A method for creating integrable nonlinear accelerator lattices is presented. Fixed points for the two-dimensional return map corresponding to the lattice are found. Minimizing the residues (an indicator of the size of the associated island) of these fixed points by varying lattice parameters eliminates large islands and regions of chaos. The resulting nonlinear systems have larger dynamical apertures and are more stable to perturbations induced by, for example, error fields.

A unified model theory of the anomalous transport of high temperature plasma, L mode and H mode, is developed. Self-sustained turbulence theory for the pressure driven mode is extended, incorporating the effect of inhomogeneous radial electric field ${\mathit{E}}_{\mathit{r}}$(r) to cover two electrically bifurcated states. Strong reductions of heat and current diffusivities, viscosity, the fluctuation amplitude, and correlation length are predicted in nonlinearly sustained turbulence. A consistent radial width of ${\mathit{E}}_{\mathit{r}}$(r) is obtained. A new stability window is also found.

A multipolar generalization of the Penning trap is presented. The case of l=1 is that of standard Penning trap. For the case of a quadrupolar magnetic field, analytic solutions are presented for cold, confined, one-species plasmas with spheroidal or spherical boundaries; for higher l values analytic solutions are given only for spherically bounded plasmas. By virtue of the sheared flow present for solutions with l>1, the classical Brillouin ratio (stored rest energy of particles/stored magnetic energy) of unity is exceeded and attains a global limit of 2 at infinitely high l.

The interaction of an intense (${10}^{16}$ W/${\mathrm{cm}}^2$), ultrashort (400 fs) 1.06 μm laser pulse normally incident on an aluminum preformed plasma was simulated with an electron kinetic code. Postprocessing with a detailed atomic model predicted the resulting K-shell x-ray spectrum. Both the very rapid time variation and the non-Maxwellian energy distribution (due to the steep gradients, energetic electrons stream from the hot into the cold plasma and enhance the excitation of Li-like satellite there) greatly modify the line ratios, even without any addition of hot electrons.

A tokamak plasma configuration is reported that simultaneously improves on the maximum stable plasma pressure, the bootstrap current contribution, and kinetic stability to temperature and density gradient driven modes in toroidal geometry. It is characterized by negative magnetic shear in the plasma interior and a peaked pressure profile. Stability to the ideal low-n external kink modes requires a conducting shell at 1.3 times the plasma minor radius. This novel plasma configuration is promising for improved plasma performance in advanced tokamak experiments.

Ion poloidal flow in tokamaks near the plasma edge has been calculated by extending neoclassical theory to include orbit squeezing, which is the reduction of the ion banana widths due to the gradient in the radial electric field. The calculated poloidal flow velocity is a significant fraction of the ion diamagnetic velocity, which can be much larger than the velocity predicted by neoclassical theory (proportional to the ion temperature gradient). The agreement with spectroscopic measurements of the poloidal rotation velocity in helium plasmas in the DIII-D tokamak is shown to be reasonably good very close to the plasma edge.

During neutral beam injection coherent magnetohydrodynamic activity occurs at low and medium β, which is driven by the energetic beam particles. As interpretation is given in terms of marginally stable global Alfvén eigenmodes (GAE), which are destabilized by Landau resonances of the far circulating particles. Toroidicity induced gaps for toroidal Alfvén eigenmodes do not occur in W7-AS but GAE modes in gaps below the shear Alfvén continua can be excited. This is investigated within a gyrofluid model, which has been used sucessfully for tokamak cases previously.

A method for generating large-amplitude plasma waves, which utilizes an optimized train of independently adjustable, intense laser pulses, is discussed and analyzed. Both the pulse widths and interpulse spacings are optimally determined such that resonance is maintained and the plasma wave amplitude is maximized. By mitigating the effects of both phase and resonant detuning, and by reducing laser-plasma instabilities, the use of appropriately tailored multiple laser pulses is a highly advantageous technique for accelerating electrons. Practical methods of producing the required pulse trains are suggested.

I present a first-principles theory of diffusion-limited aggregation in two dimensions. A renormalized mean-field approximation gives the form of the unstable manifold for branch competition, following the method of Halsey and Leibig [Phys. Rev. A 46, 7793 (1992)]. This leads to a result for the cluster dimensionality, D≊1.66, which is close to numerically obtained values. In addition, the multifractal exponent τ(3)=D in this theory, in agreement with a proposed ‘‘electrostatic’’ scaling law.

We report dielectric measurements of the orientationally disordered crystalline phase of cyclo-octanol over the frequency range 1.3 mHz–5.5 kHz. The data show that cyclo-octanol exhibits a slow relaxation that is indistinguishable in every respect from that exhibited by a supercooled liquid near its glass transition. In particular, the data obey a scaling relationship reported by Nagel and co-workers for a variety of structural glasses. These results show that cyclo-octanol is an ideal model system for studies of the glass transition, and suggest that the scaling relationship is far more universal than expected.

We have investigated the role of surface H in Si(001) homoepitaxy using in situ medium energy ion scattering and time-of-flight H recoil detection. The addition of submonolayer coverages of atomic H produce relatively modest effects on epitaxy for ${\mathit{T}}_{\mathit{g}}$≤200 °C. But at surface H concentrations surpassing 1 monolayer, we find a disruption of epitaxy, which is delayed to higher temperatures than on bare Si(001). The degradation of epitaxy correlates with the presence of surface dihydrides, which break the dimer configuration of Si(001).

