A. LoboSagamihara, 13 November LTP diagnostics Alberto Lobo ICE-CSIC & IEEC

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

A. LoboSagamihara, 13 November 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

A. LoboSagamihara, 13 November Diagnostics items use The methodology: 1. Split up total noise readout into parts –e.g., thermal, magnetic, Identify origin of excess noise of each kind 3. 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...

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

A. LoboSagamihara, 13 November LocationNTCsCommentsReq. 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 Sensor sensitivity requirement: K/  Hz, 1 mHz < f < 30 mHz Global LTP stability requirement: K/  Hz, 1 mHz < f < 30 mHz Thermal and sensor requirements

A. LoboSagamihara, 13 November Thermal damper Transfer function DMU test campaign

A. LoboSagamihara, 13 November DMU test campaign DMU EQM

A. LoboSagamihara, 13 November DMU test campaign Insulating anechoic chamber for the test Open thermal damper, wiring and DMU

A. LoboSagamihara, 13 November DMU test campaign S/HA/D Integrator N M Z /2 + - A x(t) + n(t) S N (f) + m(t) y (t) PSD y (f) PSD1(f) PSD 3 (f) PSD diff (f) Analog processing Digital processing PSD int (f) n A/D (t) S NA/D (f) + + FEE Readout electronics PC data acquisition program FEE Analog PCB FEE A/D PCB

A. LoboSagamihara, 13 November DMU test campaign Example run

A. LoboSagamihara, 13 November DMU test campaign

A. LoboSagamihara, 13 November DMU test campaign

A. LoboSagamihara, 13 November 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!

A. LoboSagamihara, 13 November NTCs magnetic properties First magnetisation curves Damaged sample!

A. LoboSagamihara, 13 November NTCs magnetic properties Summary of magnetic moments of the screened NTCs (Am 2 ):

A. LoboSagamihara, 13 November 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,

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

A. LoboSagamihara, 13 November 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

A. LoboSagamihara, 13 November 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 and low remnant magnetic moment: a = 46 mm m = 1,96 kg

A. LoboSagamihara, 13 November If a magnetic field B acts on a small volume d 3 x with remnant magnetisation M, and susceptibility , the force on this small volume is: Total force requires integration over TM volume, or: Quantification of magnetic effects Most salient feature is non-linearity of force dependence on B.

A. LoboSagamihara, 13 November MagnitudeValue DC magnetic field  T DC magnetic field gradient  T/m Magnetic field fluctuation rms PSD 650 nT/  Hz Magnetic field gradient rms PSD 250 (nT/m) /  Hz Magnetic susceptibility10 -5 Remnant magnetic moment10 -8 Am 2 Summary of magnetic requirements

A. LoboSagamihara, 13 November 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.

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

A. LoboSagamihara, 13 November Magnetometers’ accommodation

A. LoboSagamihara, 13 November 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.

A. LoboSagamihara, 13 November Multipole reconstruction theory In vacuum, A multipole expansion of B follows that corresponding to  (x) : The coefficients a lm (r) depend on the magnetisation M(x). In an obvious notation, structure is:

A. LoboSagamihara, 13 November Multipole reconstruction theory Evaluation of multipole terms is based on some assumptions: 1. Magnetisation is due to magnetic dipoles only 2. Such dipoles are outside the LCA. Somewhat legthy calculations lead to: with

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

A. LoboSagamihara, 13 November Multipole reconstruction theory Arithmetics of reconstruction algorithm: Data channels: 12 M lm dipole: 3 M lm quadrupole: 5 M lm octupole: = 8 some redundancy, OK these 3 are uniform field components = 15, 3 unknowns too many! 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

A. LoboSagamihara, 13 November Multipole reconstruction theory Simulation

A. LoboSagamihara, 13 November Multipole reconstruction theory Bottomline (qualitative)

A. LoboSagamihara, 13 November 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. Multipole reconstruction theory Summary:

A. LoboSagamihara, 13 November Magnetometers tests  -metal enclosure Billingsley TFM

A. LoboSagamihara, 13 November Magnetometers tests Billingsley TFM LTP req.

A. LoboSagamihara, 13 November Magnetometers comparative

A. LoboSagamihara, 13 November SQUID test of AMR device

A. LoboSagamihara, 13 November 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

A. LoboSagamihara, 13 November 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. Radiation Monitor

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

A. LoboSagamihara, 13 November 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

A. LoboSagamihara, 13 November RM accommoation in S/C Sun Earth

A. LoboSagamihara, 13 November In place for test at PSI, Nov-2005

A. LoboSagamihara, 13 November In place for test at PSI, Nov-2005

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

A. LoboSagamihara, 13 November 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

A. LoboSagamihara, 13 November End of Presentation