LTP diagnostics Alberto Lobo ICECSIC IEEC A Lobo

LTP diagnostics Alberto Lobo ICE-CSIC & IEEC A. Lobo Barcelona, LISA #7, 20 June 2008 1

Why is diagnostics analysis needed in the LTP? LISA’s top level sensitivity requirement is: LISA: This is so very demanding a previous LPF mission is planned, with a relaxed sensitivity requirement: LPF: Even if LTP works to top perfection, a fundamental queston remains: How do we make it to LISA’s sensitivity? A. Lobo Barcelona, LISA #7, 20 June 2008 2

DDS: Data Management & Diagnostics Subsystem Diagnostics items: DMU: • Purpose: – Noise split up • Purpose: – LTP computer • Sensors for: – Temperature – Magnetic fields – Charged particles • Hardware: • Calibration: – Heaters – Induction coils A. Lobo – Power Distribution Unit (PDU) – Data Acquisition Unit (DAU) – Data Processing Unit (DPU) • Software: – Boot SW – Application SW: ü Diagnostics items ü Phase-meter Refer to poster by ü Interfaces Barcelona, LISA #7, 20 June 2008 Conchillo & Gesa, no. 33 3

Diagnostics items use The methodology: 1. 2. 3. 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. . . A. Lobo Barcelona, LISA #7, 20 June 2008 4

Noise reduction philosophy Problem: to assess the contribution of a given perturbation to the total noise force. Approach: 1) Apply controlled perturbation a to the system 2) Measure “feed-through” coefficient between force and perturbation: 3) Measure actual a with suitable sensors 4) Estimate contribution of a by linear interpolation: 5) Substract out from total detected noise: 6) Iterate process for all identified perturbations A. Lobo Barcelona, LISA #7, 20 June 2008 5

Thermal and sensor requirements Global LTP stability requirement: 10 -4 K/ÖHz , Sensor sensitivity requirement: 10 -5 K/ÖHz , A. Lobo 1 m. Hz < f < 30 m. Hz 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 --- Barcelona, LISA #7, 20 June 2008 6

DMU test campaign Transfer function Thermal damper A. Lobo Barcelona, LISA #7, 20 June 2008 7

DMU test campaign DMU EQM A. Lobo Barcelona, LISA #7, 20 June 2008 8

DMU test campaign Open thermal damper, wiring and DMU Insulating anechoic chamber for the test A. Lobo Barcelona, LISA #7, 20 June 2008 9

DMU test campaign Digital processing Analog processing PSD 1(f) + x(t) A + m(t) n(t) SN(f) FEE Analog PCB A. Lobo + S/H A/D PSDint(f) Integrator N PSD 3(f) PSDdiff(f) + M + 2 Z-1 - n. A/D(t) SNA/D(f) FEE Readout electronics y (t) PSDy(f) 1/2 PC data acquisition program FEE A/D PCB Barcelona, LISA #7, 20 June 2008 10

DMU test campaign Test general schematics A. Lobo Barcelona, LISA #7, 20 June 2008 11

DMU test campaign Example run A. Lobo Barcelona, LISA #7, 20 June 2008 12

DMU test campaign A. Lobo Barcelona, LISA #7, 20 June 2008 13

DMU test campaign A. Lobo Barcelona, LISA #7, 20 June 2008 14

Thermal sensing summary • Fully compliant with requirements • Thermal gradients slightly distort performance at low frequency • Magnetic properties of NTCs not an issue • Research ongoing for improvements for LISA, encouraging first results Refer to poster presentation by Pep Sanjuan, no. 27 and yesterday presentation A. Lobo Barcelona, LISA #7, 20 June 2008 15

Heaters will be used to measure thermal feedthroughs Number Maximum peak to peak temp. variation within MBW Comments Req. No. 4 100 m. K as detected by closest sensor 2 per window 3. 6 4 1 on each 10 m. K on inner xouter x-face of faces of EH EH 3. 7 Suspension struts 6 100 m. K (TBC) as detected by closest sensor 1 per strut 3. 8 TOTAL 14 --- Location Optical window Inertial sensors A. Lobo Barcelona, LISA #7, 20 June 2008 16

Heaters A. Lobo Barcelona, LISA #7, 20 June 2008 17

Heaters Measurements: Temperatures T 5, T 6 in IS 1, T 12 in IS 2 Laser Metrology x 1 for IS 1, x 2 = x 1 + D for IS 2 Thermal signals: temperature closest to activated heater Data Analysis: fit data to ARMA(2, 1): • Should be OK in MBW –even beyond!–, and for each OW • Can easily be improved, if necessary, at lower frequencies A. Lobo Barcelona, LISA #7, 20 June 2008 18

Heaters Refer to poster presentation by Miquel Nofrarias, no. 38 A. Lobo Barcelona, LISA #7, 20 June 2008 19

