MAENTOUCH Simulation Giles Quéméner – IN2P3/LPC Caen Written in C++ in the ROOT-Cern framework Allow fast simulations with small details like mu-metal wires. Expertise from Pascal Vernin – Retired from CEA Saclay Many thanks to Pascal and Gilles for their help

Simple geometry 2 boîtes imbriquées 2 plans de PM Z = 1.70 Z = 3.10 Ecran 5.5 x 3.5 m2 Centre: (1.5,0,2,1.75) x y z Bobines Helmotz (0,-0.9,1.3)

Cut View Y=cste Plans PM Z=1.7 m 2.8 m Boîte externe Z=3.1 m 10 mm acier Centre = (3.8,0,1.7) 2.8 m 0.15 m Plaques de toit 2 x 10 mm acier 0.20 m 3.4 m Murs internes 10 mm acier 2.2 m Plaque de fond 10 mm acier Plaque de répartition Coussins d’air

Cut View X=cste Plans PM Z=1.7 m Boîte externe 4.2 m Z=3.1 m 10 mm acier 4.2 m Plaques de toit 2 x 10 mm acier Murs internes 10 mm acier 3.4 m Centre = (3.8,0,1.7) Plaque de fond 10 mm acier 0.20 m Only the external blue box and the IN20 wall have been simulated so far

Principle First validation of computed stray field: comparison with the field map provided by IN20 + independent calculations by P. Vernin: First trial with standard steel showed that this material is not efficient enough.  all simulations used soft iron. No real m_r curve implemented. Instead a rather safe m_r = 2000 is used and saturation (B>1.5 T) is checked in all cells.

Combination of soft iron box and IN20 wall (mm) Wall Saturation In wall Force on coils (N) Max field (G) 6 yes - 4 8 no 1.6 G 165 1.3 G 10 173 1.2 G

Combination of soft iron box and IN20 wall Example of 4 mm box, 8 mm wall

Mu-metal Shielding Mu-metal cylinder around the PMTs: 1.1 mm thick F = 219 mm h extended from 201 to 280 mm (but almost no effect at the level of the cathode and first dynode) x x x B vs Z computed along 3 different lines 5 cm mesh

Mu-metal Shielding Bx By Bz External field: Bx=0, By=0, Bz=1G Cylinder + grid + endcap NB: B<0.14 G in whole volume for Bx=1G, By=0, Bz=0 Bx By Bz

Mu-metal Shielding Bx By Bz External field: Bx=0, By=0, Bz=1G Cylinder, no grid, no endcap NB: B<0.14 G in whole volume for Bx=1G, By=0, Bz=0 Bx By Bz

Iron + Mu-metal boxes External box, outside the shielding structure Mu-metal box, tight to the inner face of the polyethylene

10mm external box + Mu-metal box

Iron + Mu-metal boxes External box, outside the shielding structure Mu-metal box, fixed to the inner face of the polyethylene

Margins Tried different thicknesses of iron and mu-metal. Meet the specification of 0.1 G between 6 and 8 mm of iron combine with 1 to 1.5 mm of mu-metal. Current design with 10 mm iron + 1.5 mm mu-metal. ~0.5 G inside the detector could be acceptable  The design provide some margin but we are sensitive to gaps between plates at the 2 mm level