Abstract
Radiofrequency cavities based on superconducting technology are widely used in particle accelerators for various applications. The cavities usually have high quality factors and hence narrow bandwidths, so the field stability is sensitive to detuning from the Lorentz force and external loads, including vibrations and helium pressure variations. If not properly controlled, the detuning can result in a serious performance degradation of a superconducting accelerator, so an understanding of the underlying detuning mechanisms can be very helpful. Recent advances in the simulation suite ace3p have enabled realistic multiphysics characterization of such complex accelerator systems on supercomputers. In this paper, we present the new capabilities in ace3p for large-scale 3D multiphysics modeling of superconducting cavities, in particular, a parallel eigensolver for determining mechanical resonances, a parallel harmonic response solver to calculate the response of a cavity to external vibrations, and a numerical procedure to decompose mechanical loads, such as from the Lorentz force or piezoactuators, into the corresponding mechanical modes. These capabilities have been used to do an extensive rf-mechanical analysis of dressed TESLA-type superconducting cavities. The simulation results and their implications for the operational stability of the Linac Coherent Light Source-II are discussed.
Highlights
Superconducting radiofrequency (SRF) cavities [1,2] are widely used to accelerate and deflect particle beams for various applications
By taking advantage of the existing finite-element framework in ACE3P, we have developed a parallel mechanical eigensolver to determine mechanical resonant frequencies and mode patterns, a parallel harmonic response solver to calculate the system response to external loads, and an analysis tool to calculate the coupling of Lorentz and external forces to the mechanical modes
For a cavity operating in an accelerator where feedback control is used to stabilize the magnitude and phase of the acceleration field, a full model of the SRF cavity is helpful to design the low-level rf system (LLRF)
Summary
Superconducting radiofrequency (SRF) cavities [1,2] are widely used to accelerate and deflect particle beams for various applications. The electromechanical cavity model developed in [8] and later advanced in [9] is based on the ordinary differential equation for a damped harmonic oscillator that is driven by internal and external forces In this model, the surface displacements of the cavity walls are expanded in terms of mechanical mode excitations and the corresponding change in the resonant frequency is computed by using the Slater perturbation technique [10]. The surface displacements of the cavity walls are expanded in terms of mechanical mode excitations and the corresponding change in the resonant frequency is computed by using the Slater perturbation technique [10] For this approach to provide accurate results, the number of modes required in the expansion needs to be determined as does the coupling of the forces to the mechanical eigenmodes.
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