IPAC2011 - List of Authors (Kuzucan, A.)

Paper	Title	Page
TUPS023	Secondary Electron Yield on Cryogenic Surfaces as a Function of Physisorbed Gases	1575
	A. Kuzucan, H. Neupert, M. Taborelli CERN, Geneva, Switzerland H. Stoeri IAP TUW, Wien, Austria
	Electron cloud is a serious limitation for the operation of particle accelerators with intense positively charged beams. It occurs if the secondary electron yield (SEY) of the beam-pipe surface is sufficiently high to induce an electron multiplication. At low surface temperatures, the SEY is strongly influenced by the nature of the physisorbed gases and by the corresponding surface coverage. These conditions occur in many accelerators operating with superconducting magnets and cold vacuum sections such as the LHC and RHIC. In this work, we investigated the variation of the SEY of copper, aluminium and electro-polished copper as a function of physisorbed N2, CO, CO2, CH4, Kr, C2H6 at cryogenic temperatures. The conditioning by electron bombardment of the surface after the physisorption of H2O on electro polished copper will also be presented. The results of the various gases are compared in order to find a rationale for the behaviour of the secondary electrons for the various adsorbates.

TUPS027	Characterization of Carbon Coatings with Low Secondary Electron Yield	1587
	C. Yin Vallgren, S. Calatroni, P. Costa Pinto, A. Kuzucan, H. Neupert, M. Taborelli CERN, Geneva, Switzerland
	Amorphous carbon (a-C) coatings can reliably be produced with a maximum secondary electron yield (SEY) close to 1 at room temperature. Measurements at low temperature (LHe) are in progress. Analysis by X-ray Photoemission Spectroscopy (XPS) shows a correlation between the lineshape of C1s spectrum in XPS and maximum SEY of the investigated samples. The initial level of oxygen on the surface of the various samples does not seem to be related to the initial maximum SEY value. However, the increase of the SEY with air exposure time on each individual sample is related to the amount of oxygen containing adsorbates. Storage in different environments has been investigated (static vacuum, aluminum foil, dry nitrogen and desiccators) and shows significant differences in the “aging” behavior. Aging is very moderate when storing samples wrapped in aluminum foil in air. Samples which have undergone aging due to inappropriate storage can be recovered nearly to the initial value of the SEY by typical surface treatments as ion bombardment, annealing under vacuum and conditioning by electron beam. However, an enhanced sensitivity to air exposures is observed for most of these curing methods.

Paper

Title

Page

Secondary Electron Yield on Cryogenic Surfaces as a Function of Physisorbed Gases

1575

A. Kuzucan, H. Neupert, M. Taborelli
CERN, Geneva, Switzerland
H. Stoeri
IAP TUW, Wien, Austria

Electron cloud is a serious limitation for the operation of particle accelerators with intense positively charged beams. It occurs if the secondary electron yield (SEY) of the beam-pipe surface is sufficiently high to induce an electron multiplication. At low surface temperatures, the SEY is strongly influenced by the nature of the physisorbed gases and by the corresponding surface coverage. These conditions occur in many accelerators operating with superconducting magnets and cold vacuum sections such as the LHC and RHIC. In this work, we investigated the variation of the SEY of copper, aluminium and electro-polished copper as a function of physisorbed N2, CO, CO2, CH4, Kr, C2H6 at cryogenic temperatures. The conditioning by electron bombardment of the surface after the physisorption of H2O on electro polished copper will also be presented. The results of the various gases are compared in order to find a rationale for the behaviour of the secondary electrons for the various adsorbates.

TUPS027

Characterization of Carbon Coatings with Low Secondary Electron Yield

1587

C. Yin Vallgren, S. Calatroni, P. Costa Pinto, A. Kuzucan, H. Neupert, M. Taborelli
CERN, Geneva, Switzerland

Amorphous carbon (a-C) coatings can reliably be produced with a maximum secondary electron yield (SEY) close to 1 at room temperature. Measurements at low temperature (LHe) are in progress. Analysis by X-ray Photoemission Spectroscopy (XPS) shows a correlation between the lineshape of C1s spectrum in XPS and maximum SEY of the investigated samples. The initial level of oxygen on the surface of the various samples does not seem to be related to the initial maximum SEY value. However, the increase of the SEY with air exposure time on each individual sample is related to the amount of oxygen containing adsorbates. Storage in different environments has been investigated (static vacuum, aluminum foil, dry nitrogen and desiccators) and shows significant differences in the “aging” behavior. Aging is very moderate when storing samples wrapped in aluminum foil in air. Samples which have undergone aging due to inappropriate storage can be recovered nearly to the initial value of the SEY by typical surface treatments as ion bombardment, annealing under vacuum and conditioning by electron beam. However, an enhanced sensitivity to air exposures is observed for most of these curing methods.