Hie-Isolde High Beta Cavity Study and Measurements

The upgrade of the ISOLDE machine at CERN foresees a superconducting linac based on two gap independently phased Nb sputtered Quarter Wave Resonators (QWRs) working at 101.28MHz and producing an accelerating field of 6MV/m on axis. A careful study of the fields in the cavity has been carried out in order to pin down the crucial e-m parameters of the structure such as peak fields, quality factor and e-m power dissipated on the cavity wall. A tuning system with about 200kHz frequency range has been developed in order to cope with fabrication tolerances. In this paper we will report on the cavity simulations. The tuning plate design will be described. Finally the frequency measurements on a cavity prototype at room temperature will be presented.Comment: 5 pages, SRF09 Conference in Berli

The exit-time problem for a Markov jump process

The purpose of this paper is to consider the exit-time problem for a finite-range Markov jump process, i.e, the distance the particle can jump is bounded independent of its location. Such jump diffusions are expedient models for anomalous transport exhibiting super-diffusion or nonstandard normal diffusion. We refer to the associated deterministic equation as a volume-constrained nonlocal diffusion equation. The volume constraint is the nonlocal analogue of a boundary condition necessary to demonstrate that the nonlocal diffusion equation is well-posed and is consistent with the jump process. A critical aspect of the analysis is a variational formulation and a recently developed nonlocal vector calculus. This calculus allows us to pose nonlocal backward and forward Kolmogorov equations, the former equation granting the various moments of the exit-time distribution.Comment: 15 pages, 7 figure

Deep carbon storage potential of buried floodplain soils.

Soils account for the largest terrestrial pool of carbon and have the potential for even greater quantities of carbon sequestration. Typical soil carbon (C) stocks used in global carbon models only account for the upper 1 meter of soil. Previously unaccounted for deep carbon pools (>1 m) were generally considered to provide a negligible input to total C contents and represent less dynamic C pools. Here we assess deep soil C pools associated with an alluvial floodplain ecosystem transitioning from agricultural production to restoration of native vegetation. We analyzed the soil organic carbon (SOC) concentrations of 87 surface soil samples (0-15 cm) and 23 subsurface boreholes (0-3 m). We evaluated the quantitative importance of the burial process in the sequestration of subsurface C and found our subsurface soils (0-3 m) contained considerably more C than typical C stocks of 0-1 m. This deep unaccounted soil C could have considerable implications for global C accounting. We compared differences in surface soil C related to vegetation and land use history and determined that flooding restoration could promote greater C accumulation in surface soils. We conclude deep floodplain soils may store substantial quantities of C and floodplain restoration should promote active C sequestration

A High Phase Advance Damped and Detuned Structure for the Main Linacs of Clic

The main accelerating structures for the CLIC are designed to operate at an average accelerating gradient of 100 MV/m. The accelerating frequency has been optimised to 11.994 GHz with a phase advance of 2{\pi}/3 of the main accelerating mode. The moderately damped and detuned structure (DDS) design is being studied as an alternative to the strongly damped WDS design. Both these designs are based on the nominal accelerating phase advance. Here we explore high phase advance (HPA) structures in which the group velocity of the rf fields is reduced compared to that of standard (2{\pi}/3) structures. The electrical breakdown strongly depends on the fundamental mode group velocity. Hence it is expected that electrical breakdown is less likely to occur in the HPA structures. We report on a study of both the fundamental and dipole modes in a CLIC_DDS_HPA structure, designed to operate at 5{\pi}/6 phase advance per cell. Higher order dipole modes in both the standard and HPA structures are also studied

High Bandwidth Wall Current Monitor for CTF3

Wall Current Monitors (WCM) are commonly used to observe the time profile and spectra of a particle beam by detecting its image current. Within the framework of the EUROTeV Programme, a WCM for CLIC and ILC having a very large bandwidth (100kHz-20GHz) is required and has been developed. A deep study of the field configuration for the device has been necessary. Consequently, the geometrical parameters crucial for a proper functioning of the structure have been found. Furthermore, the very stringent initial requests (bandwidth from 100kHz to 20GHz) were reviewed in a more critical way showing that the low frequency cutoff can be sensibly increased, thus avoiding any ferrite in the structure

Enhanced coupling design of a detuned damped structure for clic

The key feature of the improved coupling design in the Damped Detuned Structure (DDS) is focused on the four manifolds. Rectangular geometry slots and rectangular manifolds are used. This results in a significantly stronger coupling to the manifolds compared to the previous design. We describe the new design together with its wakefield damping properties.Comment: 3 pages, 8 figures, submitted to IPAC1

Dust properties at z=6.3 in the host galaxy of GRB 050904

We investigate the dust extinction properties in the host galaxy of the Gamma-Ray Burst (GRB) GRB 050904 at z=6.29 by analyzing simultaneous broad band observations of the optical and UV afterglow at three different epochs. We show that the peculiar afterglow spectral energy distribution (SED) observed at 0.5 days and at 1 day after the burst (1.6 and 3 hours rest frame) cannot be explained with dust reddening with any of the extinction curves observed at low redshift. Yet, the extinction curve recently inferred for the most distant BAL QSO at z=6.2 nicely reproduces the SED of GRB 050904 at both epochs. Our result provides an additional, independent indication that the properties of dust evolve beyond z~6. We discuss the implications of this finding within the context of the dust production mechanisms through the cosmic ages.Comment: 4 pages, 2 figures, accepted for publication in ApJ

UVES/VLT high resolution absorption spectroscopy of the GRB080330 afterglow: a study of the GRB host galaxy and intervening absorbers

We study the Gamma Ray Burst (GRB) environment and intervening absorbers by analyzing the optical absorption features produced by gas surrounding the GRB or along its line of sight. We analyzed high resolution spectroscopic observations (R=40000, S/N=3 - 6) of the optical afterglow of GRB080330, taken with UVES at the VLT ~ 1.5 hours after the GRB trigger. The spectrum illustrates the complexity of the ISM of the GRB host galaxy at z = 1.51 which has at least four components in the main absorption system. We detect strong FeII, SiII, and NiII excited absorption lines associated with the bluemost component only. In addition to the host galaxy, at least two more absorbers lying along the line of sight to the afterglow have been detected in the redshift range 0.8 < z < 1.1, each exhibiting MgII absorption. For the bluemost component in the host galaxy, we derive information about its distance from the site of the GRB explosion. We do so by assuming that the excited absorption lines are produced by indirect UV pumping, and compare the data with a time dependent photo-excitation code. The distance of this component is found to be 280+40-50 pc, which is lower than found for other GRBs (1 - 6 kpc). We identify two additional MgII absorbers, one of them with a rest frame equivalent width larger than 1A. The distance between the GRB and the absorber measured in this paper confirms that the power of the GRB radiation can influence the conditions of the interstellar medium up to a distance of at least several hundred pc. For the intervening absorbers, we confirm the trend that on average one strong intervening system is found per afterglow, as has been noted in studies exhibiting an excess of strong MgII absorbers along GRB sightlines compared to quasars.Comment: 8 Pages, 7 ps figures, A&A in pres

Topology in SU(2) Yang-Mills theory

New results on the topology of the SU(2) Yang-Mills theory are presented. At zero temperature we obtain the value of the topological susceptibility by using the recently introduced smeared operators as well as a properly renormalized geometric definition. Both determinations are in agreement. At non-zero temperature we study the behaviour of the topological susceptibility across the confinement transition pointing out some qualitative differences with respect to the analogous result for the SU(3) gauge theory.Comment: 3 pages, 4 figures, contribution to Lattice-97. Latex file including espcrc2.st