640 likes | 771 Views
VIRGO Superattenuators in next generation detectors S.Braccini, INFN-Pisa on behalf of the Virgo Collaboration. 1) SAT Seismic Isolation: Present & Future. 2) SAT “Passive Control”. 3) SAT Mechanical Glitch Noise. 2. Superattenuator. Magnetic Anti-Spring. 8 m. Blade Springs. 3. 2 Hz.
E N D
VIRGO Superattenuators in next generation detectors S.Braccini, INFN-Pisa on behalf of the Virgo Collaboration
1) SAT Seismic Isolation: Present & Future 2) SAT “Passive Control” 3) SAT Mechanical Glitch Noise 2
Superattenuator Magnetic Anti-Spring 8 m Blade Springs 3
2 Hz Ground Resonances f-2N Transmisson Frequency (Hz) Long Pendula Soft Springs Mirror 4
2 Hz Resonances f-2N Frequency (Hz) Large Inertia Thin Wires 5
Stage by Stage Measurement Thermal Noise Ground Seismic Noise Mirror Residual Seismic Noise 6
DirectMeasurement SA design e freccette 7
TF < 1.7 x 10-12 TOP 1.2 x 10-6m Hz-1/2 MIRROR 2 x 10-18m Hz-1/2 8
TF = 1.26 x 10-11 TOP MIRROR ! ! 9
Upper limitHoriz Upper limit Vertical 10
Upper limitHoriz Upper limit Vertical 11
SA design e freccette SA design e freccette X-Excitation Experiment Bypass ? 12
AdV - Seismic Isolation OK ET - Reduction of low frequency cut-off 13
Stage by Stage TF Crossing expected @ 2.5-3 Hz 14
Confirmed by direct measurements Horiz Vertical ET ETx Horizontal seismic noise dominant 15
PRESENT CROSS-OVER ET ETx 16
Change both number of filters and their distance (thus varying the total length) HORIZONTAL TF 17
HORIZONTAL 5 filters - 15 m 7 filters - 16 m 6 filters - 17 m 6 filters - 14 m TF 1.8 Hz 18
Upper limitHoriz Upper limit Vertical Vertical Attenuation 19
6 Filters (as now) TF FILTER @ 310 mHz
CONCLUSION 3rd GENERATION: Use identical technology with cross-over below 2 Hz Present SA extension 9 17 m (1.8 Hz conservative cross-over) 21
1) Seismic Isolation: Present & Future 2) “Passive Control” 3) Mechanical Glitch Noise 22
several microns mirror swing 23
Accelerometers DSP DAC Actuators ADC 24
Swing reduction by ID + ultra-low freq. passive attenuation 8 m 25
Alignment without affecting mirror swing (Payload ad hoc design) 1) Intrinsically diagonalized (Easy control) 2) “Nothing happens” in the off-diagonal world 26
Alignment transparent for SA 8 m 29
Lock Acquisition transparent for SAT 8 m
1) Longitudinal swing fraction of mm/s 2) Prealign mirror (fract. of mrads) (not affecting 1) 3) Lock acquisition (not affecting 1 - 2) 8 m 4) Reallocation & Tidal Control (not affecting 1 - 2 - 3) Residual Swing LONGITUDINAL: around 100 nm pk pk ANGLES: fractions of mrad pk pk
500 nrad RESIDUAL (OPEN LOOP) DISPLACEMENTS 100 nm SMALL LOCKING & ALIGNMENT CORRECTIONS LOW NOISE HIGH ACCURACY: 10 nrads on PR,a few nrads on test masses
RM AdV Marionetta CONTROL NOISE - OK for AdV 35
1) Seismic Isolation: Present & Future 2) “Passive Control” 3) Mechanical Glitch Noise 36
Self-organized criticality dynamics of dislocations induces a mechanical shot-noise force (1/f) 37
Potential problem in last filter(s) of the chain 38
3 VERTICAL MODES F7 -Blades 40 Hz Marionetta 15 Hz 7 Hz Reference Mass Mirror 39
MODES VISIBLE IN DARK FRINGE Displacement Strain (m Hz^-1/2) 40 Freq (Hz)
TF MEASUREMENT Blades Mar RM Mir 41
TF MEASUREMENT Mirror-Beam Displacement (m) / Vertical Force (N) 7 Hz 15 Hz 40 Hz Freq (Hz) 42
VERTICAL FORCE UPPER LIMIT z(w) = TF(w) x Fv(w) 7 Hz 40 Hz Fv_max (w) = z(w) / TF(w) 43
VERTICAL FORCE UPPER LIMIT Vertical Force (Upper Limit – N/Hz1/2) Freq (Hz) 44
VERTICAL FORCE UPPER LIMIT Vertical Force (Upper Limit – N/Hz1/2) Freq (Hz) 45
VERTICAL FORCE UPPER LIMIT Vertical Force (Upper Limit – N/Hz1/2) X TF Freq (Hz) 46
h(f) Virgo AdV 1/f noise upper limit 47
START PARENTHESIS (just for a betterunderstanding)
F Vertical Force on Marionetta MirrorDisplacementalongbeam z
Closedparenthesis h(f) Virgo AdV 1/f noise upper limit