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Charge Management

Charge Management. Charging Effects Charging Processes Charge Control Technology LISAPF eLISA Summary and way forward for eLISA. T J Sumner. Charging Effects. Metallic Enclosure (Blaser). Time dependent forces*.

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Charge Management

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  1. Charge Management Charging Effects Charging Processes Charge Control Technology LISAPF eLISA Summary and way forward for eLISA T J Sumner First eLISA Consortium Meeting - APC, Paris 22nd October 2012

  2. Charging Effects Metallic Enclosure (Blaser) • Time dependent forces* For interplanetary fields shielding from electrode housing and vacuum housing – limited by access holes  η ~ 0.01 Interplanetary fields unlikely to be of concern, but be careful to maintain conducting enclosure integrity No shielding against test-mass motion relative to housing – uncancelled interplanetary residual plus internally generated static fields *Assumes VT = 0 First eLISA Consortium Meeting - APC, Paris 22nd October 2012

  3. Common-mode voltage effects disappear to first order in force Differential-mode voltages used for charge measurement Charging Effects • Time dependent forces* *Assumes VT = 0 First eLISA Consortium Meeting - APC, Paris 22nd October 2012

  4. Charging Effects • Time dependent forces First eLISA Consortium Meeting - APC, Paris 22nd October 2012

  5. Charging Effects • Acceleration noise First eLISA Consortium Meeting - APC, Paris 22nd October 2012

  6. Charging Processes • Uncaging – significant fractions of a volt potentials left on separating metallic surfaces – either sign • Cosmic-Rays & Solar Energetic Particles • GEANT4 – particle tracking GeV to 100eV – p + He • Araújo et al. Astropart.Phys.22, 451 (2005). Galactic Cosmic Rays First eLISA Consortium Meeting - APC, Paris 22nd October 2012

  7. Charge Spectrogram Charging Processes • Solar minimum R~100 +e/s SR=34.6 +e/s/Hz1/2 • Includes estimate for additional low-energy processes First eLISA Consortium Meeting - APC, Paris 22nd October 2012

  8. FLUKA cr protons  +37 /s at solar minimum cf +41 /s Charging Processes First eLISA Consortium Meeting - APC, Paris 22nd October 2012

  9. See also Mulligan et al. JGR, Evidence for relevant non-Gaussian events Charging Processes First eLISA Consortium Meeting - APC, Paris 22nd October 2012

  10. Charging Processes • Solar Energetic Particles First eLISA Consortium Meeting - APC, Paris 22nd October 2012

  11. Charge Control • Design – trade-off within gravitational reference sensor design • Initialisation – e.g. after uncaging to deal with unknown charge residual on test-mass • Charge measurement, timed exposure to UV (with bias voltage boost) • Preparation – iterative adjustment to prepare test-mass for science data taking • Charge measurement, timed differential exposure to UV • Science data – slow continuous closed loop feedback to: • Reduce coherent artefacts in science data due to cyclic force build-up • Suppress low-frequency 1/fn (n≥1) acceleration noise • Charge measurement, timed differential exposure to UV • Radiation monitor assistance for pre-emptive strike • Recovery – rapid response to occasional large excursions • Charge measurement, timed exposure to UV (with bias voltage boost) • Caging mechanism assistance? • [Data processing – removal of artefacts from science data] • Instrument history • Radiation monitor data • Other solar activity data • Science data First eLISA Consortium Meeting - APC, Paris 22nd October 2012

  12. Technology (eLISA and LISAPF) • Hardware • UV source • Optical harness • Sensor interface coupling • Actuation/sensing electronics – [Front-end electronics] • Radiation Monitor • Electrode/Housing surfaces • Test-mass surfaces • On-board software • Charge measurement • Commanding • Closed-loop feedback • Data Processing • Identification/removal of artefacts • Quality flags • Modelling/Simulation tools • Laboratory test-bed(s) First eLISA Consortium Meeting - APC, Paris 22nd October 2012

  13. Technology (LISAPF) • LISAPF solution: First eLISA Consortium Meeting - APC, Paris 22nd October 2012

  14. Technology (LISAPF) • LISAPF hardware: • ULU (UV Lamp Unit) • ISUK • FOH First eLISA Consortium Meeting - APC, Paris 22nd October 2012

