BNL 56 MHz HOM Damper Fabrication at JLab

The Higher-Order Mode (HOM) Dampers for the Relativistic Heavy-Ion Collider’s (RHIC) 56 MHz cavity at Brookhaven National Laboratory (BNL) are currently being fabricated at JLab. The coaxial damper is primarily constructed with high RRR niobium, with a combination of niobium and sapphire rings as the filter assembly. Several design changes have been made with respect to the performance of a prototype damper – also fabricated at JLab – which was found to quench at low power. The production dampers are being tuned and tested in the JLab vertical test area (VTA) prior to delivery. Two HOM dampers will be delivered to BNL; they are to be used in the RHIC in November, 2015. This paper outlines the challenges faced in the fabrication and tuning process. INTRODUCTION Work on five HOM dampers was started at Niowave Inc. in early 2014. The majority of the parts were fabricated at Niowave, as was part of the assembly. The project was transferred to JLab in July 2014. The number of dampers to be delivered was revised to two out of the original five, to allow for installation during RHIC’s 2015 shutdown period (July – November). The two dampers would fit at the 225 degree and 270 degree positions on the RHIC cavity; they are named BNL01 and BNL03 respectively. The following tasks were to be carried out at JLab: Determine an assembly and fabrication sequence and plan, utilizing parts and assemblies received from Niowave Fabricate other required components Integrate design changes from BNL Conduct required welding, chemistry and inspection Tune fabricated dampers, including tests at 4K in the JLab vertical test area (VTA) Perform pressure and leak checks as required The two dampers are scheduled to be delivered to BNL in late September, 2015. DESIGN FEATURES A cut-away view of the HOM damper is shown in Fig. 1. The Loop resides inside the cavity and acts as the coupling mechanism. The damper is attached to the cavity via the NbTi flange.