IPAC2022 - Classification: MC7: Accelerator Technology / T19: Collimation

Paper	Title	Page
TUPOTK060	Simulations of Miscut Effects on the Efficiency of a Crystal Collimation System	1358
	M. D’Andrea, D. Mirarchi, S. Redaelli CERN, Meyrin, Switzerland
	Funding: Research supported by the HL-LHC project. The concept of crystal collimation relies on the use of bent crystals which can coherently deflect high-energy halo particles at angles orders of magnitude larger than what is obtained from scattering with conventional materials. Crystal collimation is studied to further improve the collimation efficiency at the High Luminosity Large Hadron Collider (HL-LHC). In order to reproduce the main experimental results of crystal collimation tests and to predict the performance of such a system, a simulation routine capable of modeling interactions of beam particles with crystal collimators was developed and recently integrated into the latest release of the single-particle tracking code SixTrack. A new treatment of the miscut angle, i.e. the angle between crystalline planes and crystal edges, was implemented to study the effects of this manufacturing imperfection on the efficiency of a crystal collimation system. In this paper, the updated miscut angle model is described and simulation results on the cleaning efficiency are presented, using configurations tested during Run 2 of the LHC as a case study.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK060
About •	Received ※ 07 June 2022 — Revised ※ 12 June 2022 — Accepted ※ 13 June 2022 — Issue date ※ 04 July 2022
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUPOTK061	Prospects to Apply Machine Learning to Optimize the Operation of the Crystal Collimation System at the LHC	1362
	M. D’Andrea, G. Azzopardi, M. Di Castro, E. Matheson, D. Mirarchi, S. Redaelli, G. Valentino CERN, Meyrin, Switzerland G. Ricci Sapienza University of Rome, Rome, Italy
	Funding: Research supported by the HL-LHC project. Crystal collimation relies on the use of bent crystals to coherently deflect halo particles onto dedicated collimator absorbers. This scheme is planned to be used at the LHC to improve the betatron cleaning efficiency with high-intensity ion beams. Only particles with impinging angles below 2.5 urad relative to the crystalline planes can be efficiently channeled at the LHC nominal top energy of 7 Z TeV. For this reason, crystals must be kept in optimal alignment with respect to the circulating beam envelope to maximize the efficiency of the channeling process. Given the small angular acceptance, achieving optimal channeling conditions is particularly challenging. Furthermore, the different phases of the LHC operational cycle involve important dynamic changes of the local orbit and optics, requiring an optimized control of position and angle of the crystals relative to the beam. To this end, the possibility to apply machine learning to the alignment of the crystals, in a dedicated setup and in standard operation, is considered. In this paper, possible solutions for automatic adaptation to the changing beam parameters are highlighted and plans for the LHC ion runs starting in 2022 are discussed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK061
About •	Received ※ 07 June 2022 — Revised ※ 12 June 2022 — Accepted ※ 21 June 2022 — Issue date ※ 24 June 2022
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUPOTK062	Settings for Improved Betatron Collimation in the First Run of the High Luminosity LHC	1366
	B. Lindström, A. Abramov, R. Bruce, R. De Maria, P.D. Hermes, J. Molson, S. Redaelli, F.F. Van der Veken CERN, Meyrin, Switzerland
	Funding: This work was supported by the High Luminosity LHC project The current betatron collimation system in the LHC is not optimized to absorb off-momentum particles scattered out from the primary collimators. The highest losses are concentrated in the downstream dispersion suppressor (DS). Given the increased beam intensity in the High Luminosity LHC (HL-LHC), there is concern that these losses could risk quenching the superconducting DS magnets. Consequently, a dedicated upgrade of the DS has been studied. However, at this stage, the deployment for the startup of the HL-LHC is uncertain due to delays in the availability of high-field magnets needed to integrate new collimators into the DS. In this paper, we describe the expected collimation setup for the first run of the HL-LHC and explore various techniques to improve the collimation cleaning. These include exploiting the asymmetric response of the two jaws of each primary collimator and adjusting the locally generated dispersion in the collimation insertion.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK062
About •	Received ※ 07 June 2022 — Revised ※ 14 June 2022 — Accepted ※ 15 June 2022 — Issue date ※ 23 June 2022
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

