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Summary of ARIES WP6 APEC & iFAST WP5.2 PAF joint Brainstorming & Strategy Workshop (BSW22) R. Assmann (DESY), C. Carli (CERN), A. Faus-Golfe (IJCLab), E. Fol (CERN), G. Franchetti (GSI & GU Frankfurt), R. Jacobsson (CERN), V. Kain (CERN), F. Kling (DESY), M.W. Krasny (LPNHE), R. Ischebeck (PSI), A. Scheinker (LANL), V. Shiltsev (FNAL), R. Tomas Garcia (CERN), F. Zimmermann (CERN) edited by the BSW2022 workshop organisers A. Faus-Golfe (IJCLab), G. Franchetti (GSI & GU Frankfurt), F. Zimmermann (CERN) The ARIES WP6 APEC & iFAST WP5.2 PAF joint Brainstorming & Strategy Workshop (BSW22) from 30 March to 1 April 2022 addressed (1) present and future AI accelerator applications, and (2) beam requirements and accelerators for the dark sector. For both themes a number of conclusions were formulated. For example, dielectric acceleration appears to be an interesting approach for dark sector searches, calling for a suitable DLA accelerator design and experimental demonstration, while Machine Learning will become a community standard, and should be used for the design optimization of future machines. An intriguing proposal was the use of the LHC based Gamma Factory for driving a subcritical reactor with integrated waste transmutation., This project has received funding from the European Union's Horizon 2020 Research and Innovation programme under Grant Agreements No. 730871 (ARIES) and 101004730 (iFAST).

Summary of ARIES WP6 APEC & iFAST WP5.2 PAF joint Brainstorming & Strategy Workshop (BSW22) R. Assmann (DESY), C. Carli (CERN), A. Faus-Golfe (IJCLab), E. Fol (CERN), G. Franchetti (GSI & GU Frankfurt), R. Jacobsson (CERN), V. Kain (CERN), F. Kling (DESY), M.W. Krasny (LPNHE), R. Ischebeck (PSI), A. Scheinker (LANL), V. Shiltsev (FNAL), R. Tomas Garcia (CERN), F. Zimmermann (CERN) edited by the BSW2022 workshop organisers A. Faus-Golfe (IJCLab), G. Franchetti (GSI & GU Frankfurt), F. Zimmermann (CERN) The ARIES WP6 APEC & iFAST WP5.2PAF joint Brainstorming & Strategy Workshop (BSW22) from 30 March to 1 April 2022 addressed (1) present and future AI accelerator applications, and (2) beam requirements and accelerators for the dark sector. For both themes a number of conclusions were formulated. For example, dielectric acceleration appearsto be an interesting approach for dark sector searches, calling for a suitable DLA accelerator design and experimental demonstration, while Machine Learning will become a community standard, and should be used for the design optimization of future machines. An intriguing proposal was the use of the LHC based Gamma Factory for driving a subcritical reactor with integrated waste transmutation.

Accelerators R&D

The iFAST ESRW22 workshop was organized from 31 January to 8 February 2022 in virtual space. The purpose of this workshop was to bring together experts from several areas of physics that push storage rings to "extreme use", and storage-ring accelerator experts. Precision experiments as g-2 and EDM were covered in addition to ultra-low emittance light sources, future hadron accelerators, and novel concepts such as quantum computers based on stored beams, and Gamma Factories. Also participating in this meeting were experts of lepton and hadron storage rings, who addressed topics of advanced cooling, crystalline beams, and innovative beam diagnostics., ESRW22 was organized in the frame of iFAST WP5.2.

We report a preliminary FCC-ee baseline layout for optimised placement, comment on the associated beam optics and the expected performance and highlight some of the issues that remain to be addressed.

The Product Breakdown Structure (PBS) of the Future Circular Collider (FCC) is presented. The first instance of the PBS is described in its current format, and the plans to further develop the PBS in the coming months and years are outlined.

