Fundamental power couplers are utilized in SRF accelerators to transfer RF power from a source to the accelerating cavities. However, the issue of thermal heat load during high-power transmission in continuous wave (CW) mode operation poses a significant challenge for power couplers. To address this concern critical modifications have been implemented within the warm sections of the cERL injector prototype coupler which was previously tested for 30kW power level in CW mode operation. The modification includes implementation of active water cooling in the warm section of the coupler and material change from copper coated stainless steel to oxygen free copper for the inner conductor. As a result, the thermal load at the inner and outer conductor was effectively mitigated during high power transmission in CW mode. Prior to the modifications, the inner conductor of the warm section reached a maximum temperature of 183°C at 27 kW power in CW mode. However, with the modified inner conductor with water cooling, the temperature was a mere 25°C. Additionally, the overall coupler temperature of the modified coupler was significantly reduced due to the conduction cooling effect applied to other components. These results underscore the effectiveness of the implemented modifications and represent a highly effective approach for mitigating thermal load in critical coupler components.

The Japan Atomic Energy Agency (JAEA) has been proposing an accelerator-driven nuclear transmutation system (ADS) as a future nuclear system. In preparation for the actual design of the CW proton linac for the JAEA-ADS, we are now prototyping a low-beta (around 0.2) single-spoke cavity. The cavity fabrication started in 2020. Most of the cavity parts were shaped in fiscal year 2020 by press-forming and machining. In 2021, we started welding the shaped cavity parts together. By preliminarily investigating the optimum welding conditions using mock-up test pieces, each cavity part was joined together with smooth welding beads. So far, we have fabricated the body section and the two end-plate sections. By measuring the resonant frequency of the temporarily assembled cavity, it was confirmed that there were no significant problems with the cavity fabrication.

Fundamental power couplers are utilized in SRF accelerators to transfer RF power from a source to the accelerating cavities. However, the issue of thermal heat load during high-power transmission in continuous wave (CW) mode operation poses a significant challenge for power couplers. To address this concern critical modifications have been implemented within the warm sections of the cERL injector prototype coupler which was previously tested for 30kW power level in CW mode operation. The modification includes implementation of active water cooling in the warm section of the coupler and material change from copper coated stainless steel to oxygen free copper for the inner conductor. As a result, the thermal load at the inner and outer conductor was effectively mitigated during high power transmission in CW mode. Prior to the modifications, the inner conductor of the warm section reached a maximum temperature of 183°C at 27 kW power in CW mode. However, with the modified inner conductor with water cooling, the temperature was a mere 25°C. Additionally, the overall coupler temperature of the modified coupler was significantly reduced due to the conduction cooling effect applied to other components. These results underscore the effectiveness of the implemented modifications and represent a highly effective approach for mitigating thermal load in critical coupler components.