arXiv subjects

Taro Konomi

Publications and source records attributed to Taro Konomi.

5 recordsLinked to original sources

arXiv2026

Two-port CW measurements on RF cavities: Notes on self-consistency assessment and indirect methods

In the case of a radio-frequency (RF) cavity with a mismatched input coupler, a direct calculation of the power dissipation in the cavity and the intrinsic quality factor from continuous-wave (CW) measurements may have uncertainty due to systematic errors. Formulae for an indirect calculation of these quantities are derived for the case of a cavity with two couplers of fixed coupling strength. In this approach, the signal from the pickup coupler is used to infer the amplitude of the "emitted wave" from the input coupler. A graphical method for self-consistency assessment is evaluated. The impact of frequency offsets is considered. Applications of these methods are presented, drawing on cold tests of superconducting cavities produced for the Facility for Rare Isotope Beams.

physics.acc-ph↗

arXiv2025

Report on first plasma processing trial for a FRIB quarter-wave resonator cryomodule

Plasma processing has been shown to help mitigate degradation of the performance of superconducting radio-frequency cavities, providing an alternative to removal of cryomodules from the accelerator for refurbishment. Studies of plasma processing for quarter-wave resonators (QWRs) and half-wave resonators (HWRs) are underway at the Facility for Rare Isotope Beams (FRIB), where a total of 324 such resonators are presently in operation. Plasma processing tests were done on several QWRs using the fundamental power coupler (FPC) to drive the plasma, with promising results. Driving the plasma with a higher-order mode allows for less mismatch at the FPC and higher plasma density. The first plasma processing trial for FRIB QWRs in a cryomodule was conducted in January 2024. Cold tests of the cryomodule showed a significant reduction in field emission X-rays after plasma processing.

physics.acc-ph↗

arXiv2025

Improved high-gradient performance for medium-velocity superconducting half-wave resonators: Surface preparation and trapped flux mitigation

A development effort to improve the performance of superconducting radio-frequency half-wave resonators (SRF HWRs) is underway at the Facility for Rare Isotope Beams (FRIB), where 220 such resonators are in operation. Our goal was to achieve an intrinsic quality factor (Q0) of >= 2E10 at an accelerating gradient (Ea) of 12 MV/m. FRIB production resonators were prepared with buffered chemical polishing (BCP). First trials on electropolishing (EP) and post-EP low temperature baking (LTB) of FRIB HWRs allowed us to reach higher gradient (15 MV/m, limited by quench) with a higher quality factor at high gradient, but Q0 was still below our goal. Trapped magnetic flux during the Dewar test was found to be a source of Q0 reduction. Three strategies were used to reduce the trapped flux: (i) adding a local magnetic shield (LMGS) to supplement the ``global'' magnetic shield around the Dewar for reduction of the ambient magnetic field; (ii) performing a ``uniform cool-down'' (UC) to reduce the thermoelectric currents; and (iii) using a compensation coil to further reduce the ambient field with active field cancellation (AFC). The LMGS improved the Q0, but not enough to reach our goal. With UC and AFC, we exceeded our goal, reaching Q0 = 2.8E10 at Ea = 12 MV/m.

physics.acc-ph↗

arXiv2024

Stable beam operation of approximately 1 mA beam under highly efficient energy recovery conditions at compact energy-recovery linac

A compact energy-recovery linac (cERL) has been un-der construction at KEK since 2009 to develop key technologies for the energy-recovery linac. The cERL began operating in 2013 to create a high-current beam with a low-emittance beam with stable continuous wave (CW) superconducting cavities. Owing to the development of critical components, such as the DC gun, superconducting cavities, and the design of ideal beam transport optics, we have successfully established approximately 1 mA stable CW operation with a small beam emittance and extremely small beam loss. This study presents the details of our key technologies and experimental results for achieving 100% energy recovery operation with extremely small beam loss during a stable, approximately 1 mA CW beam operation.

physics.acc-ph↗

arXiv2015

Present status of source development station at UVSOR-III

Construction and development of a source development station are in progress at UVSOR-III, a 750 MeV electron storage ring. It is equipped with an optical klystron type undulator system, a mode lock Ti:Sa Laser system, a dedicated beam-line for visible-VUV radiation and a parasitic beam-line for THz radiation. New light port to extract edge radiation was constructed recently. An optical cavity for a resonator free electron laser is currently being reconstructed. Some experiments such as coherent THz radiation, coherent harmonic radiation, laser Compton Scattering gamma-rays and optical vortices are in progress.

physics.acc-ph↗