Progress on the Design of the Magnetic Field Measurement System for elisa Ignacio Mateos Instituto de Ciencias del Espacio (CSIC-IEEC) Barcelona 10 th International LISA Symposium University of Florida, Gainesville 1
Outline 1 Introduction 2 3 4 Conclusions 2
Top level requirement for LISA elisa requirement LPF heritage LISA free fall requirement to detect GW ( ) ] 4 [ S 1/2 ω/2π δa,lisa {[1 (ω) 3 10 15 + 1 + 8 mhz ( )] }1 2 0.1 mhz ω/2π ms 2 Hz 0.1 mhz < ω/2π < 100 mhz Internal forces contribution to the total acceleration noise Magnetic effects Charge fluctuations Thermal effects Brownian motion Spacecraft self-gravity Laser radiation pressure 3
Top level requirement for LISA elisa requirement LPF heritage LISA free fall requirement to detect GW ( ) ] 4 [ S 1/2 ω/2π δa,lisa {[1 (ω) 3 10 15 + 1 + 8 mhz ( )] }1 2 0.1 mhz ω/2π ms 2 Hz 0.1 mhz < ω/2π < 100 mhz Force due to the magnetic effect: [( F = M + χ ) ] B B V µ 0 Magnetic subsystem will assess the magnetic contribution to S δa (ω) 3
Introduction elisa requirement LPF heritage In view of elisa: Main drawbacks in LPF magnetic subsystem 4
Introduction elisa requirement LPF heritage In view of elisa: Main drawbacks in LPF magnetic subsystem Sensors are distant from TMs due to their magnetic back action effect Fluxgates are heavy and bulky (94 cm3 ) less can be placed in the spacecraft Classical interpolation methods do not achieve sufficient accuracy Noise at lower elisa frequencies needs to be improved 4
Introduction elisa requirement LPF heritage In view of elisa: Main drawbacks in LPF magnetic subsystem Sensors are distant from TMs due to their magnetic back action effect Fluxgates are heavy and bulky (94 cm3 ) less can be placed in the spacecraft Classical interpolation methods do not achieve sufficient accuracy Noise at lower elisa frequencies needs to be improved 4
elisa requirement LPF heritage In view of elisa: Main drawbacks in LPF magnetic subsystem Sensors are distant from TMs due to their magnetic back action effect Fluxgates are heavy and bulky (94 cm 3 ) less can be placed in the spacecraft Classical interpolation methods do not achieve sufficient accuracy Noise at lower elisa frequencies needs to be improved 10 7 LPF Fluxgate 10 8 Requirement ASD [T Hz 1/2 ] 10 9 10 10 10 4 10 3 10 2 10 1 10 0 frequency [Hz] 4
Experiment layout Interpolation method: multipole expansion Estimated magnetic field and errors 1 Introduction elisa requirement LPF heritage 2 Experiment layout Interpolation method: multipole expansion Estimated magnetic field and errors 3 4 Conclusions 4
Experiment layout Interpolation method: multipole expansion Estimated magnetic field and errors Magnetic sources and sensor location For a first approach we consider: 8 magnetometers layout allocated around the vacuum enclosure. The magnitude and location of the magnetic sources measured for LISA Pathfinder. A batch of simulated dipoles sources with random orientations to verify the robustness of the interpolation. 1 VE Z[m] 0.8 0.6 0.4 0.2 36.47 TM y x AMR y z 46 0 1 46 97.58 0 Y[m] 1 1 0.5 X[m] 0 0.5 1 97.58 138 5
