The article reports on recent developments in the theory of secondary instability in drift-ion temperature gradient turbulence. Specifically, the article explores secondary instability as a mechanism for zonal flow generation, transport barrier dynamics and avalanche formation. These in turn are related to the space-time statistics of the drift wave induced flux, the scaling of transport with collisionality and β, and the spatio-temporal evolution of transport barriers.

Turbulence in fluids is a ubiquitous, fascinating, and complex natural phenomenon that is not yet fully understood. Unraveling turbulence in high density, high temperature plasmas is an even bigger challenge because of the importance of electromagnetic forces and the typically violent environments. Fascinating and novel behavior of hot dense matter has so far been only indirectly inferred because of the enormous difficulties of making observations on such matter. Here, we present direct evidence of turbulence in giant magnetic fields created in an overdense, hot plasma by relativistic intensity (10 18 W∕cm 2 ) femtosecond laser pulses. We have obtained magneto-optic polarigrams at femtosecond time intervals, simultaneously with micrometer spatial resolution. The spatial profiles of the magnetic field show randomness and their k spectra exhibit a power law along with certain well defined peaks at scales shorter than skin depth. Detailed two-dimensional particle-in-cell simulations delineate the underlying interaction between forward currents of relativistic energy "hot" electrons created by the laser pulse and "cold" return currents of thermal electrons induced in the target. Our results are not only fundamentally interesting but should also arouse interest on the role of magnetic turbulence induced resistivity in the context of fast ignition of laser fusion, and the possibility of experimentally simulating such structures with respect to the sun and other stellar environments.intense laser matter interaction | high energy density | astrophysical simulations | filamentary structures T he largest terrestrially available magnetic fields are generated when an intense laser pulse (intensity above 10 18 W∕cm 2 ) irradiates a solid target (1-3). The high energy density produced by laser irradiation generates relativistic electron jets, through the process of wave breaking. These relativistic electron jets carry the laser energy deep into the target ionizing and heating the colder portions behind the laser generated plasma and exciting return shielding currents. In the laboratory, such heating is extremely important for fast ignition of highly compressed targets in laser fusion (4, 5), simulation of intra planetary matter existing at ultrahigh pressure (6), ultrafast X-ray pulses (7), as well as proton and ion acceleration up to the MeV-GeV levels (3). It also serves as an excellent tool for modeling astrophysical systems (8-10). The transport of relativistic electrons through hot dense matter is very complex and is barely understood (11,12). Simulations have shown that relativistic electron transport in plasma media is fraught with severe plasma instabilities particularly the Weibel instability (13), which leads to spatial separation of forward and backward currents and eventually to the emergence of turbulent structures (14) and rapid energy dissipation. A major physical parameter that mirrors this complex physics is the giant magnetic field-as high as hundreds of megagauss-generated in this interaction. In earlier st...

We demonstrate near-100% light absorption and increased x-ray emission from dense plasmas created on solid surfaces with a periodic sub-lambda structure. The efficacy of the structure-induced surface plasmon resonance, responsible for enhanced absorption, is directly tested at the highest intensities to date (3 x 10{15} W cm{-2}) via systematic, correlated measurements of absorption and x-ray emission. An analytical grating model as well as 2D particle-in-cell simulations conclusively explain our observations. Our study offers a definite, quantitative way forward for optimizing and understanding the absorption process.

A detailed numerical simulation to understand the turbulent state of the decaying two-dimensional electron magnetohydrodynamics is presented. It is observed that the evolved spectrum is comprised of a collection of random eddies and a gas of whistler waves, the latter constituting the normal oscillatory modes of such a model. The whistlerization of the turbulent spectra has been quantified by novel diagnostics. In this work, results are presented only in the regime where the spatial excitation scales are longer than the electron skin depth. Simulations suggest that spectra at short scales are comparatively more whistlerized. The long scale field merely acts as the ambient field along which whistler waves propagate. It is also observed that, in the presence of an external magnetic field, the power spectrum acquires a distinct directional dependence. This anisotropy is dominant at short scales. It is shown that such an anisotropy at short scales results from a cascade mechanism governed by the interacting whistlers waves.

Formation of a density blob and its motion in the edge and scrape-off layer (SOL) of a tokamak plasma have been simulated using two-dimensional, two-field, fluid model equations. The simulation results show that density blobs form in the edge or in the edge-to-SOL transition region where the poloidal velocity shear is maximum. From the numerical data, a condition for density blob formation has been obtained. Dynamics of the detached blob in the edge and SOL regions has been studied. It is observed that not all the blobs that form in the edge or edge-to-SOL transition region are capable of ejection deep into the SOL. A condition for their ejection is also discussed. Radial particle transport associated with the blobs in the SOL has been calculated. It is found that about 60% of the total radial particle flux is carried out by these blobs.