1,721,220 research outputs found
Beam-Wall interaction in the LHC liner
No full textThe beam pipe foreseen for the LHC is rather unconventional. To shield the cold bore of the magnets from the synchrotron radiation emitted by protons at 7 TeV, a beam screen (the so called "liner") has been introduced practically along all the machine. The present design of the liner is a compromise among beam stability issues, vacuum requirements, heat load on the cold bore, electron cloud effects and mechanical constraints. Three main potential sources of beam energy loss in the actual LHC liner are addressed, namely the interaction with the pumping holes, the (sawtooth) surface corrugation and the effect of an azimuthally inhomogeneous metallic beam pipe modelling the high resistivity of the welding. The losses are estimated through a detailed electromagnetic analysis (by means of standard theories) seeking for analytical expressions of electromagnetic fields and/or coupling impedance. An analytical (or semi-analytical) approach is considered for each problem, to better understand the relevant parameters to be optimised. Whenever possible, the theoretical results are compared to numerical simulations and/or experimental data, sometimes found in literature and sometimes developed ad hoc. In particular, a prototype has been built and measured to check the theoretical predictions about the image currents distribution on an azimuthally inhomogeneous metallic beam pipe
Comb beam for particle-driven plasma-based accelerators
Full text linkComb beams are sub-picosecond, high-brightness electron bunch trains generated via the velocity bunching technique. Such bunch trains can be used to drive tunable and narrow band THz sources, FELs and plasma wake field accelerators. In this paper we present recent results at SPARC-LAB on the generation of comb beams for particle-driven plasma-based accelerators
Image currents in azimuthally inhomogeneous metallic beam pipes
No full textWe consider an ultrarelativistic particle traveling on axis in an infinitely long cylindrical metallic beam pipe with azimuthally varying conductivity. For a circular geometry, a semianalytical solution is obtained using the Green functions and applying approximate boundary conditions for conductors. The theory predicts an image current distribution on the pipe walls practically independent of the azimuth, at least in the frequency range relevant for future machines such as the LHC. Numerical electromagnetic simulations and bench measurements confirm the theoretical predictions. Implications for the beam-induced heating in the copper-coated, welded LHC beam screen are also addressed
Factory acceptance test of colddiag: A cold vacuum chamber for diagnostics
No full textSuperconducting insertion devices (IDs) have higher fields for a given gap and period length compared with the state-of-the-art technology of permanent magnet IDs. One of the still open issues for the development of superconducting insertion devices is the understanding of the heat intake from the electron beam. With the aim of measuring the beam heat load to a cold bore and the hope to gain a deeper understanding in the underlying mechanisms, a cold vacuum chamber for diagnostics was built. It is equipped with the following instrumentation: retarding field analyzers to measure the electron flux, temperature sensors to measure the beam heat load, pressure gauges, and mass spectrometers to measure the gas content. The flexibility of the engineering design will allow the installation of the cryostat in different synchrotron light sources. The installation in the storage ring of the Diamond Light Source is foreseen in November 2011. Here we report about the technical design of this device, the factory acceptance test and the planned measurements with electron beam. Copyright © 2011 by IPAC'11/EPS-AG
Interference effects on the coupling impedance of many holes in a coaxial beam pipe
No full textThe problem of many holes in a coaxial beam pipe is studied by means of the modified Bethe theory. The electromagnetic fields propagating in the coaxial region couple the equivalent dipole moments of the holes. The effect of the coupling on the longitudinal impedance and on the loss factor is investigated, showing that the interference phenomena are significant for such geometries
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