Ray-based calculations of backscatter in laser fusion targets

A 1D, steady-state model for Brillouin and Raman backscatter from an inhomogeneous plasma is presented. The daughter plasma waves are treated in the strong damping limit, and have amplitudes given by the (linear) kinetic response to the ponderomotive drive. Pump depletion, inverse-bremsstrahlung damping, bremsstrahlung emission, Thomson scattering off density fluctuations, and whole-beam focusing are included. The numerical code DEPLETE, which implements this model, is described. The model is compared with traditional linear gain calculations, as well as "plane-wave" simulations with the paraxial propagation code pF3D. Comparisons with Brillouin-scattering experiments at the OMEGA Laser Facility [T. R. Boehly et al., Opt. Commun. 133, p. 495 (1997)] show that laser speckles greatly enhance the reflectivity over the DEPLETE results. An approximate upper bound on this enhancement, motivated by phase conjugation, is given by doubling the DEPLETE coupling coefficient. Analysis with DEPLETE of an ignition design for the National Ignition Facility (NIF) [J. A. Paisner, E. M. Campbell, and W. J. Hogan, Fusion Technol. 26, p. 755 (1994)], with a peak radiation temperature of 285 eV, shows encouragingly low reflectivity. Re-absorption of Raman light is seen to be significant in this design.Comment: 16 pages, 19 figure

Threshold for Electron Trapping Nonlinearity in Langmuir Waves

We assess when electron trapping nonlinearity is expected to be important in Langmuir waves. The basic criterion is that the inverse of the detrapping rate nu_d of electrons in the trapping region of velocity space must exceed the bounce period of deeply-trapped electrons, tau_B = (n_e/delta n)^{1/2} 2pi/omega_pe. A unitless figure of merit, the "bounce number" N_B = 1/(nu_d tau_B), encapsulates this condition and defines a trapping threshold amplitude for which N_B=1. The detrapping rate is found for convective loss (transverse and longitudinal) out of a spatially finite Langmuir wave. Simulations of driven waves with a finite transverse profile, using the 2D-2V Vlasov code Loki, show trapping nonlinearity increases continuously with N_B for transverse loss, and is significant for N_B ~ 1. The detrapping rate due to Coulomb collisions (both electron-electron and electron-ion) is also found, with pitch-angle scattering and parallel drag and diffusion treated in a unified manner. A simple way to combine convective and collisional detrapping is given. Application to underdense plasma conditions in inertial confinement fusion targets is presented. The results show that convective transverse loss is usually the most potent detrapping process in a single f/8 laser speckle. For typical plasma and laser conditions on the inner laser cones of the National Ignition Facility, local reflectivities ~3% are estimated to produce significant trapping effects.Comment: 16 pages, 15 figures, accepted for publication in Phys. Plasma

Fiscal effects and the potential implications on economic growth of sea level rise impacts and coastal zone protection

Climate change impacts on coastal zones could be significant unless adaptation is undertaken. One particular macro-economic dimension of sea level rise (SLR) impacts that has received no attention so far is the potential stress of SLR impacts on public budgets. Adaptation will require increased public expenditure to protect assets at risk and could put additional stress on public budgets. We analyse the macroeconomic effects of SLR adaptation and impacts on public budgets. We include fiscal indicators in a climate change impact assessment focusing on SLR impacts and adaptation costs using a computable general equilibrium model extended with a detailed description of the public sector. Coastal protection expenditure is financed issuing government bonds, meaning that coastal adaptation places an additional burden on public budgets. SLR impacts are examined using several scenarios linked to three different Representative Concentration Pathways: 2.6, 4.5 and 8.5, and two Shared Socio-economic Pathways: SSP2 and SSP5. Future projections of direct damages of mean and extreme SLR and adaptation costs are generated by the Dynamic Interactive Vulnerability Assessment framework. Without adaptation, all world regions suffer a loss and public deficits increase respect to the reference scenario. Higher deficits imply higher government borrowing from household savings reducing available resources for private investments therefore decreasing capital accumulation and growth. Adaptation benefits result from two mechanisms: i) the avoided direct impacts, and ii) a reduced public deficit effect. This allows for an increased capital accumulation, suggesting that support to adaptation in deficit spending might trigger positive effects on public finance sustainability

Shifting perspectives on coastal impacts and adaptation

The Intergovernmental Panel on Climate Change reports reflect evolving attitudes in adapting to sea-level rise by taking a systems approach and recognizing that multiple responses exist to achieve a less hazardous coast.info:eu-repo/semantics/publishedVersio

Geophysical Observations of Taliks Below Drained Lake Basins on the Arctic Coastal Plain of Alaska

Lakes and drained lake basins (DLBs) together cover up to ∼80% of the western Arctic Coastal Plain of Alaska. The formation and drainage of lakes in this continuous permafrost region drive spatial and temporal landscape dynamics. Postdrainage processes including vegetation succession and permafrost aggradation have implications for hydrology, carbon cycling, and landscape evolution. Here, we used surface nuclear magnetic resonance (NMR) and transient electromagnetic (TEM) measurements in conjunction with thermal modeling to investigate permafrost aggradation beneath eight DLBs on the western Arctic Coastal Plain of Alaska. We also surveyed two primary surface sites that served as nonlake affected control sites. Approximate timing of lake drainage was estimated based on historical aerial imagery. We interpreted the presence of taliks based on either unfrozen water estimated with surface NMR and/or TEM resistivities in DLBs compared to measurements on primary surface sites and borehole resistivity logs. Our results show evidence of taliks below several DLBs that drained before and after 1949 (oldest imagery). We observed depths to the top of taliks between 9 and 45 m. Thermal modeling and geophysical observations agree about the presence and extent of taliks at sites that drained after 1949. Lake drainage events will likely become more frequent in the future due to climate change and our modeling results suggest that warmer and wetter conditions will limit permafrost aggradation in DLBs. Our observations provide useful information to predict future evolution of permafrost in DLBs and its implications for the water and carbon cycles in the Arctic