Achievements in CTF3 and Commissioning status

The aim of the latest CLIC test facility CTF3, built at CERN by an international collaboration, is to prove the main feasibility issues of the CLIC two-beam acceleration technology. Several of the main goals have been already achieved in the past years, like the full-loading linac operation mode and the delay loop principle. During 2008 also the combiner ring concept has been experimentally proven and the recombined beam has been used to generate the RF power. In parallel in the fall of the year also the probe beam line commissioning had started

Bird Community Responses to Rest-Rotation Grazing in Western Canada\u27s Grasslands

Western Canada’s native grasslands support high levels of avian diversity including both resident and migrant species. Many grassland specialist bird populations, however, are in serious decline due to widespread habitat loss resulting from agricultural conversion and adverse land management. As the primary use on remaining grasslands, cattle grazing largely determines the availability and quality of bird species’ habitat, depending on the timing, intensity, and frequency of livestock use. While adaptive multi-paddock grazing (AMP, a short duration, high-intensity grazing system that prioritises plant recovery between grazing events) is growing in popularity, comprehensive assessments of bird diversity in relation to AMP grazing practices are largely lacking. As part of a larger grazing management study, we examined how AMP grazing practices influence the taxonomic and phylogenetic diversity of bird species, compared to neighbouring (n-AMP) properties managed with more conventional grazing practices. In addition to the AMP/n-AMP contrast, we used rancher survey information to test for the influence of specific grazing practices over and above biophysical effects. Bird communities were surveyed at 309 point count locations across 38 ranches (set up as matched pairs) using visual and acoustic detection. Overall, we identified 96 bird species, of which 81 species were recorded on AMP-grazed ranches compared to 84 species on grasslands under n-AMP grazing, ranging from 10-32 species per ranch. We observed a considerable grazing management signal on species abundance and diversity including significant associations between some threatened species and n-AMP grazing. Moreover, AMP grazing, and specifically the use of higher rest-to-grazing ratios early in the growing season (prior to August 1), was associated with phylogenetically more clustered bird communities. Overall, this study highlights the potential of specialized rotational grazing systems to alter the composition and phylogenetic diversity of grassland bird communities. In conclusion, we stress the importance for prioritisation of strategic management plans to safeguard and restore North America’s grassland bird communities

High Power Test on an x-Band Slotted-Iris Accelerator Structure at NLCTA

The CLIC study group at CERN has built two X-band HDS (Hybrid Damped Structure) accelerating structures for high-power testing in NLCTA at SLAC. These accelerating structures are novel with respect to their rf-design and their fabrication technique. The eleven-cell constant impedance structures, one made out of copper and one out of molybdenum, are assembled from clamped high-speed milled quadrants. They feature the same heavy higher-order-mode damping as nominal CLIC structures achieved by slotted irises and radial damping waveguides for each cell. The X-band accelerators are exactly scaled versions of structures tested at 30 GHz in the CLIC test facility, CTF3. The results of the X-band tests are presented and compared to those at 30 GHz to determine frequency scaling, and are compared to the extensive copper data from the NLC structure development program to determine material dependence and make a basic validation of the HDS design. INTRODUCTIO

High-Power Testing of X-Band CLIC Power Generating Structures

A fundamental element of the CLIC concept is two-beam acceleration, where rf power is extracted from a high-current and low-energy beam in order to accelerate the low-current main beam to high energy. The power extraction occurs in special Xband Power Extraction and Transfer Structures (PETS). The structures are large aperture, high-group velocity and overmoded periodic structures. Following the substantial changes of the CLIC baseline parameters in 2006, the PETS design has been thoroughly updated along with the fabrication methods and corresponding rf components. Two PETS prototypes have been fabricated and high power tested. Test results and future plans are presented

Laser Wire Scanner Development on CTF II

A laser wire scanner is under development at CERN in the framework of the Compact Linear Collider study (CLIC). A first test has been carried out at the CLIC Test Facility II (CTF II) with the aim of developing a beam profile monitor for a low energy, high charge electron beam. In our set-up a 2.5 mJ, 1047 nm, 4 ps laser pulse interacts with a 50 MeV, 1 nC, 4 ps electron bunch. A scintillator detects up to 600 X-ray photons, with an average energy of 17 keV. In the present status of the experiment Thomson photons have been observed, but the signal to noise ratio is however still too low for an accurate profile measurement

Time resolved spectrometry on the CLIC Test Facility 3

The high charge (>6ìC) electron beam produced in the CLIC Test Facility 3 (CTF3) is accelerated in fully beam loaded cavities. To be able to measure the resulting strong transient effects, the time evolution of the beam energy and its energy spread must be determined with at least 50MHz bandwidth. Three spectrometer lines are installed along the linac in order to control and tune the beam. The electrons are deflected by dipole magnets onto Optical Transition Radiation (OTR) screens which are observed by CCD cameras. The measured horizontal beam size is then directly related to the energy spread. In order to provide time-resolved energy spectra, a fraction of the OTR photons is sent onto a multi-channel photomultiplier. The overall setup is described, special focus is given to the design of the OTR screen with its synchrotron radiation shielding. The performance of the time-resolved measurements are discussed in detail. Finally, the limitations of the system, mainly due to radiation problems are discussed

Latest Developments from the S-DALINAC*

The S-DALINAC is a 130 MeV superconducting recirculating electron accelerator serving several nuclear and radiation physics experiments as well as driving an infrared free-electron laser. A system of normal conducting rf resonators for noninvasive beam position and current measurement was established. For the measurement of gamma-radiation inside the accelerator cave a system of Compton diodes has been developed and tested. Detailed investigations of the transverse phasespace were carried out with a tomographical reconstruction method of optical transition radiation spots. The method can be applied also to non-Gaussian phasespace distributions. The results are in good accordance with simulations. To improve the quality factor of the superconducting 3 GHz cavities, an external 2K testcryostat was commissioned. The influence of electro-chemical polishing and magnetic shielding is currently under investigation. A digital rf-feedback-system for the accelerator cavities is being developed in order to improve the energy spread of the beam of the S-DALINAC. * Supported by the BMBF under contract no. 06 DA 820, the DFG under contract no. Ri 242/12-1 and -2 and the DFG Graduiertenkolleg 'Physik und Technik von Beschleunigern