Experiment layout Interpolation method: multipole expansion Estimated magnetic field and errors Magnetic sources and sensor location For a first approach we consider: 8 magnetometers layout allocated around the vacuum enclosure. The magnitude and location of the magnetic sources measured for LISA Pathfinder. A batch of simulated dipoles sources with random orientations to verify the robustness of the interpolation. 1 Sources Test mass Magnetometers Z[m] 0.8 0.6 0.4 0.2 0 1 0 Y[m] 1 1 0.5 X[m] 0 0.5 1 Z[m] 1 01 1 0.5 0 0.5 Y[m] 1 1 0 X[m] 1 5
Experiment layout Interpolation method: multipole expansion Estimated magnetic field and errors Interpolation method: multipole expansion The estimated magnetic field measured by an array of N sensors can be expressed as: B estimated (x, t) = µ 0 4π L l l=1 m= l M lm (t) [r l Y lm (n)] The number of magnetometers will be defined by the desired multipole order: Max. order Equivalent Terms in Num. of triaxial decomposition multipole expansion magnetometers L [L (L + 2)] [N] 1 dipole 3 1 2 quadrupole 8 3 3 octupole 15 5 4 hexadecapole 24 8 6
Experiment layout Interpolation method: multipole expansion Estimated magnetic field and errors Magnetic field reconstruction: 8 triaxial sensors Magnetic field created by the dipolar sources Multipole expansion interpolation 7
Experiment layout Interpolation method: multipole expansion Estimated magnetic field and errors Magnetic field reconstruction: Relative errors Averaged relative errors for multipole expansion Averaged relative errors at TM s position for different layouts error (%) 40 30 20 10 Bx By Bz modb 0 4 Fluxgate LPF 4 AMR 8 AMR Sensor configuration 8
Experiment layout Interpolation method: multipole expansion Estimated magnetic field and errors Magnetic field reconstruction: Relative errors Averaged relative errors for multipole expansion Averaged relative errors at TM s position for different layouts error (%) 40 30 20 10 Bx By Bz modb Error < 1 % 0 4 Fluxgate LPF 4 AMR 8 AMR Sensor configuration 8
Experiment layout Interpolation method: multipole expansion Estimated magnetic field and errors Magnetic field reconstruction: Relative errors Averaged relative errors for multipole expansion Averaged relative errors at TM s position for different layouts error (%) 40 30 20 10 Bx By Bz modb Error < 1 % Error 8 AMRs (%) B x B y B z B ε TM 0.1 0.2 0.1 0.1 σ 0.1 0.2 0.1 0.1 0 4 Fluxgate LPF 4 AMR 8 AMR Sensor configuration 8
Experiment layout Interpolation method: multipole expansion Estimated magnetic field and errors Magnetic field reconstruction: Robustness Errors due to the offset and position of the sensors error [%] 7 6 5 4 3 2 Bx By Bz error [%] 1.2 1 0.8 0.6 0.4 Bx By Bz 1 0.2 0 0 10 20 30 40 50 offset [nt] 0 0 1 2 3 4 5 position [mm] AMR s offset can be measured in flight. Fluxgate magnetometers may suffer from unpredictable offsets due to launch stresses (< 10 nt). Spatial resolution will be determined for the size of the sensor head. AMR < 1 mm and Fluxgate < 4 mm. 9
1 Introduction elisa requirement LPF heritage 2 Experiment layout Interpolation method: multipole expansion Estimated magnetic field and errors 3 4 Conclusions 9
00000 11111 00 11 Introduction Principle of operation B E I t Pump pulse creates alignment in the medium along E 10
00000 11111 00 11 Introduction Principle of operation B B E I t Pump pulse creates alignment in the medium along E I t Atomic moments precess about B at the Larmor frequency 10
