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CEA, KEK and Marui Galvanizing Company have been collaborating to apply the Vertical Electropolishing (VEP) process of elliptical SRF cavities to a 704MHz single-cell ESS-type cavity, using a rotating so called and patented "Ninja" cathode. First presented results* were promising with a gradient of 27MV/m achieved, without any heat treatment applied. The performance has been pushed further since. The cavity has undergone a heat treatment at 650°C during 10h, followed by a final VEP sequence and a baking at 120°C during 48h hours. The achieved gradient at 2K was 44MV/m (power limitation), and the quality factor Q₀ exceeding 5·10¹⁰ up to 10 MV/m. The superiority of VEP compared to standard "BCP" chemical treatment is demonstrated and we intend now to scale the process to 5-Cell β=0.86 ESS cavity. We also intend to push further the performance by applying "2-step baking" (75°C and 120°C) proposed by FNAL, which was successfully applied at CEA Saclay on 1300MHz single-cell resonators with gradients above 50MV/m achieved after VEP bulk treatment., Proceedings of the 31st International Linear Accelerator Conference, LINAC2022, Liverpool, UK

Vertical Electro-Polishing (VEP) of elliptical cavities using rotating Ninja cathodes (Marui Company patented technology) has continually been improved since 2012 and successfully applied for 1300MHz multicell ILC-type resonators. The goal of the presented study is to apply this technology to 704 MHz ESS-type resonators with both better Q₀ and accelerating gradients in mind. We intend to demonstrate the superiority of VEP compared to standard Buffer Chemical Polishing (BCP), for possible applications such as MYRRHA accelerator. We describe here the promising results achieved on β=0.86 single-cell cavity after 200 µm uniform removal. The cavity quenched at 27 MV/m without any heat treatment. The surface resistance achieved was less than 5nΩ at 1.8K. Substantial performance improvement is expected after heat treatment of the cavity and additional 20 µm VEP sequence. A cathode for 5-Cell ESS cavity is concomitantly under design stage., Proceedings of the 20th International Conference on RF Superconductivity, SRF2021, East Lansing, MI, USA

International audience; The prototype IFMIF cryomodule encloses eight superconducting 175 MHz beta 0.09 Half-Wave Resonators (HWR). They are designed together with the power coupler to accelerate a high intensity deuteron beam (125 mA) from to 5 to 9 MeV. One prototype HWR and the 8 cavities to be hosted in the cryomodule have been manufactured, prepared and tested. The paper describes the phases of the cavities development, including fabrication, processing, and RF resonant frequency management. We focus on the results of the RF tests which have been performed for all bare and jacketed HWRs in a vertical cryostat.

CEA is committed to delivering a Medium Energy Beam Transfer line and a superconducting linac (SCL) for SARAF accelerator in order to accelerate 5mA beam of either protons to 35 MeV or deuterons to 40 MeV. The SCL consists in 4 cryomodules. The first two cryomodules host 6 7 half-wave resonator (HWR) low beta cavities (β = 0.09) at 176 MHz, and the last two crymodules host 7 HWR medium beta cavities (β = 0.18). The low beta prototype was qualified, the medium beta is being qualified. The results of the RF tests will be presented in this poster., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

Marui Galvanizing Co.Ltd., and CEA have been studying Vertical Electro-Polishing (VEP) on Nb single-cell accelerating superconducting accelerator cavity with the goal of mass-production and cost-reduction, in collaboration with KEK within TYL-FJPPL Particle Physics Laboratory. Marui has invented and patented a rotative cathode called ‘i-Ninja'. The version 5 has been tested for the first time in Europe at CEA Saclay. The four wings of the cathode remove efficiently, bubbles of hydrogen, and the chosen parameters make it possible to achieve better surface and uniform material removal compared to VEP with a fixed cathode. The effect of the temperature of the cavity walls on current oscillations has been precisely studied. Two single-cell cavities have been electro-polished and tested at 2 K in vertical cryostat and the results will be presented., Proceedings of the 9th Int. Particle Accelerator Conf., IPAC2018, Vancouver, BC, Canada

