Pre-isolator Update

1. Pre-isolator Update 18th MDI Meeting F. Ramos, A. Gaddi, H. Gerwig, N. Siegrist December 17, 2010

2. “State of the art” update Yet another great example of a pre-isolator IBM/ETH Nanotechnology Center – Zurich Due to be completed by the spring of 2011 • Mechanical vibrations requirements: • Velocity less than 500 nm/s (x,y,z), below 16 Hz and less than 100 nm/s above the 16 Hz band. • Description: • Separated tool platform vibro-acoustically decoupled from building and operator platform; • Massive concrete pedestal (> 65 tons), suppressing frequencies above 25 Hz; • Tool platform with passive mechanical damping, suppressing frequencies above 3 Hz; • Active mechanical damping down to 0.5 Hz; • Operator platform decoupled from tool platform. 2

3. Quick look at the numerical simulations of the pre-isolator’s performance (LCD Note 2010-011) 3

4. FE Model Layout Lumical Beamcal QD0 SD0 MULT QF1 SF1 • Things missing in the model: • Pre-alignment mechanics • Final doublet’s geometries (using, for now, lumped masses with estimated inertias) • Final doublet’s supporting structures (girders, etc.) • Pre-isolator’s supports (using , for now, 1-D springs with appropriate stiffnesses) 4

5. Harmonic excitation in the vertical direction Vertical steady-state response at QD0 Main eigenfrequency (design) 1 Hz 51.2 Hz Inner support tube (tunned) Good performance above the first resonance peak 5

6. Harmonic excitation in the horizontal directions • Vertical steady-state response at QD0 0.05 There is a good decoupling between the different directions 0.32 6

7. Test set-up @ Point 5 (ongoing work) 7

8. Goals of the test Validate the results from the finite element model + Assess the influence of external perturbations in a noisy environment (workshop floor) + Check for energy loss mechanisms (friction, plastic deformation,...) = Evaluate the performance of a real system with the pre-isolator’s characteristics (heavy mass and low natural frequency) 8

9. 4 flexure hinges 40 ton dead-load Support beams 4 tapered steel beams 9

10. Static Deformation 205 mm 203 to 205 mm The measured static deformation matches (within 1%) the results from the finite element model. 10

11. Dynamic Performance Vertical direction – Center dead-load/support beam 12Hz 1.1Hz 6Hz A. Slaathaug – EN/MME • First resonance peak at 1.1 Hz (very close to the pre-isolator’s design goal of 1 Hz); • Good behavior up to 5 Hz; • Amplitude decreasing with ~1/ω^2 between 1.5 Hz and 5 Hz indicates very low damping of the set-up (below 1%); • Above 5 Hz, higher order resonance peaks appear and degrade the performance of the set-up; WHY? 11

12. New simulations using a detailed model of the set-up 12

13. Eigenfrequencies and Eigenmodes 1.1Hz 6.7Hz 17.8Hz 57.2Hz 13 *Main vibration modes

14. Harmonic response in the vertical direction Vertical direction – Center of dead-load/ground (excitation in the vertical direction) Vertical direction – Center of dead-load/ground (excitation in the longitudinal direction) 1 • Vibrations in the longitudinal direction induce significant movement in the vertical direction (not the case for the actual design of the pre-isolator); • Must combine the two effects to get an accurate representation of the set-up. 14

15. Combined harmonic response in the vertical direction Combine + Simulated Vertical direction – Center of dead-load Measured A. Slaathaug – EN/MME • Good match at frequencies up to 50Hz 15

16. Harmonic response in the longitudinal direction Longitudinal direction – Support beam/ground (excitation in the longitudinal direction) Simulated Measured A. Slaathaug – EN/MME • Good match at frequencies up to 40Hz. 16

17. Harmonic response in the vertical direction Vertical direction – Support beam/ground (excitation in the vertical direction) Simulated Measured A. Slaathaug – EN/MME • The model doesn’t match the measure data above 40Hz. 17

18. Summary of things to address Uncertainty in the position of the sensors Additional higher order eigenfrequencies dead-load not “rigid” Flexure hinges added ±50 mm Support structure not “rigid” A. Slaathaug – EN/MME Insufficient stiffness in the longitudinal direction Not valid if the dead-load isn’t “rigid” 18

19. Proposed changes • Replace the steel supports by concrete blocks ; • Add 4 sets of horizontal stiffeners to improve the longitudinal stiffness of the set-up; • Change the distribution of the steel blocks that make up the dead-load to improve its internal natural frequency. 19

20. Expected improvements + 1.1Hz 57.2Hz Initial design 17.8Hz 6.7Hz 1.3Hz 31.5Hz New design 72.7Hz 8.7Hz Isolation 20

21. Summary (1) • When compared with the initial simulations, the first set of measurements made on the pre-isolator test set-up showed unexpected results in the mid to high frequency range; • A refined F.E. model was created and the results match much better the measured data in low to mid range frequencies; • High frequency data calculated using the average between sensors might not be usable due to the relatively low internal eigenfrequencies of the dead-load; 21

22. Summary (2) • New measurements will be performed with a sensor placed at the center of the “dead load”, concrete blocks as a support to the set-up and horizontal stiffeners in the longitudinal direction; • The good performance of the set-up at low frequencies is promising. Nevertheless, it should be acknowledged that this design, with its several high frequency modes, is not representative of the future final design of the pre-isolator. 22

23. News • Following Holland@CERN exhibition, contacts were established with TNO Science & Industry; • They developed a 6 DOF passive/active vibration isolation table top (Kolibrie); • Includes innovations in sensor technology and placement. Current performance (transmissibility) Passive Passive+active 23