119047522
Cosmological backreaction from perturbations
We write the averaged Einstein equations in a form suitable for use with Newtonian gauge linear perturbation theory and track the size of the modifications to standard Robertson–Walker evolution on the largest scales as a function of redshift for both Einstein–de Sitter and ΛCDM cosmologies. In both cases the effective energy density arising from linear perturbations is of the order of 10−5 times the matter density, as would be expected, with an effective equation of state weff≈−1/19. Employing a modified Halofit code to extend our results to quasilinear scales, we find that, while larger, the deviations from Robertson–Walker behaviour remain of the order of 10−5.
116966118
Concerning the statistics of cosmic magnetism
Magnetic fields appear to be a generic feature of the early universe and are a natural source of secondary CMB non-Gaussianity. In recent years the statistical nature of the stresses of a primordial magnetic field has been well studied. In this paper we confirm and extend these studies at one- and two-point level, and present analytical results for a wide range of power-law spectra. We also consider two non-power law cases of interest: a blue spectrum with an extended damping tail on small scales, which could be generated by the non-linear mixing of density and vorticity; and a red spectrum with a damping tail on large scales. We then briefly consider the CMB impacts that result from such fields. While this paper focuses on the one- and two-point moments, the techniques we employ are designed to ease the analysis of the full bispectra induced by primordial magnetic fields.
119227429
INTRINSIC BISPECTRA OF COSMIC MAGNETIC FIELDS
Forthcoming data sets from the Planck experiment and others are in a position to probe the cosmic microwave background (CMB) non-Gaussianity with higher accuracy than has yet been possible, and potentially open a new window into the physics of the very early universe. However, a signal need not necessarily be inflationary in origin, and possible contaminants should be examined in detail. One such is provided by early universe magnetic fields, which can be produced by a variety of models including during an inflationary phase, at phase transitions, or seeded by cosmic defects. Should such fields have been extant in the early universe, they would provide a natural source of CMB non-Gaussianity. Knowledge of the CMB angular bispectrum requires the complete Fourier-space (or "intrinsic") bispectrum. In this paper, I consider in detail the intrinsic bispectra of an early-universe magnetic field for a range of power-law magnetic spectra.
53709253
Non-Gaussianity from cosmic magnetic fields
Magnetic fields in the early Universe could have played an important role in sourcing cosmological perturbations. While not the dominant source, even a small contribution might be traceable through its intrinsic non-Gaussianity. Here we calculate analytically the one-, two-, and three-point statistics of the magnetic stress energy resulting from tangled Gaussian fields, and confirm these with numerical realizations of the fields. We find significant non-Gaussianity, and importantly predict higher order moments that will appear between the scalar, vector, and tensor parts of the stress energy (e.g., scalar-tensor-tensor moments). Such higher order cross correlations are a generic feature of nonlinear theories and could prove to be an important probe of the early Universe.
119209860
The magnitude of the non-adiabatic pressure in the cosmic fluid
Understanding the non-adiabatic pressure, or relative entropy, perturbation is crucial for studies of early-Universe vorticity and cosmic microwave background observations. We calculate the evolution of the linear non-adiabatic pressure perturbation from radiation domination to late times, numerically solving the linear governing equations for a wide range of wavenumbers. Using adiabatic initial conditions consistent with Wilkinson Microwave Anisotropy Probe seven-year data, we find nevertheless that the non-adiabatic pressure perturbation is non-zero and grows at early times, peaking around the epoch of matter/radiation equality and decaying in matter domination. At early times or large redshifts (z= 10 000) its power spectrum peaks at a comoving wavenumber k≈ 0.2 h Mpc−1, while at late times (z= 500) it peaks at k≈ 0.02 h Mpc−1.
118519718
Gauges and cosmological backreaction
We present a formalism for spatial averaging in cosmology applicable to general spacetimes and coordinates, and allowing the easy incorporation of a wide variety of matter sources. We apply this formalism to a Friedmann-Lemaȋtre-Robertson-Walker universe perturbed to second-order and present the corrections to the background in an unfixed gauge. We then present the corrections that arise in uniform curvature and conformal Newtonian gauges.
102339269
Surface resistivity tailoring of ceramic accelerator components
Metal plasma deposition and metal ion implantation techniques have been developed that could provide a good tool for the surface modification of insulating materials for accelerator applications such as ceramics and that could provide a method for tailoring the surface resistivity over a range of many orders of magnitude. The methods make use of the metal plasma that is produced by the cathodic arc discharge; the plasma itself can be deposited onto the surface at an energy of the order of 100 eV so as to form an adherent thin film, or an energetic metal ion beam can be formed for deep implantation of the metal species below the surface so as to incorporate a controllable amount of metal into the ceramic.<<ETX>>
109145537
Some novel design features of the LBL metal vapor vacuum arc ion sources
The family of MEVVA (metal vapor vacuum arc) high current metal ion sources developed at LBL over the past several years has grown to include a number of different source versions with a wide range of some of the design and operational parameters. The MicroMEVVA source is a particularly compact version, about 2 cm diam and 10 cm long, while the MEVVA IV weighs some 30 kG. MEVVAs IV and V incorporate multiple cathode assemblies (16 and 18 separate cathodes, respectively), and the operating cathode can be switched rapidly and without downtime. The new MEVVA V embodiment is quite compact considering its broad beam (10 cm), high voltage (100 kV), and multiple cathode features. The large‐area extractor grids used in MEVVA V were fabricated using a particularly simple technique, and they are clamped into position and can thus be changed simply and quickly. The electrical system used to drive the arc is particularly simple and incorporates several attractive features. In this article we review and describe a num...
122942161
Charge state distribution studies of the metal vapor vacuum arc ion source
We have studied the charge state distribution of the ion beam produced by the MEVVA (metal vapor vacuum arc) high current metal ion source. Beams produced from a wide range of cathode materials have been examined and the charge state distributions have been measured as a function of many operational parameters. In this article we review the charge state data we have accumulated, with particular emphasis on the time history of the distribution throughout the arc current pulse duration. We find that, in general, the spectra remain quite constant throughout most of the beam pulse, as long as the arc current is constant. There is an interesting early‐time transient behavior when the arc is first initiated and the arc current is still rising, during which time the ion charge states produced are observed to be significantly higher than during the steady current region that follows.
122299704
Transport of vacuum arc plasma through straight and curved magnetic ducts
We report on an experimental investigation of the transport of a metal vapor vacuum arc plasma through straight and curved magnetic solenoids for the case of an iron plasma and for magnetic field strength up to 650 G. We find that the fraction of plasma transported increases with magnetic field strength and saturates at a field at which the ion gyroradius equals the radius of the plasma channel. The magnetic field strength at the cathode location, where the plasma is injected into the solenoid, was found to be important, and for the present work the injection efficiency optimizes at a field of about 150 G.
139645374
HIGH TECH METAL SURFACES USING ION IMPLANTATION