IPAC2015 - List of Authors (Kersevan, R.)

Paper	Title	Page
MOBD1	Preliminary Design of the High-Luminosity LHC Beam Screen with Shielding	60
	C. Garion, V. Baglin, R. Kersevan CERN, Geneva, Switzerland
	A new beam screen is needed in the High-Luminosity LHC (HL-LHC) final focusing magnets. Such an essential vacuum component, while operating in the range 40-60 K, has to ensure the vacuum performance and to prevent the beam-induced heating from reaching the cold bore which is at 1.9 K. In addition, they have to shield the cold mass from physics debris coming from the nearby beam collision points. To such purpose, energy absorbers made of tungsten alloy are installed onto the beam screen in the vacuum system. In this contribution, the proposed mechanical design is shown; it covers different thermomechanical aspects such as the behaviour during a magnet quench and the heat transfer from the tungsten absorbers to the cooling tubes. Assembly and manufacturing tolerances are also considered to evaluate the impact on the aperture. Results obtained with a short prototype assembly test are discussed.
	Slides MOBD1 [3.089 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-MOBD1
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WEPHA003	Measurement of NEG Coating Performance Variation in the LHC after the First Long Shutdown	3100
	V. Bencini, V. Baglin, G. Bregliozzi, P. Chiggiato, R. Kersevan, C. Yin Vallgren CERN, Geneva, Switzerland
	During the Long Shutdown 1 (LS1) of the Large Hadron Collider, 90% of the Non-Evaporable Getter (NEG) coated beam pipes in the Long Straight Sections (LSS) were vented to undertake the planned upgrade and consolidation programmes. After each intervention, an additional bake-out and NEG activation were performed to reach the vacuum requirements. An analysis of the coating performance variation after the additional activation cycle has been carried out by using ultimate pressure and pressure build-up measurements. In addition, laboratory measurements have been carried out to mimic the LHC coated beam pipe behaviour. The experimental data have been compared with calculation obtained by Molflow+.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPHA003
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WEPHA005	Characterization of the RF Fingers Contact Force for the LHC Warm Vacuum Bellow Modules	3106
	C. Blanch Gutiérrez, V. Baglin, G. Bregliozzi, P. Chiggiato, R. Kersevan CERN, Geneva, Switzerland
	Along the 27 Km of LHC beam pipe, various types of vacuum bellow modules are needed to compensate the mechanical misalignments of the vacuum chambers during installation and to absorb their thermal expansion during the bake-out. In order to reduce the beam impedance during operation with beams these modules are equipped with RF bridges to carry the image current. They are usually made out of a copper tube insert at one side and Cu-Be RF fingers at the other end of the module. A spring is used to keep the contact between the RF fingers and the tube insert. The geometry and the choice of this spring become critical to ensure a good electrical contact. In this paper, a description of the test bench used to measure the contact force together with the procedure applied and the measurements performed are given. A summary of the maximum radial and axial offsets between the RF fingers and the insert tube while keeping a good electrical contact is presented.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPHA005
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WEPHA006	Recommissioning of the COLDEX Experiment at CERN	3109
	R. Salemme, V. Baglin, F. Bellorini, G. Bregliozzi, K. Brodzinski, P. Chiggiato, P. Costa Pinto, P. Gomes, A. Gutierrez, V. Inglese, B. Jenninger, R. Kersevan, E. Michel, M. Pezzetti, B. Rio, A. Sapountzis CERN, Geneva, Switzerland
	COLDEX (Cold bore Experiment), installed in the Super Proton Synchrotron (SPS) at CERN, is a test vacuum sector used in 2001-2004 to validate the Large Hadron Collider (LHC) cryogenic vacuum system with LHC type proton beams. Its cryostat houses a 2.2 m long copper perforated beam screen surrounded by a stainless steel cold bore, both individually temperature controlled down to 5 and 3 K, respectively. In the framework of the development for the High Luminosity upgrade of the LHC (HL-LHC), COLDEX has been re-commissioned in 2014. The objective of this re-commissioning is the validation of the performance of amorphous carbon coatings at cryogenic temperature with LHC type beams. The existing COLDEX beam screen has been dismounted and carbon coated, while a complete overhaul of the vacuum, cryogenic and control systems has been carried out. This contribution describes the phases of re-commissioning and reviews the current experimental set-up. An overview of the possible measurements with COLDEX, in view of its HL-LHC experimental program, is also presented.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPHA006
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WEPHA007	Amorphous Carbon Coatings at Cryogenic Temperatures with LHC Type Beams: First Results with the COLDEX Experiment	3112
	R. Salemme, V. Baglin, G. Bregliozzi, P. Chiggiato, R. Kersevan CERN, Geneva, Switzerland
	Extrapolations of electron cloud data from the Large Hadron Collider (LHC) Run 1 to the High Luminosity upgrade (HL-LHC) beam parameters predict an intolerable increase of heat load on the beam screens of the inner triplets. Amorphous carbon (a-C) coating of the beam screen surface is proposed to reduce electron cloud production, thereby minimising its dissipated power. To validate this solution, the COLDEX experiment has been re-commissioned. Such equipment mimics the performance of the LHC cold bore and beam screen cryogenic vacuum system in presence of LHC beams in the Super Proton Synchrotron (SPS). The main objective of the study is the performance evaluation of a-C coatings while operating the beam screen in the 10 to 60 K temperature range and cold bore below 3 K. This paper reviews the status of COLDEX and the results obtained during its first experimental runs.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPHA007