00000 11111 00 11 00 11 00 11 Introduction Principle of operation B B 180 O B E E I t Pump pulse creates alignment in the medium along E I t Atomic moments precess about B at the Larmor frequency I 2ω L t Pump pulses are synchronized and reinforce the macroscopic moments 10
00000 11111 00 11 00 11 00 11 00 11 Introduction Principle of operation B B 180 O B E E I Pump pulse creates alignment in the t I Atomic moments precess about B at the t I 2ω L t Pump pulses are synchronized and medium along E Larmor frequency ψ reinforce the macroscopic moments φ E After Cell Before Cell y E z B z x Aligned media rotates the polarization plane of the probe beam (Faraday effect) 10
Amplitude modulated non-linear magneto optical rotation (AM NMOR) Atomic Magnetometer λ /2 Probe Analizer Balanced polarimeter PD1 Lock in Signal Polarizer λ /2 Pump PD2 Ref Mod. Laser is tuned to a magnetically sensitive transition (D 1 or D 2 line) Light is linearly polarized before vapor cell Optical rotation of the light is measured with a balanced polarimeter Signal is demodulated with a reference frequency equal to the Larmor frequency ITO heaters are not necessary at the cell 2-beams configuration optimize sensitivity 11
AM NMOR: Block diagram LD PD PID TIA PD1 PD2 Balanced polarimeter LD Controller TEC λ /4 DAVLL λ /2 ND Thermal act. LD Frequency stabilization Monitored data DFB Lens OI BS Iris Glass Pulse Gen. AOM +BD 0 th 1 st λ /2 Probe Laser Iris BD LP +BD Current Source λ /2 Glass LP Cs Cell Coils Pump Laser Iris Pump PD 5 layer shielding PD1 TIA PD2 Balanced polarimeter Ref Lock in R θ Output of the lock-in (X-in-phase and Y-out-phase and reference frequency) Frequency and power at different points of the laser LD current and temperature Output of the polarimeters (single and differential) Environmental and applied magnetic field (with environmental temperature) 12
AM NMOR: Block diagram LD PD PID TIA PD1 PD2 Balanced polarimeter LD Controller TEC DFB Lens OI λ /4 DAVLL λ /2 ND Thermal act. LD Frequency stabilization BS Iris Glass Pulse Gen. AOM +BD 0 th 1 st λ /2 Probe Laser Iris BD LP +BD Current Source λ /2 Glass LP Cs Cell Coils Pump Laser Iris Pump PD 5 layer shielding PD1 TIA PD2 Balanced polarimeter Ref Lock in R θ Lorentzian distribution is obtained by sweeping around Ω L Signal changes during long measurement Zero phase is less sensitive to power fluctuations Zero-phase feedback loop to keep acquire Ω m locked to resonance Amplitude [mv] 8 6 4 2 0 2 X Lockin Y Lockin 4 1.93 1.935 1.94 1.945 1.95 1.955 1.96 frequency [Hz] x 10 4 12
AM NMOR: Block diagram LD PD PID TIA PD1 PD2 Balanced polarimeter LD Controller TEC DFB Lens OI λ /4 DAVLL λ /2 ND Thermal act. LD Frequency stabilization BS Iris Glass Pulse Gen. AOM +BD 0 th 1 st λ /2 Probe Laser Iris BD LP +BD Current Source λ /2 Glass LP Cs Cell Coils Pump Laser Iris Pump PD 5 layer shielding PD1 TIA PD2 Balanced polarimeter Ref Lock in R θ Lorentzian distribution is obtained by sweeping around Ω L Signal changes during long measurement Zero phase is less sensitive to power fluctuations Zero-phase feedback loop to keep acquire Ω m locked to resonance Amplitude [mv] 8 6 4 2 100 Amplitude Phase 50 0 50 Phase [degree] 0 100 1.93 1.935 1.94 1.945 1.95 1.955 1.96 frecuency [Hz] x 10 4 12
