Jean Michel Laurent

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.

Electron cloud studies and analyses at SPS for LHC-type beams

A summary of the main results obtained so far from the electron cloud studies using strip detectors, pick-ups, COLDEX and a 100 MHz coaxial resonator will be presented. The spatial and energy distributions of the electrons in the cloud measured by the strip detectors will be detailed and compared to the results obtained with a conventional retarding field detector. The evidence of the scrubbing effect and of the NEG coatings as remedies to reduce the electron cloud activity will also be shown. In a second part, the improved hardware of the experiments will be presented together with the program of measurements foreseen for the 2003 SPS run.

Distributed Sputter-Ion Pumps for Use in Low Magnetic Fields

Measurements of the ignition characteristic of large diameter anode cells indicate a more than proportional increase of cell radius for a given reduction of Bi. Considerations of conductance have lead to an open anode configuration with several layers of perforated metal sheets. The pumping speed is found to be larger than for anodes with conventional cylinders. Moreover, since the electrons can move more freely inside the anode the discharge ignites at a lower magnetic field. Scaling from our measurements on model pumps, we expect to obtain with a single row of anode cells, designed to ignite at a field below 0.02 T, a linear pumping speed of about 60 l/sm at a transition field of about 0.1 T.

RF test benches for electron cloud studies

In the framework of the CERN program on the electron cloud effects in existing and future accelerators, a coaxial multipacting test stand was built. It consists of a 100 mm diameter vacuum chamber forming the outer conductor and 6 wires cageaerial-type as the inner conductor. In order to simulate the bunched beam, this test stand is submitted to short RF pulses. The available field strength in a travelling wave mode allows to trigger electron multipacting in as received or baked stainless steel surfaces, but not in chambers treated to reduce the secondary emission yield. Thus a number of upgrades in the bench set-up have been pursued, mainly in two directions. The first one is a general improvement on mismatches and losses. Second, instead of dumping the pulsed power into a load, it is re-circulated in a multiple frequency ring resonator. For this purpose, we designed a directional coupler with several kV DC isolation, very low transmission losses and a four octave bandwidth. In this paper, we give an overview of the present status of the set-up highlighting the latest improvements.

Molecular desorption of a nonevaporable getter St 707 irradiated at room temperature with synchrotron radiation of 194 eV critical photon energy

Photon stimulated molecular desorption from a nonevaporable getter (NEG) St 707® (SAES Getters™) surface after conditioning and after saturation with isotopic carbon monoxide [cf. nomenclature in Handbook of Chemistry and Physics, 74th edition, edited by D. R. Lide (CRC Press, Boca Raton, 1994)] 13C18O, has been studied on a dedicated beamline at the EPA ring at CERN. The synchrotron radiation of 194 eV critical energy and with an average photon intensity of ∼1×1017 photons s−1 was impinging on the sample at perpendicular incidence. It is found that the desorption yields η (molecules/photon) of the characteristic gases in an UHV system (hydrogen, methane, carbon monoxide, and carbon dioxide) for a freshly activated NEG and for a NEG fully saturated with 13C18O are lower than that of 300 °C baked stainless steel.