(Some) noise hunting issues at Virgo Gabriele Vajente 11th ILIAS WP1 meeting Hannover, January 22-23 2007

Summary Searching for a good operating point ITF sensitivity and longitudinal offsets Alignment noise projections Implementing HACR at Virgo

Searching for the good operating point…

Virgo scheme Beams B1 = dark fringe B2 = ITF reflection B5 = BS pick-off B7 = north arm transmission B8 = west arm transmission Scanning F-P on B1 DOFs DARM = differential long arms CARM = common long arms MICH = short michelson PRCL = recycling cavity

How to define a good O.P. The ITF is at resonance, meaning powers are min/max at the locking point In particular Carrier resonates in PRC: B5_DC is maximum Fringe is dark: B1_DC is minimum Sidebands resonate in PRC: B5_2f_ACq is maximum A consequence Sidebands are well balanced at every port BS pick-off beam demodulated at 2W gives an estimate of sidebands power into PRC

The old story But changing only MICH offsets is not enough to reach a good operating point Evidence that MICH offsets was not good (November 10th) DF power PRC power DF ratio PRC sidebands ITF reflection North transmission X axis = offset on MICH

The idea MICH and PRCL loop are strongly related Try to explore MICH-PRCL space by changing both offsets Spiral experiment Change simultaneously the two offsets Error signals are reconstructed using Pr_B2_3f_ACp = ITF reflection demodulated at 3W Pr_B5_ACq = BS pick-off demodulated Add electronic offsets to these two signals Need to wait 2 hours after lock to let the ITF “warm up” B5_d2_ACq B2_3f_d1_ACp

Spiral experiments First “historical” one (November 24th 2006) Proved the technique works Second experiment centered around ”normal” locking point Identified a new point, one night lock on it Third experiment, centered around the new point

Sidebands imbalance at DF First experiment Dark fringe ratio Sidebands inside PRC Sidebands imbalance at DF OFFSET ON B5_ACq [ADC counts] Power inside PRC OFFSET ON B2_3f_ACp [ADC counts]

Conclusions of the first experiment Moving to lower right corner: Fringe is darker B5_2f_ACq is higher Sidebands are more balanced But B5_DC is lower Left the ITF locked all the night (from 23.00LT 28th to 8.00LT 29th) with new offsets B2_3f_d1_ACp = 800 B5_d2_ACq = -8000 Reached a bit more than 4 Mpc Never obtained with B2_3f

Second experiment Second experiment (1100,-11000)

Second experiment (1600,0)

Second experiment

Second experiment (1250, -6000)

Conclusions of the second experiment Three good candidates identified Darkest fringe at (1100,-11000) Maximum sidebands power in PRC at (1600,0) Highest horizon at (1250, -6000) The idea was to test all this points, measuring a sensitivity But only the first one was briefly tested so far

Improvements in sensitivity NSNS Horizon (opt) PRC power B2_3f offset B5 offset Loop UGFs Some lock signals DARM PRCL MICH

Improvements in sensitivity Dark fringe Reconstructed h

Conclusions on the operating point The “normal” locking position is not the best operating point Changing offsets it is possible to improve sensitivity quite a lot (horizon from 3 to 4.5 Mpc) Still some tuning to do… During WSR7 the ITF was run with an offset on B2_3f only What to do next Check repeatability (alignment issues?) Offsets on CARM and DARM? Find a new O.P. and tune parameters

Alignment noise projections

Measurements of alignment N.P. Two methods: Injection of noise (double zero @ 0 Hz, double pole @ 10 Hz, double pole @ 50 Hz) Injection of lines 13, 72, 119 Hz Estimation of transfer functions and noise projection for dark fringe

Some results / NE tx Coherence DF vs correction with noise Correction signal with and without noise Green stars are TF computed with the lines Trans. Func. Correction to DF with noise D.F. with and without noise

Some results / NI tx Coherence DF vs correction with noise Correction signal with and without noise Green stars are TF computed with the lines Trans. Func. Correction to DF with noise D.F. with and without noise

Some results / BS tx Coherence DF vs correction with noise Correction signal with and without noise Green stars are TF computed with the lines D.F. with and without noise Trans. Func. Correction to DF with noise

Transfer function estimation with lines Coherence at lines (PR is not good) Trans. Func. at lines (PR is not good)

Noise projection / tx (WSR7 sensitivity)

Noise projections / ty (WSR7 sensitivity)

Implementing HACR at Virgo

Status Started developing VirgoHACR Very good performances C code based on HACR algorithm Full interface with Virgo Data Distribution via FdIO library Output is a text file with events for the moment Will be a MySQL database, to better interface with GEO report system Very good performances 1 s of data, 1 channel @ 20 kHz analyzed in about 10 ms of machine time Limited by data access Some test peformed

Tests with simulated data… Map of short FFTs, white noise with bursts

Tests with simulated data… All events are found, parameters are reconstructed well

Test with simulated data… Accuracy in time and frequency reconstruction

Starting tests on dark fringe signal… Short FFTs map

Starting tests on dark fringe signal… Mean FFT map

Starting tests on dark fringe signal… Threshold crossing

Conclusions on VirgoHACR Code seems to work fine Need some time to tune parameters for dark fringe Still to do Optimize parameter reconstruction Output to database Integration with GEO reports builder to create automatic reports