Internal note:First thoughts on the synergetic use of the FCC-ee collider and its injector complex for photon science and other applications

This document discusses the machine parameters and expected luminosity performance for the proposed future circular lepton collider FCC-ee. Particular emphasis is put on availability, physics run time, and efficiency. Key per- formance assumptions are compared with the operational experience of several past and present colliders including their injectors — LHC, LEP/LEP-2, PEP-II, KEKB, BEPCII, DAFNE, SLC and the SPS complex.

This paper sketches the glorious past and the tantalizing future of circular e⁺e⁻ colliders, highlighting some of the key issues., Proceedings of the 62th ICFA ABDW on High Luminosity Circular e$^+$e$^-$ Colliders, eeFACT2018, Hong Kong, China

In the collisions of proposed future circular colliders, like FCC-ee and CEPC, the beamstrahlung regime is classical, i.e. with an "Upsilon parameter" much smaller than 1. In the classical regime, for a constant electromagnetic field a simple relation exists between the average photon energy u and the average squared photon energy u², which is the same as for standard synchrotron radiation in storage rings. This relation breaks down, however, if the electromagnetic field is not constant in time and position, as is the case for a beam-beam collision. We derive an analytical expression for u²/u², considering the case of Gaussian-bunch collisions with crossing angle (and possibly crab waist). We compare our result with the photon energies obtained in beam-beam simulation for FCC-ee at beam energies of 45.6 GeV and 175 GeV, using the two independent codes BBWS and Guineapig. Finally, we re-optimize the FCC-ee parameters of a possible mono-chromatization scheme for direct Higgs production at 125 GeV, derived previously, by applying the refined expression for the rms photon energy., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

The Large Hadron electron Collider (LHeC) is a proposed future particle physics project colliding 60 GeV electrons from a recirculating energy-recovery linac (ERL) with 7 TeV protons stored in the LHC. The ERL technology allows for much higher beam current and, therefore, higher luminosity than a traditional linac. The high-current high-energy electron beam can also be used to drive a free electron laser (FEL). In this study we investigate the performance of an LHeC based FEL, operated in the self-amplified spontaneous emission mode, for which we choose a final electron beam energy of 40 GeV and aim for X-ray wavelengths of less than 1 ˚A. We demonstrate that such FEL would have the potential to provide orders of magnitude higher peak power, peak brilliance and average brilliance, than any other FEL either existing or proposed.

In previous work it was shown that at high proton-beam energies, synchrotron radiation is an important source of beam-screen heating, of beam-related vacuum pressure in- crease, and of primary photoelectrons, which can contribute to electron-cloud formation. We have used the Synrad3D code developed at Cornell to simulate the photon distribu- tions in the arcs of the LHC, HL-LHC, and FCC-hh. In par- ticular, for the LHC we studied the effect of the ‘sawtooth’ chamber. In this paper, specific results of the Synrad3D simulations are compared with simulations by another code, Synrad+, developed at CERN, and with experimental data from a synchrotron-light beam line at BESSY II for actual LHC vacuum-chamber samples.

Direct s-channel Higgs production in e⁺e⁻ collisions is of interest if the centre-of-mass energy spread can be reduced to be comparable to the width of the standard model Higgs boson. A monochromatization scheme could be employed in order to achieve the desired reduction, by introducing a non-zero horizontal dispersion of opposite sign for the two colliding beams at the interaction point. In high-energy high-luminosity circular colliders, beamstrahlung may increase the energy spread and bunch length. The horizontal emittance blow up due to beamstrahlung, a new effect not present in past monochromatization proposals, may degrade the performance, especially the luminosity. We study, for the FCC-ee at 62.5 GeV beam energy, how we can optimize the IP optics parameters (betax*, Dx*) along with the number of particles per bunch so as to obtain maximum luminosity at a desired target value of the collision energy spread., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

In the frame of the HL-LHC project, a few accelerator dipole and quadrupole magnets of higher critical field and/or larger aperture are being produced. The new inner triplet quadrupoles and dispersion-suppressor dipoles are made from Nb3Sn superconductor, which supports a higher field than the classical Nb-Ti magnets used for the LHC. For the longer term future, it has been proposed to replace a fraction of the Nb-Ti arc magnets in the LHC arcs with Nb3Sn magnets of higher field (e.g. 11 T), in order to boost the beam energy. Here we examine several options: the replacement of every third dipole by a stronger one, the substitution of the present Nb-Ti quadrupole by Nb3Sn combined-function magnets, the excitation of the horizontal orbit correctors, and pushing all the dipole magnets to their ultimate field. We discuss challenges and constraints, including issues related to mechanical aperture, powering, or other hardware limitations, and we estimate the potential energy reach for each of the options.

