16565778
Electrical properties of carbon fiber support systems
Abstract Carbon fiber support structures have become common elements of detector designs for high energy physics experiments. Carbon fiber has many mechanical advantages but it is also characterized by high conductivity, particularly at high frequency, with associated design issues. This paper discusses the elements required for sound electrical performance of silicon detectors employing carbon fiber support elements. Tests on carbon fiber structures are presented indicating that carbon fiber must be regarded as a conductor for the frequency region of 10–100 MHz. The general principles of grounding configurations involving carbon fiber structures will be discussed. To illustrate the design requirements, measurements performed with a silicon detector on a carbon fiber support structure at small radius are presented. A grounding scheme employing copper–kapton mesh circuits is described and shown to provide adequate and robust detector performance.
122603752
CMS Data Processing Workflows during an Extended Cosmic Ray Run
The CMS Collaboration conducted a month-long data taking exercise, the Cosmic Run At Four Tesla, during October-November 2008, with the goal of commissioning the experiment for extended operation. With all installed detector systems participating, CMS recorded 270 million cosmic ray events with the solenoid at a magnetic field strength of 3.8 T. This paper describes the data flow from the detector through the various online and offline computing systems, as well as the workflows used for recording the data, for aligning and calibrating the detector, and for analysis of the data.
2642397
Beam Position Monitoring Using the Hom-Signals from a Damped and Detuned Accelerating Structure
The Next and Global Linear Collider (NLC/GLC) designs require precision alignment of the beam in the accelerator structures to reduce short range wakefields. The moderately damped and detuned structures themselves provide suitable higher order mode (HOM) signals to measure this alignment. The modes in the lowest dipole band, whose frequencies range from 14-16 GHz, provide the strongest signals. To determine the position resolution they provide, an NLC/GLC prototype structure that was installed in the ASSET facility of the SLAC Linac was instrumented to downmix and digitize these signals. The beam position within the structure was determined by simultaneously measuring the signals at three frequencies (14.3, 15, 15.7 GHz) corresponding to modes localized at the beginning, the middle and the end of the 60 cm long structure. A resolution of 1 micron was achieved even with 28 dB signal attenuation, which is better than the 5 micron resolution required for the NLC/GLC.
55153082
A multi-moded rf delay line distribution system for the next linear collider
The Delay Line Distribution System (DLDS) is an alternative to conventional pulse compression, which enhances the peak power of rf sources while matching the long pulse of those sources to the shorter filling time of accelerator structures. We present an implementation of this scheme that combines pairs of parallel delay lines of the system into single lines. The power of several sources is combined into a single waveguide delay line using a multi-mode launcher. The output mode of the launcher is determined by the phase coding of the input signals. The combined power is extracted from the delay line using mode-selective extractors, each of which extracts a single mode. Hence, the phase coding of the sources controls the output port of the combined power. The power is then fed to the local accelerator structures. We present a detailed design of such a system, including several implementation methods for the launchers, extractors, and ancillary high power rf components. The system is designed so that it can handle the 600 MW peak power required by the NLC design while maintaining high efficiency.
55114627
T2K neutrino flux prediction
The Tokai-to-Kamioka (T2K) experiment studies neutrino oscillations using an off-axis muon neutrino beam with a peak energy of about 0.6 GeV that originates at the Japan Proton Accelerator Research Complex accelerator facility. Interactions of the neutrinos are observed at near detectors placed at 280 m from the production target and at the far detector—Super-Kamiokande—located 295 km away. The flux prediction is an essential part of the successful prediction of neutrino interaction rates at the T2K detectors and is an important input to T2K neutrino oscillation and cross section measurements. A FLUKA and GEANT3-based simulation models the physical processes involved in the neutrino production, from the interaction of primary beam protons in the T2K target, to the decay of hadrons and muons that produce neutrinos. The simulation uses proton beam monitor measurements as inputs. The modeling of hadronic interactions is reweighted using thin target hadron production data, including recent charged pion and kaon measurements from the NA61/SHINE experiment. For the first T2K analyses the uncertainties on the flux prediction are evaluated to be below 15% near the flux peak. The uncertainty on the ratio of the flux predictions at the far and near detectors is less than 2% near the flux peak.
