Seismic sensors in PACMAN Peter Novotny 1 st

Seismic sensors in PACMAN Peter Novotny 1 st PACMAN workshop 3 rd February 2015, CERN

Outline • • • Why seismic sensors in PACMAN How seismic sensors work PACMAN requirements to sensors State of the art seismic sensors Current work Conclusions Seismic sensors in PACMAN - Peter NOVOTNY - 3 rd February 2015 2

Why we need seismic sensor? • Ground is shaking all the time even if we don’t see or feel it. Power Spectral Density of ground motion for different sites Cultural noise Micro seismic peak Seismic sensors in PACMAN - Peter NOVOTNY - 3 rd February 2015 3

Why we need seismic sensor? • When measuring beam position with nm resolution we need to know how this ground motion propagate through the bench and influence our measurements. • Therefore we want to measure ground motion at different positions of the bench. Seismic sensors in PACMAN - Peter NOVOTNY - 3 rd February 2015 4

How seismic sensors work? Theoretical principle Transducer Seismic sensors in PACMAN - Peter NOVOTNY - 3 rd February 2015 5

Transducers Seismic sensor with electromagnetic transducer Transducer Seismic sensors in PACMAN - Peter NOVOTNY - 3 rd February 2015 6

Types of transducers • • Resistive Capacitive Piezoelectric LVDT - Linear variable differential transformer Optical (Interferometers, encoders) Elmg. – coil + magnet Eddy current … Seismic sensors in PACMAN - Peter NOVOTNY - 3 rd February 2015 7

Sensor parameters • • Bandwidth – fmin - fmax Sensitivity S – conversion factor from D, V, A to Volts Self noise N – determine resolution R = N/S – smallest measureable value Dynamic range – Max/Min measureable value Active/passive – need of power supply Weight and dimensions Robustness against magnetic stray field and radiation Seismic sensors in PACMAN - Peter NOVOTNY - 3 rd February 2015 8

PACMAN requirements for sensor • Bandwidth = 0. 1 Hz – ≈200 Hz • Resolution ≤ 0. 1 nm (rms@1 Hz) which means high sensitivity and low self-noise • Stray magnetic fields resistance different mg. field on the ground than on the magnets • Dynamic range ≥ 80 d. B from 0. 1 nm to at least 1µm • Weight < few kg & compact size to fit inside the bench Seismic sensors in PACMAN - Peter NOVOTNY - 3 rd February 2015 9

State of the art sensors Different types of sensors for different use like: • Natural ground motion measurement (tides, waves) • Earthquakes monitoring • Oil and gas exploration Geophones • Building, bridges structural monitoring • Nuclear test ban treaty monitoring • … Seismometers Piezo-accelerometers MEMS accelerometers Seismic sensors in PACMAN - Peter NOVOTNY - 3 rd February 2015 Force balanced optical accelerometers 10

Geophones • Output voltage proportional to ground velocity above natural frequency. • Simple and compact solution • Low noise but also low sensitivity Our requirements: ü ü ü × × Low noise Weight and size Price Sensitivity Resolution Bandwidth Magnetic resistance Seismic sensors in PACMAN - Peter NOVOTNY - 3 rd February 2015 11

Seismometers • Output voltage is proportional to ground velocity in certain frequency bandwidth. • Utilise the feedback control of mass position to extend bandwidth to low frequencies. Our requirements: ü ü • • Very low noise × Magnetic resistance Resolution × Price Bandwidth Weight and size Seismic sensors in PACMAN - Peter NOVOTNY - 3 rd February 2015 12

Piezo-accelerometers • Output voltage is proportional to ground acceleration below natural frequency. • High self noise at lower frequencies Our requirements: Bandwidth Weight and size Magnetic resistance Price High self noise at low freq. × Resolution ü ü ü • × Seismic sensors in PACMAN - Peter NOVOTNY - 3 rd February 2015 13

MEMS accelerometers • Output voltage is proportional to ground acceleration below natural frequency. Principle (similar freq. characteristic as piezo-acc. ) • High self noise because of light mass. Our requirements: ü ü × × Bandwidth Weight and size Magnetic resistance Price High self noise Resolution MEMS realisation Final product Seismic sensors in PACMAN - Peter NOVOTNY - 3 rd February 2015 14

Promising candidates Short period seismometer CP ZM 500 Bandwidth [Hz] Noise@1 Hz [nm/s 2/√Hz] Short period seismometer Guralp CMG-6 T Force balanced optical accelerometers PACMAN CP ZM 500 CMG-6 T Optical acc. 0. 1 - 200 0. 1 - 100 0. 1 – 1 k 4 0. 3 2. 5 20 Measurements and tests need to be done to check requirements fit. Seismic sensors in PACMAN - Peter NOVOTNY - 3 rd February 2015 15

Noise in seismic sensors !Noise is the most limiting parameter of sensor resolution! Sources of noise: • Thermomechanical (Brownian) noise • Molecular collisions with mass • Thermoelectrical (Johnson) noise • Random thermal excitation of charge carriers • Other semiconductor electronic noise • Schottky noise • Flicker 1/f noise • Discretisation noise • ADC converters Seismic sensors in PACMAN - Peter NOVOTNY - 3 rd February 2015 16

Noise comparison Acquisition hardware noise is also very important and should be below sensor noise. Seismic sensors in PACMAN - Peter NOVOTNY - 3 rd February 2015 17

Current work • Characterization of the seismic sensors available on the market and those developed by Laboratories • Comparison of their TF, S/N ratio and bandwidths • Investigation of alternative and innovative approaches: – – – Optical transducers (Interferometers, Fibre Bragg grating) Molecular Electronic Transducers (MET) Tunnelling effect Noise reduction in MEMS accelerometers … Seismic sensors in PACMAN - Peter NOVOTNY - 3 rd February 2015 18

Current work • Measurements and data processing Seismic sensors in PACMAN - Peter NOVOTNY - 3 rd February 2015 19

Next steps • Development of the optimum sensor for PACMAN • Integration into the PACMAN bench. • Analysis of the performances and robustness. Seismic sensors in PACMAN - Peter NOVOTNY - 3 rd February 2015 20

Conclusions • We need seismic sensors to know how GM has influence on the beam position measurement. • Many state of the art sensors exist but were designed for different purposes (don’t match PACMAN requirements). • Some of them seem promising. • Measurements needs to be done to test their performance. • Investigation of new technologies and possible improvements. • Development of optimum senor for PACMAN, integration to bench and analysis of its performance. Seismic sensors in PACMAN - Peter NOVOTNY - 3 rd February 2015 21

Thank you for your attention!

Backup slides

How does seismic sensor work? Transfer functions: Laplace transform Natural frequency !! Information about absolute motion is in relative motion!!

Few sensors and their producers Producer GURALP ion Sercel (Mark Products) Kinemetrics (Streckeisen) Nanometrics REFTEK Lennartz electronic Metrozet Eentec SINUS Geo. SIG Endevco Wilcoxon DYTRAN DJB Instruments MMF Brüel & Kjær PCB COLIBRYS METTECH GEOTECH INSTRUMENTS type of sensors Seismometers geophones Seismometers + FBA Seismometers + FBA FDBCK MET geophones + FBA Piezo-velocity sensor geophones + FBA accelerometers accelerometers MET Seismometers

Secondments • Development of the seismic sensor for stabilisation of the Final Focus (of CLIC) • Equivalent of 7 months (already started) • Their measuring and control system • High precision mechanic manufacturer • 3 months starting in April 2015 • Project: • Measurement and adjustment techniques for precision applications