AM NMOR: Block diagram LD PD Pulse Gen. PID TIA PD1 PD2 Balanced polarimeter LD Controller TEC λ /4 DAVLL λ /2 ND Thermal act. LD Frequency stabilization Probe beam polarimeter High gain TIA: 11 mv/na DFB Lens OI Iris Glass AOM +BD 0 th 1 st λ /2 Probe Laser Signal is modulated between 1 Hz and hundreds of khz Dominant noise contributions: e 2 n,op TIA, i2 SN, e2 R f High SNR measurements can be made BS Iris BD LP +BD Current Source ASD [A Hz 1/2 ] λ /2 Glass LP 10 12 10 13 10 14 10 15 10 16 Cs Cell Coils Pump Laser Iris Total noise Pump PD 5 layer shielding TIA + 2 nd stage 2 nd stage Shot noise e n,op TIA e Rf,t i n,op TIA PD1 TIA PD2 Balanced polarimeter Ref Lock in 10 2 10 1 10 0 10 1 10 2 10 3 10 4 10 5 frequency [Hz] R θ 12
AM NMOR: Block diagram LD PD PID TIA PD1 PD2 Balanced polarimeter LD Controller TEC DFB Lens OI λ /4 DAVLL λ /2 ND Thermal act. LD Frequency stabilization BS Iris Glass Pulse Gen. AOM +BD 0 th 1 st λ /2 Probe Laser Iris BD LP +BD Current Source λ /2 Glass LP Cs Cell Coils Pump Laser Iris Pump PD 5 layer shielding PD1 TIA PD2 Balanced polarimeter Ref Lock in R θ Current source for the applied magnetic field Main magnetic field to be applied is 2.5 µt 0.02 pt @100 Hz and 10 pt @0.1 mhz Hz Hz Dominant noise contribution is due to the reference voltage Thermal contribution appears outside the elisa BW Current noise [A Hz 1/2 ] 10 8 10 12 10 10 10 13 10 12 210 14 10 2 10 1 10 0 10 1 10 frequency [Hz] Eq. magnetic field noise [T Hz 1/2 ] 12
Magnetometer setup: Optical board 13
Introduction Magnetometer setup: 133 Cs Cell, probe and pump board 14
Equivalent magnetic field noise: B app 2.5 µt 10 9 10 10 Atomic Mag Floating Load High stable COTS ASD [T Hz 1/2 ] 10 11 10 12 10 13 10 14 10 4 10 3 10 2 10 1 frequency [Hz] 15
Equivalent magnetic field noise: B app 2.5 µt 10 9 10 10 Atomic Mag Floating Load High stable COTS ASD [T Hz 1/2 ] 10 11 10 12 10 13 50 pt Hz 1/2 @ 0.1 mhz! 10 14 10 4 10 3 10 2 10 1 frequency [Hz] 15
Equivalent magnetic field noise: Fluxgate vs AMR vs atomic magnetometer LPF Fluxgate 10 8 Requirement ASD [T Hz 1/2 ] 10 9 10 10 10 11 10 12 10 13 10 4 10 3 10 2 10 1 10 0 frequency [Hz] 16
Equivalent magnetic field noise: Fluxgate vs AMR vs atomic magnetometer 10 8 Requirement LPF Fluxgate AMR Mag Feedback + Flipping ASD [T Hz 1/2 ] 10 9 10 10 10 11 10 12 10 13 10 4 10 3 10 2 10 1 10 0 frequency [Hz] 16
Equivalent magnetic field noise: Fluxgate vs AMR vs atomic magnetometer 10 8 Requirement LPF Fluxgate AMR Mag Feedback + Flipping Atomic AM NMOR ASD [T Hz 1/2 ] 10 9 10 10 10 11 10 12 10 13 10 4 10 3 10 2 10 1 10 0 frequency [Hz] 16
Conclusions Multipole expansion with the proposed sensor configuration has produced reliable results to estimate the magnetic field at the positions of the TM. Improvement in the accuracy of the magnetic field reconstruction has been achieved due to the small size and low magnetic back action of the AMRs, which enables the possibility to place more sensors and locate them closer to the TMs. Based on the experience with LISA Pathfinder, the use of AMRs with a dedicated noise reduction technique seems nowadays the most suitable technology for elisa. Atomic magnetometer s noise based on AM NMOR shows promising results at elisa frequencies 50 pt Hz 1/2. Further work: what happens at chip-scale? 17
Thank you! 17