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The last acceleration stage of the deuteron beam of the LIPAc linear accelerator is provided by eight superconducting cavities in a cryomodule (SRF Linac). Each cavity needs a magnet package, which consists of a solenoid for beam focusing and two vertical and horizontal dipole correctors for beam steering. The superconducting coils are fed by vapour cooled current leads. The beam position monitor is part of the magnet helium vessel. The series fabrication of eight sets of magnets and current leads has been performed by Elytt Energy, under CIEMAT follow-up. This paper describes the final design used for production, the main challenges addressed during fabrication, together with the quality control procedure, acceptance tests and qualification criteria to validate both the magnets and current leads. Currently some activities are being performed in the magnet helium vessels for improvement of surfaces for handling inside the clean room and reducing the risk of presence of particulate contaminations in the beam tube.

The road transportation of critical components for cryogenic cryomodules is a challenging task. Indeed, the shipping and the handling of fundamental sub-assemblies can expose these components to harmful dynamic loads that can jeopardize their structural integrity. This article has the purpose of developing a finite element multibody model capable of assessing the acceleration on a test coupler for a cavity of the Single Spoke Resonator 1 subjected to a typical road transportation trip. A multibody model consisting of rigid bodies and finite element–imported flexible bodies has been created allowing a comparison of the simulated and experimental acceleration. Afterwards, an experimental on-road test, whose set-up is described in this article, has been carried out at Fermilab with instrumented components. Being able to effectively simulate and validate the dynamic effects on such sub-assemblies makes it possible, for the future, to simulate more complex structures subject to dynamic loadings, such as the entire cryomodules during shipping. Furthermore, the results from the simulations can be used to guide the design of new suspension systems suitable for the reduction mitigation of structural vibration during the road transportation of cryomodules.

Superconducting 499.8-MHz radio frequency (rf) cavities have been proposed for the High Energy Photon Source (HEPS), a 6-GeV diffraction-limited synchrotron light source currently under construction in Beijing. Being an active third-harmonic system, two cavities shall provide 3.5-MV rf voltage and 400 kW of beam power to enable a complex rf gymnastics required by a novel injection scheme. Adopting the veteran KEKB-type 500-MHz single-cell geometry, the cavity design has been focused on optimizing its mechanical properties. Various cavity wall thickness and external stiffening mechanisms were investigated to reinforce the cavity to ensure compliance to the pressure vessel codes under different working conditions from a bare cavity to a dressed cavity in the cryomodule. Small margins on operational pressure previously reported on this type of cavity have been largely improved with slightly reduced yet acceptable frequency tunability. Extensive design optimizations have been conducted aiming for lower stress, larger elastic buckling pressure, and higher frequencies of mechanical modes to cause microphonics, while the frequency tunability, pressure sensitivity, and Lorentz force detuning were being carefully monitored. In view of the HEPS’s lifetime, cavity fatigue was examined. This constitutes a comprehensive design optimization of the 499.8-MHz single-cell superconducting cavity with improved mechanical properties.

The Proton Improvement Plan II (PIP-II) that will be installed at Fermilab is the first U.S. accelerator project that will have significant contributions from international partners. CEA joined the international collaboration in 2018, and will deliver 10 low-beta cryomodules as In-Kind Contribution to the PIP-II project, with cavities supplied by LASA-INFN and power couplers and tuning systems supplied by Fermilab. This paper presents the CEA scope of work that includes the design, manufacturing, assembly and tests of the cryomodules and the upgrade of the existing infrastructures to the PIP-II requirements., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

Present superconducting accelerators require a central refrigeration system and piping to distribute liquid helium and nitrogen. Stand-alone cryocooler-based systems are of significant interest both to scientific and industrial customers, as they allow applications at facilities where no cryogenic equipment and expertise exists, where it is undesirable to develop additional cryogenic systems, or where a mobile system that can be transported between beamlines or facilities is required. The technical challenge of this approach is to minimize the heat losses to the liquid helium so that commercially available, self-contained cryocoolers are able to handle the thermal load. This article presents an improved design for a stand-alone quarter-wave resonator (QWR) cryomodule based on commercially available cryocoolers. This cryomodule has a particular application in the Argonne Tandem Linac Accelerator System intensity upgrade project, where it will house a 72.75 MHz QWR for beam energy adjustments to experimental areas, where no helium cryogenic systems exist. The described cryomodule may also be the critical part of a turnkey system with application to material processing, semiconductor manufacturing, food irradiation, and homeland security. The development of low-heat loss peripheral components reduces the cost and widens applicability of the system. We will discuss the cryomodule and RF coupler designs, including numerical thermal and structural analyses.

