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LTP diagnostics

LTP diagnostics. Alberto Lobo ICE-CSIC & IEEC. LISA ’s top level sensitivity requirement is:. LISA :. for . This is so very demanding a previous LPF mission is planned, with a relaxed sensitivity requirement:. LPF :. Why is diagnostics analysis

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LTP diagnostics

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  1. LTP diagnostics Alberto Lobo ICE-CSIC & IEEC Sagamihara, 13 November 2008

  2. LISA’s top level sensitivity requirement is: LISA: for . This is so very demanding a previous LPF mission is planned, with a relaxed sensitivity requirement: LPF: Why is diagnostics analysis needed in the LTP? Even ifLPF works to top perfection, a fundamental queston remains: How do we make it to LISA’s sensitivity? Sagamihara, 13 November 2008

  3. DDS: Data Management& Diagnostics Subsystem • Diagnostics items: • Purpose: • Noise split up • Sensors for: • Temperature • Magnetic fields • Charged particles • Calibration: • Heaters • Induction coils • DMU: • Purpose: • LTP computer • Hardware: • Power Distribution Unit (PDU) • Data Acquisition Unit (DAU) • Data Processing Unit (DPU) • Software: • Boot SW • Application SW: • Diagnostics items • Phase-meter • Interfaces Sagamihara, 13 November 2008

  4. Diagnostics items use • The methodology: • Split up total noise readout into parts –e.g., thermal, magnetic,... • Identify origin of excess noise of each kind • Orient future research in appropriate direction for improvement 1. Sensitive diagnostics hardware needs to be designed and built 2.a) Suitable places for monitoring must be identified. b) Algorithms for information extraction need to be set up. 3. Creative research activity thereafter... Sagamihara, 13 November 2008

  5. Approach: 1) Apply controlled perturbation a to the system 2) Measure “feed-through” coefficient between force and perturbation: 3) Measure actuala with suitable sensors 4) Estimate contribution of a by linear interpolation: 5) Check against a physical model of perturbations 6) Subtract out from total detected noise: Noise reduction philosophy Problem: to assess the contribution of a given perturbation to the total noise force. Sagamihara, 13 November 2008

  6. Location NTCs Comments Req. No Optical Bench 4 Near base corners 3.1 Optical Windows 4 2 per OW 3.2 Inertial Sensors 8 2 on each of the outer x-faces of the IS EH 3.3 LCA mounting struts 6 1 per strut, near centre 3.4 Total 22 --- --- Thermal and sensor requirements Global LTP stability requirement: 10-4 K/ÖHz , 1 mHz < f < 30 mHz Sensor sensitivity requirement: 10-5 K/ÖHz , 1 mHz < f < 30 mHz Sagamihara, 13 November 2008

  7. DMU test campaign Transfer function Thermal damper Sagamihara, 13 November 2008

  8. DMU test campaign DMU EQM Sagamihara, 13 November 2008

  9. DMU test campaign Open thermal damper, wiring and DMU Insulating anechoic chamber for the test Sagamihara, 13 November 2008

  10. Digital processing Analog processing PSD3(f) PSDdiff(f) PSDint(f) PSD1(f) + + + y (t) PSDy(f) Integrator N x(t) S/H A/D M 2 A Z-1 + + - m(t) n(t) SN(f) nA/D(t) SNA/D(f) 1/2 FEE Readout electronics PC data acquisition program FEE Analog PCB FEE A/D PCB DMU test campaign Sagamihara, 13 November 2008

  11. DMU test campaign Example run Sagamihara, 13 November 2008

  12. DMU test campaign Sagamihara, 13 November 2008

  13. DMU test campaign Sagamihara, 13 November 2008

  14. NTCs magnetic properties In IEEC we eventually discovered the NTCs, used both as temeperature sensors and heaters in the EH, have magnetic properties: Nickel parts are inside the device Damaged sample! Sagamihara, 13 November 2008