Mastery of Standard Buffered Chemical Polishing (with mixture of hydrofluoric, nitric and phosphoric acids) is of paramount importance for the treatment of SRF resonators with complex geometry has IFMIF half-wave resonators, in order to control accurately their frequency evolution. Furthermore, strong and unexpected asymmetry in removals has recently been observed after BCP treatment of ESS-medium beta resonators. The goal of this study is to investigate accurately influence of parameters such as surface geometry and orientation, acid temperature, agitation and their coupling on the removal rate. We will also focus on the influence of by-products such has NOx on kinetics. The mixture used is HF(40%)- HNO3(65%)-H3PO4(85%) with ratio 1-1-2.4., Proceedings of the 18th Int. Conf. on RF Superconductivity, SRF2017, Lanzhou, China

The SaTHoRI test stand (Satellite de Tests Horizontal des Résonateurs IFMIF) aims to characterize a jacketed and fully dressed cavity with its coupler and tuner. A dedicated test cryostat has been manufactured and is connected to an existing horizontal test cryostat which provides the cryogenic coolant. A RF source ' provided by the IFMIF collaboration, one of the four RF sources which will be used for the cryomodule at Rokkasho ' has been installed and commissioned at CEA. This paper describes the test stand and presents the first results., Proceedings of the 18th Int. Conf. on RF Superconductivity, SRF2017, Lanzhou, China

Marui Galvanizing Co. Ltd. has been improving Vertical Electro-Polishing (VEP) technology for Nb superconducting RF cavity in collaboration with KEK. In this collaboration, we developed a unique cathode namely Ninja cathode for VEP treatment of Nb cavities. We have already reported that longitudinal symmetry in niobium removal and surface state of a single cell cavity were improved after VEP using the Ninja cathode. In this article, we report a result of accelerating gradient evaluation for 1.3 GHz single cell RF cavity after VEP with Ninja cathode in collaboration with KEK and CEA Saclay., Proceedings of the 18th Int. Conf. on RF Superconductivity, SRF2017, Lanzhou, China

CEA Saclay in collaboration with IPN Orsay is in charge of the ESS elliptical cavities cryomodule design, prototyping and series production. Two cryomodule prototypes are being developed and will be tested at CEA Saclay before starting the series production. The main cryomodule design features are first reminded. We present the cavities and couplers test results and the achieved assembly sequences of the first medium beta cavities cryomodule demonstrator M-ECCTD. The progress on the preparation of the CEA cryomodule test station is given. The procurement status and development plan of the second high beta demonstrator H-ECCTD are also reported. Finally we give the components procurement progress and the assembly strategy of the 30 series cry-omodules to be integrated at CEA before delivery to ESS at Lund., Proceedings of the 18th Int. Conf. on RF Superconductivity, SRF2017, Lanzhou, China

The IFMIF accelerator aims to provide an accelerator-based D-Li neutron source to produce high intensity high energy neutron flux to test samples as possible candidate materials to a full lifetime of fusion energy reactors. A prototype of the low energy part of the accelerator is under construction at Rokkasho in Japan. It includes one cryomodule containing 8 half-wave resonators (HWR) operating at 175 MHz and eight focusing solenoids. This paper presents the status of the IFMIF SRF Linac., Proceedings of the 18th Int. Conf. on RF Superconductivity, SRF2017, Lanzhou, China

The ESS elliptical superconducting Linac consists of two types of 704.42 MHz cavities, medium and high beta, to accelerate the beam from 216 MeV (spoke cavity Linac) up to the final energy at 2 GeV. The last Linac optimization, called Optimus+, has been carried out taking into account the limitations of SRF cavity performance (field emission). The medium and high-beta parts of the Linac are composed of 36 and 84 elliptical cavities, with geometrical beta values of 0.67 and 0.86 respectively. This work presents the latest vertical test results on ESS medium and high beta elliptical cavity prototypes equipped with helium tank. We describe the cavity preparation procedure from buffer chemical polishing to vertical test., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

The IFMIF accelerator aims to provide an accelerator-based D-Li neutron source to produce high intensity high energy neutron flux to test samples as possible candidate materials to a full lifetime of fusion energy reactors. A prototype of the low energy part of the accelerator is under construction at Rokkasho in Japan. It includes one cryomodule containing 8 half-wave resonators (HWR) operating at 175 MHz .The first manufactured HWR has passed low power tests at 4.2K in vertical cryostat succesfully and exceeds the specifications. It has also been tested in the dedicated horizontal Sathori cryostat equiped with its cold tuning system. The serial production and qualification tests of the 8 cavities which will eventually equip the cryomodule are carried out in parallel. In this paper, we focus on the HWR preparation and test results and give a status of the manufacturing activities., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

The first ESS prototype cryomodule with medium beta cavities named M-ECCTD is being assembled at CEA Saclay. The Q curves of the 4 cavities mounted inside the cryomodule are presented, and the four power couplers have been conditioned at high power before their assembly onto the cavity string. Completion of the M-ECCTD assembly outside clean room is in progress as well as the finalization of the RF power test stand preparation. RF power tests of the M-ECCTD will be performed during summer 2017. CEA is preparing the production of the ESS medium and high beta cryomodules of the series before the test of the M-ECCTD and the contracts for the procurement of the most critical components have already been signed, Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

A 1.3 GHz single-cell niobium (Nb) coupon cavity was vertically electropolished (VEPed) with three different Ninja cathodes which were specially designed for VEP of 1.3 GHz superconducting RF elliptical (ILC/Tesla type) cavities. The cathodes were fabricated to have different surface areas and different distances between cathode surface and the equator. The Ninja cathode prepared with an enhanced cathode surface area was covered with a meshed shield to avoid bubble attack on the surface of the cavity cell. It has been turned out that the anode-cathode distance and the cathode area affect surface morphology of the equator. A smooth equator surface was obtained in the cases in which the cathode surface was geometrically close to the equator or instead the cathode surface area was sufficiently larger. Two 1.3 GHz ILC/Tesla type single-cell cavities VEPed with the Ninja cathodes and using optimized conditions showed good performance in vertical tests., Proceedings of the 28th Linear Accelerator Conf., LINAC2016, East Lansing, MI, USA

The ESS elliptical superconducting Linac consists of two types of 704.42 MHz cavities, medium and high beta, to accelerate the beam from 216 MeV (spoke cavity Linac) up to the final energy at 2 GeV. The last Linac optimization, called Optimus+ [1], has been carried out taking into account the limitations of SRF cavity performance (field emission). The medium and high-beta parts of the Linac are composed of 36 and 84 elliptical cavities, with geometrical beta values of 0.67 and 0.86 respectively. This work presents the latest vertical test results on ESS medium beta elliptical cavity prototypes. We describe the cavity preparation procedure from buffer chemical polishing to vertical test. Finally magnetic probes (Fluxgate) were installed on the cavity to determine magnetic field background during vertical test. The latest vertical test results showed that our cavity design performance are beyond requirements., Proceedings of the 28th Linear Accelerator Conf., LINAC2016, East Lansing, MI, USA

The European Spallation Source (ESS) accelerator is a large superconducting linac under construction in Lund, Sweden. A collaboration between CEA Saclay, IPN Orsay and ESS-AB is established to design the elliptical cavities cryomodule of the linac. It is foreseen to build and test two cryomodule demonstrators within the next two years. We present the design evolution and the fabrication status of the cryomodule components housing four cavities. The latest test results of two prototype cavities are shown. The cryomodule assembly process and the on-going testing infrastructures at CEA Saclay are also described., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

Two prototypes of elliptical superconducting cavities have been designed and manufactured in the frame of the French-Swedish agreement for ESS. These 5-cell cavities have a beta value of 0.86 and their frequency is 704.42 MHz. The nominal accelerating gradient on the ESS accelerator is 19.9 MV/m at 2K. We present the manufacturing status of the cavities by two different vendors as well as the specific means which have been developed for the cavity treatments performed at CEA after delivery. We emphasis the activities performed on the first bare cavities recently received at CEA such as the RF measurement and tuning operations, the cleaning and chemical treatments and the clean room assembly including high pressure rinsing. Finally, first test results at 2K in vertical cryostat are reported., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany

The prototype IFMIF cryomodule encloses eight superconducting 175 MHz beta 0.09 Half-Wave Resonators (HWR). They are designed together with the power coupler to accelerate a high intensity deuteron beam (125 mA) from to 5 to 9 MeV. One prototype HWR and the 8 cavities to be hosted in the cryomodule have been manufactured, prepared and tested. The paper describes the phases of the cavities development, including fabrication, processing, and RF resonant frequency management. We focus on the results of the RF tests which have been performed for all bare and jacketed HWRs in a vertical cryostat., Proceedings of the 19th International Conference on RF Superconductivity, SRF2019, Dresden, Germany