More than 30,000 accelerators are in operation worldwide. Of these less than 1% are devoted to basic research. Prominent among the latter are high-energy parti- cle colliders — powerful engines of discovery and precision measurement, which have played an essential role in establishing the standard model of particle physics. Tech- nological innovation has allowed building colliders for ever higher energy and better performance, at decreasing specific cost. New concepts will allow reaching even higher luminosities and energies throughout the coming century. One cost-effective strategy for future collider implementation is staging. For example, a future circular collider could first provide electron-positron collisions, then hadron collisions (proton-proton and heavy-ion), and, finally, the collision of muons. Indeed, cooling-free muon colliders, realizable in a number of ways, promise an attractive and energy-efficient path towards lepton collisions at tens of TeV. While plasma accelerators and dielectric accelerators offer unprecedented gradients, the construction of a high-energy collider based on these advanced technologies still faces a number of challenges. Pushing the accelerating gradi- ents or bending fields ever further, the breakdown of the QED vacuum may, or may not, set an ultimate limit to electromagnetic acceleration.

Direct s-channel Higgs production in e+e− collisions is of interest if the centre-of-mass energy spread can be reduced to be comparable to the width of the standard model Higgs boson. A monochromatization scheme could be employed in order to achieve the desired reduction, by introducing a non-zero horizontal dispersion of opposite sign for the two colliding beams at the interaction point. In high-energy high-luminosity circular colliders, beamstrahlung may in- crease the energy spread and bunch length. The horizontal emittance blow up due to beamstrahlung, a new effect not present in past monochromatization proposals, may degrade the performance, especially the luminosity. We study, for the FCC-ee at 62.5 GeV beam energy, how we can optimize the IP optics parameters ( β∗x, D∗x) along with the number of particles per bunch so as to obtain maximum luminosity at a desired target value of the collision energy spread.

A large circular e+e− collider followed by a highest-energy hadron collider in the same tunnel promises the most far-reaching physics program for the post-LHC era, and such a facility could well serve the particle physics community through the end of the 21st century. Two such projects are presently proposed: The Future Circular Collider, in a global collaboration hosted by CERN, and the combination of Circular Electron Positron Collider and Super Proton-Proton Collider, advanced by IHEP Beijing. Over the centre-of-mass energy range from 90 to about 365 GeV, covering all known heavy elements of the Standard Model, from the Z resonance to the top-quark threshold, the circular e+e− collider offers a high luminosity and exquisite energy efficiency. The high luminosity is maintained by top-up injection from a full-energy booster synchrotron. On the Z pole and at the WW threshold resonant depolarisation will allow for a precision energy calibra- tion at the ppm level. This article summarizes and compares the designs of FCC-ee and CEPC, covering the latest accelerator layouts and beam parameters, R&D plans, ongoing prototyping of key technologies, such as for the SRF system, and possible implementation schedules.

In previous work it was shown that at high proton-beam energies, synchrotron radiation is an important source of beam-screen heating, of beam-related vacuum pressure in- crease, and of primary photoelectrons, which can contribute to electron-cloud formation. We have used the Synrad3D code developed at Cornell to simulate the photon distribu- tions in the arcs of the LHC, HL-LHC, and FCC-hh. In par- ticular, for the LHC we studied the effect of the ‘sawtooth’ chamber. In this paper, specific results of the Synrad3D simulations are compared with simulations by another code, Synrad+, developed at CERN, and with experimental data from a synchrotron-light beam line at BESSY II for actual LHC vacuum-chamber samples.