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WEPHA009	Propagation of Radioactive Contaminants Along the Isolde Beamline	3115
	R. Kersevan, M. Ady, A. Dorsival, A. Gottberg, M. Maietta, G. Vandoni CERN, Geneva, Switzerland
	The vacuum system of RIB facilities is entirely hermetical, with storage of effluents and controlled release to atmosphere after a decay time. In Isolde, distributed primary pumping is sectorized in three parts, but all effluents are conveyed together in a unique tank. Thus, highly contaminated gas from the target and front end may be mixed with less contaminated gas from the beam transfer lines. This study aims at analysing and quantifying the distribution and propagation of neutral rare gas radioactive isotopes along the Isolde beam-line by numerical simulation (steady-state and time resolved Test-Particle Monte-Carlo, Molflow+) and experimental means. The time-resolved Monte-Carlo integrates decay time for the propagating species. To measure the distribution of contaminants, sampling filters are installed at the exhaust of the vacuum turbo-molecular pumps. Comparison between simulation and experiment shows excellent agreement, confirming the pertinence of the Monte-Carlo tool to radioactive species propagation. The filtering effect of magnetic sectors, the RFQ Cooler, and Buncher on the propagating neutral isotopes are quantified.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPHA009
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WEPHA010	The Vacuum System of the Extra-Low Energy Antiproton Decelerator ELENA at CERN	3119
	R. Kersevan CERN, Geneva, Switzerland
	The Extra-Low ENergy Antiproton decelerator (ELENA) project is under way since 2011. In the past 3 years, it has considerably evolved into a detailed design for the ring and the transfer lines. It is a small machine, ~30 m in circumference, with a rather tight specification for the average pressure seen by the anti-proton beams injected by the anti-proton decelerator (AD). The average pressure in ELENA must be limited to 4x10^-12 mbar (H2-equivalent) in order to limit the charge-exchange losses during the rather long deceleration process (several tens of seconds), during which the energy of the beam is reduced and the electron-cooler is used twice in order to decrease the transverse emittance of the anti-proton beam. This paper will discuss the design of the chambers of the injection line, extraction line and the ring. It will also mention the actual status of the vacuum system for the transfer lines to the experiments, LNE, which are under finalisation. The results of detailed 3D simulations made with the test-particle montecarlo code Molflow+ will be discussed, alongside with the choice for the pumping system, mainly distributed NEG-coatings and integrated NEG/ion-pumps.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPHA010
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WEPHA011	Photodesorption and Electron Yield Measurements of Thin Film Coatings for Future Accelerators	3123
	R. Kersevan, M. Ady, P. Chiggiato CERN, Geneva, Switzerland T. Honda, Y. Tanimoto KEK, Tsukuba, Japan
	The performance of future accelerators could be limited by electron cloud phenomena and high photodesorption yields. For such a reason, the study of secondary electron and photodesorption yields of vacuum materials is essential. The eradication or mitigation of both secondary electron and molecule desorption could strongly reduce the beam scrubbing time and increase the availability of nominal beams for experiments. Surface modifications with the desired characteristics can be achieved by thin-film coatings, in particular made of amorphous carbon and non-evaporable getters (NEG). In the framework of a new collaboration, several vacuum chambers have been produced, and different coatings on each of them have been applied. The samples were then irradiated at KEK’s Photon Factory with SR light of 4 keV critical energy during several days, allowing the measurement of the photodesorption yield as a function of the photon dose. This paper presents the experiment and briefly summarizes the preliminary photodesorption and photoelectron yield data of different coatings. The results can be used for future machine design with similar conditions, such as the FCC-hh.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPHA011
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WEPHA012	Synchrotron Radiation Distribution and Related Outgassing and Pressure Profiles for the HL-LHC Final Focus Magnets	3127
	R. Kersevan CERN, Geneva, Switzerland
	The HL-LHC final focus area, from D2 to the interaction point, has been modelled based on the latest vacuum chamber geometry and orbits. The synchrotron radiation (SR) fans are computed using the Monte Carlo code SYNRAD⁺, in the dipole approximation regime. The angular and energy dependence of the reflectivity of the copper surfaces is considered, as well as the surface roughness. Once the SR distributions are computed, they are converted into outstanding profiles by using data available in literature. The test-particle Monte Carlo code Molflow+ is then used and the related pressure profiles and gas density distribution are computed. This allows an optimization of the pattern of the perforations on the tungsten-shielded beam screen proposed for this area. It is shown that the resultant gas density is below the limit dictated by the ATLAS and CMS detectors.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPHA012
Export •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Page

