1. Tracking ions inside PRISMA E.Farnea INFN Sezione di Padova

2. The PRISMA Magnetic Spectrometer E. Fioretto INFN - LNL E. Fioretto INFN - LNL 195 MeV 36 S + 208 Pb,  lab = 80 o E (a.u.)  E (a.u.) Z=16 Z=28 X Y X position Y position  E/E < 2% Z/  Z ~ 60 for Z=20 Z/  Z ~ 60 for Z=20  t < 500 ps  X = 1 mm  Y = 2 mm  t ~ 350 ps,  X = 1 mm  Y = 1 mm MCP Q Dipole MWPPAC IC Z, A,  of the recoils through combination of:  Energy  TOF    Focal plane position Direction from the start detector

3. A possible approach In principle, once a detailed 3D map of the fields is known, the transportation through PRISMA is fully determined by the entrance position and by the magnetic rigidity: Where M D, M Q are called transportation matrices. In practice, high-order polynomial expansions are used (see eg A.Lazzaro, NIM A570, 192 (2007)) to invert the matrices and determine the trajectory of the ions.

4. The present approach In the case of PRISMA, we can take a simplified approach: 1)Ideal magnetic elements are considered, reabsorbing fringe effects with a redefinition of the geometry (effective length) 2)The trajectory from the dipole to the focal plane is essentially in the dispersion plane (~20cm vertical displacement vs ~400cm path) 3)Given the size of the MCP start detector, the trajectories entering the quadrupole are essentially para-axial 4)Once the magnetic rigidity of the ions is fixed, their motion is determined by the ratio of the magnetic fields, B D /B Q rather than their exact values In practice an iterative procedure is followed

5. The iterative procedure Guess rigidity (curvature radius) Transport to quadrupole (straight line) Transport through quadrupole Transport to dipole (straight line) Transport through dipole (arc of circle) Focal plane coincides with observed? New guess rigidity Validate event with IC information No Yes C++ and FORTRAN versions available

6. Results Original algorithmPresent algorithm The results with experimental PRISMA data are of the same quality as those obtained with the original algorithm used in GSORT Few iterations per cycle are needed, fast enough for on-line (spy) implementation

7. The PRISMA presort library User just needs to create an instance of a prismaManager object prismaManager takes care of creating instances of other relevant objects Experiment-specific configuration decoded from configuration files User just asks for information to prismaManager, which will “forward the question to” the proper object Data need to be formatted in a native format (not ADF, not yet available at the time of developing the library)

8. Implementation into Narval Just completed, results soon to be seen …