Superconducting β=1 quarter-wave geometry of 166.6 MHz has been proposed as main accelerating cavities for the high-energy photon source (HEPS) storage ring. HEPS is a 6-GeV kilometer-scale synchrotron light source promising ultralow emittance currently being constructed in Beijing. A proof-of-principle cavity has been previously in-house developed and vertical-tested achieving excellent cryogenic performances. A helium jacket was subsequently designed adopting a simple structure and an integrated magnetic field shielding. The mechanical properties of the dressed cavity were largely improved focusing on pressure sensitivity, stress, and Lorentz force detuning, while frequency tunability and microphonics were carefully monitored. Elastic buckling and fatigue were also examined. The helium jacket was later fabricated and welded directly with the niobium cavity. Mounted with an input power coupler and tuners, the dressed cavity was finally assembled in a modified cryomodule and tested at both 4.2 and 2.0 K. The favored low-pressure sensitivity and small Lorentz force detuning were confirmed. Microphonics spectrum was scanned and measured, presenting good consistencies with simulation predictions. Finally, the cavity was successfully tuned to the operating frequency of 166.6 MHz at cold and its frequency could be regulated within a ±3-Hz range. This article covers the mechanical aspects in the development and horizontal cryogenic tests of the first dressed 166.6-MHz superconducting cavity.

Close to 780 superconducting 1.3-GHz accelerating cavities made of bulk niobium have been installed in the European X-ray free electron laser (E-XFEL) linear accelerator. The linac can operate at a mean gradient (Eacc) of ca. 23 MV/m in the nominal short pulse (SP) operation mode with 1.4-ms pulses and a repetition rate of 10 Hz. An R&D program at Deutsches Elektronen-Synchrotron (DESY) is ongoing since 2011 on the feasibility of a continuous wave (CW) upgrade of the E-XFEL accelerator. In this publication, a modification of the low-level radio frequency (LLRF) control system to the CW mode is presented. Currently, the control system successfully stabilizes accelerating field for the SP mode. The demanding E-XFEL specifications of 0.01% for the field amplitude and 0.01° for the phase stability are required to keep the photon beam quality for all experimental stations. The proposed modification has been implemented and tested to verify the system versatility for SP and CW operation modes. The tests were conducted for a prototype E-XFEL cryomodule XM-3. As for the series cryomodules, this prototype contains eight superconducting 1.3-GHz cavities. The results presented here confirm that the same LLRF system can be used with minor software modifications for either operation mode (CW or SP). However, the CW mode requires a more complex RF-power management and more precise control, especially when cavities operate with very high loaded quality factor ( $Q_{\mathrm{ l}}$ ) of the order of 6E7. The achieved stability for such high- $Q_{\mathrm{ l}}$ is also presented and discussed.

The Facility for Rare Isotope Beams will be completed in late 2021. We report here on the current efforts to commission the first stages of the 200-MeV/u superconducting, continuous wave heavy-ion linac. The statuses of the cryogenic plant and its distribution system, the accelerator cryomodule commissioning and operations, the ion source and front end transport development, the radio-frequency quadrupole commissioning, and thenbeam dynamics development to support high-power operation are reviewed. Plans for commissioning the remainder of the linac systems are presented.

At the Korea Multi-purpose Accelerator Complex (KOMAC), a 100-MeV high-power proton linac has been used for proton-beam irradiation services for various applications and research programs, including material science, bio-medical science, semiconductor applications, as well as nuclear physics and basic science, since commissioning of the machine in 2013. Recently, demands for fast neutrons from users in the semiconductor industries are increasing to test the semiconductor device SER (soft error rate) or SEE (single event effect). At present, we provide pilot services to users with pulsed white-spectrum neutrons (max. neutron energy ∼100 MeV) generated at the beam dump, which is made of copper. However, the neutron energy should be increased at least to 200 MeV to meet international standards such as ISO26262 or JEDEC89A. For the upgrade of the linac energy to 200 MeV, we conducted a preliminary design study, including superconducting radio-frequency (SRF) based linac structure, a neutron generation target and a neutron utilization facility. The upgrade plan for the KOMAC linac, along with the preliminary results of the design study on the superconducting linac and neutron generation facility, will be given in this paper.