Preliminary Design of the High-Luminosity LHC Beam Screen with Shielding

60

C. Garion, V. Baglin, R. Kersevan
CERN, Geneva, Switzerland

A new beam screen is needed in the High-Luminosity LHC (HL-LHC) final focusing magnets. Such an essential vacuum component, while operating in the range 40-60 K, has to ensure the vacuum performance and to prevent the beam-induced heating from reaching the cold bore which is at 1.9 K. In addition, they have to shield the cold mass from physics debris coming from the nearby beam collision points. To such purpose, energy absorbers made of tungsten alloy are installed onto the beam screen in the vacuum system. In this contribution, the proposed mechanical design is shown; it covers different thermomechanical aspects such as the behaviour during a magnet quench and the heat transfer from the tungsten absorbers to the cooling tubes. Assembly and manufacturing tolerances are also considered to evaluate the impact on the aperture. Results obtained with a short prototype assembly test are discussed.

Slides MOBD1 [3.089 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-MOBD1

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WEPHA003

Measurement of NEG Coating Performance Variation in the LHC after the First Long Shutdown

3100

V. Bencini, V. Baglin, G. Bregliozzi, P. Chiggiato, R. Kersevan, C. Yin Vallgren
CERN, Geneva, Switzerland

During the Long Shutdown 1 (LS1) of the Large Hadron Collider, 90% of the Non-Evaporable Getter (NEG) coated beam pipes in the Long Straight Sections (LSS) were vented to undertake the planned upgrade and consolidation programmes. After each intervention, an additional bake-out and NEG activation were performed to reach the vacuum requirements. An analysis of the coating performance variation after the additional activation cycle has been carried out by using ultimate pressure and pressure build-up measurements. In addition, laboratory measurements have been carried out to mimic the LHC coated beam pipe behaviour. The experimental data have been compared with calculation obtained by Molflow+.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPHA003