TUPOTK063	CERN Linac4 Chopper Dump: Operational Experience and Future Upgrades	1370
	C.J. Sharp, P. Andreu Muñoz, M. Calviani, G. Costa, L.S. Esposito, R. Franqueira Ximenes, D. Grenier, E. Grenier-Boley, J.R. Hunt, A.M. Krainer, C.Y. Mucher, C. Torregrosa CERN, Meyrin, Switzerland
	The Chopper Dump in the Linac4 accelerator at CERN is a beam-intercepting device responsible for the absorption of the 3 MeV H⁻ ion beam produced by the Linac4 source and deflected upstream by an electromagnetic chopper. It allows a portion of the beam, which would otherwise fall into the unstable region of the radiofrequency buckets in the Proton Synchrotron Booster, to be dumped at low energy with minimal induced radiation. It may also be used to absorb the entire beam. With peak currents of 25 to 45 mA and shallow penetration, this results in large deposited energy densities, thermal gradients and mechanical stresses. Additional constraints arise from geometric integration, vacuum and radiation protection requirements. Material selection, beam-matter interaction studies and thermo-structural analyses are important aspects of the design process. The Chopper Dump underwent modification in 2019 following observed material degradation in the original version of the device. The experience gained, modifications made and observations noted since then are detailed herein. Against this background, the design and analysis of an upgraded device, intended to cope with future operational conditions, is outlined and discussed.
DOI •	reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK063
About •	Received ※ 20 May 2022 — Revised ※ 12 June 2022 — Accepted ※ 13 June 2022 — Issue date ※ 26 June 2022
Cite •	reference for this paper using ※ BibTeX, ※ LaTeX, ※ Text/Word, ※ RIS, ※ EndNote (xml)

Paper

Title

Page

Simulations of Miscut Effects on the Efficiency of a Crystal Collimation System

1358

M. D’Andrea, D. Mirarchi, S. Redaelli
CERN, Meyrin, Switzerland

Funding: Research supported by the HL-LHC project.
The concept of crystal collimation relies on the use of bent crystals which can coherently deflect high-energy halo particles at angles orders of magnitude larger than what is obtained from scattering with conventional materials. Crystal collimation is studied to further improve the collimation efficiency at the High Luminosity Large Hadron Collider (HL-LHC). In order to reproduce the main experimental results of crystal collimation tests and to predict the performance of such a system, a simulation routine capable of modeling interactions of beam particles with crystal collimators was developed and recently integrated into the latest release of the single-particle tracking code SixTrack. A new treatment of the miscut angle, i.e. the angle between crystalline planes and crystal edges, was implemented to study the effects of this manufacturing imperfection on the efficiency of a crystal collimation system. In this paper, the updated miscut angle model is described and simulation results on the cleaning efficiency are presented, using configurations tested during Run 2 of the LHC as a case study.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK060

About •

Received ※ 07 June 2022 — Revised ※ 12 June 2022 — Accepted ※ 13 June 2022 — Issue date ※ 04 July 2022

Cite •

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

TUPOTK061

Prospects to Apply Machine Learning to Optimize the Operation of the Crystal Collimation System at the LHC

1362

M. D’Andrea, G. Azzopardi, M. Di Castro, E. Matheson, D. Mirarchi, S. Redaelli, G. Valentino
CERN, Meyrin, Switzerland
G. Ricci
Sapienza University of Rome, Rome, Italy