  15. Technology • LISAPF validation status: • ICL test-bed results -  - demonstrated rapid discharge • First Trento torsion balance results -  - bipolar control, measurement, noise • Discharge Modelling/simulation -  - agreement with experiment • DFACS closed loop operations -  - devised viable algorithm • Subsequent Trento torsion balance results -  - inability to achieve bipolar control – surface properties implicated • LISAPF Discharge Working Group – see later • Radiation monitor beam tests - - Wass and Hollington First eLISA Consortium Meeting - APC, Paris 22nd October 2012

  16. LISAPF Dicharge Working Group • S2-ASD-RP-3230, Discharge Working Group Executive Summary • Problem: Discharge efficiency compromised by mismatch between surface properties of primary and secondary surfaces • Reflectivity • QY • Photo-electron energy distribution First eLISA Consortium Meeting - APC, Paris 22nd October 2012

  17. LISAPF Discharge Working Group • Recommendations from DWG: • ISS FM manufacturing adaptations • Apply ‘tube mirror’ to ISUKs JF02 and JF04 • Adapt gold coating (specification) for TM spheres First eLISA Consortium Meeting - APC, Paris 22nd October 2012

  18. LISAPF Discharge Working Group • Recommendations from DWG: • ISS FM manufacturing adaptations • Apply ‘tube mirror’ to ISUKs JF02 and JF04 • Adapt gold coating (specification) for TM spheres • ISH FM AIT adaptations • Apply plasma cleaning to surfaces before AIT • Handling requirements for defined “no-touch” zones on surfaces • Nitrogen storage of surfaces at all possible times • Apply bake-out of integrated ISS FM at 125°C • Apply UV cleaning of surfaces in the integrated ISS FM (pending qualification success) First eLISA Consortium Meeting - APC, Paris 22nd October 2012

  19. ISUK Modification Render of final design after iteration with CGS First eLISA Consortium Meeting - APC, Paris 22nd October 2012

  20. ISUK Modification • ISUK mirrors before coating • Prior to final iteration • Coating trials at Selex Galileo optical coatings First eLISA Consortium Meeting - APC, Paris 22nd October 2012

  21. Technology (eLISA) Tripling a red laser with BBO  212nm • LISA Studies: • Hardware • Controlled surface preparation • Improved/more detailed microphysics modelling/understanding • UV Lamps - shorten wavelength, second technology – Laser diodes/LEDs • Radiation Monitor definition • Operations • How to deal with two test-masses in the same spacecraft in a co-ordinated way? • Data artefacts, Live time • How to deal with three spacecraft in a co-ordinated way? • Data artefacts, moderate SEPS varying spatially/temporally from one spacecraft to another, Live time • Use of radiation monitor within the control loop • Data Analysis • Simulator including effects induced by both charge and charge control operations • Identification of artefacts • Removal of artefacts • Data Quality indicators • AOB • More space weather studies • GEANT4 with new spacecraft • Lessons from LISAPF First eLISA Consortium Meeting - APC, Paris 22nd October 2012

  22. ESA Technology Study AO/1-6482/10/NL/HB - LISA CHARGE MANAGEMENT SYSTEM Facility for longer term First eLISA Consortium Meeting - APC, Paris 22nd October 2012

  23. AO/1-6482/10/NL/HB - LISA CHARGE MANAGEMENT SYSTEM Phase 1 Phase 2 First eLISA Consortium Meeting - APC, Paris 22nd October 2012

  24. Some progress SRIS First eLISA Consortium Meeting - APC, Paris 22nd October 2012

  25. Some progress UVDM First eLISA Consortium Meeting - APC, Paris 22nd October 2012

  26. Tripling a red laser with BBO  212nm UV Light Sources UV LEDS SETI CRYSTAL-IS First eLISA Consortium Meeting - APC, Paris 22nd October 2012

  27. UV Light Sources – A/C synchronisation? Complicated by additional AC First eLISA Consortium Meeting - APC, Paris 22nd October 2012

  28. Summary • Charge control is crucial for eLISA operations • Charge control is crucial to the eLISA noise budget • Charge control impacts on the whole payload/(system?) • LISAPF will probably demonstrate that all aspects of charge control for eLISA are viable but marginal • There is still a long ‘shopping list’ of improvements/ optimisations required for eLISA First eLISA Consortium Meeting - APC, Paris 22nd October 2012

  29. Way Forward First eLISA Consortium Meeting - APC, Paris 22nd October 2012

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