Intrabeam scattering and the coasting beam in the HERA proton ring

Undesired coasting beam of protons has been detected in the HERA proton ring in high energy storage operation. This mainly disturbs the operation of the HERA-B experiment, and can have some impact on H1 and ZEUS where it generates background spikes (depending also on the collimator settings). In this work we present a collection of data and facts, to be taken as starting point for further theoretical and experimental studies. We propose Intra Beam Scattering as a possible physical mechanism for creating the coasting beam and discuss the implications of this longitudinal dynamics model on observables such as the bunch length, energy spread, dc current and reaction rate at the HERA-B wires. The results seem to be in qualitative agreement with the measurements

Validation of frequency and mode extraction calculations from time-domain simulations of accelerator cavities

The recently developed frequency extraction algorithm [G.R. Werner and J.R. Cary, J. Comp. Phys. 227, 5200 (2008)] that enables a simple FDTD algorithm to be transformed into an efficient eigenmode solver is applied to a realistic accelerator cavity modeled with embedded boundaries and Richardson extrapolation. Previously, the frequency extraction method was shown to be capable of distinguishing M degenerate modes by running M different simulations and to permit mode extraction with minimal post-processing effort that only requires solving a small eigenvalue problem. Realistic calculations for an accelerator cavity are presented in this work to establish the validity of the method for realistic modeling scenarios and to illustrate the complexities of the computational validation process. The method is found to be able to extract the frequencies with error that is less than a part in 10^5. The corrected experimental and computed values differ by about one parts in 10^$, which is accounted for (in largest part) by machining errors. The extraction of frequencies and modes from accelerator cavities provides engineers and physicists an understanding of potential cavity performance as it depends on shape without incurring manufacture and measurement costs

Presidential History

News release announces the Presidential History of the University of Dayton

First Observation of Self-Amplified Spontaneous Emission in a Free-Electron Laser at 109 nm Wavelength

We present the first observation of Self-Amplified Spontaneous Emission (SASE) in a free-electron laser (FEL) in the Vacuum Ultraviolet regime at 109 nm wavelength (11 eV). The observed free-electron laser gain (approx. 3000) and the radiation characteristics, such as dependency on bunch charge, angular distribution, spectral width and intensity fluctuations all corroborate the existing models for SASE FELs.Comment: 6 pages including 6 figures; e-mail: [email protected]

Machine layout and performance

The Large Hadron Collider (LHC) is one of the largest scientific instruments ever built. Since opening up a new energy frontier for exploration in 2010, it has gathered a global user community of about 7,000 scientists working in fundamental particle physics and the physics of hadronic matter at extreme temperature and density. To sustain and extend its discovery potential, the LHC will need a major upgrade in the 2020s. This will increase its luminosity (rate of collisions) by a factor of five beyond the original design value and the integrated luminosity (total collisions created) by a factor ten. The LHC is already a highly complex and exquisitely optimised machine so this upgrade must be carefully conceived and will require about ten years to implement. The new configuration, known as High Luminosity LHC (HL-LHC), will rely on a number of key innovations that push accelerator technology beyond its present limits. Among these are cutting-edge 11-12 tesla superconducting magnets, compact superconducting cavities for beam rotation with ultra-precise phase control, new technology and physical processes for beam collimation and 300 metre-long high-power superconducting links with negligible energy dissipation. The present document describes the technologies and components that will be used to realise the project and is intended to serve as the basis for the detailed engineering design of HL-LHC

Observations of electron cloud phenomena at PETRA III

PETRA III is a third generation synchrotron radiation facility at DESY, which is presently operated with positron beams. Regular user operation started in mid 2010 after a commissioning phase which began in April 2009. The design current of 100 mA has been achieved but with different number of bunches and bunch to bunch distances than originally foreseen since a strong vertical emittance growth was observed for the design bunch filling pattern with 960 bunches. During machine studies different bunch filling patterns have been tested. In 2012 two scrubbing runs with 480 bunches and a bunch to bunch spacing of 16 ns have been done. The recent measurements indicate that the scrubbing runs have mitigated the emittance growth. Furthermore conditioning effects have been observed during the user runs in 2011. The results from the measured emittances and tune spectra are reported