Export •

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

WEPHA005

Characterization of the RF Fingers Contact Force for the LHC Warm Vacuum Bellow Modules

3106

C. Blanch Gutiérrez, V. Baglin, G. Bregliozzi, P. Chiggiato, R. Kersevan
CERN, Geneva, Switzerland

Along the 27 Km of LHC beam pipe, various types of vacuum bellow modules are needed to compensate the mechanical misalignments of the vacuum chambers during installation and to absorb their thermal expansion during the bake-out. In order to reduce the beam impedance during operation with beams these modules are equipped with RF bridges to carry the image current. They are usually made out of a copper tube insert at one side and Cu-Be RF fingers at the other end of the module. A spring is used to keep the contact between the RF fingers and the tube insert. The geometry and the choice of this spring become critical to ensure a good electrical contact. In this paper, a description of the test bench used to measure the contact force together with the procedure applied and the measurements performed are given. A summary of the maximum radial and axial offsets between the RF fingers and the insert tube while keeping a good electrical contact is presented.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPHA005

Export •

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

WEPHA006

Recommissioning of the COLDEX Experiment at CERN

3109

R. Salemme, V. Baglin, F. Bellorini, G. Bregliozzi, K. Brodzinski, P. Chiggiato, P. Costa Pinto, P. Gomes, A. Gutierrez, V. Inglese, B. Jenninger, R. Kersevan, E. Michel, M. Pezzetti, B. Rio, A. Sapountzis
CERN, Geneva, Switzerland

COLDEX (Cold bore Experiment), installed in the Super Proton Synchrotron (SPS) at CERN, is a test vacuum sector used in 2001-2004 to validate the Large Hadron Collider (LHC) cryogenic vacuum system with LHC type proton beams. Its cryostat houses a 2.2 m long copper perforated beam screen surrounded by a stainless steel cold bore, both individually temperature controlled down to 5 and 3 K, respectively. In the framework of the development for the High Luminosity upgrade of the LHC (HL-LHC), COLDEX has been re-commissioned in 2014. The objective of this re-commissioning is the validation of the performance of amorphous carbon coatings at cryogenic temperature with LHC type beams. The existing COLDEX beam screen has been dismounted and carbon coated, while a complete overhaul of the vacuum, cryogenic and control systems has been carried out. This contribution describes the phases of re-commissioning and reviews the current experimental set-up. An overview of the possible measurements with COLDEX, in view of its HL-LHC experimental program, is also presented.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPHA006

Export •

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

WEPHA007

Amorphous Carbon Coatings at Cryogenic Temperatures with LHC Type Beams: First Results with the COLDEX Experiment

3112

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

Extrapolations of electron cloud data from the Large Hadron Collider (LHC) Run 1 to the High Luminosity upgrade (HL-LHC) beam parameters predict an intolerable increase of heat load on the beam screens of the inner triplets. Amorphous carbon (a-C) coating of the beam screen surface is proposed to reduce electron cloud production, thereby minimising its dissipated power. To validate this solution, the COLDEX experiment has been re-commissioned. Such equipment mimics the performance of the LHC cold bore and beam screen cryogenic vacuum system in presence of LHC beams in the Super Proton Synchrotron (SPS). The main objective of the study is the performance evaluation of a-C coatings while operating the beam screen in the 10 to 60 K temperature range and cold bore below 3 K. This paper reviews the status of COLDEX and the results obtained during its first experimental runs.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPHA007