RF characteristics of unloaded quality factor (Q0) and accelerating electric field (Eacc) were measured for superconducting quarter-wave resonator (QWR) in order to verify the performance. For the accurate measurement of RF characteristics, the measurement method of Q0 based RF power and RF coupling coefficient was used, and the measurement uncertainty was calculated with statistics analysis of systematic error in RF measurement system. The superconducting QWR was designed with a resonant frequency of 101.28 MHz and an accelerating electric field (Eacc) of 6 MV/m at a cavity dissipation power of 10 W in the high-intensity and energy isotope separator online device (HIE-ISOLDE) project at CERN. Q-slopes and RF coupling coefficients were measured for three QWRs at the resonant frequency 101.28 MHz. Q0 values of QWRs were measured 4.55 × 108, 3.78 × 108 and 3.17 × 108 at the 6 MV/m, respectively, and the measurement uncertainty of Q0 and Eacc were calculated 2.92% and 3.32%. Performances of superconducting QWRs were acceptable to operate the beam acceleration with consideration of cryomodule capacity in HIEISOLDE project.

SPIRAL2 is a superconducting accelerator for protons, deuterons and heavy ions delivering a maximum beam power of 200 kW at 40 MeV (for deuteron beams). 26 superconducting quarter wave cavities are operated at 4.4 K, plunged in a liquid helium bath with a drastic phase separator pressure control. Previous years have seen the development of advanced process control for cryogenics allowing to cope with high heat load dynamics thanks to an automatic heat dissipation compensation and a model based control. The latter is based on models, using the Simcryogenics library, optimized and linearised in the Programmable Logic Controllers. The SPIRAL2 operation has demonstrated that such control allows to keep the specified conditions for RF and beam operation even at levels of heat load dissipation approaching the physical limits of the cryogenic system. These developments allowed to synthesise a virtual observer of the dynamic heat load dissipated by the cavities. The present paper summarises the development of such observer based on the physical thermodynamic model and on machine learning techniques., Proceedings of the 31st International Linear Accelerator Conference, LINAC2022, Liverpool, UK

CEA is in charge of the tuning regulation systems for the SARAF-Linac project. These tuning systems will be used with LLRF to regulate the 3 Rebuncher cavities and the HWR cavities of the 4 cryomodules. These systems were already tested on the Rebuncher and Equipped Cavity Test stands to test respectively the warm and cold tunings. This paper describes the hardware and software architectures. Both tuning systems are based on Siemens PLC and EPICS-PLC communication. Ambiant temperature technology is based on SIEMENS motor controller solution whereas the cold one combines Phytron and PhyMOTION solutions., Proceedings of the 18th International Conference on Accelerator and Large Experimental Physics Control Systems, ICALEPCS2021, Shanghai, China

For several years, CEA has been involved in the development of superconducting linac for fusion related project, with the goal to develop an high flux neutrons source to test and qualify specific materials to be used in fusion power plants. In the framework of the ITER Broder Approch, a prototype cryomodule is under construction in Japan for the IFMIF/EVEDA phase(Engineering Validation and Engineering Design Activities) and the construction of the Accelerator Prototype (LIPAc) at Rokkasho, fully representative of the IFMIF low energy (9 MeV) accelerator (125 mA of D⁺beam in continuous wave). Meanwhile, the design studies of a plant called DONES (Demo Oriented NEutron Source, derived from IFMIF) started, with a superconducting linac made of 5 cryomodules. These one are based on the same principles as the one developed for IFMIF/EVEDA, but taking into account the lessons learnt from the prototype. This paper will present the similarities but also the differences between the cryomodules for IFMIF/EVEDA and DONES., Proceedings of the 20th International Conference on RF Superconductivity, SRF2021, East Lansing, MI, USA

Proceedings of the 31st International Linear Accelerator Conference, LINAC2022, Liverpool, UK 31st International Linear Accelerator Conference, LINAC2022, Liverpool, UK, 28 Aug 2022 - 2 Sep 2022; [Geneva] : JACoW Publishing, Geneva, Switzerland 747-749 (2022). doi:10.18429/JACoW-LINAC2022-THPOPA01, The goal of FLASH2020+ upgrade is to increase the energy of the FLASH accelerator, which allows the use of even shorter wavelengths, which, in turn, will allow new research. For this purpose, during the shutdown in 2022, two superconducting accelerator modules for ACC2 and ACC3 will be replaced by new ones. To fully realize the potential of these cryomodules XFEL type of waveguide distributions will be installed on them. In addition, the existing ACC4 and ACC5 cryomodules will also be equipped with the new waveguide distributions, similar XFEL type. These waveguide distributions will be modified and improved so that the machine can operate with the maximum energy due to individual power supply for each cavity. Furthermore, three RF stations will receive a new klystron waveguide distribution, which will improve the reliability of all systems. The specific waveguide distributions have been developed, produced and tested at the Waveguide Assembly and Test Facility (WATF) at DESY. All together will lead to increasing the electron beam energy from 1.25 to 1.35 GeV. This paper presents data on the production and tuning of waveguide distribution systems for the FLASH2020+ upgrade at DESY., Published by JACoW Publishing, Geneva, Switzerland, [Geneva]

