Closed Orbit Distortion and the Beam-Beam Interaction

We study the applicability of beam-beam deflection techniques as a tuning tool for the SLAC/LBL/LLNL B factory, PEP-II. Assuming that the closed orbits of the two beams are separated vertically at the interaction point by a local orbit bump that is nominally closed, we calculate the residual beam orbit distortions due to the beam-beam interaction. Difference orbit measurements, performed at points conveniently distant from the IP, provide distinct coordinate- or frequency-space signatures that can be used to maintain the beams in collision and perform detailed optical diagnostics at the IP. A proposal to test this method experimentally at the TRISTAN ring is briefly discussed

Diffusive transport and self-consistent dynamics in coupled maps

The study of diffusion in Hamiltonian systems has been a problem of interest for a number of years. In this paper we explore the influence of self-consistency on the diffusion properties of systems described by coupled symplectic maps. Self-consistency, i.e. the back-influence of the transported quantity on the velocity field of the driving flow, despite of its critical importance, is usually overlooked in the description of realistic systems, for example in plasma physics. We propose a class of self-consistent models consisting of an ensemble of maps globally coupled through a mean field. Depending on the kind of coupling, two different general types of self-consistent maps are considered: maps coupled to the field only through the phase, and fully coupled maps, i.e. through the phase and the amplitude of the external field. The analogies and differences of the diffusion properties of these two kinds of maps are discussed in detail.Comment: 13 pages, 14 figure

Beam-beam stability in the SSC. A preliminary report

The stability of proton orbits in the SSC is threatened by two principle elements in the beam system: magnet errors and the beam-beam interaction. Of these, magnet errors are considered to be of greater importance because they are more tenacious. Beam-beam effects can be reduced if necessary by widening the beam crossing angle. Magnet errors, however, cannot be removed and their effects are difficult to compensate for. The stability of the beam system is characterized by a curve in the two-dimensional amplitude plane which separates dynamically stable trajectories, at small amplitudes, from dynamically unstable trajectories, at large amplitudes. The area of stable motion is refered to here as the ``stability aperture``. Protons outside the stability aperture exhibit chaotic motion and are lost rapidly from the beam. Those inside the aperture, in the absence of single particle scattering, remain confined indefinitely. Although the edge of the stability aperture is not a ``fine line``, as it would be for a one-degree-of-freedom system with time dependence, the amplitudes representing the transition from stable to unstable motion are fairly well defined in the SSC. The primary purpose of this investigation is to roughly determine the size and shape of the stability aperture induced by the beam-beam interaction alone, and its dependence on the principle machine parameters. This information, together with a determination of the magnet error aperture and the combined total aperture, is needed to select the nominal beam crossing angle

Flip-Flop Modes in Symmetric and Asymmetric Colliding-Beam Storage Rings

A model of self-consistent beam blow-up in a colliding beam storage ring is described which explains the appearance of flip-flop modes in both symmetric and asymmetric beam systems. It derives the strong-strong steady-states and their stabilities from the weak-strong behavior. This model agrees well with the observed flip-flop behavior in storage rings, including the hysteresis seen when the beams are flipped from one asymmetric steady state to the other. It can be used to predict the behavior of proposed facilities in which the two colliding beams are characterized by different parameters

Caesium Incorporated Triple Cation Perovskites Deliver Fully Reversible and Stable Nanoscale Voltage Response

Perovskite solar cells that incorporate small concentrations of Cs in their A-site have shown increased lifetime and improved device performance. Yet, the development of fully stable devices operating near the theoretical limit requires understanding how Cs influences perovskites’ electrical properties at the nanoscale. Here, we determine how the chemical composition of three perovskites (MAPbBr3, MAPbI3, and Cs-mixed) affects their short- and long-term voltage stabilities, with <50 nm spatial resolution. We map an anomalous irreversible electrical signature on MAPbBr3 at the mesoscale, resulting in local Voc variations of ∼400 mV, and in entire grains with negative contribution to the Voc. These measurements prove the necessity of high spatial resolution mapping to elucidate the fundamental limitations of this emerging material. Conversely, we capture the fully reversible voltage response of Cs-mixed perovskites, composed by Cs0.06(MA0.17FA0.83)0.94Pb­(I0.83Br0.17)3, demonstrating that the desired electrical output persists even at the nanoscale. The Cs-mixed material presents no spatial variation in Voc, as ion motion is restricted. Our results show that the nanoscale electrical behavior of the perovskites is intimately connected to their chemical composition and macroscopic response

