Development and validation of the thermal diagnostics instrumentation in lisa pathfinder

This thesis focuses on the issues related to the thermal diagnostics aboard the space mission LISA Pathfinder (LPF). LPF is a technological mission devoted to put to test critical subsystems for the LISA mission. LISA will be the first space born gravitational wave (GW) observatory with the main objective of detecting GWs. GWs are ripples of the space-time geometry caused by acceleration of masses in an asymmetric way. Their detection requires put test masses (TMs) in an almost perfect inertial frame (or free fall).Non-inertial forces perturbing the TMs must be less than 6 fN/sqrt(Hz) in the frequency range of 0.1 mHz to 0.1 Hz and the noise in the measurement between the TMs (separated by 5 Gm) must be of 40 pm/sqrt(Hz) in the same band. To reduce the risks of a direct launch of LISA, ESA has decided to first launch LPF to put all the LISA technologies to test.The payload of LPF, the LISA Technology Package (LTP), contains two TMs placed in two cylinders inside a single spacecraft (SC) and an interferometric system that measures the relative distance between them. The SC isolates the TMs from the external disturbances but internal stray forces will still perturb the TMs. Their levels must be bounded not to challenge the free fall accuracy. One of these disturbances is temperature fluctuations and the aspects related to their measurement are the leitmotif of this thesis.In chapter 1 we have presented how temperature fluctuations couple into the key subsystems of the LTP to degrade their performance. The foreseen effects are radiation pressure, radiometer effect, temperature coefficient of optical components, etc. Onground estimations conclude that the temperature stability in the LTP must be less than 100 microK/sqrt(Hz) in the frequency range of 1 mHz to 30 mHz (LTP band). Since temperature fluctuations are an important issue in LPF and in LISA, a thermal diagnostic subsystem is needed aboard both missions.The task of the thermal diagnostics in the LTP is twofold: on the one hand, temperature fluctuations in different subsystems must be measured with noise levels of 10 microK/sqrt(Hz) in the LTP band. On the other hand, a set of heaters will generate heat pulses that in conjunction with temperature measurements will be used to estimate the actual coupling between temperature and systems performance. These actions will provide information on the behaviour of the system and will permit to identify the fraction of noise in the system coming from temperature issues. The main function of LPF, as precursor mission of LISA, is the understanding of all the noise sources in the system. This will provide clues to the final leap from LPF sensitivity to LISA one.The main investigations carried out during this thesis can be split into three main categories: (i) the design and validation of the LTP temperature measurement subsystem (TMS); (ii) the extension of the system to the LISA requirements; and (iii) the analysis of the in-flight thermal experiments in the LTP. The thesis is organised as follows: in chapter 2 we describe the designed electronics and the temperature sensors chosen. Aspects related to the coupling of the TMS with other subsystems nearby are discussed in chapter 3. Chapter 4 focuses on the design of the testbed needed for the validation of the TMS. Two different testbeds are described: one for the LTP measurement bandwidth (MBW) and another one for the LISA MBW, 0.1 mHz. In chapter 5 we present the results of the test campaigns: the prototype, the engineering model and the flight model systems were put to test. The results of the investigations in the LISA band are also shown. Chapter 6 contains investigations in view of LISA requirements to reduce excess noise at very low frequency and to reduce the floor noise of the measurement. Chapter 7 focuses on the thermal experiment on-board LPF: a set of thermal excitations are proposed to extract information of the thermal behaviour of the key subsystems of the LTP

Identificació i caracterització de termòmetres d'alta precisió per a la missió espacial LPF

