are heated on an approximately picosecond time scale with a laser-accelerated proton beam.The cooling and expansion of the heated foams can be modeled with appropriately initialized radiation-hydrodynamics codes;xRAGE code is used in this work.The primary experimental diagnostic is the streaked optical pyrometer,which images a narrow band of radiation from the rear surface of the heated material.Presented are xRAGE modeling results for both solid aluminum targets and carbonized resorcinol-formaldehyde foam targets,showing that the foam appears to cool slowly on the pyrometer because of partial transparency.So that simulations of cooling foam are processed properly,it is necessary to account for finite optical depth in the photosphere calculation,and the methods for performing that calculation are presented in depth.
文摘Experiments on the National Ignition Facility show that multi-dimensional effects currently dominate the implosion performance. Low mode implosion symmetry and hydrodynamic instabilities seeded by capsule mounting features appear to be two key limiting factors for implosion performance. One reason these factors have a large impact on the performance of inertial confinement fusion implosions is the high convergence required to achieve high fusion gains.To tackle these problems, a predictable implosion platform is needed meaning experiments must trade-off high gain for performance. LANL has adopted three main approaches to develop a one-dimensional(1D) implosion platform where 1D means measured yield over the 1D clean calculation. A high adiabat, low convergence platform is being developed using beryllium capsules enabling larger case-to-capsule ratios to improve symmetry. The second approach is liquid fuel layers using wetted foam targets. With liquid fuel layers, the implosion convergence can be controlled via the initial vapor pressure set by the target fielding temperature. The last method is double shell targets. For double shells, the smaller inner shell houses the DT fuel and the convergence of this cavity is relatively small compared to hot spot ignition. However,double shell targets have a different set of trade-off versus advantages. Details for each of these approaches are described.
