The influence of charge-mode operation of a XeCl laser on the beam profile

The shape of the beam profile of a discharge excited XeCl excimer laser using a spiker-sustainer electrical circuit has been varied from a `bell¿-, through a `top-hat¿-, to a `camel-back¿-profile by varying the delay between the spiker pulse and the main-current with the circuit operating in the charge-mode. Fine-tuning of the beam profile can be done by varying the charging voltage of the main pulse forming network or the temperature of a gas purifier regulating the Xe and HCl partial pressures

The injector microtron for the TEUFEL infrared laser

Progress is reported on a 25 MeV injector racetrack microtron for a 10 ¿m radiation free electron laser (TEUFEL project). The accelerator exhibits transverse focusing in 180° inhomogeneous two-sector dipole magnets which are slightly rotated with respect to each other in the bending plane. This provides closed orbits, isochronism and a large transverse acceptance. Details on this unconventional microtron focusing system will be given. An analytical treatment, based on conformal mapping, of the field near pole boundaries and at the hill-valley boundaries in the microtron dipole is compared with Poisson calculated results and with field measurements. The design of a model accelerating cavity is presented together with field measurements based on the perturbation ball method

Developments of the TEUFEL injector racetrack microtron

In this paper we report on developments of the 25 MeV racetrack microtron (RTM) that will be the electron source for the second phase of the TEUFEL project, to generate radiation of 10 µm in a 2.5 cm period hybrid undulator. The theoretical understanding of this unconventional, azimuthally varying field type of RTM has been extended. A comparison of analytically calculated orbit stability with that based on measured data will be presented; orbit calculations using measured field data show the designed performance. Construction and tuning of the 1300 MHz, 2.2 MV microwave cavity have been completed, and signal level measurements have been performed. The overall assembly of the microtron is nearing completion. At present a vacuum pressure better than 5 × 10-7 Torr is achieved

Evaluation of the Surface Energy Balance System (SEBS) applied to ASTER imagery with flux-measurements at the SPARC 2004 site (Barrax, Spain)

Accurate quantification of the amount and spatial variation of evapotranspiration is important in a wide range of disciplines. Remote sensing based surface energy balance models have been developed to estimate turbulent surface energy fluxes at different scales. The objective of this study is to evaluate the Surface Energy Balance System (SEBS) model on a landscape scale, using tower-based flux measurements at different land cover units during an overpass of the ASTER sensor over the SPARC 2004 experimental site in Barrax (Spain). A sensitivity analysis has been performed in order to investigate to which variable the sensible heat flux is most sensitive. Taking into account their estimation errors, the aerodynamic parameters (hc, z0M and d0) can cause large deviations in the modelling of sensible heat flux. The effect of replacement of empirical derivation of these aerodynamic parameters in the model by field estimates or literature values is investigated by testing two scenarios: the Empirical Scenario in which empirical equations are used to derive aerodynamic parameters and the Field Scenario in which values from field measurements or literature are used to replace the empirical calculations of the Empirical Scenario. In the case of a homogeneous land cover in the footprints of the measurements, the Field Scenario only resulted in a small improvement, compared to the Empirical Scenario. The Field Scenario can even worsen the result in the case of heterogeneous footprints, by creating sharp borders related to the land cover map. In both scenarios modelled fluxes correspond better with flux measurements over uniform land cover compared to cases where different land covers are mixed in the measurement footprint. Furthermore SEBS underestimates sensible heat flux especially over dry and sparsely vegetated areas, which is common in single-source models

Measurement of W Polarisation at LEP

The three different helicity states of W bosons produced in the reaction e+ e- -> W+ W- -> l nu q q~ at LEP are studied using leptonic and hadronic W decays. Data at centre-of-mass energies \sqrt s = 183-209 GeV are used to measure the polarisation of W bosons, and its dependence on the W boson production angle. The fraction of longitudinally polarised W bosons is measured to be 0.218 \pm 0.027 \pm 0.016 where the first uncertainty is statistical and the second systematic, in agreement with the Standard Model expectation