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Length and angular control loops in LIGO

Length and angular control loops in LIGO. Stefan Ballmer Massachusetts Institute of Technology LIGO Hanford Observatory. Goal. Overview of the LSC and ASC control loop fabric Find corresponding data channels (error / control signal) Find corresponding filters of the control system.

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Length and angular control loops in LIGO

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  1. Length and angularcontrol loops in LIGO Stefan Ballmer Massachusetts Institute of Technology LIGO Hanford Observatory 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 Stefan Ballmer, MIT / LIGO Hanford

  3. transmitted power photodiodes Ly pickoff signal ly Laser lx Lx symmetric signal antisymmetric signal Reading the signals Frequency Response of the LIGO Interferometer T970084-00.pdf Stefan Ballmer, MIT / LIGO Hanford

  4. Length Sensing and Control 4 loops: • DARM • CARM/CM • MICH • PRC Stefan Ballmer, MIT / LIGO Hanford

  5. The DARM loop Stefan Ballmer, MIT / LIGO Hanford

  6. The common mode servo • Is an analog servo… Stefan Ballmer, MIT / LIGO Hanford

  7. The common mode servo Stefan Ballmer, MIT / LIGO Hanford

  8. The PRC loop Stefan Ballmer, MIT / LIGO Hanford

  9. The MICH loop 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 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) 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) 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_ULH1:SUS-ETMX_SENSOR_URH1:SUS-ETMX_SENSOR_LLH1:SUS-ETMX_SENSOR_LR • Wave front sensors (WFS) • Error signal: H1:ASC-WFS1_QPH1: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_PH1:ASC-ETMX_Y etc. Stefan Ballmer, MIT / LIGO Hanford

  14. Angle Sensing and Control • Transmission QPD’s • Error signal: H1:ASC-QPDX_PH1:ASC-QPDX_Y etc. • Beam splitter centering servo • Slow servo Stefan Ballmer, MIT / LIGO Hanford

  15. Where are the filter files? • Foton readable files at • http://blue.ligo-wa.caltech.edu/hanford1/cvs/lho/chans/ • http://london.ligo-la.caltech.edu/cds/llo/chans/ • Matlab function to read filters: • http://blue.ligo-wa.caltech.edu/hanford1/j/dtt/sballmer/matlabfilter/ Stefan Ballmer, MIT / LIGO Hanford

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