El present projecte es centra en la identificació i caracterització de sensors de temperatura per a ser utilitzats en la missió espacial LPF (LISA Pathfinder). Aquesta missió és la precursora d’una missió definitiva anomenada LISA (Laser Interferometer Space Antenna) que té com a objectiu la detecció d’ones gravitacionals provinents de forats negres massius i/o sistemes binaris; el fenomen de la radiació d’ones gravitacionals fou predit i caracteritzat per Einstein al 1918 i encara no ha estat confirmat de forma completa. El rang de freqüència extremadament baix (0.1 mHz a 0.1 Hz) així com les ínfimes variacions en la distància dels cossos provocades per les ones gravitacionals (d’ordres de 10-10-10-11 m en cossos separats per 5×106 km) obliguen a dissenyar un sistema de mesura extremadament sensible. La idea principal de la missió LISA és col·locar una sèrie de masses de prova en pura caiguda lliure a l’espai separades entre sí per 5 milions de km i així intentar detectar possibles variacions en la distància entre elles mitjançant interferometria. La missió LPF simplement pretén fer una sèrie de tests sobre els sistemes de control i mesura que s’utilitzaran a LISA, per tant, és una missió de caràcter purament tecnològic per a comprovar la viabilitat de LISA que, bàsicament, consisteix en mantenir uns nivells de soroll (d’acceleració residual entre les masses de prova) de (Aquí hi va una fórmula que està a l'arxiu "memòria") Aquests nivells de soroll (en la missió LPF es veuen relaxats un ordre de magnitud) poden ser provocats per qualsevol pertorbació que aparegui al satèl·lit, és per aquest motiu que un sistema de diagnòstic extremadament sensible ha de ser dissenyat i caracteritzat per a poder detectar petites fluctuacions que puguin induir acceleracions residuals. En el present projecte, el sistema de diagnòstic estudiat fa referència a les possibles pertorbacions tèrmiques susceptibles d’aparèixer durant la missió. Per tant, és necessari disposar d’uns sensors de temperatura que permetin mesurar variacions de temperatura de l’ordre de 0.1 mK amb una estabilitat superior als 4 10 K/ Hz − entre 1 mHz i 30 mHz. Per aconseguir un sistema de mesura que assoleixi aquests nivells de sensibilitat s’ha dissenyat una electrònica especialment silenciosa i s’han realitzat diferents tests (han consistit en aconseguir un entorn extremadament aïllat de les fluctuacions de temperatura externes per així poder determinar inestabilitats pròpies del sensor i de la seva electrònica associada) amb diferents tecnologies (bàsicament sensors de Platí i termistors NTC). Els resultats obtinguts i l’anàlisi de les dades mostren com els termistors NTC es comporten de forma menys sorollosa i per tant, en una primera aproximació seran probablement els utilitzats en el disseny definitiu del sistema de mesura de temperatura que anirà a bord del satèl·lit de la missi

Sub-Femto-g free fall for space-based gravitational wave observatories : LISA Pathfinder results

We report the first results of the LISA Pathfinder in-flight experiment. The results demonstrate that two free-falling reference test masses, such as those needed for a space-based gravitational wave observatory like LISA, can be put in free fall with a relative acceleration noise with a square root of the power spectral density of 5.2 +/- 0.1 fm s(-2)/root Hz, or (0.54 +/- 0.01) x 10(-15) g/root Hz, with g the standard gravity, for frequencies between 0.7 and 20 mHz. This value is lower than the LISA Pathfinder requirement by more than a factor 5 and within a factor 1.25 of the requirement for the LISA mission, and is compatible with Brownian noise from viscous damping due to the residual gas surrounding the test masses. Above 60 mHz the acceleration noise is dominated by interferometer displacement readout noise at a level of (34.8 +/- 0.3) fm/root Hz, about 2 orders of magnitude better than requirements. At f <= 0.5 mHz we observe a low-frequency tail that stays below 12 fm s(-2)/root Hz down to 0.1 mHz. This performance would allow for a space-based gravitational wave observatory with a sensitivity close to what was originally foreseen for LISA.Peer ReviewedPostprint (published version

State-space modelling for heater induced thermal effects on LISA pathfinder's test masses