In recent years, three schemes for producing low-emittance muon beams have been proposed: (1) positron-electron annihilation above threshold using a positron storage ring with a thin target, (2) laser/FEL-photon back-scattering off high-energy proton beams circulating in the LHC or FCC-hh, (3) the Gamma factory concept where partially stripped heavy ions collide with a laser pulse to directly generate muons. The Gamma factory would also deliver copious amounts of positrons which could in turn be used as source for option (1). On the other hand the top-up booster of the FCC-ee design would be an outstanding positron storage ring, at the right beam energy, around 45 GeV. After rapid acceleration the muons, produced in one of the three or four ways, could be collided in machines like the SPS, LHC or FCC-hh. Possible collider layouts are suggested.

Plasma linear colliders have been proposed as next or next-next generation energy-frontier machines for high-energy physics. I investigate possible fundamental limits on energy and luminosity of such type of colliders, considering acceleration, multiple scattering off plasma ions, intrabeam scattering, bremsstrahlung, and betatron radiation. The question of energy efficiency is also addressed.

In the frame of the HL-LHC project, a few accelerator dipole and quadrupole magnets of higher critical field and/or larger aperture are being produced. The new inner triplet quadrupoles and dispersion-suppressor dipoles are made from Nb3Sn superconductor, which supports a higher field than the classical Nb-Ti magnets used for the LHC. For the longer term future, it has been proposed to replace a fraction of the Nb-Ti arc magnets in the LHC arcs with Nb3Sn magnets of higher field (e.g. 11 T), in order to boost the beam energy. Here we examine several options: the replacement of every third dipole by a stronger one, the substitution of the present Nb-Ti quadrupole by Nb3Sn combined-function magnets, the excitation of the horizontal orbit correctors, and pushing all the dipole magnets to their ultimate field. We discuss challenges and constraints, including issues related to mechanical aperture, powering, or other hardware limitations, and we estimate the potential energy reach for each of the options.

Since the first proton collisions at the CERN Intersecting Storage Rings (ISR) hadron colliders have defined the energy frontier. Noteworthy are the conversion of the Super Proton Synchrotron (SPS) into a proton-antiproton collider, the Tevatron proton-antiproton collider, as well as the abandoned SSC in the United States, and early forward-looking studies of even higher-energy colliders. Hadron colliders are likely to determine the pace of particle-physics progress also during the next hundred years. Discoveries at past hadron colliders were essential for establishing the so-called Standard Model of particle physics. The world’s present flagship collider, the Large Hadron Collider (LHC), including its high-luminosity upgrade (HL-LHC), is set to operate through the second half of the 2030’s. Further increases of the energy reach during the 21st century require another, still more powerful hadron collider. Three options for a next hadron collider are presently under investigation. The Future Circular Collider (FCC) study, hosted by CERN, is designing a 100 TeV collider, to be installed inside a new 100 km tunnel in the Lake Geneva basin. A similar 100-km collider, called Super proton-proton Collider (SppC), is being pursued by CAS- IHEP in China. In either machine, for the first time in hadron storage rings, synchrotron radiation damping will be significant, with a damping time of the order of 1 hour. In parallel, the synchrotron-radiation power emitted inside the cold magnets becomes an important design constraint. One important difference between FCC and SppC is the magnet technol- ogy. FCC uses 16 Tesla magnets based on Nb3Sn superconductor, while SppC magnets shall be realized with cables made from iron-based high- temperature superconductor. Initially the SppC magnets are assumed to provide a more moderate dipole field of 12 T, but they can later be pushed to a final ultimate field of 24 T. A third collider presently under study is the High-Energy LHC (HE-LHC), which is a higher energy collider in the existing LHC tunnel, exploiting the FCC magnet technology in order to essentially double the LHC energy at significantly higher luminosity.

This document discusses the machine parameters and expected luminosity performance for the proposed future circular lepton collider FCC-ee. Particular emphasis is put on availability, physics run time, and efficiency. Key per- formance assumptions are compared with the operational experience of several past and present colliders including their injectors — LHC, LEP/LEP-2, PEP-II, KEKB, BEPCII, DAFNE, SLC and the SPS complex.

