Date: Thu, 4 Sep 2003 11:54:23 -0700 (PDT) From: Matthew Evans X-Sender: mevans@canopus To: Hiroaki Yamamoto cc: Biplab Bhawal , vsanni@ligo.caltech.edu, malik@ligo.caltech.edu, ambrosio@ligo.caltech.edu, kells_b@ligo.caltech.edu, lmatone@ligo.caltech.edu, franzen@ligo-la.caltech.edu, yoshida_s@ligo-la.caltech.edu, frolov_v@ligo-la.caltech.edu, lazz@ligo.caltech.edu, miyakawa_o@ligo.caltech.edu Subject: Re: tomorrow's e2e Physics meeting (an outline) MIME-Version: 1.0 X-RAVMilter-Version: 8.4.1(snapshot 20020919) (acrux) X-RAVMilter-Version: 8.4.2(snapshot 20021217) (becrux) > I would like to hear the summary of the new SimLIGO release, 030902, > which is used to develop the Matt's ASC design and to test the stability > with radiation pressure effect existing. And an accident that 3 UL coils > burned out. Here is an outline of what I will talk about: #### LIGO ASC Science Objective of the ASC - reduce seismic/control induced alignment motion to prevent sideband (and carrier) power fluctuation from deteriorating sensitivity or altering DARM -> AS_Q gain by more than 1% - initial target, alignment fluctuations < 50 urad and power fluctuations < 10 % Objective of my work on the SimLIGO ASC - understand the alignment sensing system - design a robust control system that meets the science objective - transfer that understanding and design to the commissioning team Challenges - non-diagonal sensing matrix (worse than anticipated with SB on SB) - non-constant sensing matrix (mode overlap and power fluctuations) - significant and variable radiation pressure effects - IFO inertia - simulation of burnt-out coils =) #### SimLIGO ASC Interferometer Simulation - includes radiation pressure - includes non-resonant sideband on resonant sideband contribution Overall Design - Two forms of alignment control - global: {WFS, QPD} -> input matrix -> servo filters -> mirrors http://www.ligo-wa.caltech.edu/~sigg/power_angle/newASC.pdf - local: optlevs -> mirrors Input Matrix - transforms sensor signals into angular position estimates for all mirrors (in micro-radians) - a "selective" inverse of the sensing matrix - optimized for robustness against variations in the sensing matrix - current matrix: WFS1 and dQPD -> dETM and dITM WFS3 and cQPD -> cETM and cITM WFS2a -> RM WFS2b -> BS Servo Filters - compensate for mechanical system - can be different each mirror (i.e., OL on or off?) - current servos dETM and dITM : UGF ~ 5 Hz, disabled optical levers cETM and cITM : UGF ~ 5 Hz, disabled optical levers RM : crosses optical lever below 0.1 Hz BS : crosses optical lever below 0.1 Hz Radiation Pressure (a.k.a., Optical Spring) Compensations - no explicit compensation - robust servo design - large gain margins - UGF away from resonance frequency - will add explicit compensation soon to allow for more sophisticated servo design (needed at the sites) #### How SimLIGO ASC helps LIGO ASC The LIGO ASC system is currently in a state of flux. A good deal of work is going into designing and commissioning a functional system, but there have been a number of stumbling blocks along the way. SimLIGO offers a low cost and rapidly changeable testbed for ASC systems. The work on SimLIGO, if performed in conjunction with the efforts at the site, should help to speed the development of a robust ASC system which will improve interferometer sensitivity and duty cycle. -Matt