A Parallel Time Domain Thermal Solver for Transient Analysis of Accelerator Cavities

Simulation of thermal effects in accelerator cavity is normally performed assuming steady state solution where a static thermal solver suffices to evaluate temperature gradients and impacts on mechanical design. However, during the rf pulse ramp up or the machine system cooldown process, when the field in the cavity changes rapidly, transient effects need to be taken into account. Although commercial software packages are available to handle these kinds of transient effects, they become less effective for solving large-scale problems arising from the fine details of a geometry or at the system scale. A time domain thermal solver has been developed in the parallel finite element multi-physics code suite ACE3P with integrated electromagnetic, thermal and mechanical modeling capabilities. The implementation takes advantage of the parallel computation infrastructure of ACE3P and shares most of the ingredients in mesh generation, matrix assembly, time advancement scheme and postprocessing. In this paper, we will outline the finite element formulation of the transient thermal problem and verify the implementation against analytical solutions and existing numerical results. The thermal solver has also been coupled to ACE3P mechanical solver, allowing stress and strain analysis during the transient stage. Application of the transient thermal solver to realistic accelerator cavities will be presented.