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In the Superconducting RF Test Facility (STF) in KEK, the cooldown test for the STF-2 cryomdoule with 12 cavities has been done totally three times since 2014. In 2016, the 3rd cooldown test for the STF-2 cryomodule including the capture cryomodule with 2 cavities was successfully carried out. The main achievement is the vector-sum operation with 8 cavities at average accelerating gradient of 31 MV/m as the ILC specification (2 of 8 cavities achieved 36 MV/m with piezo compensation), and the others are the measurement for Lorenz Force Detuning (LFD) and unloaded Q value, and Low Level RF (LLRF) study, etc. In this paper, the result for the STF-2 cryomodule in three cooldown tests will be presented in detail., Proceedings of the 18th Int. Conf. on RF Superconductivity, SRF2017, Lanzhou, China

This paper describes the development of a superconduct- ing quarter-wave resonator for use in an intense low-β-ion linear accelerator. The prototype cavity was fabricated from bulk Nb, inner cavity surface processing was per- formed, and vertical testing was carried out. In the vertical test, a Q-value of 8.7·10⁸ was obtained with an operating field gradient of 4.5 MV/m at a frequency of 75.5 MHz. Here, we describe the results of the performance tests and various phenomena we experienced during the tests. After the vertical tests, the helium vessel was assembled and the prototype resonator was integrated into a cryomodule. Initial cooldown testing results are described. Performance testing of the cryomodule is continuing. The situation of upgrade of the RIKEN heavy-ion RIKEN Linac (RILAC) is also reported., Proceedings of the 18th Int. Conf. on RF Superconductivity, SRF2017, Lanzhou, China

In the Superconducting RF Test Facility (STF) in KEK, the cooldown test for the STF-2 cryomodule with 12 cavities has been done totally three times since 2014. In 2016, the 3rd cooldown test for the STF-2 cryomodule including the capture cryomodule with 2 cavities, which was used for Quantum Beam Project in 2012, was successfully done. The main purpose is the vector-sum operation with 8 cavities at average accelerating gradient of 31 MV/m as the ILC specification, and the others are the measurement for Lorenz Force Detuning (LFD) and unloaded Q value, and Low Level RF (LLRF) study, etc. During 8 cavities operation, piezo actuators were used for the compensation of LFD, and the feed-forward and vector-sum control system by LLRF worked perfectly for keeping the lowest forward power and the stable flat-top of accelerating gradient. In this paper, the result for the STF-2 cryomodule in the 3rd cooldown test will be presented in detail., Proceedings of the 8th Int. Particle Accelerator Conf., IPAC2017, Copenhagen, Denmark

Development of a superconducting quarter-wavelength resonator (SC-QWR) was started at RIKEN Nishina Center to realize a low-velocity part of high-intensity ion linac. First prototype of the SC-QWR, frequency of which is 75.5 MHz, is fabricating now*. Preparation of its partial components such as outer conductor, stem, bottom plate, and top plate was almost completed, and we are now studying a low-power RF property by clamping the every components as an assembly to obtain data for frequency tuning. After the adjustment of geometry of components and welding them, surface treatment by buffered chemical polishing and high-pressure rinsing will be performed in the summer. Preparation of vertical test for the SC-QWR is also in progress at KEK. The first result of vertical test for the prototype of SC-QWR will be presented in this contribution. This work was funded by the ImPACT Program of Council for Science, Technology and Innovation (Cabinet Office, Government of Japan)., Proceedings of the 28th Linear Accelerator Conf., LINAC2016, East Lansing, MI, USA

The high power test for STF-2 cryomodule has completed successfully in 2015. Before cooldown of cryomodule, at first, the input coupler conditioning at room temperature is done with detuned cavities. After cooldown, the cavity conditioning, which is the main part in the performance test, is done by monitoring the radiation level measured at three locations around the cryomodule, and the heating and RF output at two HOM (Higher Order Mode) couplers. Consequently, it became clear the average accelerating gradient is 30 MV/m for STF-2 cryomodule (39 MV/m at max. and 15 MV/m at min.), and the second cavity string with four cavities had the significant performance degradation by heavy field emission due to the additional clean room work in the STF tunnel. As the following next steps, there are the LFD (Lorenz Force Detuning) measurement, LFD compensation by piezo, and long run for check of stable operation at high gradient. In the long run around 32 MV/m, each cavity without degradation showed the stable operation with the successful LFD compensation by piezo and RF feedback system. In this paper, the detailed test result will be presented., Proceedings of the 7th Int. Particle Accelerator Conf., IPAC2016, Busan, Korea

