ELECTROMECHANICAL ANALYSIS OF SCDTL STRUCTURES

Abstract

The Side Coupled Drift Tube Linac (SCDTL) i sa3G Hz accelerating structure for proton therapy linac designed for TOP-IMPLART, an Intensity Modulated Proton Linear Accelerator for Radio-Therapy. The structure is made up of short DTL accelerating tanks for low current proton beams, coupled by side coupling cavities. The purpose of this paper is to report on the analysis of electromagnetic and the thermo-mechanical behavior for the SCDTL structure. The 3D electromagnetic analysis is used to derive the power dissipation on the structure; then one can infer the temperature distribution and deformation field in order to eventually evaluate their feedback on the electromagnetic properties of the structure as, for instance, the cavity resonant frequency shift. Such a multi-physics” analysis has been performed for different supporting stem geometries in order to optimize the shunt impedance and the R/Q for SCDTL cavities. ELECTROMECHANICAL ANALYSIS The power losses (PL) in the SCDTL [1] are due to the field interaction with its copper cavity surfaces. The detuning in the resonant regime, caused by the structural deformation due to the resulting heat loading, has to be monitored. A two-ways coupling between the electromagnetic and the thermo-mechanical 3D analysis is necessary to quantify the “thermo-mechanical feedback” on the resonant frequency ( f 0). Such electromechanical analysis is carried out with ANSYS codes, exploiting the coupling technology among multi-physics solvers of the ANSYS Workbench platform. Similar analysis has been reported in Ref. [2]. The ANSYS Workbench platform has made possible a different approach summarized in the following simulation flow: 1. ANSYS HFSS (Driven modal solver): electromagnetic simulation and calculation of f 0 for unperturbed condition and PL;