Divergence of the Chaotic Layer Width and Strong Acceleration of the Spatial Chaotic Transport in Periodic Systems Driven by an Adiabatic ac Force

We show for the first time that a {\it weak} perturbation in a Hamiltonian system may lead to an arbitrarily {\it wide} chaotic layer and {\it fast} chaotic transport. This {\it generic} effect occurs in any spatially periodic Hamiltonian system subject to a sufficiently slow ac force. We explain it and develop an explicit theory for the layer width, verified in simulations. Chaotic spatial transport as well as applications to the diffusion of particles on surfaces, threshold devices and others are discussed.Comment: 4 pages including 3 EPS figures, this is an improved version of the paper (accepted to PRL, 2005

The PS 40 MHz bunching cavity

A 40 MHz cavity has been designed and built at CERN as part of the preparation of the PS as injector for LHC. The cavity will provide the necessary bunch spacing of 25 ns prior to injection into SPS and subsequently LHC. The mechanical design of the copper coated steel cavity was dominated by space constraints in the PS tunnel and by vacuum requirements. The salient design features described are i) tight, multipactor-free, capacitive coupling from the power amplifier, ii) fast RF feedback, iii) inductively coupled tuners, iv) an efficient, pneumatically operated gap short-circuit. The operation cycle consists of an adiabatic capture up to 100 kV gap voltage, a non-adiabatic jump to 300 kV, and subsequent bunch rotation. The multipactor voltage level at the gap lies below the operating voltage range and is easily passed through. A fast RF feedback system with a total group delay of 220 ns copes with heavy beam loading (1011 protons/bunch) and prevents unwanted interaction with other beams in the PS. The cavity has recently been installed, the nominal gap voltage of 300 kV has been attained, and bunch lengths below 8 ns have been achieved in first tests at nominal intensity. Experimental results are reported

Diffusion on a solid surface: Anomalous is normal

We present a numerical study of classical particles diffusing on a solid surface. The particles' motion is modeled by an underdamped Langevin equation with ordinary thermal noise. The particle-surface interaction is described by a periodic or a random two dimensional potential. The model leads to a rich variety of different transport regimes, some of which correspond to anomalous diffusion such as has recently been observed in experiments and Monte Carlo simulations. We show that this anomalous behavior is controlled by the friction coefficient, and stress that it emerges naturally in a system described by ordinary canonical Maxwell-Boltzmann statistics

Role of doped layers in dephasing of 2D electrons in quantum well structures

The temperature and gate voltage dependences of the phase breaking time are studied experimentally in GaAs/InGaAs heterostructures with single quantum well. It is shown that appearance of states at the Fermi energy in the doped layers leads to a significant decrease of the phase breaking time of the carriers in quantum well and to saturation of the phase breaking time at low temperature.Comment: 4 pages, 6 figure

Effects of pressure on diffusion and vacancy formation in MgO from non-empirical free-energy integrations

The free energies of vacancy pair formation and migration in MgO were computed via molecular dynamics using free-energy integrations and a non-empirical ionic model with no adjustable parameters. The intrinsic diffusion constant for MgO was obtained at pressures from 0 to 140 GPa and temperatures from 1000 to 5000 K. Excellent agreement was found with the zero pressure diffusion data within experimental error. The homologous temperature model which relates diffusion to the melting curve describes well our high pressure results within our theoretical framework.Comment: 4 pages, latex, 1 figure, revtex, submitted to PR

Reconciling Semiclassical and Bohmian Mechanics: III. Scattering states for continuous potentials

In a previous paper [J. Chem. Phys. 121 4501 (2004)] a unique bipolar decomposition, Psi = Psi1 + Psi2 was presented for stationary bound states Psi of the one-dimensional Schroedinger equation, such that the components Psi1 and Psi2 approach their semiclassical WKB analogs in the large action limit. The corresponding bipolar quantum trajectories, as defined in the usual Bohmian mechanical formulation, are classical-like and well-behaved, even when Psi has many nodes, or is wildly oscillatory. A modification for discontinuous potential stationary stattering states was presented in a second paper [J. Chem. Phys. 124 034115 (2006)], whose generalization for continuous potentials is given here. The result is an exact quantum scattering methodology using classical trajectories. For additional convenience in handling the tunneling case, a constant velocity trajectory version is also developed.Comment: 16 pages and 14 figure

Electron-electron interaction at decreasing kFlk_Fl

The contribution of the electron-electron interaction to conductivity is analyzed step by step in gated GaAs/InGaAs/GaAs heterostructures with different starting disorder. We demonstrate that the diffusion theory works down to $k_F l\simeq 1.5-2$, where $k_F$ is the Fermi quasimomentum, $l$ is the mean free paths. It is shown that the e-e interaction gives smaller contribution to the conductivity than the interference independent of the starting disorder and its role rapidly decreases with $k_Fl$ decrease.Comment: 5 pages, 6 figure