MHI's activities for development of Superconducting Quarter Wave Resonator (QWR) are reported. MHI has experiences of developments and fabrications of several superconducting ellipse cavities. And now MHI is developing the superconducting QWR for heavy ion accelerators., Proceedings of the 13th Heavy Ion Accelerator Technology Conference, HIAT2015, Yokohama, Japan

At KEK, a proposal is being prepared for a new linac-based proton driver that can accelerate the proton beam up to 9 GeV with 9 MW beam power and 100 mA peak current. In this report, we present the study on the front end design of the linac, which will accelerate the beam to 1.2 GeV: The baseline layout, the acceleration energy structure, RF characteristics of components, cryomodule configurations, and the detailed design of half-wave resonator 1., Proceedings of the 7th Int. Particle Accelerator Conf., IPAC2016, Busan, Korea

In RIKEN Nishina Center, for the purpose of development of elemental technology for the superconducting linear accelerator, the designing and construction of accelerator system based on superconducting quarter-wavelength resonator are carried out. The basic designs of the input coupler are as follows: The resonance frequency of the cavity is 75.5 MHz and assumed beam loading is about 1 kW. Double vacuum windows, which are disk-type, are adopted. A thermal anchor of 40 K is installed near the cold-window. The optimum positions of the cold-window and the thermal anchor depending on the effective RRR of copper-plate are being studied. In this contribution, the details of these designs will be reported. This work was funded by ImPACT Program of Council for Science, Technology and Innovation (Cabinet Office, Government of Japan)., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

As the next step of the quantum beam project, the STF2 project is in progress at KEK. Eight 9-cell SC cavities and one superconducting quardrapole magnet were assembled into the cryomodule called CM1. Four 9-cell SC cavities were assembled into the cryomodule called CM2a. These two cryomodules were connected as one unit, and the examination of completion by a prefectural government was carried out. The target value of beam energy in the STF2 accelerator is 400 MeV with a beam current of 6 mA. The first cool down test for low power level RF measurements was performed in autumn of 2014. In this paper, the assembly procedure of the STF2 cryomodules and the results of the low-power measurement are reported., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

Recently we proposed a new project aimed at intensity upgrade of uranium beams of RIKEN RIBF. In this new project, construction of a superconducting linac is planned replacing the injector cyclotron so called RRC. The RIKEN superconducting linac consists of 14 cryomodules each of which contains four quarter-wave-resonators (QWRs) in each. The QWR operates at an rf frequency of 73 MHz in the continuous wave mode with beta as low as 0.055-1.008. A coaxial probe-type RF fundamental power-coupler which transmits RF power of several kW will be utilized for beam loading of 1.3 kW/resonator at the maximum with Qext of several x10⁶. Tuning of the resonant frequency will be realized with a mechanical tuner pressing the resonator wall in the direction parallel to the beam. This year, we started a development of a test cryomodule with SC-QWRs. In this paper, design studies for a SC-QWR and its cryomodule, e.g., QWR, coupler, and, tuner will be presented together with a construction schedule of the prototype. Prototyping of a superconducting cavity and its test cryomodule was funded by ImPACT Program of Council for Science, Technology and Innovation (Cabinet Office, Government of Japan)., Proceedings of the 17th International Conference on RF Superconductivity, SRF2015, Whistler, BC, Canada

The Compact Energy Recovery Linac (cERL) project is ongoing at KEK in order to demonstrate excellent ERL performance as a future light source. The cERL injector was already constructed with its diagnostic beamline and successfully commissioned from April to June in 2013. In the next step, the cERL recirculation loop with a main superconducting linac and merger and dump sections has been constructed and its commissioning is scheduled to start in December 2013. Significant progress is expected by the IPAC14 conference date. In this presentation, we will describe the present status of the cERL including future developments., Proceedings of the 5th Int. Particle Accelerator Conf., IPAC2014, Dresden, Germany