In recent years, three schemes for producing low-emittance muon beams have been proposed: (1) positron-electron annihilation above threshold using a positron storage ring with a thin target, (2) laser/FEL-photon back-scattering off high-energy proton beams circulating in the LHC or FCC-hh, (3) the Gamma factory concept where partially stripped heavy ions collide with a laser pulse to directly generate muons. The Gamma factory would also deliver copious amounts of positrons which could in turn be used as source for option (1). On the other hand the top-up booster of the FCC-ee design would be an outstanding positron storage ring, at the right beam energy, around 45 GeV. After rapid acceleration the muons, produced in one of the three or four ways, could be collided in machines like the SPS, LHC or FCC-hh. Possible collider layouts are suggested.

In previous work it was shown that at high proton-beam energies, synchrotron radiation is an important source of beam-screen heating, of beam-related vacuum pressure in- crease, and of primary photoelectrons, which can contribute to electron-cloud formation. We have used the Synrad3D code developed at Cornell to simulate the photon distribu- tions in the arcs of the LHC, HL-LHC, and FCC-hh. In par- ticular, for the LHC we studied the effect of the ‘sawtooth’ chamber. In this paper, specific results of the Synrad3D simulations are compared with simulations by another code, Synrad+, developed at CERN, and with experimental data from a synchrotron-light beam line at BESSY II for actual LHC vacuum-chamber samples.

A large circular e+e��� collider followed by a highest-energy hadron collider in the same tunnel promises the most far-reaching physics program for the post-LHC era, and such a facility could well serve the particle physics community through the end of the 21st century. Two such projects are presently proposed: The Future Circular Collider, in a global collaboration hosted by CERN, and the combination of Circular Electron Positron Collider and Super Proton-Proton Collider, advanced by IHEP Beijing. Over the centre-of-mass energy range from 90 to about 365 GeV, covering all known heavy elements of the Standard Model, from the Z resonance to the top-quark threshold, the circular e+e��� collider offers a high luminosity and exquisite energy efficiency. The high luminosity is maintained by top-up injection from a full-energy booster synchrotron. On the Z pole and at the WW threshold resonant depolarisation will allow for a precision energy calibra- tion at the ppm level. This article summarizes and compares the designs of FCC-ee and CEPC, covering the latest accelerator layouts and beam parameters, R&D plans, ongoing prototyping of key technologies, such as for the SRF system, and possible implementation schedules.

This document discusses the machine parameters and expected luminosity performance for the proposed future circular lepton collider FCC-ee. Particular emphasis is put on availability, physics run time, and efficiency. Key per- formance assumptions are compared with the operational experience of several past and present colliders including their injectors — LHC, LEP/LEP-2, PEP-II, KEKB, BEPCII, DAFNE, SLC and the SPS complex.

Several novel concepts could help the muon collider be- come a reality. These concepts include parametric ionization cooling, low-emittance muon production by positron anni- hilation (LEMMA scheme), production of low-emittance muon or positron beams using the Gamma Factory concept, and strategies to upgrade large accelerator complexes, like the LHC or the FCC, into a highest-energy muon collider. The muon collider workshop organized by ARIES APEC at Padua in July 2018 gathered the international community in order to review the recent progress and to formulate a common R&D strategy. Several important conclusions and recommendations were drawn.

Since the first proton collisions at the CERN Intersecting Storage Rings (ISR) hadron colliders have defined the energy frontier. Noteworthy are the conversion of the Super Proton Synchrotron (SPS) into a proton-antiproton collider, the Tevatron proton-antiproton collider, as well as the abandoned SSC in the United States, and early forward-looking studies of even higher-energy colliders. Hadron colliders are likely to determine the pace of particle-physics progress also during the next hundred years. Discoveries at past hadron colliders were essential for establishing the so-called Standard Model of particle physics. The world’s present flagship collider, the Large Hadron Collider (LHC), including its high-luminosity upgrade (HL-LHC), is set to operate through the second half of the 2030’s. Further increases of the energy reach during the 21st century require another, still more powerful hadron collider. Three options for a next hadron collider are presently under investigation. The Future Circular Collider (FCC) study, hosted by CERN, is designing a 100 TeV collider, to be installed inside a new 100 km tunnel in the Lake Geneva basin. A similar 100-km collider, called Super proton-proton Collider (SppC), is being pursued by CAS- IHEP in China. In either machine, for the first time in hadron storage rings, synchrotron radiation damping will be significant, with a damping time of the order of 1 hour. In parallel, the synchrotron-radiation power emitted inside the cold magnets becomes an important design constraint. One important difference between FCC and SppC is the magnet technol- ogy. FCC uses 16 Tesla magnets based on Nb3Sn superconductor, while SppC magnets shall be realized with cables made from iron-based high- temperature superconductor. Initially the SppC magnets are assumed to provide a more moderate dipole field of 12 T, but they can later be pushed to a final ultimate field of 24 T. A third collider presently under study is the High-Energy LHC (HE-LHC), which is a higher energy collider in the existing LHC tunnel, exploiting the FCC magnet technology in order to essentially double the LHC energy at significantly higher luminosity.

