IPAC2022 - List of Authors (Petit, V.)

Paper	Title	Page
TUOXSP1	Origin and Mitigation of the Beam-Induced Surface Modifications of the LHC Beam Screens	780
	V. Petit, P. Chiggiato, M. Himmerlich, S. Marinoni, H. Neupert, M. Taborelli, L.J. Tavian CERN, Meyrin, Switzerland
	All over Run 2, the LHC beam-induced heat load on the cryogenic system exhibited a wide scattering along the ring. Studies ascribed the heat source to electron cloud build-up, indicating an unexpected high Secondary Electron Yield (SEY) of the beam screen surface in some LHC regions. The inner copper surface of high and low heat load beam screens, extracted during the Long Shutdown 2, was analysed. On the low heat load ones, the surface was covered with the native Cu2O oxide, while on the high heat load ones CuO dominated at surface, and it exhibited a very low carbon coverage. Such chemical modifications increase the SEY and inhibit a proper conditioning of the affected surfaces. Following this characterisation, the mechanisms for CuO build-up in the LHC beam pipe were investigated on a newly commissioned cryogenic system allowing electron irradiation, surface chemical characterisation by X-ray Photoelectron Spectroscopy and SEY measurements on samples held below 15 K. In parallel, curative solutions against the presence of CuO in the LHC beam screens were explored, which could be implemented in-situ to recover a proper conditioning and lower the beam-induced heat load.
	Slides TUOXSP1 [2.669 MB]
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUOXSP1
About •	Received ※ 17 May 2022 — Revised ※ 10 June 2022 — Accepted ※ 17 June 2022 — Issue date ※ 05 July 2022
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

THPOTK035	Thermo-Mechanical Modeling and Thermal Performance Analysis of Beam Vacuum Line Interconnections and Cold Warm Transitions in HL-LHC Long Straight Section Magnets	2839
	J. Harray, C. Garion, V. Petit CERN, Meyrin, Switzerland
	The HL-LHC upgrade, aiming at increasing the LHC levelled luminosity by factor of five, relies on new superconducting magnets requiring a new beam vacuum system. Along with the challenges related to magnet design, the beam optic configuration exposes this new equipment to stringent conditions for vacuum and cryogenic performance. Both cold-warm transitions and magnet interconnections appear to be delicate components that are crucial for the thermal heat transfer between diverse subsystems. The proposed study aims at assessing the heat loads to the cryogenic system and the temperature fields in the vacuum system. A nonlinear static thermal analysis is first performed. A thermo-mechanical approach is developed to capture additional thermal resistance arising from contact between components and their behaviour during cool-down. The system is then studied under dynamic operations when beams are circulating and colliding. A thorough analysis of beam-induced heat loads under ultimate conditions highlights the different relevant contributions. Finally, the transient response of the systems is computed to assess thermal time constants.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOTK035
About •	Received ※ 08 June 2022 — Revised ※ 11 June 2022 — Accepted ※ 27 June 2022 — Issue date ※ 29 June 2022
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Page

Origin and Mitigation of the Beam-Induced Surface Modifications of the LHC Beam Screens

780

V. Petit, P. Chiggiato, M. Himmerlich, S. Marinoni, H. Neupert, M. Taborelli, L.J. Tavian
CERN, Meyrin, Switzerland

All over Run 2, the LHC beam-induced heat load on the cryogenic system exhibited a wide scattering along the ring. Studies ascribed the heat source to electron cloud build-up, indicating an unexpected high Secondary Electron Yield (SEY) of the beam screen surface in some LHC regions. The inner copper surface of high and low heat load beam screens, extracted during the Long Shutdown 2, was analysed. On the low heat load ones, the surface was covered with the native Cu2O oxide, while on the high heat load ones CuO dominated at surface, and it exhibited a very low carbon coverage. Such chemical modifications increase the SEY and inhibit a proper conditioning of the affected surfaces. Following this characterisation, the mechanisms for CuO build-up in the LHC beam pipe were investigated on a newly commissioned cryogenic system allowing electron irradiation, surface chemical characterisation by X-ray Photoelectron Spectroscopy and SEY measurements on samples held below 15 K. In parallel, curative solutions against the presence of CuO in the LHC beam screens were explored, which could be implemented in-situ to recover a proper conditioning and lower the beam-induced heat load.

Slides TUOXSP1 [2.669 MB]

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUOXSP1

About •

Received ※ 17 May 2022 — Revised ※ 10 June 2022 — Accepted ※ 17 June 2022 — Issue date ※ 05 July 2022

Cite •

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

THPOTK035

Thermo-Mechanical Modeling and Thermal Performance Analysis of Beam Vacuum Line Interconnections and Cold Warm Transitions in HL-LHC Long Straight Section Magnets

2839

J. Harray, C. Garion, V. Petit
CERN, Meyrin, Switzerland

The HL-LHC upgrade, aiming at increasing the LHC levelled luminosity by factor of five, relies on new superconducting magnets requiring a new beam vacuum system. Along with the challenges related to magnet design, the beam optic configuration exposes this new equipment to stringent conditions for vacuum and cryogenic performance. Both cold-warm transitions and magnet interconnections appear to be delicate components that are crucial for the thermal heat transfer between diverse subsystems. The proposed study aims at assessing the heat loads to the cryogenic system and the temperature fields in the vacuum system. A nonlinear static thermal analysis is first performed. A thermo-mechanical approach is developed to capture additional thermal resistance arising from contact between components and their behaviour during cool-down. The system is then studied under dynamic operations when beams are circulating and colliding. A thorough analysis of beam-induced heat loads under ultimate conditions highlights the different relevant contributions. Finally, the transient response of the systems is computed to assess thermal time constants.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-THPOTK035

About •

Received ※ 08 June 2022 — Revised ※ 11 June 2022 — Accepted ※ 27 June 2022 — Issue date ※ 29 June 2022

Cite •

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