We present a method for performing electronic structure calculations without the explicit use of a basis. We combine a finite-difference approach with ab initio pseudopotentials. In contrast to methods which use a plane wave basis, our calculations are performed completely in ‘‘real space.’’ No artifacts such as supercell geometries need be introduced for localized systems. Although this approach is easier to implement than one with a plane wave basis, no loss of accuracy occurs. The electronic structure of several diatomic molecules, ${\mathrm{Si}}_2$, ${\mathrm{C}}_2$, ${\mathrm{O}}_2$, and CO, are calculated to illustrate the utility of this method.

We show that, in contrast to local spin density, the self-interaction corrected local spin density provides a correct description of the γ phase of Ce metal. It correctly accounts for the volume and magnetic moment collapse at the γ→α transition, in good agreement with experiment.

The electronic structure of cerium is calculated in the self-interaction corrected, local spin density approximation. In this formalism the electronic eigenstates may be described as either localized or delocalized. Two competing local minima of the total energy functional are found. The γ phase is found to be excellently described with one f electron per atom being localized. In contrast, the α phase is best described with delocalized f electrons. The total energy is approximately equal in the two phases allowing for a low-pressure transition between them in accordance with experiment.

Inverse photoemission measurements of cerium compounds reveal a strong energy dependence near the Ce ${\mathit{M}}_5$ (3${\mathit{d}}_{5/2}$→4f) absorption edge. Two separate resonances, resulting from configuration mixing in the ground state, are identified for the first time. Their relative intensities reflect the different hybridization strengths in various Ce-based materials. Because of its site and symmetry selectivity, resonant inverse photoemission is potentially a valuable technique for the investigation of correlated materials, complementary to the well-established resonant photoemission spectroscopy.

We have observed antiabsorption resonances when alkali metals are adsorbed on Cu(111). The resonances occur at ħ${\mathrm{\omega }}_0$≊0.1 eV and cannot be attributed to phonon modes. We show that the experimental data can be consistently explained by attributing the resonances to vibrations, parallel to the surface, of a pinned surface charge density wave (CDW). We estimate the CDW effective mass to be ${\mathit{m}}^{\mathrm{*}}$≊500${\mathit{m}}_{\mathit{e}}$ per electron in the condensate.

Electromagnetic resonances along a ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_{7\mathrm{-}\mathrm{\delta }}$ bicrystal grain boundary junction made it possible to determine the ratio between the barrier/boundary thickness and the relative dielectric constant ${\mathit{t}}_{\mathit{d}}$/${\mathrm{\varepsilon }}_{\mathit{r}}$, the London penetration depth ${\lambda }_{\mathit{L}}$, and to estimate the surface resistance ${\mathit{R}}_{\mathit{s}}$ at the interfaces of the grains. From resonances at 256–638 GHz, their Q values, and the Stewart-McCumber parameter, we find ${\mathit{t}}_{\mathit{d}}$/${\mathrm{\varepsilon }}_{\mathit{r}}$≊0.4 nm, ${\lambda }_{\mathit{L}}$=140±30 nm, and ${\mathit{R}}_{\mathit{s}}$∼20 mΩ at f=280 GHz. This indicates that the boundary is dielectric, and that the grains are well superconducting within 5–20 nm from the boundary interfaces.

We study the low temperature dynamics of a single flux line in a bulk type-II superconductor, driven by the Lorentz force acting near the sample surfaces, both near and above the depinning threshold. We find a novel instability of the flux line motion at large driving currents. The power spectrum of the voltage noise generated by the moving flux line in the presence of random pinning has a ${\mathrm{\omega }}^{0.5}$ and ${\mathrm{\omega }}^{\mathrm{-}0.5}$ form for ω<${\mathrm{\omega }}_1$ and ω>${\mathrm{\omega }}_1$, respectively, where ${\mathrm{\omega }}_1$→0 at the depinning threshold.

From a very simple description of vortices and pinning centers, we obtain nonlinear density profiles of vortices in type-II dirty superconductors that result from changing an external magnetic field. The results confirm a modified Bean model description of these systems, following the Kim empirical form that relates the current inside the material to the local magnetic field. We also obtain realistic magnetization hysteresis loops and examine the discrete evolution of the density profiles in our systems. This evolution is not continuous, but takes place by the occurrence of avalanches of vortices promoted by the addition or extraction of vortices from the edges of the system.

We report on transport measurements in the mixed state of ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ single crystals using the dc flux transformer geometry. In the vortex fluid regime we have observed the onset of a nonlocal conductivity. At lower temperatures, close to but above the phase transition temperature the vortices become effectively three dimensional in character. This is in sharp contrast to recent flux transformer experiments on ${\mathrm{Bi}}_2$${\mathrm{Sr}}_2$${\mathrm{CaCu}}_2$O which have failed to see a nonlocal conductivity, confirming the two-dimensional character at high temperatures of the vortices in that system. These observations suggest that in a finite temperature interval, the vortex state in ${\mathrm{YBa}}_2$${\mathrm{Cu}}_3$${\mathrm{O}}_7$ is a line liquid.