First-order ion-optics calculations for an Accelerator Mass Spectrometry system using SRIM and S3M

In this paper, we describe the transport of a simulated beam, created with the S3M beam generation module, along the real beam line of the Accelerator Mass Spectrometry (AMS) facility located at Centro Nacional de Aceleradores (CNA, Seville, Spain). The beam transport through the optical system was determined using the transfer-matrix method, which can easily calculate the beam envelopes without having to track all individual particles, evaluating the ability of such systems and saving computation time. The beam size results given by S3M were compared to the real beam size in three of the four image points that the system has (P1, P2 and P3), corresponding with the position of Faradays Cups where the 127I current was measured, obtaining a good agreement between them. This suggests that the first order approximation model is enough to simulate the optical behavior of the system. It is shown that the beam line has a focusing behavior, minimizing the beam size from ±3 mm at the exit of the ion source to ±1.09 mm at the detector's entrance window. Using the beam emittance diagram simulations, it is shown that when ions pass through the stripper, the angles of their trajectories are altered by scattering with the gas molecules and the geometrical emittance enlarges, according to Liouville's Theorem. The study presented in this work gives confidence and open new perspectives in simulations with S3M in AMS facilities contributing to the understanding of their optical behavior.