209835030
Alignment of the CMS Silicon Tracker during Commissioning with Cosmic Rays
This is the Pre-print version of the Article. The official published version of the Paper can be accessed from the link below - Copyright @ 2010 IOP
112319037
Relativistic klystrons
Experimental work is underway to investigate the feasibility of using relativistic klystrons as a power source for future high-gradient accelerators. The aim is to develop a high-power (500-MW) short-wavelength (2.6-cm) relativistic klystron with beam kinetic energy greater than 1 MeV. Two different relativistic klystron configurations have been built and tested: a high-gain multicavity klystron at 11.4 GHz and a low-gain two-cavity subharmonic buncher driven at 5.7 GHz. In both configurations power is extracted at 11.4 GHz. In order to understand the basic physics issues involved in extracting RF from a high power beam, both a single resonant cavity and a multicell traveling-wave structure were used for energy extraction. A previously reported problem of high-power RF pulse shortening was overcome, and peak RF power levels of 170 MW have been achieved with the RF pulse of the same duration as the beam current pulse.<<ETX>>
110606846
RDDS cell design and optimization for the linear collider linacs
Each of the JLC/NLC main linacs will consist of /spl sim/1 million complex 3D accelerating cells that make up the 1.8 meter Rounded Damped Detuned Structures (RDDS) along its eight kilometer length. The RDDS is designed to provide maximum accelerating gradient to the beam while being able to suppress the long-range transverse wakefields to a satisfactory level. Using the 2D finite element code, Omega2, a 15% improvement in shunt impedance is found by changing the basic cell shape from a straight cylinder to a round outer wall contour that connects to slightly bulging circular disk noses. The HOM damping manifold is then designed around this optimal cell shape to improve the cell-to-manifold coupling for the dipole mode and the vacuum conductance under the frequency and minimal Q-reduction constraints for the fundamental mode. We use both MAFIA and the 3D finite element Omega3 code for this step to obtain a manifold geometry that consists of a round waveguide with additional narrow coupling slots that cut into the cell disks. As a time and cost saving measure for the JLC/NLC, the RDDS cell dimensions are being determined through computer modeling to within fabrication precision so that no tuning may be needed once the structures are assembled. At the X-band operating frequency, this corresponds to an error of a few microns in the cell radius. Such a level of resolution requires highly accurate field solvers and vast amount of computer resources. We will present calculations with the parallel code Omega3P that utilizes massively parallel computers such as the Cray T3E at NERSC. The numerical results will be compared with cold test measurements performed on RDDS prototypes that are diamond-turned with dimensions based on Omega3P simulations.
111372158
Design, Fabrication and Measurement of the First Rounded Damped Detuned Accelerator Structure (RDDS1)
As a joint effort in the JLC/NLC research program, the authors have developed a new type of damped detuned accelerator structure with optimized round-shaped cavities (RDDS). This paper discusses some important R and D aspects of the first structure in this series (RDDS1). The design aspects covered are the cell design with sub-MHz precision, HOM detuning, coupling and damping technique and wakefield simulation. The fabrication issues covered are ultra-precision cell machining with micron accuracy, assembly and diffusion bonding technologies to satisfactorily meet bookshelf, straightness and cell rotational alignment requirements. The measurements described are the RF properties of single cavities and complete accelerator section, as well as wakefields from the ASSET tests at SLAC. Finally, future improvements are also discussed.
15391415
Studies of Room Temperature Accelerator Structures for the ILC Positron Source
There are many challenges in the design of the normal-conducting portion of the ILC positron injector system such as achieving adequate cooling with the high RF and particle loss heating, and sustaining high accelerator gradients during millisecond-long pulses in a strong magnetic field. The proposed design for the positron injector contains both standing-wave and traveling-wave L-band accelerator structures for high RF efficiency, low cost and ease of fabrication. This paper presents results from several studies including particle energy deposition for both undulator based and conventional positron sources, cooling system design, accelerator structure optimization, RF pulse heating, cavity frequency stabilization, and RF feed system design.
118844175
Cosmic Duality and Statefinder Diagnosis of Spinor Quintom
In this paper, we study the possible connections among different Spinor Quintom Dark Energy (DE) models by the aid of duality. Then we apply the statefinder diagnostic to these models. By this diagnostic pair {$\{r,s\}$}, we differentiate one Quintom DE model from the others in a model independent manner. A class of evolutionary trajectories of these Spinor Quintom models are presented in the statefinder parameter planes. We also obtain the current locations of the parameters $r$ and $s$, and these locations correspond to different models in statefinder parameter planes theoretically.