Etude de la désorption moléculaire induite par transitions électroniques dans les surfaces techniques

L'étude des particules créées lors des collisions protons-protons à 7 TeV, qui se produiront dans le Large Hadron Collider (LHC), permettra aux physiciens des hautes énergies de mieux comprendre la structure de la matière et de notre univers. Pour construire une telle machine, de nouvelles technologies vont devoir être développées. Ces technologies nécessitent de mieux comprendre les problèmes physiques qui se produiront dans l'accélérateur. Un des problèmes est de s'assurer de la durée de vie des faisceaux. Celle-ci est directement liée au nombre de molécules présentes dans les chambres à vide.

Experimental Study of Diamond Like Carbon (DLC) Coated Electrodes for Pulsed High Gradient Electron Gun

For the SwissFEL Free Electron Laser project at the Paul Scherrer Institute, a pulsed High Gradient (HG) electron gun was used to study low emittance electron sources. Different metals and surface treatments for the cathode and anode were studied for their HG suitability. Diamond Like Carbon (DLC) coatings are found to perform exceptionally well for vacuum gap insulation. A set of DLC coated electrodes with different coating parameters were tested for both vacuum breakdown and photo electron emission. Surface electric fields over 250MV/m (350 - 400kV, pulsed) were achieved without breakdown. From the same surface, it was possible to photo-emit an electron beam at gradients up to 150MV/m. The test setup and the experimental results are presentedComment: 4 pages, 14 figures, IPMHVC 2010 : IEEE International Power Modulator and High Voltage Conferenc

Molecular Desorption of a NEG St 707 Irradiated at Room Temperature with Synchrotron Radiation of 194 eV Critical Photon Energy

Photon stimulated molecular desorption from a NEG St 707 (SAES Getters$^{TM}$) surface after conditioning and after saturation with isotopic carbon monoxide, 13C18O, has been studied on a dedicated beam line at the EPA ring at CERN. The synchrotron radiation of 194 eV critical energy and with an average photon intensity of ~1 10**17 photons.s**-1 was impinging on the sample at perpendicular incidence. It is found that the desorption yields h 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

Electron Stimulated Molecular Desorption of a NEG St 707 at Room Temperature

Electron stimulated molecular desorption (ESD) from a NEG St 707 (SAES GettersTM) sample after conditioning and after saturation with isotopic carbon monoxide2,13C18O, has been studied on a laboratory setup. Measurements were performed using an electron beam of 300 eV kinetic energy, with an average electron intensity of 1.6 1015 electrons s-1. The electrons were impinging on the 15 cm2 target surface at perpendicular incidence. It is found that the desorption yields h (molecules/electron) of the characteristic gases in an UHV system (hydrogen, methane, water, carbon monoxide, carbon dioxide) for a fully activated NEG as well as for a NEG fully saturated with 13C18O are lower than for OFHC copper baked at 120oC. A small fraction only of the gas which is required to saturate the getter surface can be re-desorbed and thus appears to be accessible to ESD

Vibrational Stability of NLC Linac accelerating structure

The vibration of components of the NLC linac, such as accelerating structures and girders, is being studied both experimentally and analytically. Various effects are being considered including structural resonances and vibration caused by cooling water in the accelerating structure. This paper reports the status of ongoing work.Comment: 3 pages 8 figures Presented at EPAC 2002 Paris Franc