ICAP 2002 Abstracts and Posters

Software correctionin the MAGNEX large acceptance spectrometer

Abstract

The large-acceptance MAGNEX spectrometer, presently under construction at the INFN, Laboratori Nazionali del Sud, Catania, is an instrument intended for the study of nuclear reactions with both stable (primary) and unstable (secondary) beams, the latter coming from the ISOL-type facility EXCYT [1]. It consists of two magnetic elements, a quadrupole and a multipurpose bending magnet, the provides focusing strength in the vertical plane and the latter both momentum dispersion and horizontal focus by rotation of the entrance and exit boundaries.

Numerical ray-tracing calculations have been done in order to optimise magnetic element shapes and field strengths [2,3]. The goal of the calculations was to provide a momentum resolving power of 2000 in a large phase space defined by a solid angle of about 50 msr and a momentum acceptance of +-10%.

Both hardware and software methods are essential in achieving the required spectrometer performances. Detailed simulations of the whole spectrometer including the trajectory reconstruction algorithm have been done. Differential algebraic techniques have been used for the computation of the transfer maps up to high-order. We found that an order of reconstruction of 10 is needed to reach the required energy resolution.

As a consequence a precise knowledge of the three-dimensional magnetic field of the particle spectrograph is necessary. Unfortunately this method is extremely sensitive to the fluctuation on the measured values of the magnetic field, especially for high orders of computation. So in our case the differential algebraic method has to be implemented with a full-3D interpolation algorithm of the field able to provide an efficient smoothing of noisy data.

We found that the trajectory reconstruction algorithm alone is not able to ensure the required energy resolution. In fact the coupling of aberrations with the detector finite resolutions together with the straggling effects that particles undergo when they cross the target and the detector put a limit on any software technique. To minimize the effects of these perturbations a careful design of the first order layout, including high order modelling of the dipole boundaries has been done. In addition a quite sophisticated detection system has been developed to fit such stringent constraints.

[1] - http://web2.lns.infn.it/celona/index.html

[2] - A.Cunsolo et al., NIM A481 (2002) 48

[3] - A.Cunsolo et al., NIM A484 (2002) 56

F.Cappuzzello, A.Cunsolo, A.Foti, A.Lazzaro, C.Nociforo, S.Orrigo, V.Shchepunov, J.S.Winfield

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