IPAC2011 - List of Authors (Taborelli, M.)

Paper	Title	Page
MOPC038	Engineering Design and Fabrication of Tapered Damped X-band Accelerating Structures	157
	A. Solodko, D. Gudkov, A. Samoshkin JINR, Dubna, Moscow Region, Russia S. Atieh, A. Grudiev, G. Riddone, M. Taborelli CERN, Geneva, Switzerland
	The accelerating structures (AS) are one of the main components of the Compact LInear Collider (CLIC), under study at CERN. Each AS contains about 30 copper disks, which form the accelerating cavity. A fully featured AS is very challenging and requires several technologies. Different damping methods, waveguides, vacuum manifolds, slots and choke, result in various design configurations. In the CLIC multibunch AS, called TDS (Tapered Damped Structure), each cell is damped by its four waveguides, which are extended by channels machined in dedicated external vacuum manifolds. The manifolds combine few functions such as damping, vacuum pumping and cooling. Silicon carbide absorbers, fixed inside of each manifold, are required for effective damping of High Order Modes. CERN is producing X-band RF structures in close collaboration with a large number of laboratories taking advantage of their large expertise and test facilities. The fabrication includes several steps from the machining to the final assembly, including quality controls. This paper describes the engineering design and fabrication procedure of the X-band AS with damping material, by focusing on few technical solutions.

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.

TUPS028	Performance of Carbon Coating for Mitigation of Electron Cloud in the SPS	1590
	C. Yin Vallgren, P. Chiggiato, P. Costa Pinto, H. Neupert, G. Rumolo, E.N. Shaposhnikova, M. Taborelli CERN, Geneva, Switzerland
	Amorphous carbon (a-C) coatings have been tested in electron cloud monitors (ECM) in the Super Proton Synchrotron (SPS) and have shown for LHC type beams a reduction of the EC current by a factor 10⁴ compared to stainless steel (SS). This performance has been maintained for more than 2 years under SPS operation conditions. Secondary electron yield (SEY) laboratory data confirm that after 1 year of SPS operation, the coating maintains a SEY below 1. The compatibility of coexisting SS and a-C surfaces has been studied in an ECM having coated and uncoated areas. The results show no degradation of the properties of the a-C areas. The performance of diamond like carbon (DLC) coating has also been studied. DLC shows a less effective reduction of the EC current than a-C, but conditioning is faster than for SS. Three a-C coated dipoles were inserted in the SPS. However, even with no EC detected, the dynamic pressure rise is similar to the one observed in the SS reference dipoles. Measurement in a new ECM equipped with clearing electrodes to verify the relation between pressure signals and intensity of the EC, as well as an improvement of the diagnostics in the dipoles are in progress.

Paper

Title

Page

Engineering Design and Fabrication of Tapered Damped X-band Accelerating Structures

157

A. Solodko, D. Gudkov, A. Samoshkin
JINR, Dubna, Moscow Region, Russia
S. Atieh, A. Grudiev, G. Riddone, M. Taborelli
CERN, Geneva, Switzerland

The accelerating structures (AS) are one of the main components of the Compact LInear Collider (CLIC), under study at CERN. Each AS contains about 30 copper disks, which form the accelerating cavity. A fully featured AS is very challenging and requires several technologies. Different damping methods, waveguides, vacuum manifolds, slots and choke, result in various design configurations. In the CLIC multibunch AS, called TDS (Tapered Damped Structure), each cell is damped by its four waveguides, which are extended by channels machined in dedicated external vacuum manifolds. The manifolds combine few functions such as damping, vacuum pumping and cooling. Silicon carbide absorbers, fixed inside of each manifold, are required for effective damping of High Order Modes. CERN is producing X-band RF structures in close collaboration with a large number of laboratories taking advantage of their large expertise and test facilities. The fabrication includes several steps from the machining to the final assembly, including quality controls. This paper describes the engineering design and fabrication procedure of the X-band AS with damping material, by focusing on few technical solutions.

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.

TUPS028

Performance of Carbon Coating for Mitigation of Electron Cloud in the SPS

1590

C. Yin Vallgren, P. Chiggiato, P. Costa Pinto, H. Neupert, G. Rumolo, E.N. Shaposhnikova, M. Taborelli
CERN, Geneva, Switzerland

Amorphous carbon (a-C) coatings have been tested in electron cloud monitors (ECM) in the Super Proton Synchrotron (SPS) and have shown for LHC type beams a reduction of the EC current by a factor 10⁴ compared to stainless steel (SS). This performance has been maintained for more than 2 years under SPS operation conditions. Secondary electron yield (SEY) laboratory data confirm that after 1 year of SPS operation, the coating maintains a SEY below 1. The compatibility of coexisting SS and a-C surfaces has been studied in an ECM having coated and uncoated areas. The results show no degradation of the properties of the a-C areas. The performance of diamond like carbon (DLC) coating has also been studied. DLC shows a less effective reduction of the EC current than a-C, but conditioning is faster than for SS. Three a-C coated dipoles were inserted in the SPS. However, even with no EC detected, the dynamic pressure rise is similar to the one observed in the SS reference dipoles. Measurement in a new ECM equipped with clearing electrodes to verify the relation between pressure signals and intensity of the EC, as well as an improvement of the diagnostics in the dipoles are in progress.