The OSE (Offline Simulations Environment) simulator of the LPF (LISA Pathfinder) mission is intended to simulate the different experiments to be carried out in flight. Amongst these, the thermal diagnostics experiments are intended to relate thermal disturbances and interferometer readouts, thereby allowing the subtraction of thermally induced interferences from the interferometer channels. In this paper we report on the modelling of these simulated experiments, including the parametrisation of different thermal effects (radiation pressure effect, radiometer effect) that will appear in the Inertial Sensor environment of the LTP (LISA Technology Package). We report as well how these experiments are going to be implemented in the LTPDA toolbox, which is a dedicated tool for LPF data analysis that will allow full traceability and reproducibility of the analysis thanks to complete recording of the processes.Postprint (published version

Resistive-based micro-kelvin temperature resolution for ultra-stable space experiments

High precision temperature measurements are a transversal need in a wide area of physical experiments. Space-borne gravitational wave detectors are a particularly challenging case, requiring both high precision and high stability in temperature measurement. In this contribution, we present a design able to reach 1 µK/Hz---v in most of the measuring band down to 1 mHz, and reaching 20 µK/Hz---v at 0.1 mHz. The scheme is based on resistive sensors in a Wheatstone bridge configuration which is AC modulated to minimize the 1/f noise. As a part of our study, we include the design of a test bench able to guarantee the high stability environment required for measurements. We show experimental results characterising both the test bench and the read-out, and discuss potential noise sources that may limit our measurement.Peer ReviewedPostprint (published version

Identificació i caracterització de termòmetres d'alta precisió per a la missió espacial LPF

El present projecte es centra en la identificació i caracterització de sensors de temperatura per a ser utilitzats en la missió espacial LPF (LISA Pathfinder). Aquesta missió és la precursora d’una missió definitiva anomenada LISA (Laser Interferometer Space Antenna) que té com a objectiu la detecció d’ones gravitacionals provinents de forats negres massius i/o sistemes binaris; el fenomen de la radiació d’ones gravitacionals fou predit i caracteritzat per Einstein al 1918 i encara no ha estat confirmat de forma completa. El rang de freqüència extremadament baix (0.1 mHz a 0.1 Hz) així com les ínfimes variacions en la distància dels cossos provocades per les ones gravitacionals (d’ordres de 10-10-10-11 m en cossos separats per 5×106 km) obliguen a dissenyar un sistema de mesura extremadament sensible. La idea principal de la missió LISA és col·locar una sèrie de masses de prova en pura caiguda lliure a l’espai separades entre sí per 5 milions de km i així intentar detectar possibles variacions en la distància entre elles mitjançant interferometria. La missió LPF simplement pretén fer una sèrie de tests sobre els sistemes de control i mesura que s’utilitzaran a LISA, per tant, és una missió de caràcter purament tecnològic per a comprovar la viabilitat de LISA que, bàsicament, consisteix en mantenir uns nivells de soroll (d’acceleració residual entre les masses de prova) de(Aquí hi va una fórmula que està a l'arxiu "memòria")Aquests nivells de soroll (en la missió LPF es veuen relaxats un ordre de magnitud) podenser provocats per qualsevol pertorbació que aparegui al satèl·lit, és per aquest motiu que unsistema de diagnòstic extremadament sensible ha de ser dissenyat i caracteritzat per a poderdetectar petites fluctuacions que puguin induir acceleracions residuals. En el presentprojecte, el sistema de diagnòstic estudiat fa referència a les possibles pertorbacionstèrmiques susceptibles d’aparèixer durant la missió. Per tant, és necessari disposar d’unssensors de temperatura que permetin mesurar variacions de temperatura de l’ordre de 0.1mK amb una estabilitat superior als 4 10 K/ Hz − entre 1 mHz i 30 mHz. Per aconseguir unsistema de mesura que assoleixi aquests nivells de sensibilitat s’ha dissenyat una electrònicaespecialment silenciosa i s’han realitzat diferents tests (han consistit en aconseguir un entorn extremadament aïllat de les fluctuacions de temperatura externes per així poder determinarinestabilitats pròpies del sensor i de la seva electrònica associada) amb diferents tecnologies(bàsicament sensors de Platí i termistors NTC). Els resultats obtinguts i l’anàlisi de les dadesmostren com els termistors NTC es comporten de forma menys sorollosa i per tant, en unaprimera aproximació seran probablement els utilitzats en el disseny definitiu del sistema demesura de temperatura que anirà a bord del satèl·lit de la missi

