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C Brousse, J. Bosina, J. Erhart, H. Fillunger, M. Klopf, D Moser, M. Thoma, G. Konrad:
"Design of the Magnetic Shielding for NoMoS";
Poster: 66th annual meeting of the Austrian Physical Society (ÖPG), Wien; 27.09.2016 - 29.09.2016.

The new instrument NoMoS is a novel type of momentum spectrometer, currently under development at the Stefan Meyer Institute. Its main component is an R×B magnet which determines the momentum of charged particles by their drift in a circular magnetic field (about 150 mT). First measurements with neutrons are planned at the Institut-Laue-Langevin in Grenoble/France. For measurements at ultimate statistics, NoMoS will be installed at PERC (up to 6 T), a new facility at the FRM II in Garching/Germany. In order not to disturb other experiments in the vicinity of NoMoS, we have designed a variable magnetic shielding.
The finite element method (COMSOL Multiphysics) has been used to determine the most suited geometry for the shielding. The following considerations were taken into account: the magnetic stray field is suppressed to the cardiac pacemaker level (0.5 mT at less than 2.5 m), the internal magnetic field and its homogeneity (around 10−4) are not disturbed, the additional forces onto the coils are not destructive, and the shielding deals with the limited space conditions (max. width 5 m).
For experimental reasons, the magnet geometry is non-axisymmetric and therefore has to be simulated in 3D. To reduce the computing time and simultaneously increase the numerical accuracy, we simulated only one half of the geometry, taking advantage of the symmetry both of magnet and shielding. However, to study the influence of the shielding on the particle trajectories we had to simulate the full geometry. The design of the magnetic shielding for NoMoS will be presented.