Fundamental and HOM Couplers

Cylindrical shell silicon carbide (SiC) higher-order-mode (HOM) beamline absorbers (BLA) were developed and high-power tested for the 591 MHz single-cell superconducting radio frequency (SRF) cavities in the Electron Storage Ring of the Electron-Ion Collider. The material properties of the BLA are crucial for HOM damping and wakefield performance. However, discrepancies were observed between the material parameters measured from small SiC samples and those of the full SiC cylinder used in the BLA, which has a radius of 137 mm. To address this, a coaxial-type test setup was designed to measure the transmission characteristics and extract the material parameters of SiC. These parameters can be used for accurate HOM analysis in the 591 MHz SRF cavity string design.

A 591 MHz superconducting RF cavity is designed for the Electron Storage Ring (ESR) of the Electron-Ion Collider (EIC), providing an accelerating voltage of up to 4 MV. Based on the requirements for Robinson stability and suppression of multipacting effects, four key physical parameters are specified: the fundamental mode frequency should be 591 MHz ± 0.1 MHz; the R/Q of the fundamental mode (591 MHz) must be less than 80 Ω; the peak electric field should be less than 40 MV/m; and the peak magnetic field should be less than 80 mT. To meet these goals with minimal computation time, we propose using the multi-objective optimization algorithm NSGA-III (Non-dominated Sorting Genetic Algorithm III) for cavity geometry design. We combined the Poisson Superfish electromagnetic simulation with the genetic algorithm in a Python environment. A Pareto-optimal front was obtained after about 50,000 iterations. The peak electric field was successfully reduced by 20% without deteriorating the other three objectives. In the future, these datasets can be analyzed using machine learning algorithms to identify patterns relevant to various axisymmetric cavities for different beam manipulation applications.

Stainless steel bellows are used to connect the 197 MHz superconducting crab cavities, to compensate for the cavity displacement due to cryogenic temperature changes. The impedance of the bellows should be evaluated for both wakefield effects and the potential high order trapped modes. In the nominal bellows one longitudinal trapped mode was found at 2252 MHz, located between two nearby harmonic frequency lines in the beam spectrum for the 0.7 A average current with 290 proton bunches. Mechanical simulations were performed to evaluate the compressed, extended, and transversely deformed states of the bellows. The trapped modes in all configurations remained well confined within the two harmonic frequencies. The ohmic losses of the trapped modes are calculated accounting for the mechanical and electrical conductivity at both 4 K and room temperature. The differences were found to be negligible, indicating that the bellows can also be used in the cold-to-warm transition between the crab cavity and the beam pipe. A preliminary short-range wakefield was calculated as a basis for subsequent long-range wakefield analysis.

A fundamental-mode power coupler (FPC) for the 591 MHz superconducting RF (SRF) cavities is currently being designed and prototyped for use in the Electron Storage Ring of the Electron-Ion Collider. Due to limitations in power source availability and in consideration of the FPC fabrication schedule, the initial high-power tests of the prototyped FPCs are planned to be conducted using a 704 MHz power source. The conditioning box to be used has been structurally modified based on the existing design. Multipacting simulations have been carried out for both the FPC and the conditioning box under high-power conditions. The simulation results will be compared with subsequent experimental tests to provide references for future high-power testing at 591 MHz.

Electron-Ion Collider (EIC) is a next generation particle accelerator to be built at Brookhaven National Laboratory, in partnership with Thomas Jefferson National Accelerator Facility. In Electron Storage Ring (ESR), 18 single-cell 591 MHz SRF cavities are required to compensate for energy loss from synchronic radiation. Effective damping of higher-order-modes (HOMs) is also critical to ensure beam stability. This paper presents the design of the single-cell 591 MHz cavity, including cavity geometry optimization, multipacting evaluation, HOM damping analysis.

In EIC Electron Storage Ring (ESR), 18 single-cell 591 MHz SRF cavities are required to compensate for up to 10 MW energy loss from synchronic radiation. There are two FPCs to deliver 800 kW RF power to each cavity. The FPC was design and under prototyping. This paper presents the FPC design and manufacture progress of FPC.

The Electron Ion Collider (EIC) pushes the limits of superconducting radio frequency systems to fulfil a variety of accelerator physics requirements. Thomas Jefferson National Accelerator Facility (TJNAF) and Brookhaven National Laboratory (BNL) in partnership are leading an international collaboration designing and building 46 independent superconducting cavity resonators comprised of 4 unique cavity types. The 4 systems all operate at 2.0 K and separately provide a range of capabilities such as compensating a 25 mrad collision crossing angle with > 11 MV of 197 MHz and 3 MV of 394 MHz deflecting voltage per crab cavity, coupling up to 800 kW of power per SRF cavity compensating the 10 MW of beam losses in the 2.5 A electron storage ring, storing and ramping the energy of the 1 A hadron storage ring, and providing the high voltage necessary to rapidly accelerate single 28 nC bunches to variable energies between 5 and 18 GeV for injection into the electron storage ring. This presentation will overview the challenges and proposed solutions for these systems and outline our future plans for the high-power superconducting cavities, 500 kW fundamental power couplers, and >60 kW beam line absorbers