Structure and phase transitions in A-site ordered RBaMn2O6 (R = Pr, Nd) perovskites with a polar ground state

We report here a structural study of RBaMn2O6 (R = La, Pr, and Nd) compounds by means of synchrotron radiation x-ray powder diffraction and Raman spectroscopy. The three compounds are A-site ordered perovskites adopting the prototypical tetragonal structure at high temperature. A ferromagnetic transition is observed in the LaBaMn2O6 sample and the lattice parameters undergo anisotropic changes at TC related to the orientation of the magnetic moments. Both PrBaMn2O6 and NdBaMn2O6 have a structural transition coupled to an electronic localization and an antiferromagnetic transition. In both cases, the x-ray diffraction patterns reveal that the lowtemperature phase is orthorhombic with lattice parameters a + b, b − a, and c with respect to the tetragonal phase. Two possible solutions belonging to the space groups Pmam and P21am can yield accurate refinements of the x-ray patterns. However, the active modes in the low-temperature phase disclosed by the Raman spectroscopy clearly point to the noncentrosymmetric space group, P21am. The symmetry analysis of this transition unveils that the primary modes belong to the irreducible representations M5− and GM5− and the main distortions correspond to rotations of the MnO6 octahedra and an asymmetric combination of stretching and scissoring modes of the basal oxygens in these octahedra. We conclude that the low-temperature phase is polar and the main contribution comes from the displacement of oxygen atoms from their centrosymmetric positions. However, negligible contribution from the asymmetric stretching associated with a Jahn-Teller distortion is found in this structural transition, suggesting the lack of ferroic orbital ordering of eg (3dx2−y2 ) orbitals in the orthorhombic ab plane. There is only one inequivalent site for the Mn atom in the low-temperature polar phase so charge ordering cannot account for the electronic localization having a structural origin.The authors would like to acknowledge the Servicio General de Apoyo a la Investigación from Universidad de Zaragoza. Granted beam time at ALBA synchrotron is appreciated (Proposal No. 2018093038). For financial support, we thank the Spanish Ministerio de Ciencia, Innovación y Universidades (Projects No. RTI2018-098537-B-C22 and No. RTI2018-098537-B-C21 cofunded by ERDF from EU, and Severo Ochoa FUNFUTURE, CEX2019-000917-S) and Diputación General de Aragón (Project No. E12-20R).Peer reviewe

Sub-Femto-g free fall for space-based gravitational wave observatories : LISA Pathfinder results

We report the first results of the LISA Pathfinder in-flight experiment. The results demonstrate that two free-falling reference test masses, such as those needed for a space-based gravitational wave observatory like LISA, can be put in free fall with a relative acceleration noise with a square root of the power spectral density of 5.2 +/- 0.1 fm s(-2)/root Hz, or (0.54 +/- 0.01) x 10(-15) g/root Hz, with g the standard gravity, for frequencies between 0.7 and 20 mHz. This value is lower than the LISA Pathfinder requirement by more than a factor 5 and within a factor 1.25 of the requirement for the LISA mission, and is compatible with Brownian noise from viscous damping due to the residual gas surrounding the test masses. Above 60 mHz the acceleration noise is dominated by interferometer displacement readout noise at a level of (34.8 +/- 0.3) fm/root Hz, about 2 orders of magnitude better than requirements. At f <= 0.5 mHz we observe a low-frequency tail that stays below 12 fm s(-2)/root Hz down to 0.1 mHz. This performance would allow for a space-based gravitational wave observatory with a sensitivity close to what was originally foreseen for LISA.Peer Reviewe