More than 30,000 accelerators are in operation worldwide. Of these less than 1% are devoted to basic research. Prominent among the latter are high-energy parti- cle colliders — powerful engines of discovery and precision measurement, which have played an essential role in establishing the standard model of particle physics. Tech- nological innovation has allowed building colliders for ever higher energy and better performance, at decreasing specific cost. New concepts will allow reaching even higher luminosities and energies throughout the coming century. One cost-effective strategy for future collider implementation is staging. For example, a future circular collider could first provide electron-positron collisions, then hadron collisions (proton-proton and heavy-ion), and, finally, the collision of muons. Indeed, cooling-free muon colliders, realizable in a number of ways, promise an attractive and energy-efficient path towards lepton collisions at tens of TeV. While plasma accelerators and dielectric accelerators offer unprecedented gradients, the construction of a high-energy collider based on these advanced technologies still faces a number of challenges. Pushing the accelerating gradi- ents or bending fields ever further, the breakdown of the QED vacuum may, or may not, set an ultimate limit to electromagnetic acceleration.

Le présent rapport résume la méthode adoptée par le groupe de l’étude FCC pour élaborer un scénario d’emplacement équilibré selon les trois piliers du projet 1) l’excellence scientifique, 2) la compatibilité territoriale et 3) les risques liés à la mise en œuvre du projet. Il décrit les exigences et les contraintes du processus d’élaboration d’un scénario et illustre par des exemples concrets la manière dont elles sont prises en compte lors de la détermination de la configuration et de l’emplacement. Le présent rapport montre également l’évolution du scénario étudié, entre le début de l’étude exploratoire en 2014 et la proposition d’un scénario de base pour l’emplacement en 2021. Ce scénario optimisé servira de référence pour approfondir les diverses composantes de l’étude de faisabilité (par exemple, études de la stabilité souterraine, propositions d’accès au site pendant les phases de construction et d’exploitation, scénarios pour la fourniture d’électricité et d’eau, approches pour la gestion des matériaux excavés, développement de potentiels de synergie locale, questions d’intégration paysagère, propositions de mesures d’accompagnement et de compensation). Après huit années de travaux d’étude par une équipe multidisciplinaire d'environ 100 membres, il apparaît que le scénario le plus équilibré est celui d’un collisionneur circulaire d’une circonférence de l’ordre de 91 km, comprenant huit sites de surface. Le processus d’élaboration itératif des scénarios est documenté dans le présent document. L’existence d’une communauté d’utilisateurs suffisamment importante s’engageant à exploiter l’infrastructure pendant plusieurs décennies est une condition préalable pour justifier une telle infrastructure de recherche. Les scénarios prévoyant un collisionneur nettement plus petit, c’est-à-dire d’une circonférence inférieure à 90 km, ne répondent pas aux exigences de performance d’un tel programme de recherche devant attirer une masse critique de scientifiques. Les propositions d’emplacement territorial adapté à des scénarios prévoyant un collisionneur d’une circonférence nettement supérieure à 91 km et comprenant plus de huit sites de surface se heurtent à des impossibilités de compatibilité territoriale et risques de réalisiation. Enfin, seules deux classes de configuration et d’emplacement avec un ensemble très limité de scénarios entrent dans le périmètre des limites de faisabilité géologique : entre 89 à 91 km avec huit sites de surface et entre 97 et 98 km avec douze sites de surface. À ce jour, seuls des scénarios à 91 km et huit sites de surface semblent pouvoir satisfaire aux trois exigences suivantes: performances scientifiques acceptables, compatibilité avec les contraintes territoriales et compatibilité avec les contraintes géologiques et techniques. On verra ici que l’un des scénarios (PA31), se détache, sur la base d’une analyse multicritères. Il est retenu pour des études approfondies qui nécessitent des activités sur place, des échanges étroites avec des services compétents dans les deux États Hôtes et avec les parties prenantes dans le périmètre de l'implantation.