  15. First magnetisation curves NTCs magnetic properties Damaged sample! Sagamihara, 13 November 2008

  16. NTCs magnetic properties Summary of magnetic moments of the screened NTCs (Am2): Sagamihara, 13 November 2008

  17. NTCs magnetic properties Assessment of magnetic noise generated by NTCs: These two terms add, and are due to the quadratic coupling of the magnetic field due to TM susceptibility. Independent calculations done at IEEC and ESA reach similar conclusions that the noise is not very significant for the LTP budget, Sagamihara, 13 November 2008

  18. NTCs magnetic properties Excerpt from S2-EST-TN-2026 (2-Oct-2008): Sagamihara, 13 November 2008

  19. Thermal sensing summary • Fully compliant with requirements • Thermal gradients slightly distort performance at low frequency • Can be improved by dithering the bridge voltage with a saw-tooth • signal --not applicable to LPF, but useful for LISA. • Magnetic properties of NTCs: not an issue of major concern, though • some precautions are recommended. • Research ongoing for improvements for LISA, encouraging • first results Sagamihara, 13 November 2008

  20. Magnetic disturbances in the LTP • Main problem is magnetic noise. This is due to various causes: • Random fluctuations of magnetic field and its gradient • DC values of magnetic field and its gradient • Remnant magnetic moment of TM and its fluctuations • Residual high frequency magnetic fields Test masses are a AuPt alloy 70% Au + 30% Pt of low susceptibility a = 46 mm m = 1,96 kg and low remnant magnetic moment: Sagamihara, 13 November 2008

  21. Quantification of magnetic effects If a magnetic field B acts on a small volume d3x with remnant magnetisation M, and susceptibility c, the force on this small volume is: Total force requires integration over TM volume, or: Most salient feature is non-linearity of force dependenceonB. Sagamihara, 13 November 2008

  22. Magnitude Value DC magnetic field 10 mT DC magnetic field gradient 5 mT/m Magnetic field fluctuation rms PSD 650 nT/ÖHz Magnetic field gradient rms PSD 250 (nT/m) /ÖHz Magnetic susceptibility 10-5 Remnant magnetic moment 10-8 Am2 Summary of magnetic requirements Sagamihara, 13 November 2008

  23. Magnetic sensor requirements Req 2: A minimum 4 magnetometers. Req 2-1: Resolution of 10 nT/sqrt(Hz) within MBW. Req 2-2: Two magnetometers located along x-axis, each as close as possible to the centre of one of the TM, not farther than 120 mm. Req 2-3: The other two may be offset from the x-axis by an amount not larger than 120 mm (TBC), their x coordinate should fall between the IS's at distances TBC. Req 2-4: Operation of magnetometers compatible with full science performance. Req 2-5: Final exact choice of magnetometer locations depends on final configuration of magnetic sources. Limited adjustment of magnetometer positions to within +/- 10 cm along x, y and z must be allowed until system CDR. Sagamihara, 13 November 2008

  24. Magnetometer layout • Magnetometers type: • 4 Flux-gate, 3-axis • magnetometers • Model is TFM100G2 from • Billingsley Magnetics. Areas for magnetometer accommodation Sagamihara, 13 November 2008

  25. Magnetometers’ accommodation Sagamihara, 13 November 2008

  26. Magnetic field reconstruction • Exact reconstruction not possible with 4 magnetometers and • around 50 dipole sources (+solar panel) • Tentative approaches attempted so far: • Linear interpolation • Weighted interpolation –various schemes • Statistical simulation (“equivalent sources”) • Best possible: Multipole field structure estimation: • Only feasible up to quadrupole approximation, though, • given only four magnetometers in LCA. Sagamihara, 13 November 2008

  27. Multipole reconstruction theory In vacuum, A multipole expansion of B follows that corresponding to y(x): The coefficients alm(r) depend on the magnetisation M(x). In an obvious notation, structure is: Sagamihara, 13 November 2008

  28. Somewhat legthy calculations lead to: with Multipole reconstruction theory • Evaluation of multipole terms is based on some assumptions: • Magnetisation is due to magnetic dipoles only • Such dipoles are outside the LCA. Sagamihara, 13 November 2008