Molecular cross-sections for high-resolution spectroscopy of super-Earths, warm Neptunes, and hot Jupiters

High-resolution spectroscopy (HRS) has been used to detect a number of species in the atmospheres of hot Jupiters. Key to such detections is accurately and precisely modelled spectra for cross-correlation against the R ≳ 20 000 observations. There is a need for the latest generation of opacities which form the basis for high signal-to-noise detections using such spectra. In this study we present and make publicly available cross-sections for six molecular species, H2O, CO, HCN, CH4, NH3, and CO2 using the latest line lists most suitable for low- and high-resolution spectroscopy. We focus on the infrared (0.95–5 μm) and between 500 and 1500 K where these species have strong spectral signatures. We generate these cross-sections on a grid of pressures and temperatures typical for the photospheres of super-Earth, warm Neptunes, and hot Jupiters using the latest H2 and He pressure broadening. We highlight the most prominent infrared spectral features by modelling three representative exoplanets, GJ 1214 b, GJ 3470 b, and HD 189733 b, which encompass a wide range in temperature, mass, and radii. In addition, we verify the line lists for H2O, CO, and HCN with previous high-resolution observations of hot Jupiters. However, we are unable to detect CH4 with our new cross-sections from HRS observations of HD 102195 b. These high-accuracy opacities are critical for atmospheric detections with HRS and will be continually updated as new data become available

Self-consistent chaos in the beam-plasma instability

The effect of self-consistency on Hamiltonian systems with a large number of degrees-of-freedom is investigated for the beam-plasma instability using the single-wave model of O'Neil, Winfrey, and Malmberg.The single-wave model is reviewed and then rederived within the Hamiltonian context, which leads naturally to canonical action- angle variables. Simulations are performed with a large (10[sup 4]) number of beam particles interacting with the single wave. It is observed that the system relaxes into a time asymptotic periodic state where only a few collective degrees are active; namely, a clump of trapped particles oscillating in a modulated wave, within a uniform chaotic sea with oscillating phase space boundaries. Thus self-consistency is seen to effectively reduce the number of degrees- of-freedom. A simple low degree-of-freedom model is derived that treats the clump as a single macroparticle, interacting with the wave and chaotic sea. The uniform chaotic sea is modeled by a fluid waterbag, where the waterbag boundaries correspond approximately to invariant tori. This low degree-of-freedom model is seen to compare well with the simulation

Mitogenomes uncover extinct penguin taxa and reveal island formation as a key driver of speciation

The emergence of islands has been linked to spectacular radiations of diverse organisms. Although penguins spend much of their lives at sea, they rely on land for nesting, and a high proportion of extant species are endemic to geologically young islands. Islands may thus have been crucial to the evolutionary diversification of penguins. We test this hypothesis using a fossil-calibrated phylogeny of mitochondrial genomes (mitogenomes) from all extant and recently extinct penguin taxa. Our temporal analysis demonstrates that numerous recent island-endemic penguin taxa diverged following the formation of their islands during the Plio-Pleistocene, including the Galápagos (Galápagos Islands), northern rockhopper (Gough Island), erect-crested (Antipodes Islands), Snares crested (Snares) and royal (Macquarie Island) penguins. Our analysis also reveals two new recently extinct island-endemic penguin taxa from New Zealand’s Chatham Islands: Eudyptes warhami sp. nov. and a dwarf subspecies of the yellow-eyed penguin, Megadyptes antipodes richdalei ssp. nov. Eudyptes warhami diverged from the Antipodes Islands erect-crested penguin between 1.1 and 2.5 Ma, shortly after the emergence of the Chatham Islands (∼3 Ma). This new finding of recently evolved taxa on this young archipelago provides further evidence that the radiation of penguins over the last 5 Ma has been linked to island emergence. Mitogenomic analyses of all penguin species, and the discovery of two new extinct penguin taxa, highlight the importance of island formation in the diversification of penguins, as well as the extent to which anthropogenic extinctions have affected island-endemic taxa across the Southern Hemisphere’s isolated archipelagos