IPAC2016 - List of Authors (Salemme, R.)

Paper	Title	Page
MOPOR026	Measurement of the Energy Distribution Function of Electrons Generated by Radio-frequency Induced Multipacting in a Beam Pipe	664
	M. Van Gompel, F. Caspers, P. Costa Pinto, R. Leber, A. Romano, R. Salemme, M. Taborelli CERN, Geneva, Switzerland
	The development of Electron Multipacting (EM) in high intensity particle accelerators depends, amongst others, on the Secondary Electron Yield (SEY) of surfaces facing the beam. In-situ studies of electron clouds in particle accelerators must cope with operation schedule and other technical constrains. To overcome these difficulties, CERN implemented a Multipactor test bench, where EM is generated by Radio-Frequency (RF), using the beam pipes as a coaxial resonators. This tool was already successfully used to assess the effectiveness of low SEY carbon coatings on dipoles of the SPS at CERN and to study the conditioning dynamics of beam pipes. In this paper we present the development of an in-house built Retarding Field Energy Analyser (RFEA) to measure the Electrons Energy Distribution Function (EEDF) in the Multipactor test bench. The design of the electrodes was based on simulations in order to optimize sensitivity and energy resolution. The setup was tested with an electron gun at different energies before insertion in the Multipactor test bench. The evolution of the EEDF is measured at different RF powers. Feasibility to perform measurements in the machine is discussed.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPOR026
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THPMY007	Vacuum Performance of Amorphous Carbon Coating at Cryogenic Temperature with Presence of Proton Beams	3663
	R. Salemme, V. Baglin, G. Bregliozzi, P. Chiggiato CERN, Geneva, Switzerland
	Amorphous carbon (a-C) coating is the baseline electron multipacting mitigation strategy proposed for the Inner Triplets (IT) in the High Luminosity upgrade of the Large Hadron Collider (HL-LHC). As of 2014, the COLD bore EXperiment (COLDEX) is qualifying the performance of a-C coating at cryogenic temperature in a LHC type cryogenic vacuum system. In this paper, the experimental results following a cryogenic vacuum characterization of a-C coating in the 5 to 150 K temperature range are reviewed. We discuss the dynamic pressure rise, gas composition, dissipated heat load and electron activity observed within an accumulated beam time of 9 Ah. The results of dedicated experiments including pre-adsorption of different gas species (H2, CO) on the a-C coating are discussed. Based of phenomenological modeling, up-to-date secondary emission input parameters for a-C coatings are retrieved for electron cloud build-up simulations. Finally, first implications for the HL-LHC ITs design are drawn.
DOI •	reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-THPMY007
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Page

Measurement of the Energy Distribution Function of Electrons Generated by Radio-frequency Induced Multipacting in a Beam Pipe

664

M. Van Gompel, F. Caspers, P. Costa Pinto, R. Leber, A. Romano, R. Salemme, M. Taborelli
CERN, Geneva, Switzerland

The development of Electron Multipacting (EM) in high intensity particle accelerators depends, amongst others, on the Secondary Electron Yield (SEY) of surfaces facing the beam. In-situ studies of electron clouds in particle accelerators must cope with operation schedule and other technical constrains. To overcome these difficulties, CERN implemented a Multipactor test bench, where EM is generated by Radio-Frequency (RF), using the beam pipes as a coaxial resonators. This tool was already successfully used to assess the effectiveness of low SEY carbon coatings on dipoles of the SPS at CERN and to study the conditioning dynamics of beam pipes. In this paper we present the development of an in-house built Retarding Field Energy Analyser (RFEA) to measure the Electrons Energy Distribution Function (EEDF) in the Multipactor test bench. The design of the electrodes was based on simulations in order to optimize sensitivity and energy resolution. The setup was tested with an electron gun at different energies before insertion in the Multipactor test bench. The evolution of the EEDF is measured at different RF powers. Feasibility to perform measurements in the machine is discussed.

DOI •

reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-MOPOR026

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

THPMY007

Vacuum Performance of Amorphous Carbon Coating at Cryogenic Temperature with Presence of Proton Beams

3663

R. Salemme, V. Baglin, G. Bregliozzi, P. Chiggiato
CERN, Geneva, Switzerland

Amorphous carbon (a-C) coating is the baseline electron multipacting mitigation strategy proposed for the Inner Triplets (IT) in the High Luminosity upgrade of the Large Hadron Collider (HL-LHC). As of 2014, the COLD bore EXperiment (COLDEX) is qualifying the performance of a-C coating at cryogenic temperature in a LHC type cryogenic vacuum system. In this paper, the experimental results following a cryogenic vacuum characterization of a-C coating in the 5 to 150 K temperature range are reviewed. We discuss the dynamic pressure rise, gas composition, dissipated heat load and electron activity observed within an accumulated beam time of 9 Ah. The results of dedicated experiments including pre-adsorption of different gas species (H2, CO) on the a-C coating are discussed. Based of phenomenological modeling, up-to-date secondary emission input parameters for a-C coatings are retrieved for electron cloud build-up simulations. Finally, first implications for the HL-LHC ITs design are drawn.

DOI •

reference for this paper ※ DOI:10.18429/JACoW-IPAC2016-THPMY007

Export •

reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)