H. Henke

The Large Hadron Collider (LHC) in the LEP tunnel

After the remarkable start-up of LEP, the installation of a Large Hadron Collider, LHC, in the LEP tunnel will open a new era for the High Energy Physics. This report summarizes the main LHC parameters and subsytems and describes the more recent studies and developments.

Status of the LEP accelerating structure

The LEP (Large Electron Positron colliding beam accelerator) uses a dual-frequency acceleration system consisting of coupled accelerating and storage cavities. Basic design features of this system with its accessories and tuning system are described. One hundred and thirty cavities have been built by industry; the assembly and conditioning with RF power were done at CERN. All cavities are now installed in the LEP tunnel. The procedures used and first experiences are presented.<<ETX>>

Charge Passing off-Axis through a Cylindrical Resonator with Beam Pipes

A charge is considered which passes off-axis through a cylindrical resonator with two semi-infinite beam pipes. In the pipe region the fields are represented by the source fields plus a continuous spectrum of waveguide modes and in the resonator region by an infinite, discrete set of resonator modes. Matching the fields at the common interface yields a set of linear equations for the expansion coefficients. The involved integrals are solved with the residuum calculus, where the poles are located so that only waves travelling away from the resonator region are taken into account. By truncating the system, numerical results were derived for the longitudinal and transverse impedance which, contrary to periodic systems, also have real parts due to radiation into the pipes.

Structure studies for the CERN Linear Collider CLIC

Each linac proposed for the CERN Linear Collider (CLIC) is composed of 50000 25-cm-long-accelerator sections operating at 29 GHz with gradients of 80 MV/m to produce beam energies of 1 TeV. Basic structure parameters have been established, and fabrication of these sections by the electroforming and machine-and-braze techniques is being investigated. Results obtained from various prototype test pieces are given and discussed.<<ETX>>

Development and First Results with a Storage Resonator Enhancing the Shunt Impedance of an Electron Accelerating Cavity

In electron storage rings where the bunch repetition rate is low the dissipation of RF power in the accelerating cavity can be reduced by modulating the RF. A scheme using the energy oscillation between a storage resonator and the accelerating cavity has been successfully tested. Results of both low-and high-power tests at 500 MHz as well as design considerations for a 352 MHz prototype are presented.

Comparison between smooth and AG focusing for the CLIC main linac

It is pointed out that future linear colliders with extremely low emittance beams seems to require strong BNS damping in order to cope with wakefield effects. Under this condition the smooth focusing approximation is overoptimistic as compared to AG focusing. For the CERN Linear Collider (CLIC) it is found that the emittance blow-up due to wakefields in a nonperfect machine is about one order to magnitude smaller for smooth than for AG focusing.<<ETX>>

Thermal Analysis and Loss in Shunt Impedance of the LEP Accelerating Cell

Basic formulae governing thermal flow in water-cooled solids are qiven. By calculating the heat dissipation at room temperature of the LEP accelerating cell with the program SUPERFISH and then using this as input to the thermal analysis program DOT, the surface temperatures and losses at full power have been estimated. Good agreement is obtained when these LEP results are scaled and compared with measurements made on similar accelerating structures in PEP and PETRA. The calculated decrease in shunt impedance of 4.2% with respect to the room temperature value has been stubstantiated by experimental measurements on a prototype LEP cavity.