Study of Supports for the Final Doublets of Atf2*

We investigated supports for the final doublets of ATF2 with vertical relative motion to the floor of final doublets below 10nm. Our calculations of relative motion were done by using data of ATF ground motion. We studied the vibratory behaviour of a steel lightweight honeycomb table as a base for fixing magnets. First, the table was fixed to the floor by four steel feet at its corners. Its first vertical resonance was at 41Hz, which induces a non negligible relative motion (5.7nm) compared to ATF2 tolerances. Modal shape measurements show that the six first resonances of the table (below 150Hz) are rigid body modes in the six degrees of freedom. The conclusion of these measurements is that the table is very rigid and well adapted for ATF2 project but the rigidity of the four steel feet is not sufficient compared to the rigidity of the table. Consequently, the table was fixed to the floor on one entire face to break these six rigid body modes by three large steel plates. The first vertical resonance was then at higher frequencies (92Hz), which show that good boundary conditions were chosen for the table. The relative motion was then low (3.5nm above 0.1Hz) compared to ATF2 tolerances. To finish, we studied the vibratory behaviour of one ATF2 FD sextupole and one ATF2 FD quadrupole with their intermediary supports made at LAPP and used to fix these magnets to the honeycomb table. The measurements showed that the final doublets with their intermediary supports were well designed because the first resonance of sextupoles and quadrupoles was at high frequency (above 100 Hz and at 76Hz respectively), which induced a small relative motion of final doublets to the floor compared to ATF2 tolerances.