Le présent rapport résume la méthode adoptée par le groupe de l’étude FCC pour élaborer un scénario d’emplacement équilibré selon les trois piliers du projet 1) l’excellence scientifique, 2) la compatibilité territoriale et 3) les risques liés à la mise en œuvre du projet. Il décrit les exigences et les contraintes du processus d’élaboration d’un scénario et illustre par des exemples concrets la manière dont elles sont prises en compte lors de la détermination de la configuration et de l’emplacement. Le présent rapport montre également l’évolution du scénario étudié, entre le début de l’étude exploratoire en 2014 et la proposition d’un scénario de base pour l’emplacement en 2021. Ce scénario optimisé servira de référence pour approfondir les diverses composantes de l’étude de faisabilité (par exemple, études de la stabilité souterraine, propositions d’accès au site pendant les phases de construction et d’exploitation, scénarios pour la fourniture d’électricité et d’eau, approches pour la gestion des matériaux excavés, développement de potentiels de synergie locale, questions d’intégration paysagère, propositions de mesures d’accompagnement et de compensation). Après huit années de travaux d’étude par une équipe multidisciplinaire d'environ 100 membres, il apparaît que le scénario le plus équilibré est celui d’un collisionneur circulaire d’une circonférence de l’ordre de 91 km, comprenant huit sites de surface. Le processus d’élaboration itératif des scénarios est documenté dans le présent document. L’existence d’une communauté d’utilisateurs suffisamment importante s’engageant à exploiter l’infrastructure pendant plusieurs décennies est une condition préalable pour justifier une telle infrastructure de recherche. Les scénarios prévoyant un collisionneur nettement plus petit, c’est-à-dire d’une circonférence inférieure à 90 km, ne répondent pas aux exigences de performance d’un tel programme de recherche devant attirer une masse critique de scientifiques. Les propositions d’emplacement territorial adapté à des scénarios prévoyant un collisionneur d’une circonférence nettement supérieure à 91 km et comprenant plus de huit sites de surface se heurtent à des impossibilités de compatibilité territoriale et risques de réalisiation. Enfin, seules deux classes de configuration et d’emplacement avec un ensemble très limité de scénarios entrent dans le périmètre des limites de faisabilité géologique : entre 89 à 91 km avec huit sites de surface et entre 97 et 98 km avec douze sites de surface. À ce jour, seuls des scénarios à 91 km et huit sites de surface semblent pouvoir satisfaire aux trois exigences suivantes: performances scientifiques acceptables, compatibilité avec les contraintes territoriales et compatibilité avec les contraintes géologiques et techniques. On verra ici que l’un des scénarios (PA31), se détache, sur la base d’une analyse multicritères. Il est retenu pour des études approfondies qui nécessitent des activités sur place, des échanges étroites avec des services compétents dans les deux États Hôtes et avec les parties prenantes dans le périmètre de l'implantation.

The design of smaller and less costly gantries for carbon ion particle therapy represents a major challenge to the diffusion of this treatment. Here we present the work done on the linear beam optics of possible gantry layouts, differing for geometry, momentum acceptance, and magnet technology, which share the use of combined function superconducting magnets with a bending field of 4T. We performed parallel-to-point and point-to-point optics matching at different magnification factors to provide two different beam sizes at the isocenter. Moreover, we considered the orbit distortion generated by magnet errors and we introduced beam position monitors and correctors. The study, together with considerations on the criteria for comparison, is the basis for the design of a novel and compact gantry for hadrontherapy., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand