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The superconducting booster linac at RIKEN (SRILAC) has ten 73-MHz quarter-wavelength resonators (QWRs) that are contained in three cryomodules. The beam commissioning of SRILAC was successfully performed in January 2020. Frequency tuning during cold operation is performed by compressing the beam port of the cavity with stainless wires and decreasing the length of each beam gap, similar to the method adopted at ANL and FRIB. However, each tuner is driven by a motor connected to gears, instead of using gas pressure. Since the intervals of the QWRs are small due to the beam dynamics, a compact design for the tuner was adopted. Each cavity was tuned to the design frequency, which required frequency changes of 3 kHz to 7 kHz depending on the cavity. Although no piezoelectric actuator is mounted on the tuning system, phase noise caused by microphonics can be sufficiently reduced by a phase-locked loop using a newly developed digital LLRF. The details of the tuning system as well as the digital LLRF will be presented., Proceedings of the 20th International Conference on RF Superconductivity, SRF2021, East Lansing, MI, USA

We will report on the current progress of High-Q/High-G R using three 1.3 GHz 9-cell TESLA shape niobium superconducting cavities at the High Energy Accelerator Research Organization (KEK). These cavities are made of bulk niobium of fine grain material with RRR >300 and have been annealed at 900 degrees for 3 hours. The cavity performances were evaluated at the Superconducting RF Test Facility at KEK (KEK-STF) after 2-step bake (70-75°C 4 h + 120°C 48 h), electropolishing at low temperature, and fast cooling procedure were applied to these cavities. In this study, obtained results will be compared with the baseline measurement for the standard recipe at KEK., Proceedings of the 20th International Conference on RF Superconductivity, SRF2021, East Lansing, MI, USA

Nb₃Sn Superconducting radiofrequency (SRF) cavities has been researched and developed at Center for Applied Superconducting Accelerator (CASA), KEK. One of effec-tive tools for research on the performance of SRF cavities is a temperature mapping (T-map) system for detecting small increases in temperature. It is a thermometer array positioned precisely on an outer surface of cavity wall. Thermometer should cover at least from the range of typi-cal operating temperature of 4 K to the transition tempera-ture of 18 K, for the Nb₃Sn SRF cavities. Therefore, car-bon resistor can not be used as a cheap thermometer due to low sensitivity at this temperature range. In this pro-ceeding, we report the results of the test for various com-mercially available diodes as a thermometer for T-map system. The sensitivity, stability and the repeatability are measured, cooled by a GM cryocooler., Proceedings of the 13th International Particle Accelerator Conference, IPAC2022, Bangkok, Thailand

The Japan Atomic Energy Agency (JAEA) has proposed an accelerator-driven subcritical system (ADS) to efficiently reduce high-level radioactive waste generated at nuclear power plants. One of the challenging R aspects of ADS is the reliability of the accelerator. In preparation for the full-scale design of the CW proton linac for the JAEA-ADS, we are now prototyping a low-beta (around 0.2) single spoke cavity. Since there is no experience in Japan in manufacturing a superconducting spoke cavity, prototyping and performance testing of the cavity is essential to ensure the feasibility of the JAEA-ADS linac. In the Japanese fiscal year 2021, we have started welding cavity parts together. By preliminarily examining the electron beam welding conditions, each press-formed niobium part was joined with a smooth welding bead. The current status of the spoke cavity prototyping for the JAEA-ADS linac is presented., Proceedings of the 31st International Linear Accelerator Conference, LINAC2022, Liverpool, UK

Vapor diffusion Nb₃Sn coating system was developed at KEK. At most 1.3GHz 3-cell cavity can be coat with the coating system. The coating system consists of a coating chamber made of Nb, a vacuum furnace for heating the Nb chamber, and a heating device of Tin in the crucible. The Nb chamber vacuum and the furnace vacuum are isolated to prevent contamination from the furnace. There is a heating device for increasing Tin vapor pressure. In this presentation, the design and construction of the coating system are reported., Proceedings of the 20th International Conference on RF Superconductivity, SRF2021, East Lansing, MI, USA

We report on an investigation of the effect of a new baking process called "furnace baking" on the quality factor. Furnace baking is performed as the final step of the cavity surface treatment; the cavities are heated in a vacuum furnace in a temperature range of 200-800C for 3 h, followed by high-pressure rinsing and radio-frequency measurement. We find the anti-Q-slope for cavities furnace-baked at a temperature range of 250 to 400C and a reduction in the residual resistance for all cavities. In particular, an extremely high Q value of 5·10¹⁰ at 16 MV/m and 2.0 K is obtained for cavities furnace-baked at 300C., Proceedings of the 20th International Conference on RF Superconductivity, SRF2021, East Lansing, MI, USA

In this contribution we report on two topics regarding recent activities on 9-cell TESLA-type cavities at the High Energy Accelerator Research Organization (KEK). First, we give an overview of the inner surface treatments and vertical test (VT) results of four fine grain 9-cell TESLA-type cavities over the last one and a half years. Secondly, we report on the upgrade of the VT DAQ system at the Superconducting RF Test Facility (STF) at KEK. In this upgrade, most components of the VT system were integrated in an EPICS control system. Based on Control System Studio (CSS) and Python a new user interface was created, improving the workflow during and after VTs at STF., Proceedings of the 20th International Conference on RF Superconductivity, SRF2021, East Lansing, MI, USA

A new superconducting booster linac, so-called SRILAC, has been constructed at the RIKEN Nishina Center to upgrade the acceleration voltage of the existing linac in order to enable further investigation of new super-heavy elements and the production of useful RIs. The SRILAC consists of 10 TEM quarter-wavelength resonators made from pure niobium sheets which operate at 4.5 K. We succeeded to develop high performance SC-cavities which satisfies the required Q₀ of 1E+9 with a wide margin. Installation of the cryomodule and He refrigerator system was completed by the end of FY2018, and the first cooling test was performed in September 2019. After various tests of the RF system, the beam acceleration was successfully commissioned in January 2020. In June 2020, the beam supply to the experiment was started. In this talk, I will report on the beam commissioning of SRILAC as well as the status of the frequency tuner and the differential pump system., Proceedings of the 20th International Conference on RF Superconductivity, SRF2021, East Lansing, MI, USA

A superconducting Compact Energy Recovery Linac (cERL) for electrons was constructed in 2013 at KEK to demonstrate energy recovery concept with low emittance, high-current CW beams of more than 10 mA for future multi-GeV ERL. Recently this cERL was operated not only to demonstrate energy recovery linac high current beam operation but also to promote and conduct a variety of industrial applications such as FEL, THz operation and Rare Isotope Production and irradiation for some materials. In this talk, I will present the status of the studies to realize the stable high-current low emittance CW beam and some applications with this beam., Proceedings of the 20th International Conference on RF Superconductivity, SRF2021, East Lansing, MI, USA

The Japan Atomic Energy Agency (JAEA) tandem booster is one of the pioneering superconducting heavy ion linac in the world. It consists of 40 QWRs with an operation frequency of 130 MHz and β_{opt}=0.1, and has potential to accelerate various ions up to Au to 10 MeV/u. The user operation was started in 1994, however, it has been suspended since the Great East Japan Earthquake in 2011. Recently, we started activities to investigate and improve the performance of the QWR cavities towards the restart of the tandem booster. In addition, design work of new lower beta cavities to improve the acceleration efficiency of heavier ions such as Uranium has been launched. Now we are surveying some operation frequencies and types of cavities including multi-gap QWR with use of electro-magnetic simulation of the cavities. In this work, the current status of the R program for the JAEA tandem facility is presented., Proceedings of the 20th International Conference on RF Superconductivity, SRF2021, East Lansing, MI, USA

Medium grain (MG) niobium disc which is directly sliced from forged ingot is newly investigated for the cavity material. An effective cost reduction can be achieved using MG niobium since rolling process which is necessary for typical niobium sheet can be skipped during MG niobium production. Grain size of MD niobium is 200-300 um which is much smaller than large grain (LG) niobium directly sliced from melted niobium ingot. Hence, the formability of MG niobium is expected to be much better than LG niobium. KEK has started fabrication of cavity using MG niobium. In this talk, characteristic of MG niobium during fabrication will be reported., Proceedings of the 20th International Conference on RF Superconductivity, SRF2021, East Lansing, MI, USA

At KEK, Nb₃Sn vapor diffusion R for High-Q has just started. We have performed Nb₃Sn coating on niobium samples and characterized these samples. We optimized the cavity coating parameter from the result of characterized samples. After optimizing the parameter, we have performed Nb₃Sn coating on a TESLA-like single-cell Nb cavity and measured cavity performance in vertical tests. This presentation presents the result of the cavity coating and performance results., Proceedings of the 20th International Conference on RF Superconductivity, SRF2021, East Lansing, MI, USA

During the preparatory phase of the International Linear Collider (ILC) project, all technical development and engineering design needed for the start of ILC construction must be completed, in parallel with intergovernmental discussion of governance and sharing of responsibilities and cost. The ILC Preparatory Laboratory (Pre-lab) is conceived to execute the technical and engineering work and to assist the intergovernmental discussion by providing relevant information upon request. It will be based on a worldwide partnership among laboratories with a headquarters hosted in Japan. This proposal, prepared by the ILC International Development Team and endorsed by the International Committee for Future Accelerators, describes an organisational framework and work plan for the Pre-lab. Elaboration, modification and adjustment should be introduced for its implementation, in order to incorporate requirements arising from the physics community, laboratories, and governmental authorities interested in the ILC., 48 pages, 5 figures

A superconducting rf (SRF) cryomodule for International Linear Collider(ILC) Main Linac equips focus/steering magnets. The magnets are "superferric" magnets with four superconducting (SC) race track coils conductively cooled from the cryomodule LHe supply pipe. The quadrupole field gradient and dipole field are 40 T/m and 0.1 T, respectively. The magnet length and iron-pole radius are 1 m and 0.045 m, respectively. It is known that dark current is generated at SRF cavities and accelerated through the following linac string. The dark current reaches and heats the SC magnets. It is estimated that the power deposition in the magnet may reach more than a few watts and temperature of the SC coils may locally reach to critical temperature of NbTi. It is important to make the magnet not reach quench with sufficient conduction cooling. We aim to realize the SC magnet which can stably operate under such condition. We plan to develop test coils made of three types of SC materials, NbTi, Nb₃Sn, and MgB₂ and study thermal characteristics and stability . We will develop a short model magnet, based on the test coil results. Here, we will present the magnet design study and the R plan., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

The pressure test was performed using a fine grain (FG) and a large grain (LG) niobium cavities. The cavity is 1.3 GHz 3-cell TESLA-like shape. The cavity was housed in a steel vessel. Water is supplied into the vessel and the cavity outside is pressurized. The applying pressure and the natural frequency of cavity were measured during the pressure test. The FG and LG cavities were deformed greatly and the pressure dropped suddenly at 3.4 MPa and 1.6 MPa, respectively. The frequency shifted up to 3.4 MHz and 1.3 MHz, respectively. There was no leak after the pressure test, so the cavity did not rupture under above pressure. The result of the pressure at LG cavity is less half than that of the FG cavity. We calculated the stress distribution in the structure by applying outer water pressure using a FEM. The maximum stress at cell when above test pressure is applied, are 146 MPa in FG and 73 MPa in LG, respectively. These stresses are similar to tensile strength of niobium specimen measure by ourselves. The result of pressure tests agrees well with the calculation., Proceedings of the 12th International Particle Accelerator Conference, IPAC2021, Campinas, SP, Brazil

In the main linac (ML) of the KEK-cERL, two superconducting cavities with high loaded Q (QL ¿ 1×107) are operated in continuous wave (CW) mode. It is important to control and suppress the microphonics detuning owing to the low bandwidth of the cavities. We evaluated the background microphonics detuning by the low level radio frequency system during the beam operation. Interestingly, a ¿field level dependence microphonics¿ phenomenon was observed on one of the cavities in the ML. Several frequency components were suddenly excited if the cavity field is above a threshold field (~3 MV/m). We found that this threshold field is probably related with the cavity quench limits despite the unclear inherent physical mechanism. Furthermore, in order to optimize the cavity resonance control system for better microphonics rejection, we have measured the mechanical transfer function between the fast piezo tuner and cavity detuning. Finally, we validated this model by comparing the model response with actual system response., Proceedings of the 63th ICFA Advanced Beam Dynamics Workshop on Energy Recovery Linacs, ERL2019, Berlin, Germany

HOM damping in the superconducting cavities has been becoming increasingly important for high current beam acceleration. Though some HOM damping devices have already been used with success at moderate currents, they have some inherent disadvantages for high current in principle. We have proposed the new type of the HOM coupler using the C-shaped wave guide (CSWG). The CSWG is structured by topologically transforming a rectangular waveguide into coaxial-like structure whose inner and outer conductors are connected with a plate. Similar to the rectangular waveguide, the CSWG has cutoff frequency whose half wave length is approximately equal to the mean circumference. This enables a smaller low-pass filter than the rectangular waveguide. Since the inner conductor can be easily cooled through the plate and the outer conductor, this prevents the connector for HOM power extraction from temperature rising. These characteristics of the CSWG-type HOM coupler can solve the disadvantages of the conventional damping devices. The properties of sufficient HOM damping were confirmed by the measurements with the CSWG-type HOM couplers equipped to the cavity models., Proceedings of the 63th ICFA Advanced Beam Dynamics Workshop on Energy Recovery Linacs, ERL2019, Berlin, Germany

A compact energy-recovery linac (cERL) have been operating since 2013 at KEK to develop critical components for ERL facility. Details of design, construction and the result of initial commissioning are already reported*. This paper will describe the details of further improvements and researches to achieve higher averaged beam current of 1 mA with continuous-wave (CW) beam pattern. At first, to keep the small beam emittance produced by 500 kV DC-photocathode gun, tuning of low-energy beam transport is essential. Also, we found some components degrades the beam quality, i.e., a non-metallic mirror which disturbed the beam orbit. Other important aspects are the measurement and mitigation of the beam losses. Combination of beam collimator and tuning of the beam optics can improve the beam halo enough to operate with 1 mA stably. The cERL has been operated with beam energy at 20 MeV or 17.5 MeV and with beam rep-rate of 1300 MHz or 162.5 MHz depending on the purpose of experiments. In each operation, the efficiency of the energy recovery was confirmed to be better than 99.9 %., 10th International Particle Accelerator Conference

A new superconducting booster linac (SRILAC) at the RIKEN heavy-ion linac is under construction. Ten 73-MHz low-beta quarter-wavelength resonators (QWRs) that operate at 4 K have been fabricated from pure niobium sheets. The cavity parts were assembled by electron beam welding. The resonant frequency for each cavity was adjusted by changing the lengths of the straight sections before welding. The performance and frequency were evaluated by vertical tests. All the cavities exceeded the design specifications of Q₀ = 1x10⁹ and E_{acc} = 6.8 MV/m. Details of the fabrication and frequency tuning as well as the performance of the cavities are reported., Proceedings of the 19th International Conference on RF Superconductivity, SRF2019, Dresden, Germany

KEK has been carried out high-Q/high-G R, to realize high performance of SRF cavities toward ILC. KEK constructed a new furnace, which is dedicated for N-infusion studies. We performed more than 10 times of N-infusion trials using 1.3 GHz single-cell cavities. Some results showed better Q-values up to high field, however, some results showed degraded Q-E slopes probably due to contamination. Improvement of accelerating gradient is not observed at moment. We have tried to clean the furnace and Nitrogen injection line to reduce the effect of contamination. Details of procedures of N-infusion, results of vertical tests, condition of the furnace including RGA spectrum and Nb sample analysis results are shown., Proceedings of the 19th International Conference on RF Superconductivity, SRF2019, Dresden, Germany

A prototype cryomodule with a superconducting quarter- wave resonator (SC QWR) has been developed at RIKEN Radioactive Isotope Beam Factory (RIBF). During the last SRF conference, we presented the performance of our first SC QWR and the first cool-down test of its cryomodule. Since then, we have continued our efforts to improve cavity performance and succeeded in recovering deteriorated Q₀. In this paper, we report what we constructed and learned from the prototype, including design issues with the cavity and its cryomodule. Design issues related to the new SC QWRs and their cryomodules for the SC linac booster of the RIKEN Heavy-Ion Linac (RILAC) are described as well., Proceedings of the 19th International Conference on RF Superconductivity, SRF2019, Dresden, Germany

Large grain (LG) niobium is directly sliced from niobium ingot. LG niobium sheet has larger crystal size than that of fine grain (FG) niobium which is forged and rolled, and normally used as the SRF cavity materials. It is expected that higher Q-value can be achieved using LG niobium sheet. And, effective reduction in material cost can be also achieved by LG niobium since forge and rolling process are skipped. On the other hand, there are some difficulties in fabrication since it has large deformation due to strong anisotropy. Cavity fabrication facility in KEK has been fabricated 1, 3 and 9-cell elliptical cavities made by LG niobium and RF tested in vertical cryostat. In this talk, the fabrication process and test results from these cavities will be presented., Proceedings of the 19th International Conference on RF Superconductivity, SRF2019, Dresden, Germany

Superconducting conduction electron guns can realize high acceleration voltage and high beam repetition. KEK has been developing the 1.3 GHz elliptical type 1.5 cell superconducting RF gun to investigate fundamental performance. The surface cleaning methods and tools were developed by using KEK SRF gun cavity #1 and surface peak electric field reached to 75 MV/m without field emission. We will apply this technique to the SRF gun cavity #2 for beam operation. The gun cavity #2 equips the helium jacket, frequency tuner cathode position adjuster to operate the electron beam. The RF structure was designed based on the gun cavity #1. The cathode rod is made of Nb. The photocathode deposited on the cathode rod will be cool down to 2K to minimize thermal emittance. The fabrication of the gun cavity #2 and helium jacket were completed. 4 times vertical tests were carried out. We will report the vertical test results and preparation of the horizontal test., Proceedings of the 19th International Conference on RF Superconductivity, SRF2019, Dresden, Germany

The staged installation and commissioning of LIPAc is ongoing at Rokkasho Fusion Institute of QST, Japan for validating the low energy section of the IFMIF deuteron accelerator up to 9 MeV. The LIPAc Superconducting Radio Frequency accelerator (SRF) cryomodule is assembled under the responsibility of the EU Home Team, and the assembly work recently started at Rokkasho in March 2019. To fulfil the cleanliness requirements for the assembly process, QST took the responsibility to prepare the infrastructure of a cleanroom and associated devices. In this present paper, the details of the preparation work for the cryomodule assembly made by QST will be presented., Proceedings of the 19th International Conference on RF Superconductivity, SRF2019, Dresden, Germany

At RIKEN Nishina Center, the RIKEN Heavy-Ion Linac (RILAC) is undergoing an upgrade of its acceleration voltage in order to allow it further investigation of new super-heavy elements. In this project, a new superconducting (SC) booster linac, so-called SRILAC, is being developed and constructed. The SRILAC consists of 10 TEM quarter-wavelength resonators made of pure niobium sheets which operate at 4 K. The target performance of each cavity is set as Q₀ of 1×10⁹ with its accelerating gradient of 6.8 MV/m. Recently we succeeded to develop high performance SC-cavities which satisfies the requirement with a wide margin. The cryomodule assembly is under way, and installation of cryomodules and He liquefaction system will be completed by the end of FY2018. The cooling-down test is scheduled in the Q1 of FY2019. This contribution makes a report on the construction status of the SRILAC., Proceedings of the 19th International Conference on RF Superconductivity, SRF2019, Dresden, Germany

The Japan Atomic Energy Agency (JAEA) is proposing an accelerator-driven subcritical system (ADS) as a future project to transmute long-lived nuclides to short-lived or stable ones. In the JAEA-ADS, a high-power proton beam of 30 MW with a final beam energy of 1.5 GeV is required with a high reliability. Furthermore, the accelerator needs to be operated in a continuous wave mode in order to be compatible with the reactor operation. As the first step toward the detailed design of the JAEA-ADS linac, we are planning to demonstrate a high-field measurement by prototyping a low-beta single spoke resonator (SSR1). We performed the electromagnetic design, and confirmed that the cavity performances of the SSR1 model with and without dimensional constraint., Proceedings of the 19th International Conference on RF Superconductivity, SRF2019, Dresden, Germany

Mitsubishi Heavy Industries Machinery Systems (MHI-MS) have developed manufacturing process of superconducting cavities for a long time. In this presentation, recent progress will be reported., Proceedings of the 19th International Conference on RF Superconductivity, SRF2019, Dresden, Germany

The new beam line for the industrial applications is constructed at the cERL (compact Energy Recovery LINAC) in KEK. In these applications, only north straight sections of cERL consisting of injector and main LINAC will be used. The test for the radio isotope production and electron beam irradiation for the materials are firstly planned with very small beam current without energy recovery., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

EUV Lithography is going to HVM (high volume manufacturing) stage with 250-W-class laser-produced plasma sources and it is important to develop a new-type EUV light source to meet future demand for higher power. Energy-recovery linac based free-electron lasers (ERL-FELs) are possible candidates of a high-power EUV light source that can distribute 1 kW power to multiple scanners simultaneously. In Japan, an ERL-FEL based EUV light source has been designed using available technologies without much development to demonstrate generation of EUV power more than 10 kW and the EUV-FEL Light Source Study Group for Industrialization has been established since 2015 to realize industrialization of the light source and the related items. For industrialization, high availability is essential as well as high power and reduction of the light source size is also required. In this paper, we will report an overview of the designed ERL-FEL light source for EUV lithography and some activities for the industrialization and describe considerations and developments for obtaining high availability and size reduction of the light source., Proceedings of the 10th Int. Particle Accelerator Conf., IPAC2019, Melbourne, Australia

A temperature and magnetic field mapping system for a single cell superconducting cavity is being developed at KEK. The mapping system is used to observe the temperature distribution and the ambient magnetic field distribution around the outer surface of the cavity. A total of 36 boards at every 10 degrees are attached on the cavity. Each board consists of 15 carbon resistors of 100 Ω at room temperature and 3 AMR sensors of X, Y and Z directions at the equator. The calibration of the resisters and AMR sensors were carefully and precisely carried out at low temperature. The data logging system using NI loggers is enabled to measure within 1 ms in the whole cavity surface. The initial test results in the vertical test of the single-cell cavity will be reported in this paper., Proceedings of the 19th International Conference on RF Superconductivity, SRF2019, Dresden, Germany

