1. Last stage SA F7 monitor/control
Passaquieti Roberto
University of Pisa & INFN-Pisa
KAGRA-VIRGO Joint Meeting 18th Apr. 2016

2. SA Filter-7 monitor/control: origin/specs
The Filter-7 (F7) monitor/control was first introduced in Virgo in 2003 after the Superattenuators (SA) installation/integration (initially not foreseen)
Initial Virgo commissioning experienced serious problems with the SA setup monitor and control
Tight constraints with frequent mechanical contacts
Hard damping of the LF SA modes ( mHz) excited by the Locking action forces
The Virgo monitor/control architecture
Specs:
Operation in HV
Precision (~ 0.1 mm, ~ 0.1 mrad), long term efficiency and reliability
Longitudinal X, Z and yaw (ThY) d.o.f. monitor/control
3 horiz. LVDTs (Sens. ~ 130 mV / mm, noise spectr m / Hz) sharing the secondary winding with a collocoted constant gradient Maxwell magnet-coil actuators
Vertical Z d.of.
On board LVDT measuring the vertical displ.of the floating filter “crossbar” (sum of all 6 SA filter LVDT s) (Sens. ~ 570 mV / mm, noise spectr m /  Hz)
Angulat pitch (ThX) and roll (ThZ)
High precision and HV campatible bi-axial ball tiltmeter (Res.= 0.1 microrad)

3. Virgo F7: mecanical constraintsz x y
Virgo F7 working point constraints:
longitudinal X, Z d.o.f.: < ± 4 mm
vertical Y : < ± 7 mm
angular x< 3mrad, z < 8 mrad,y <10 mrad

4. Virgo F7: damping scheme
 dashpot (F7ground)
M  = -  d /d t 1 2 5 6 27 35
Virgo Marionette-Mirror TF
Marionette-Mirror TF without damp.
Marionette-Mirror Transfer Function with damping (F7-ground)
=0.5
16 mHz
32 mHz

5. Virgo F7: actuator/sensor device
Primary coil
Magnet
Secondary coils
voltage/displacement: mV/mm
force/current:  = 73 mN/A
Wide ±20 mm linear range dynamics to limit seism. noise

6. Virgo F7: monitor/control installation

7. AdV F7 monitor/control upgrade
In AdV w.r.t. Virgo most of the F7 mechanical constraints have disappeared:
the old IVC was removed from the test-masses towers
Still the increased complexity of the F7-payload system required the upgrade of the F7 monitor/control.
the actuation on the F7 body was extended to all 6 d.o.f. (Virgo x,z,thy)
Following our experience we merged the requiered 6 sensors (3 hor.+3 vert.) and 6 actuators into 6 Virgo-like collocated Maxwell pairs of magnet-coils systems
maximum force: 50mN;
max noise ~ 1 10Hz;
low force gradient: < 1%/mm (to not reintroduce seismic noise);

8. AdV: New F7 monitor/control prototyping
Space constraints induced a little re-scaling of the coil dimensions but still keeping a consistent dinamical range:
axial clearance: 12 mm;
radial clearance: a few cm;
operating volume: 10x10x10 mm3;
maximum force: 50mN;
max noise ~ 1 10Hz;
low force gradient: < 1%/mm (to not reintroduce seismic noise).
During the prototyping phase we tested new LVDT devices with a moving ferrite core in place of the moving primary coil:
experienced a better sensing but with a much reduced linearity range.
For the final set-up we came back to the Virgo F7 LVDT scheme:
secondary Maxwell coils pairs fixed to groungd, with a the primary coil fixed on the F7 body, free to move inside the operating volume of the secondary windings.
F7 monitor/control prototypes with ferrites

9. From prototype to final AdV design

10. Rendering of the AdV F7-payload system
New IVC vessel
F7 mon./contr. system