  29. Fit criterion is to minimise squared error: Multipole reconstruction theory Idea is now to fit measured field values to a limited multipole expansion model. Arithmetic sets such limit to quadrupole: Sagamihara, 13 November 2008

  30. Arithmetics of reconstruction algorithm: Data channels: 12 Mlm dipole: 3 Mlm quadrupole: 5 Mlm octupole: 7 these 3 are uniformfield components 3+5 = 8 < 12 => some redundancy, OK 3+5+7 = 15, 3 unknowns too many! Multipole reconstruction theory • Summing up: • Full multipole structure up to quadrupole level. • This is poor, only first order polynomial approximation • Errors large --easily 300%, and rather unpredictable • Weighting procedure seems better, but also unpredictable Sagamihara, 13 November 2008

  31. Multipole reconstruction theory Simulation Sagamihara, 13 November 2008

  32. Multipole reconstruction theory Bottomline (qualitative) Sagamihara, 13 November 2008

  33. Multipole reconstruction theory Summary: • Ways to improve magnetic diagnostics accuracy: • Fluxgates are: • Only 4 • Far from TMs • Large size –long sensor heads, ~2 cm We have recently started preliminary activites at IEEC to assess feasibility of using AMR’s as an alternative to fluxgates. This kind of research is intended for LISA. Sagamihara, 13 November 2008

  34. Magnetometers tests m-metal enclosure Billingsley TFM Sagamihara, 13 November 2008

  35. Magnetometers tests LTP req. Billingsley TFM Sagamihara, 13 November 2008

  36. Magnetometers comparative Sagamihara, 13 November 2008

  37. SQUID test of AMR device Sagamihara, 13 November 2008

  38. Magnetic diagnostics summary • Fluxgate magnetometers are extremely sensitive • Sensor core is large => space resolution limits • Sensor core is permalloy => distance to TM constraints • Box is large and somewhat heavy => few sampling positions • AMRs indicate good sensitivity • They are very tiny • Weakly magnetic –due to small mass • More thorough investigation needed –underway at IEEC Sagamihara, 13 November 2008

  39. Radiation Monitor • Ionising particles will hit the LTP, causing spurious signals in the IS. • These are mostly protons (~90%), but there are also He ions (~8%) • and heavier nuclei (~2%). • Charging rates vary depending on whether • Galactic Cosmic Rays (GCR), or • Solar Energetic Particles (SEP) • hit the detector, as they present different energy spectra. • This has been shown by extensive simulation work at ICL. • Therefore a Radiation Monitor should provide the ability to distinguish • GCR from SEP events. • This means RM needs to determine energies of detected particles. • Use of RM is to obtain frequent determinations of charging rates, and • correlate them with IS charge management system. Sagamihara, 13 November 2008

  40. Radiation Monitor ICL simulations, based on GEANT-4. (Peter Wass and Henrique Araujo) Sagamihara, 13 November 2008

  41. Radiation Monitor • It is a particle counter with some • specific capabilities: • It counts particle hits • Retrieves spectral information • (coincident counts) • Can (statistically) tell GCR • from SEP events • Electronics is space qualified Sagamihara, 13 November 2008

  42. RM accommoation in S/C Sun Earth Sagamihara, 13 November 2008

  43. In place for test at PSI, Nov-2005 Sagamihara, 13 November 2008

  44. In place for test at PSI, Nov-2005 Sagamihara, 13 November 2008

  45. Radiation Monitor data Radiation Monitor data are formatted in a histogram-like form. A histogram is generated and sent (to OBC) every 614.4 sec. Sagamihara, 13 November 2008

  46. Summary • Thermal diagnostics: • Sensors fully in place • Heaters: in place, and integrating in EMP • Improved sensitivity towards LISA in progress • Magnetic diagnostics: • Sensors fully in place, sub-optimum expected performance • Research in progress towards LISA • Coils fully in place, working on EMP • Radiation Monitor: • EQM built, green light to FM, PSI tests coming up • More on RM in Tim’s talk Sagamihara, 13 November 2008

  47. End of Presentation Sagamihara, 13 November 2008

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