The Compact Energy Recovery Linac (cERL) at KEK is a test accelerator in order to develop key components to realize remarkable ERL performance as a future light source. After the beam commissioning in December 2013, the legal current limit has been increased step-by-step like 1 uA, 10 uA, and 100 uA. Survey for the source of beam losses has been conducted in each step, and the study on beam dynamics and tuning has also been carried out. As a next step, 1 mA operation is scheduled in February 2016. In parallel to the increase in beam current, a laser Compton scattering (LCS) system which can provide high-flux X-ray to a beamline has been successfully commissioned. We report recent progress in various kinds of beam tuning: improvement of electron gun performance, high bunch charge operation, mitigation of beam losses, LCS optics tuning and bunch compression for THz radiation., The 7th International Particle Accelerator Conference (IPAC2016)

Precise alignment of accelerator cavities is important in realizing a low emittance beam. Especially in the cases of superconducting cavities installed in a cryomodule, it is difficult to mechanically measure the position of the cavities. By measuring higher-order-modes (HOM) excited by a beam, the electrical center of the cavities can be estimated. We have developed a HOM measurement system for the injector superconducting accelerator cavities of KEK ERL test accelerator (cERL).Comparing the HOM signals of the three independent cavities in the cryomodule, we estimated the relative positioning errors of the three cavities., Proceedings of the 18th Int. Conf. on RF Superconductivity, SRF2017, Lanzhou, China

Nitrogen infusion (N-infusion) is new surface treatment technique for niobium SRF (Superconducting RF) cavities. After cooling down from 800 degree C heat treatment, a vacuum furnace and cavities are kept 120 degree C, 48 hours with about 3 Pa Nitrogen. Improvement of Q-value and accelerating gradient is expected. We used J-PARC furnace, since N-infusion procedure requires clean vacuum furnace. It has a cryo-pump and turbo molecular pumps and its vacuum system is oil-free system. Six times of N-infusion tests were carried out, while changing vacuum condition, N-infusion temperature, Nitrogen pressure, niobium material and so on. Niobium caps were mounted on cavities to avoid contaminations on inner surfaces. Some of trials were successful and vertical test results showed improvement of Q-values and accelerating gradient. However, some of them were not. Most of bad cases showed degradation of Q-values above 5 MV/m. Details of heat treatment procedure including N-infusion and vertical test results are shown in this presentation., Proceedings of the 29\textsuperscript{th} Linear Accelerator Conf., LINAC2018, Beijing, China

Higher Order Modes (HOM) absorbers for superconducting cavities have been developing at TOSHIBA in collaboration with High Energy Accelerator Research Organization (KEK) since 2015. A new prototype HOM absorber for 1.3 GHz 9-cell superconducting cavity was fabricated. An AlN lossy dielectrics cylinder was brazed with a thin copper plate, and the cool-down tests by nitrogen gas was carried out. The copper plate and a copper cylinder were joined by electron beam welding. SUS flanges were electron beam welded to both ends of the copper cylinder to fabricate a whole prototype HOM absorber. Fabrication process of the prototype HOM absorber will be presented in this paper., Proceedings of the 19th International Conference on RF Superconductivity, SRF2019, Dresden, Germany

The nitrogen infusion is the new surface treatment technique for improving the RF loss and the maximum accelerating gradient of superconducting cavity. In this process, it is important to be carried out continuously both the 800 C annealing in vacuum and 120 C nitrogen infusion without exposure to the atmosphere. The annealing serves activation process by removing the oxide layer. The in-situ nitrogen infusion system was prepared to investigate whether nitrogen infusion effect or something changes happen in the case of applying nitrogen infusion technique without removing the oxide layer. It can only introduce nitrogen into a cavity during 120 C low temperature baking and transport a cavity to the vertical test system without exposure to the atmosphere. We tried to infuse nitrogen to a single cell by keeping 120 C and 48 hours with 3 Pa nitrogen. The cavity was annealed in another furnace and applied high pressure rinsing before nitrogen infusion. The vertical test result was same Q as the normal 120 C baking without nitrogen. It suggests that oxide layer prevents infusion of nitrogen. In this poster, the in-situ nitrogen infusion system and vertical test results will be reported., Proceedings of the 29\textsuperscript{th} Linear Accelerator Conf., LINAC2018, Beijing, China