SRF Modules Research Articles

Status and upgrades of radio frequency system at Taiwan Photon Source

In order to meet the upcoming RF power requirements of TPS, a five-year upgrade project to construct a new RF station was completed in early 2022. This new RF station mainly consists of an SRF module, a 300-kW SSPA, an analog LLRF control system, RF transmission components, and accessary cooling systems. Test results of the SRF module and 300-kW SSPA met the expected performances. Also presented are the operation statistics of the two original RF stations and the ongoing upgrades. Meantime between RF failures during TPS user time reached 600 hours in 2022, while the construction and tests on DLLRF control system, power combination of klystron and SSPA, and 2-cell 1.5-GHz SRF module have all progressed well.

Mitigation of multipacting, enhanced by gas condensation on the high power input coupler of a superconducting RF module, by comprehensive warm aging

Excitation of multipacting, enhanced by gas condensation on cold surfaces of the high power input coupler in a SRF module poses the highest challenge for reliable SRF operation under high average RF power. This could prevent the light source SRF module from being operated with a desired high beam current. Off-line long-term reliability tests have been conducted for the newly constructed 500-MHz SRF KEKB type modules at an accelerating RF voltage of 1.6-MV to enable prediction of their operational reliability in the 3-GeV Taiwan Photon Source (TPS), since prediction from mere production performance by conventional horizontal test is presently unreliable. As expected, operational difficulties resulting from multipacting, enhanced by gas condensation, have been identified in the course of long-term reliability test. Our present hypothesis is that gas condensation can be slowed down by preserving the vacuum pressure at the power coupler close to that reached just after its cool down to liquid helium temperatures. This is achievable by reduction of the power coupler out-gassing rate through comprehensive warm aging. Its feasibility and effectiveness has been experimentally verified in a second long term reliability test. Our success opens the possibility to operate the SRF module free of multipacting trouble and opens a new direction to improve the operational performance of next generation SRF modules in light sources with high beam currents.

Operational Characteristics of the 200-m Flexible Cryogenic Transfer System

A proper cryogenic environment is essential for the operation of superconducting devices. A test area for the superconducting radio-frequency modules (SRF) has been established in the RF laboratory at National Synchrotron Radiation Research Center in Taiwan; these modules require much liquid helium during conditioning and performance tests; a cooling capacity of 120 W is expected for the acceptance test of the SRF module. The cryogenic environment of the test area is completed on transferring the liquid helium over a remarkable length of 205 m from the two cryogenic plants at Taiwan Light Source, with a valve box located at each end to control and to measure the cryogenic flow. Flexible cryogenic transfer lines of concentric four-tube type are chosen for both the supply of liquid helium and the return of cold helium gas. Functional examination of this long transfer system was first achieved with a 500-L Dewar in the radio-frequency laboratory; an SRF module was then installed in the test area for practical operation. The primary concern about the cryogenic transfer system is the heat loss; a measurement technique based on the principle of thermodynamics is developed and proposed herein. With the available sensors inside the valve boxes and the heaters inside the 500-L Dewar and the test SRF module, this technique has proved promissing from the measured results.

Deciphering gene expression program of MAP3K1 in mouse eyelid morphogenesis

Embryonic eyelid closure involves forward movement and ultimate fusion of the upper and lower eyelids, an essential step of mammalian ocular surface development. Although its underlying mechanism of action is not fully understood, a functional mitogen-activated protein kinase kinase kinase 1 (MAP3K1) is required for eyelid closure. Here we investigate the molecular signatures of MAP3K1 in eyelid morphogenesis. At mouse gestational day E15.5, the developmental stage immediately prior to eyelid closure, MAP3K1 expression is predominant in the eyelid leading edge (LE) and the inner eyelid (IE) epithelium. We used laser capture microdissection (LCM) to obtain highly enriched LE and IE cells from wild type and MAP3K1-deficient fetuses and analyzed genome-wide expression profiles. The gene expression data led to the identification of three distinct developmental features of MAP3K1. First, MAP3K1 modulated Wnt and Sonic hedgehog signals, actin reorganization, and proliferation only in LE but not in IE epithelium, illustrating the temporal-spatial specificity of MAP3K1 in embryogenesis. Second, MAP3K1 potentiated AP-2α expression and SRF and AP-1 activity, but its target genes were enriched for binding motifs of AP-2α and SRF, and not AP-1, suggesting the existence of novel MAP3K1-AP-2α/SRF modules in gene regulation. Third, MAP3K1 displayed variable effects on expression of lineage specific genes in the LE and IE epithelium, revealing potential roles of MAP3K1 in differentiation and lineage specification. Using LCM and expression array, our studies have uncovered novel molecular signatures of MAP3K1 in embryonic eyelid closure.

Suppression of Thermal Oscillation Induced by Liquid-Nitrogen in the CESR-Type SRF Module

A superconducting radio-frequency module of CESR type serves as the accelerating cavity at the Taiwan Light Source (TLS) in the National Synchrotron Radiation Research Center. During its routine operation at TLS beginning in 2005, a strong correlation of the movement of the cavity's frequency tuner with the temperature variation of parts cooled with liquid nitrogen was observed. After comprehensive tests on a testing SRF module, satisfactory suppression of the thermal oscillation was achieved. A phase separator with pressure regulation supplied liquid nitrogen to the SRF module, and a thermally insulated buffer tank was installed between the SRF module and the warmer of the exhausted nitrogen. Regulation of either the flow rate of nitrogen or the pressure in the buffer tank improved the temperature stability with an appropriate setting. The motion of the frequency tuner resulting from the temperature fluctuation thereby became suppressed. Identical SRF modules are currently operated in other colliders and light sources such as CESR, CLS, DLS and SSRF; this work is thus essential to improve the operation performance of the SRF module of CESR type for accelerator application.

Operational experience of the superconducting RF module at TLS

An industrially manufactured CESR-type SRF module has been routinely operated at the Taiwan Light Source (TLS) at the National Synchrotron Radiation Research Center (NSRRC) since the beginning of March 2005. The original goals of doubling the electron beam current to increase the synchrotron light intensity and of eliminating the instability caused by the interaction of the electron beams with the cavity’s higher-order modes have been successfully demonstrated. The greatest challenge to the operational reliability, the short mean time between failures, has been successfully overcome. This work reports the operational experience and status of the SRF module at TLS, toward a maximum beam current of 400 mA in decay mode, of 300 mA in top-up mode and of 200 mA in routine operation, over last six months.