ILIAS Geneva 29 March 2007 Virgo suspension control progress E. Majorana INFN Mirror Suspension Control workgroup

EM-ILIAS Thermal noise Soft isolator concept: 1.very efficient passive attenuation 2.active controls for normal mode damping The usual “standard-super-attenuator” suspension …

EM-ILIAS The mission of Mirror Suspension Control workgroup: commissioning-oriented activity Virgo sensitivity (at LF !)Virgo duty-cycle In fall 2006 the majority of main ITF control issues had been addressed: - lock acquisition strategy - automatic alignment (~) -suspensions and local controls allowed all above To start noise hunting, stable operation was needed: => MSC performance started to be integrated in ITF issues

EM-ILIAS Our plan was clear thanks to the previous efforts of MSC Workgroup, during the first part of the commissioning, and to some ideas matured meanwhile. Unavoidable acknowledgments to my friends and colleagues Giovanni Losurdo and Paolo Ruggi

EM-ILIAS Disturbance rejection Sensor blending optimization Global Inverted Pendulum Control Interface with ITF Angular control strategies (Local/automatic) Beam centering All-the-possible-handles (completion needed!) Lock force re-allocation (BS) SA-chain damping from ground Vertical damping Safe-and-soft operation interfaces Noise budget Suspension control chain (read-out,numerical,digital,actuator) NOW

EM-ILIAS Focus on: - improvement of disturbance rejection - reduction of control noise through the suspension - reduction of ITF coupling with the control noise

EM-ILIAS > disturbance rejection: vertical damping needed (1/9) V-damp ON/OFF vs alignment

EM-ILIAS > disturbance rejection: vertical damping needed (2/9) One-By-One ALL OFF ALL ON O-B-O OFF O-B-O OFF No crucial Improvement during OBO OFF Test. Clear Improvement All OFF/ON Relationship with Angular fluctuations

EM-ILIAS > disturbance rejection: vertical damping needed (3/9) TOP stage Last stage ITF One-By-One (detailed)

EM-ILIAS > disturbance rejection: top stage sensor blending (4/9) ACC LVDT + HP LP cross IP f crossover = 50 mHz Trade-off between: 30 mHz (wind disturbance through ACC) and 70 mHz (  seism disturbance through LVDT) Winter issues: STD scheme and blending used until Dec 2006

EM-ILIAS mHz crossover N-arm 70 mHz crossover W-arm cavities locked independently pulling back the crossover: benefit expected unexpected ! wind-noise  seism (sea) produces angular excitation of the payload. wind (reasonably through the tilt) fake acceleration re-injected. Key solutions : - smart experiments to simulate the disturbance ; - tools to optimize the blending on-the-fly ; - other smart ideas ….

EM-ILIAS Sensor blending: TWO-SIDE OPTIMIZATION characterizing Suspension-control_vs_disturbance

EM-ILIAS hybrid filters (on-the-fly tuning) mix =0.5 : “medium” attenuation of  seism noise oldnew mix =0 (wind): not worse than old filters against  seism + tilt noise attenuation below 50 mHz oldnew mix =1 (  seism) : “strong” attenuation of  seism noise with slightly worsened tilt noise attenuation. oldnew > disturbance rejection: top stage sensors, first attempts (5/9) ACC LVDT HP  s LP  s IP HPw LPw cross + + mix The answer is worked out through a deeper analysis How much is it enough ? OUR TARGET

EM-ILIAS hybrid filters in use: noise percolation paths Calm period mix= Hz, (IP notch) Pitch excitation (payload mode) yaw bump (due to large zM correction) Large zM due to tilt disturbance through accelerometers 3 mechanisms (at least): F0_z zCorr, F0_z  x, F0_z  y > disturbance rejection: top stage sensors (6/9)

EM-ILIAS WSR7, heuristic threshold for mix adjustment in-line wind (mix 0)sea (mix 1)hic sunt leones > disturbance rejection: top stage sensors (7/9)