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 Au. Pt alloy a = 46 mm m = 1, 96 kg 70% Au + 30% Pt of low susceptibility and low remnant magnetic moment: A. Lobo Barcelona, LISA #7, 20 June 2008 20

Quantification of magnetic effects If a magnetic field B acts on a small volume d 3 x 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 dependence on B. A. Lobo Barcelona, LISA #7, 20 June 2008 21

Summary of magnetic requirements Magnitude Value 10 m. T DC magnetic field 5 m. T/m DC magnetic field gradient Magnetic field fluctuation rms PSD Magnetic field gradient rms PSD 650 n. T/ÖHz 250 (n. T/m) /ÖHz Magnetic susceptibility Remnant magnetic moment A. Lobo Barcelona, LISA #7, 20 June 2008 10 -5 10 -8 Am 2 22

Magnetic sensor requirements Req 2: A minimum 4 magnetometers. Req 2 -1: Resolution of 10 n. T/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. Lobo Barcelona, LISA #7, 20 June 2008 23

Magnetometer layout Magnetometers type: • 4 Flux-gate, 3 -axis magnetometers Model is TFM 100 G 2 from Billingsley Magnetics. Areas for magnetometer accommodation A. Lobo Barcelona, LISA #7, 20 June 2008 24

Magnetometers’ accommodation A. Lobo Barcelona, LISA #7, 20 June 2008 25

Magnetic field map A. Lobo Barcelona, LISA #7, 20 June 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. A. Lobo Barcelona, LISA #7, 20 June 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: A. Lobo Barcelona, LISA #7, 20 June 2008 28

Multipole reconstruction theory Evaluation of multipole terms is based on some assumptions: 1. 2. Magnetisation is due to magnetic dipoles only Such dipoles are outside the LCA. Somewhat legthy calculations lead to: with A. Lobo Barcelona, LISA #7, 20 June 2008 29

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. Lobo Barcelona, LISA #7, 20 June 2008 30

Multipole reconstruction theory Arithmetics of reconstruction algorithm: Data channels: 12 Mlm dipole: 3 Mlm quadrupole: 5 Mlm octupole: 7 these 3 are uniform field components 3+5 = 8 < 12 => some redundancy, OK 3+5+7 = 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 100%, and rather unpredictable • Order of magnitude should be OK A. Lobo Barcelona, LISA #7, 20 June 2008 31

Multipole reconstruction theory 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. A. Lobo Barcelona, LISA #7, 20 June 2008 32

Magnetometers tests m-metal enclosure Billingsley TFM A. Lobo Barcelona, LISA #7, 20 June 2008 33

Magnetometers tests LTP req. Billingsley TFM A. Lobo Barcelona, LISA #7, 20 June 2008 34

Magnetometers comparative A. Lobo Barcelona, LISA #7, 20 June 2008 35

SQUID test of AMR device A. Lobo Barcelona, LISA #7, 20 June 2008 36

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 Refer to poster presentation by Nacho Mateos, no. 33 A. Lobo Barcelona, LISA #7, 20 June 2008 37

Control coils Philosophy: to apply controlled periodic magnetic fields: Force comes then a two frequencies: measure c (w ~ 1 m. Hz) Coils must be long (2400 turns), to maintain reduced heat dissipation (~few m. W). A. Lobo Barcelona, LISA #7, 20 June 2008 38

Control coils Purpose: • To measure c in flight • To measure M in flight • To drive magnetic noise Coils must comply with suitable reqs. of power and stability. Workings with DMU have been successfully tested and reported. A. Lobo Barcelona, LISA #7, 20 June 2008 39

General LTP layout Coil Magnetometer Coil A. Lobo Magnetometer Barcelona, LISA #7, 20 June 2008 40

Radiation Monitor Ionising particles will hit the LTP, causing spurious signals in the IS. These are mostly protons (~90%), but there 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. A. Lobo Barcelona, LISA #7, 20 June 2008 41

Radiation Monitor ICL simulations, based on GEANT-4. (Peter Wass and Henrique Araujo) A. Lobo Barcelona, LISA #7, 20 June 2008 42

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. Lobo Barcelona, LISA #7, 20 June 2008 43

RM accommoation in S/C Sun Earth A. Lobo Barcelona, LISA #7, 20 June 2008 44

In place for test at PSI, Nov-2005 A. Lobo Barcelona, LISA #7, 20 June 2008 45

In place for test at PSI, Nov-2005 A. Lobo Barcelona, LISA #7, 20 June 2008 46

Radiation Monitor data are formatted in a histogram-like form. A histogram is generated and sent (to OBC) every 614. 4 sec. A. Lobo Barcelona, LISA #7, 20 June 2008 47

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. Lobo Barcelona, LISA #7, 20 June 2008 48

End of Presentation A. Lobo Barcelona, LISA #7, 20 June 2008 49