Export •

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

WEPHA009

Propagation of Radioactive Contaminants Along the Isolde Beamline

3115

R. Kersevan, M. Ady, A. Dorsival, A. Gottberg, M. Maietta, G. Vandoni
CERN, Geneva, Switzerland

The vacuum system of RIB facilities is entirely hermetical, with storage of effluents and controlled release to atmosphere after a decay time. In Isolde, distributed primary pumping is sectorized in three parts, but all effluents are conveyed together in a unique tank. Thus, highly contaminated gas from the target and front end may be mixed with less contaminated gas from the beam transfer lines. This study aims at analysing and quantifying the distribution and propagation of neutral rare gas radioactive isotopes along the Isolde beam-line by numerical simulation (steady-state and time resolved Test-Particle Monte-Carlo, Molflow+) and experimental means. The time-resolved Monte-Carlo integrates decay time for the propagating species. To measure the distribution of contaminants, sampling filters are installed at the exhaust of the vacuum turbo-molecular pumps. Comparison between simulation and experiment shows excellent agreement, confirming the pertinence of the Monte-Carlo tool to radioactive species propagation. The filtering effect of magnetic sectors, the RFQ Cooler, and Buncher on the propagating neutral isotopes are quantified.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPHA009

Export •

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

WEPHA010

The Vacuum System of the Extra-Low Energy Antiproton Decelerator ELENA at CERN

3119

R. Kersevan
CERN, Geneva, Switzerland

The Extra-Low ENergy Antiproton decelerator (ELENA) project is under way since 2011. In the past 3 years, it has considerably evolved into a detailed design for the ring and the transfer lines. It is a small machine, ~30 m in circumference, with a rather tight specification for the average pressure seen by the anti-proton beams injected by the anti-proton decelerator (AD). The average pressure in ELENA must be limited to 4x10^-12 mbar (H2-equivalent) in order to limit the charge-exchange losses during the rather long deceleration process (several tens of seconds), during which the energy of the beam is reduced and the electron-cooler is used twice in order to decrease the transverse emittance of the anti-proton beam. This paper will discuss the design of the chambers of the injection line, extraction line and the ring. It will also mention the actual status of the vacuum system for the transfer lines to the experiments, LNE, which are under finalisation. The results of detailed 3D simulations made with the test-particle montecarlo code Molflow+ will be discussed, alongside with the choice for the pumping system, mainly distributed NEG-coatings and integrated NEG/ion-pumps.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPHA010

Export •

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

WEPHA011

Photodesorption and Electron Yield Measurements of Thin Film Coatings for Future Accelerators

3123

R. Kersevan, M. Ady, P. Chiggiato
CERN, Geneva, Switzerland
T. Honda, Y. Tanimoto
KEK, Tsukuba, Japan

The performance of future accelerators could be limited by electron cloud phenomena and high photodesorption yields. For such a reason, the study of secondary electron and photodesorption yields of vacuum materials is essential. The eradication or mitigation of both secondary electron and molecule desorption could strongly reduce the beam scrubbing time and increase the availability of nominal beams for experiments. Surface modifications with the desired characteristics can be achieved by thin-film coatings, in particular made of amorphous carbon and non-evaporable getters (NEG). In the framework of a new collaboration, several vacuum chambers have been produced, and different coatings on each of them have been applied. The samples were then irradiated at KEK’s Photon Factory with SR light of 4 keV critical energy during several days, allowing the measurement of the photodesorption yield as a function of the photon dose. This paper presents the experiment and briefly summarizes the preliminary photodesorption and photoelectron yield data of different coatings. The results can be used for future machine design with similar conditions, such as the FCC-hh.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPHA011

Export •

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

WEPHA012

Synchrotron Radiation Distribution and Related Outgassing and Pressure Profiles for the HL-LHC Final Focus Magnets

3127

R. Kersevan
CERN, Geneva, Switzerland

The HL-LHC final focus area, from D2 to the interaction point, has been modelled based on the latest vacuum chamber geometry and orbits. The synchrotron radiation (SR) fans are computed using the Monte Carlo code SYNRAD⁺, in the dipole approximation regime. The angular and energy dependence of the reflectivity of the copper surfaces is considered, as well as the surface roughness. Once the SR distributions are computed, they are converted into outstanding profiles by using data available in literature. The test-particle Monte Carlo code Molflow+ is then used and the related pressure profiles and gas density distribution are computed. This allows an optimization of the pattern of the perforations on the tungsten-shielded beam screen proposed for this area. It is shown that the resultant gas density is below the limit dictated by the ATLAS and CMS detectors.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2015-WEPHA012

Export •

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