8/13/2004 Stefan Ballmer, MIT / LIGO Hanford 1 Length and angular control loops in LIGO Stefan Ballmer Massachusetts Institute of Technology LIGO Hanford Observatory

8/13/2004 Stefan Ballmer, MIT / LIGO Hanford 2 Goal Overview of the LSC and ASC control loop fabric Find corresponding data channels (error / control signal) Find corresponding filters of the control system

8/13/2004 Stefan Ballmer, MIT / LIGO Hanford 3 Reading the signals Laser antisymmetric signal symmetric signal pickoff signal transmitted power photodiodes LyLy LxLx lxlx lyly Frequency Response of the LIGO Interferometer T pdf

8/13/2004 Stefan Ballmer, MIT / LIGO Hanford 4 Length Sensing and Control 4 loops: DARM CARM/CM MICH PRC

8/13/2004 Stefan Ballmer, MIT / LIGO Hanford 5 The DARM loop SensingCavity pole (~90Hz,~180Hz for H2) Error signalAS_Q Control filter bankH1:LSC-DARM Control signalDARM_CTRL Actuation calibration (S3) (H1) ~1.7nm/ct, Pendulum at 0.76Hz, Q=10

8/13/2004 Stefan Ballmer, MIT / LIGO Hanford 6 The common mode servo Is an analog servo… SensingDouble cavity pole (~1Hz, ~2Hz for H2) Error signalREFL_I ActuationLaser frequency

8/13/2004 Stefan Ballmer, MIT / LIGO Hanford 7 The common mode servo

8/13/2004 Stefan Ballmer, MIT / LIGO Hanford 8 The PRC loop Sensingflat (due to high CM gain) Error signalPOB_I Control filter bankH1:LSC-PRC Control signalPRC_CTRL Actuation calibration (S3) (H1) ~3nm/ct, Pendulum at 0.76Hz, Q=10 Acting on recycling mirror (RM)

8/13/2004 Stefan Ballmer, MIT / LIGO Hanford 9 The MICH loop Sensingflat Error signalPOB_Q Control filter bankH1:LSC-MICH Control signalMICH_CTRL Actuation calibration (S3) (H1) ~3nm/ct, Pendulum at 0.76Hz, Q=10 Acting on beam splitter (BS) and recycling mirror (RM)

8/13/2004 Stefan Ballmer, MIT / LIGO Hanford 10 Known couplings 1 MICH->DARM  AS_Q 140 times less sensitive to BS than to differential ETM’s (build-up)  MICH loop acts on BS  MICH loop shot noise limited above ~50Hz 2 solutions:  A) until end of S3 (mid S3 at LLO): run MICH loop at low BW (UGF ~11Hz) & filter MICH_CTRL  B) now: run MICH loop at high BW (UGF >50Hz), send MICH_CTRL to ETM’s to cancel known BS motion  reduces coupling by ~40, but MICH_CTRL still significant noise source

8/13/2004 Stefan Ballmer, MIT / LIGO Hanford 11 Known couplings 2 PRC->DARM  Coupling due to arm imbalance (~1/400 for H1), has zero at cavity pole  PRC loop shot noise limited above ~50Hz (same diode as MICH!) Again same 2 solutions:  PRC correction (send PRCH_CTRL to ETM’s) implemented after S3  reduces coupling only by ~2 since arm imbalance is modulated (microseism)

8/13/2004 Stefan Ballmer, MIT / LIGO Hanford 12 Adaptive Input Matrix Arm power and sideband buildup do fluctuate (~10% LHO, ~20%LLO)  Front-end code calculates new input matrix element on the fly (since S3)  Both arm powers and NSPOB are filtered before used (Modules: H1:LSC-NPTRX, H1:LSC-NPTRY, H1:LSC-NSPOB) DARMH1:LSC-ICMTRX_01 MICHH1:LSC-ICMTRX_23 PRCH1:LSC-ICMTRX_12 CM MCL path (static at LLO during S3) H1:LSC-ICMTRX_34

8/13/2004 Stefan Ballmer, MIT / LIGO Hanford 13 Angle Sensing and Control Per optic:  Optical lever –Error signal: H1:SUS-ETMX_OPLEV_PERROR H1:SUS-ETMX_OPLEV_YERROR –Control Signal: H1:SUS-ETMX_OPLEV_POUT H1:SUS-ETMX_OPLEV_YOUT  Local Damping –Error signal: H1:SUS-ETMX_SENSOR_UL H1:SUS-ETMX_SENSOR_UR H1:SUS-ETMX_SENSOR_LL H1:SUS-ETMX_SENSOR_LR Wave front sensors (WFS) –Error signal: H1:ASC-WFS1_QP H1:ASC-WFS2_IP H1:ASC-WFS2_QP H1:ASC-WFS3_IP H1:ASC-WFS4_IP (and …1_QY etc. for yaw) –Control signal H1:ASC-ETMX_P H1:ASC-ETMX_Y etc.

8/13/2004 Stefan Ballmer, MIT / LIGO Hanford 14 Angle Sensing and Control Transmission QPD’s  Error signal: H1:ASC-QPDX_P H1:ASC-QPDX_Y etc. Beam splitter centering servo  Slow servo

8/13/2004 Stefan Ballmer, MIT / LIGO Hanford 15 Where are the filter files? Foton readable files at   Matlab function to read filters: 