Francesco Ruggiero

A 3 TeV

A possible design of a multi-TeV e+e- linear collider is presented. The design is based on the CLIC (Compact Linear Collider) two-beam technology proposed and developed at CERN. Though the study has shown that this technology is applicable to a linear collider with centre-of-mass energies from 500 GeV or less up to 5 TeV, the present report focuses on the nominal energy of 3 Te V. First, a short overview is given of the physics that could possibly be done with such a collider. Then, the description of the main-beam complex covers the injection system, the 30 GHz main linac, and the beam delivery system. The presentation of the RF power source includes the beam-generation scheme, the drive-beam decelerator, which consists of several 625 m long units running parallel to the main linac, and the power-extraction system. Finally, brief outlines are given of all the CLIC test facilities. They cover in particular the new CLIC test facility CTF3 which will demonstrate the feasibility of the power production technique, albeit on a reduced scale, and a first full-scale single-drive-beam unit, CLICI, to establish the overall feasibility of the scheme.

e^+ e^-

Novel measurements of the electron cloud have been performed in the SPS in 2004. The LHC beam in the SPS consists of a number of short bunch trains. By varying the distance between these trains it is possible to test the survival of the electrons after the bunch passage. In this paper, results from simulations and experiments are compared.

Linear Collider Based on CLIC Technology

We discuss the predicted electron cloud build up in the arcs and the long straight sections of the LHC, and its possible consequences on heat load, beam stability, long-term emittance preservation, and vacuum. Our predictions are based on computer simulations and analytical estimates, parts of which have been benchmarked against experimental observations at the SPS.

Electron Cloud Measurements in the SPS in 2004

We shortly review electron cloud effects in the CERN Large Hadron Collider. In particular, we discuss recent simulations showing a significant reduction of the beam induced heat load on the cold beam screen with weak satellite bunches at 5 ns from the main proton bunches. This can be an effective solution to shorten the conditioning period required to lower the secondary electron yield of the screen surface.

Present understanding of electron cloud effects in the Large Hadron Collider

The two rings of the LHC beam vacuum system have a total length of about 54 km of which almost 48 km will be at 1.9 K, the temperature of the superconducting magnets. The total synchrotron radiation power emitted by the two beams is 0.41 Wm/sup -1/. A a so-called beam screen, maintained at a temperature between 5 K and 20 K by gaseous helium flow, is inserted in the magnet cold bore to intercept this power. We discuss the beam screen, magnetic permeability/vapour pressure aspects, beam screen vacuum behaviour, photon-induced gas desorption, intermagnet connection, pressure measurement, warm sections and the insulation vacuum.

Collective instabilities in the LHC : electron cloud and satellite bunches

We consider an ultra-relativistic particle travelling on-axis in an infinitely long cylindrical metallic beam pipe with azimuthally varying conductivity. A semi-analytical solution, obtained by applying approximate boundary conditions, 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. We discuss numerical simulations and bench measurements which confirm the theoretical predictions. Implications for the beam-induced ohmic losses in the copper coated, welded LHC beam screen are also addressed.

The Large Hadron Collider vacuum system

Longitudinal echo signals can be produced in the CERN-SPS by exciting a coasting proton beam at 120 GeV/c with two short RF pulses at different harmonics of the revolution frequency, separated by a suitable time-delay. We show here how one can measure energy distributions and longitudinal diffusion coefficients by using longitudinal beam echoes. The energy spread measured in this manner is in an excellent agreement with the data obtained from the Schottky signal.

Image currents in azimuthally inhomogeneous metallic beam pipes

Super-bunches are long bunches with a flat longitudinal profile, which could potentially increase the LHC luminosity in a future upgrade. We present example parameters and discuss a variety of issues related to such super-bunches, including beam-beam tune shift, tune footprints, crossing schemes, luminosity, intrabeam scattering, and electron cloud. We highlight the benefits, disadvantages and open questions.