Recently, artificially constructed metamaterials have become of considerable interest, because these materials can exhibit electromagnetic characteristics unlike those of any conventional materials. Artificial magnetism and negative refractive index are two specific types of behavior that have been demonstrated over the past few years, illustrating the new physics and new applications possible when we expand our view as to what constitutes a material. In this review, we describe recent advances in metamaterials research and discuss the potential that these materials may hold for realizing new and seemingly exotic electromagnetic phenomena.

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Metamaterials and negative refractive index.

Recent theory has predicted a superlens that is capable of producing sub–diffraction-limited images. This superlens would allow the recovery of evanescent waves in an image via the excitation of surface plasmons. Using silver as a natural optical superlens, we demonstrated sub–diffraction-limited imaging with 60-nanometer half-pitch resolution, or one-sixth of the illumination wavelength. By proper design of the working wavelength and the thickness of silver that allows access to a broad spectrum of subwavelength features, we also showed that arbitrary nanostructures can be imaged with good fidelity. The optical superlens promises exciting avenues to nanoscale optical imaging and ultrasmall optoelectronic devices.

http://science.sciencemag.org/content/sci/308/5721/534.full.pdf

Sub-Diffraction-Limited Optical Imaging with a Silver Superlens

A universal instability of many-dimensional oscillator systems

Artificially engineered metamaterials are now demonstrating unprecedented electromagnetic properties that cannot be obtained with naturally occurring materials. In particular, they provide a route to creating materials that possess a negative refractive index and offer exciting new prospects for manipulating light. This review describes the recent progress made in creating nanostructured metamaterials with a negative index at optical wavelengths, and discusses some of the devices that could result from these new materials.

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Optical negative-index metamaterials

Inertial confinement fusion (ICF) is an approach to fusion that relies on the inertia of the fuel mass to provide confinement. To achieve conditions under which inertial confinement is sufficient for efficient thermonuclear burn, a capsule (generally a spherical shell) containing thermonuclear fuel is compressed in an implosion process to conditions of high density and temperature. ICF capsules rely on either electron conduction (direct drive) or x rays (indirect drive) for energy transport to drive an implosion. In direct drive, the laser beams (or charged particle beams) are aimed directly at a target. The laser energy is transferred to electrons by means of inverse bremsstrahlung or a variety of plasma collective processes. In indirect drive, the driver energy (from laser beams or ion beams) is first absorbed in a high‐Z enclosure (a hohlraum), which surrounds the capsule. The material heated by the driver emits x rays, which drive the capsule implosion. For optimally designed targets, 70%–80% of the d...

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Development of the indirect‐drive approach to inertial confinement fusion and the target physics basis for ignition and gain

A theory of collisionless electrostatic drift wave turbulence in a circular cylinder with shear is presented. A renormalized electron drift kinetic equation which is consistent with conservation of energy is derived. For low levels of turbulence, a perturbative solution indicates that the turbulence has a stabilizing effect and that total mode spectrum energy decreases. For strongly turbulent regimes, results quantitatively but not qualitatively different from those of Hirshman and Molvig are found. In particular, additional stabilizing terms lead to a lower saturation amplitude, but the basic picture of turbulent destabilization competing against linear and nonlinear shear damping persists.

Theory of the renormalized dielectric for electrostatic drift wave turbulence in tokamaks

The small-inverse-aspect-ratio boundary layer approximation, which has been used previously to describe the analytic structure of a driven non-ideal toroidal Alfven eigenmodes (TAEs), is applied to a numerical stability calculation for the TAEs in ITER and TFTR plasmas. Away from TAE gaps (singular layers), zero beta cylindrical magnetohydrodynamics (MHDs) determines the generic structure of the outer solutions. Within each gap, a detailed kinetic treatment is used to include (i) modifications to the fluid equations arising from E// and finite Larmor radius, (ii) collisional damping from trapped electrons, (iii) collisionless (Landau) damping from passing ions and (iv) drive from finite-orbit-width fusion alpha particles and beam ions. The model is valid for arbitrary toroidal mode number and predicts the growth/damping rate of both the MHD-like TAE (that which is predicted by MHD theory) and the relevant kinetic TAEs

Mode structure and stability of toroidal Alfven eigenmodes in ITER and TFTR DT plasmas

A magnetohydrodynamic (MHD) ballooning mode formalism and calculation is developed to show how a field‐line‐following code can be used to study MHD stability. The asymptotic analysis of the ballooning equation yields the Mercier condition. It is shown that first‐order equilibrium effects on the vacuum fields from finite pressure cancel the intrinsically destabilizing term of the Mercier condition. A ballooning unstable solution is found in a Heliac configuration that has a magnetic well at zero beta and a rotational transform that increases radially outward.

Ballooning mode calculations in stellarators

Several problems in the physics of L→H transition and pedestal formation are examined using a simple and universal sandpile model, which incorporates key features of a confined plasma, namely, diffusion, shear induced bistability of turbulent transport, and a local magnetohydrodynamic (MHD) limit on the gradient. The main focus of this study is the effect of ambient diffusion, representative of neoclassical transport, on hysteresis and edge relaxation phenomena. The transport function of the sandpile bifurcates to a multivalued function with increasing deposition, and, as a consequence, a hysteresis in the L→H→L transition is observed. With pedestal formation, diffusive losses increase at the expense of the turbulent flux. This effect prolongs the time needed to reach the MHD stability boundary, and thus provides a positive feedback on the pedestal. The gradient in the pedestal is more rigid and, due to diffusive smoothing, can reach the critical value at all radii simultaneously. Hence an avalanche, star...

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Hysteresis and relaxation in bistable diffusive sandpile

The recent experimentally inferred values of multiplicity of deuterium-tritium fusion catalysed by muons have increased the interest in muon catalysed fusion reactors. Since the main energy expended is in pion (and consequent muon) production, it is tried to minimize the pion loss by magnetically confining pions where they are created. At the present time, it does not appear possible to achieve an energy gain by pure fusion, but it is possible to gain energy by combining catalysed fusion with fission blankets. Two new ideas for improvement of the muon fusion reactor concept are presented. The first idea is to combine the target which creates pions, the converter of pions to muons, and the synthesizer in one vessel (synergetic concept). This is accomplished by injecting a tritium or deuterium beam of 1 GeV per nucleon into DT fuel contained in a magnetic mirror. The confined pions slow down and decay to muons which are confined in the fuel whereby muon loss is kept small. The quantity of tritium necessary to keep the reactor viable has been derived. The second idea is to collect the beam passing through the target for reuse and to recirculate it, while directing the strongly interacting portion of the beam to electronuclear blankets. The present concepts are at the margin of known technologies and are based on known physical processes and data.

http://iopscience.iop.org/article/10.1088/0029-5515/27/4/001/pdf

Marshall N. Rosenbluth

Papers

Theory of the renormalized dielectric for electrostatic drift wave turbulence in tokamaks

Mode structure and stability of toroidal Alfven eigenmodes in ITER and TFTR DT plasmas

Ballooning mode calculations in stellarators

Hysteresis and relaxation in bistable diffusive sandpile

Muon catalysed fusion-fission reactor driven by a recirculating beam