CEA is committed to delivering a Medium Energy Beam Transfer line and a superconducting linac (SCL) for SARAF accelerator in order to accelerate 5 mA beam of either protons from 1.3 MeV to 35 MeV or deuterons from 2.6 MeV to 40 MeV. The SCL consists in four cryomodules. The first two identical cryomodules host 6 half-wave resonator (HWR) low beta cavities (β= 0.09) at 176 MHz. The last two identical cryomodules will host 7 HWR high-beta cavities (β = 0.18) at 176 MHz. The low-beta prototypes was qualified in 2019. Low-beta series manufacturing is on-going. The high-beta prototype was first tested in 2019 but failed. A new prototype was tested in the end of 2020. This contribution will present the results of the tests for low- and high-beta SARAF cavities, series and prototypes., Proceedings of the 20th International Conference on RF Superconductivity, SRF2021, East Lansing, MI, USA

Proceedings of the 31st International Linear Accelerator Conference, LINAC2022, Liverpool, UK 31st Linear Accelerator Conference, LINAC2022, Liverpool, United Kingdom, 28 Aug 2022 - 2 Sep 2022; [Geneva] : JACoW Publishing, Geneva, Switzerland 212-214 (2022). doi:10.18429/JACoW-LINAC2022-MOPOGE25, The Accelerator and Science and Technology Centre (ASTeC) is responsible for delivering 88 High Beta (HB) cavities as part of the European Spallation Source (ESS) facility in Sweden. The bulk Niobium Superconducting Radio Frequency (SRF) cavities operate at 704 MHz. They have been fabricated in industry and are currently being tested at Daresbury Laboratory and Deutsches Elektronen-Synchrotron (DESY). They will then be delivered to Commissariat à l’énergie atomique et aux énergies alternatives (CEA) Saclay, France for integration into cryomodules. To date, 50 cavities have been conditioned and evaluated and 36 cavities have been delivered to CEA. This paper discusses the experiences and testing of the cavities performed to date at both sites., Published by JACoW Publishing, Geneva, Switzerland, [Geneva]

The Proton Improvement Plan - II (PIP-II) project is underway at Fermilab with an international collaboration involving CEA in the development and testing of 650 MHz cryomodules. The risk analysis related to cryomodule operation proposed to add a vacuum gauge on the power coupler to prevent the untimely rupture of its ceramic. Due to the advanced design of the cryomodules, the gauge needs to be integrated inside the insulation vacuum to reduce the impact of this new modification. The lack of experience feedback on a similar operating condition requires an experimental validation before the implementation. This article details the experimental tests carried out before the approval of this solution., Proceedings of the 20th International Conference on RF Superconductivity, SRF2021, East Lansing, MI, USA

The Proton Improvement Plan II (PIP-II) that will be installed at Fermilab is the first U.S. accelerator project that will have significant contributions from international partners. CEA joined the international collaboration in 2018, and is responsible of the 650 MHz low-beta section made of 9 cryomodules, with the design of the cryostat (i.e the cryomodule without the cavities, the power couplers and the frequency tuning systems) and the manufacturing of its components, the assembly and tests of the pre-production cryomodule and the 9 series ones. This paper will present the design of the 650 MHz low-beta cryomodule., Proceedings of the 20th International Conference on RF Superconductivity, SRF2021, East Lansing, MI, USA

The prototype High Beta 650 MHz cryomodule (pHB650 CM) has been designed by an integrated design team, consisting of Fermilab (USA), CEA (France), STFC UKRI (UK), and RRCAT (India). The manufacturing and assembly of this prototype cryomodule is being done at Fermilab, whereas the production cryomodules will be manufactured and assembled by STFC-UKRI. As the first PIP-II cryomodule for which standardization was applied, the design, manufacturing and assembly of this cryomodule led to significant lessons being learnt and experiences gathered. These were incorporated into the design of the pre-production Single Spoke Resonator Type 2 cryomodule (ppSSR2 CM) and the pre-production Low Beta 650 MHz cryomodule (ppLB650 CM). This paper presents the pHB650 CM lessons learned and experiences gathered from the design to the lower coldmass assembly and how this cryomodule has a positive impact on all the next Proton Improvement Plan-II (PIP-II) cryomodules due to the standardization set up among SSR and 650 cryomodules., Proceedings of the 31st International Linear Accelerator Conference, LINAC2022, Liverpool, UK