EM-ILIAS LP/HP optimization, given the standard actual corrector (cross) CL TF ACC LVDT HPLP mix cross IP seism mix=0.70 mix=0.90 mix=0.95 mix=1 LP/HP ratio versus CL TF Hz Two regions can be distinguished: A) LP/HP ratio plays a role attenuating LVDT sensor disturbance (  seism) B) No effect of LP/HP attenuation LVDT noise projection into zCorr 1) Hz V/sqrt(Hz) > disturbance rejection: top stage sensors (8/9)

EM-ILIAS WSR7 => WSR8 (optimization example) Hz  ms -2 HP: anti-wind (  previousWSR7 WSR8 LP: accel. comparison note: cleaner (LP+HP=1) blending allows to re-tune HP to reduce tilt re-injection patches added to LP to reduce mirror tilt excitation due to SA  seismic noise disturbance (=> heavier computation…)

EM-ILIAS WSR7 => WSR8 optimization Hz  ms -2 LP: anti-  seism previousWSR7 WSR8 accel. comparison

EM-ILIAS WSR7 => WSR8 overall tuning (mix 0-1) LP/HP mix 0 => 1 wind => sea mix 1 => 0 sea => wind A) assessing how much it is enough to enhance LP/HP to beat tilt re-injection is not easy. B) more data needed in windy-only conditions… C) optimization not significantly efficient around the crossing frequency.

EM-ILIAS Marionette locking force can be distributed to both input and End mirrors Since WSR8 the lock correction is applied to four marionettes (NI,NE,WI,WE) instead of two (NE,WE): A) reduction of direct locking force budget and B) non-linear torque negligible in case of wind (=> reduction of large zM by a factor 2 lightens gain request to AA). > disturbance rejection and noise budget: 4-marionette (9/9)

EM-ILIAS Novel strategy (…one smart idea): GLOBAL OPTIMIZATION anti-  seism plus coherent wind compensation

EM-ILIAS GIPC (Global Inverted Pendulum Control) benefits: wind disturbance rejection, lock acquisition, duty-cycle. Once the ITF is locked, the mirror position, provided by the Global Control, can be used instead of LVDTs, referred to the ground. Features: - automatic engagement (soft!) - anti-wind blending in NE-WE-BS-PR - anti-  seism in NI-WI GC (reconstructed z) LVDT Splitted anti-  seism /anti-  seism

EM-ILIAS Example1: NE_GIPC,WE_GIPC only NE “follows” NIWE “follows” WI step9

EM-ILIAS Example 2: NE_ GIPC, WE_ GIPC only step9

EM-ILIAS Example 3: NE_ GIPC, WE_ GIPC, BS_ GIPC, PR_ GIPC step9

EM-ILIAS Example3: NE_GIPC,WE_GIPC only Thanks to GIPC benefit to Automatic Alignment step9 Short suspension (i.e.beam) improvement necessary ?

EM-ILIAS A major effort necessary at LF during stormy weather! Next improvements and studies EM-MSC A curiosity: in November GIPC had already been tested but we needed to improve our knowledge and to optimize the blending

EM-ILIAS Example 4:environmental (central Bld. shock absorption)

EM-ILIAS > noise budget: actuation noise & reallocation -Suitable resistors are used to reduce coil-drivers noise (ln=lownoise/HP=highPowe to accomplish sensitivity/locking) -a trade-off with DAC noise using Emphasis/deemphasis was found. Still some work:  BS requires marionette reallocation.  WE,NE have a  seism peak that should be reduced by further force reallocation to the marionette. Too large correction directly on the mirror Low frequency component that can be moved upwards (marionette)

EM-ILIAS > synthesis: net improvement of recent activity Much more  seism and similar peak at 130 mHz In this example: - red data (now) show up much larger  seism In spite of this: => the force reallocated to the marionette is smaller

EM-ILIAS > conclusions It was mandatory to accomplish this task by considering the suspension system as a single component of the interferometer The development was a bit delayed by the requirement of checking the performance under actual environmental disturbance. Tools to emulate crucial situation have been developed. A large effort was spent on sensing optimization and on “soft operation” Now it is possible to reduce by a factor 3 the rms disturbance due to the wind, while  seism (sea) does not seem to be the main source of problems. To be done before (possibly before the MegaRun): -further technical noise reduction -improvement of short suspension performance (InjB,MC,OutB)