Ilya Berdnikov, Cornell University. Characterization of the LIGO 40m Lab Mode Cleaner Digital Suspensions Summer Project by Ilya Berdnikov Mentors: Alan Weinstein, Dennis Ugolini, and Ben Abbott

Ilya Berdnikov, Cornell University. Project Goals 1.Understand the Mode Cleaner (MC) digital suspensions. 2.Diagonalize the suspensions. 3.Measure the damping Q. 4.Calibrate the suspensions. 5.Measure suspension noise. 6.What’s left.

Ilya Berdnikov, Cornell University. Understanding Suspensions Suspensions Optical Sensors Electro- Magnetic Actuators (OSEMs) –Problems with OSEMs. Damping. Digital is GOOD.

Ilya Berdnikov, Cornell University. Suspension Controllers

Ilya Berdnikov, Cornell University. EPICS screen

Ilya Berdnikov, Cornell University. Diagonalizing Suspensions Why diagonalize? –Position-Pitch coupling –Position-Yaw coupling Diagonalization –Sensing (input) matrix –Actuation (output) matrix

Ilya Berdnikov, Cornell University. Sensing matrix diagonalization “Suspension Controller Tuning Procedure” LIGO-T A MATLAB code –Modification Gathering data –Undamp, excite optic. MC2ULLLURLR Pos Pit Yaw

Ilya Berdnikov, Cornell University. Output matrix diagonalization Drive the optic –0.2Hz, 0.1Vpp Vary the matrix –Pitch (LL, LR) –Yaw (UL, LL) Look on QPD. Results: –Input = 900 DAQ counts –Pitch = 2 counts (<1.5%) –Yaw = 0.4 counts (<0.05%) MC1 doesn’t diagonalize. Problems with lower OSEMs.

Ilya Berdnikov, Cornell University. Collect data –Fit damped sinusoid, get . – Results: Measuring damping Q Quality of Damping Excite the optic –Undamp the optic –Drive it 1Hz, 30mVpp MC1MC2MC3

Ilya Berdnikov, Cornell University. Calibrating Suspensions Sensor and coil voltage to microns of magnet motion. Move optic through one FSR –FSR =  m/2 –Compute  V/532 nm for each OSEM and coil. –Needs locked mode cleaner Calibrated pitch/yaw sliders –Sliders calibrated to give mrad/V. –Use of geometry of mirror, arm lengths. –Less precise. Scan across a distant optic –Use the geometry, arm lengths. Eyeballing distances – ok for order of magnitude result.

Ilya Berdnikov, Cornell University. Measure suspension noise Power spectra of sensors gives noise. Nominal noise in design spec: Measured noise is in –Calibration will provide the conversion factor of to compare the data with the spec. Is it good enough?

Ilya Berdnikov, Cornell University. What’s left Fix MC1 lower OSEMs, diagonalize MC1. Calibrate suspension motion. –Use either of the methods After calibration, compare actual suspension noise with with design. Improve damping (?)

Ilya Berdnikov, Cornell University. Acknowledgements I would like to thank my mentor Dr. Alan Weinstein for making this summer possible. I would also be completely helpless without Ben Abbott and Dennis Ugolini. Great thanks to them.