We present here a description of field emission (FE) measurements set-up developed for elliptical cryomodules test activities at Lund Test Stand 2. A test campaign of field emission measurements has been developed and optimized during cryomodules tests. The scintillator detectors (and their respective shields), chosen for these measurements, have been characterized and optimized. The field emission application has been developed and integrated in the cryomodules tests operator interface. The Initial test results are presented and commented., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

Eight of the medium and high beta cryomodules deliv-ered to ESS by CEA are tested at CEA before delivery; the two medium and high beta prototypes and the three first of each type of the series. The goal of these tests is to validate the assembly and the performances on few cryomodules before the next cryomodules of the series are delivered to ESS. This paper summarizes the general results obtained during the tests at 2 K and at high RF power, Pmax = 1.1 MW. The cavities reach the ESS re-quirements, E_{acc} = 16.7 MV/m (Medium beta) and 19.9 MV/m (High beta) with an efficient compensation of the Lorentz detuning by the piezo tuner over the full RF pulse length of 3.6 ms at 14 Hz. After the successful tests at CEA, the first cryomodules have been shipped to ESS where the final acceptance test are performed., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

The SPIRAL2 cryogenic system has been designed to cool down and maintain stable operation conditions of the 26 LINAC superconducting resonating cavities at a temperature of 4.5 K or lower. The control system of the cryogenic system of the LINAC is based on an architecture of 20 PLCs. Through an independent network, it drives the instrumentation, the cryogenic equipment, the 26 brushless motors of the frequency tuning system, interfaces the Epics Control System, and communicates process information to the Low Level Radio Frequency, vacuum, and magnet systems. Its functions are to ensure the safety of the cryogenic system, to efficiently control the cooldown of the 19 cryomodules, to enslave the frequency tuning system for the RF operation, and to monitor and analyze the data from the process. A model based Linear Quadratic regulation controls simultaneously both phase separators the liquid helium level and pressure. This control system also makes it possible to perform a number of virtual verification tests via a simulator and a dedicated PLC used to develop advanced model based control, such as a real time heat load estimator based on a Luenberger Filter, Proceedings of the 18th International Conference on Accelerator and Large Experimental Physics Control Systems, ICALEPCS2021, Shanghai, China

The third harmonic superconducting cryomodule is being designed for the Shanghai High repetition rate XFEL and Extreme light facility (SHINE) project, which is under construction. In contrast to the European X-ray Free Electron Laser (E-XFEL) project, the 3.9 GHz cryomodules in the SHINE project will operate in the continuous wave regime with higher radio frequency average power for both cavities and couplers. We propose a 3.9 GHz fundamental power coupler with an adjustable antenna length, for satisfying the SHINE project requirements. Here, we describe the 3.9 GHz fundamental power coupler’s design considerations and power requirements for various operating modes of the SHINE Linac. We also present the results of the radio frequency simulation and optimization, including the studies on multipacting and thermal analysis of the proposed 3.9 GHz coupler.

SNRC and CEA collaborate to the upgrade of the SARAF accelerator to 5 mA CW 40 Mev deuteron and proton beams and also closely to the control system. CEA is in charge of the Control System (including cabinets) design and implementation for the Injector (upgrade), MEBT and Super Conducting Linac made up of 4 cryomodules hosting HWR cavities and solenoid packages. This paper gives a detailed presentation of the control system architecture from hardware and EPICS software points of view. The hardware standardization relies on MTCA.4 that is used for LLRF, BPM, BLM and FC controls and on Siemens PLC 1500 series for vacuum, cryogenics and interlock. CEA IRFU EPICS Environment (IEE) platform is used for the whole accelerator. IEE is based on virtual machines and our MTCA.4 solutions and enables us to have homogenous EPICS modules. It also provides a development and production workflow. SNRC has integrated IEE into a new IT network based on advanced technology. The commissioning is planned to start late summer 2021., Proceedings of the 18th International Conference on Accelerator and Large Experimental Physics Control Systems, ICALEPCS2021, Shanghai, China