TASCA Monte-Carlo Simulation Program and Program for Studying Ion-Optical Parameters of Dipole and Quadrupole Magnets from Field Maps

Ion-optical calculations are often performed as a first step when designing magnetic systems. As a second step Monte-Carlo simulations are performed of EVaporation Residue (EVR) trajectories through the separator, varying parameters like target thickness, gas pressure and magnet field. Such a program is very useful to optimize all system parameters and to plan and to prepare experiments. The new TASCA Monte-Carlo SIMulation program (TSIM) is based on the Berkeley Gas-filled Separator SIMulation program (BSIM) [1]. TSIM uses magnetic field maps of the TASCA dipole and quadrupole magnets, simulated by the program KOMPOT [2]. Trajectories are simulated in three steps. As a first step the event generator code TRIMIN (TRIM INput code) generates EVRs in the target material. The following tools and input parameters are used to characterize these EVRs: a) the energy loss for the primary beam in the target material is calculated by SRIM [3] or LISE [4]; b) Gaussian type distributions with realistic widths are assumed for the primary beam energy and angular spread; c) a beam energy is randomly chosen within the excitation function for every EVR birth. A depth in the target material corresponding to this energy is determined; d) initial position of compound nuclei trajectories and recoil energies are simulated. They are modified by neutron evaporation with a kinetic energy of ~2 MeV emitted in random direction. As an output TRIMIN gives recoil energies, position distributions and angular distributions for the EVRs inside the target, which are used as an input for the second step of the simulation process. Here EVRs are transmitted from their initial target position through remaining target material using the SRIM code [3]. The output file with recoil energy distributions and angle distributions of EVRs exiting the target serves as an input file for the last step of the TSIM calculation. This part of the simulation program, based on the original BSIM program, was adapted for TASCA taking especially into account the TASCA geometry like target position, dimensions of ducts and the detector position with variations of the detector size. Transmitting EVRs through the gas-filled separator, straggling, energy loss and charge-exchange are taken into account. Fig.1 shows simulated trajectories of EVRs from the Ca + U reaction with TASCA; i.e. the dipole magnet followed by the first horizontally focusing quad and the second vertically focusing one; see refs. [5, 6] for more information. TSIM can be used to optimize target thickness or duct shapes and it can also be used to find the best gas pressure for a specific reaction and magnet settings. Figure 1: EVR trajectory simulations in TASCA projected in the horizontal (upper panel) and vertical (lower panel)