Funding: Research supported by the HL-LHC project.
Crystal collimation relies on the use of bent crystals to coherently deflect halo particles onto dedicated collimator absorbers. This scheme is planned to be used at the LHC to improve the betatron cleaning efficiency with high-intensity ion beams. Only particles with impinging angles below 2.5 urad relative to the crystalline planes can be efficiently channeled at the LHC nominal top energy of 7 Z TeV. For this reason, crystals must be kept in optimal alignment with respect to the circulating beam envelope to maximize the efficiency of the channeling process. Given the small angular acceptance, achieving optimal channeling conditions is particularly challenging. Furthermore, the different phases of the LHC operational cycle involve important dynamic changes of the local orbit and optics, requiring an optimized control of position and angle of the crystals relative to the beam. To this end, the possibility to apply machine learning to the alignment of the crystals, in a dedicated setup and in standard operation, is considered. In this paper, possible solutions for automatic adaptation to the changing beam parameters are highlighted and plans for the LHC ion runs starting in 2022 are discussed.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK061

About •

Received ※ 07 June 2022 — Revised ※ 12 June 2022 — Accepted ※ 21 June 2022 — Issue date ※ 24 June 2022

Cite •

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

TUPOTK062

Settings for Improved Betatron Collimation in the First Run of the High Luminosity LHC

1366

B. Lindström, A. Abramov, R. Bruce, R. De Maria, P.D. Hermes, J. Molson, S. Redaelli, F.F. Van der Veken
CERN, Meyrin, Switzerland

Funding: This work was supported by the High Luminosity LHC project
The current betatron collimation system in the LHC is not optimized to absorb off-momentum particles scattered out from the primary collimators. The highest losses are concentrated in the downstream dispersion suppressor (DS). Given the increased beam intensity in the High Luminosity LHC (HL-LHC), there is concern that these losses could risk quenching the superconducting DS magnets. Consequently, a dedicated upgrade of the DS has been studied. However, at this stage, the deployment for the startup of the HL-LHC is uncertain due to delays in the availability of high-field magnets needed to integrate new collimators into the DS. In this paper, we describe the expected collimation setup for the first run of the HL-LHC and explore various techniques to improve the collimation cleaning. These include exploiting the asymmetric response of the two jaws of each primary collimator and adjusting the locally generated dispersion in the collimation insertion.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK062

About •

Received ※ 07 June 2022 — Revised ※ 14 June 2022 — Accepted ※ 15 June 2022 — Issue date ※ 23 June 2022

Cite •

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

TUPOTK063

CERN Linac4 Chopper Dump: Operational Experience and Future Upgrades

1370

C.J. Sharp, P. Andreu Muñoz, M. Calviani, G. Costa, L.S. Esposito, R. Franqueira Ximenes, D. Grenier, E. Grenier-Boley, J.R. Hunt, A.M. Krainer, C.Y. Mucher, C. Torregrosa
CERN, Meyrin, Switzerland

The Chopper Dump in the Linac4 accelerator at CERN is a beam-intercepting device responsible for the absorption of the 3 MeV H⁻ ion beam produced by the Linac4 source and deflected upstream by an electromagnetic chopper. It allows a portion of the beam, which would otherwise fall into the unstable region of the radiofrequency buckets in the Proton Synchrotron Booster, to be dumped at low energy with minimal induced radiation. It may also be used to absorb the entire beam. With peak currents of 25 to 45 mA and shallow penetration, this results in large deposited energy densities, thermal gradients and mechanical stresses. Additional constraints arise from geometric integration, vacuum and radiation protection requirements. Material selection, beam-matter interaction studies and thermo-structural analyses are important aspects of the design process. The Chopper Dump underwent modification in 2019 following observed material degradation in the original version of the device. The experience gained, modifications made and observations noted since then are detailed herein. Against this background, the design and analysis of an upgraded device, intended to cope with future operational conditions, is outlined and discussed.

DOI •

reference for this paper ※ https://doi.org/10.18429/JACoW-IPAC2022-TUPOTK063

About •

Received ※ 20 May 2022 — Revised ※ 12 June 2022 — Accepted ※ 13 June 2022 — Issue date ※ 26 June 2022

Cite •

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