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

2. First eLISA Consortium Meeting - APC, Paris 22nd October 2012 Charging Effects Time dependent forces* For interplanetary fields shielding from electrode housing and vacuum housing – limited by access holes  η ~ 0.01 *Assumes V T = 0 Metallic Enclosure (Blaser)  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

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

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

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

6. First eLISA Consortium Meeting - APC, Paris 22nd October 2012 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

7. First eLISA Consortium Meeting - APC, Paris 22nd October 2012 Charging Processes primary solarGCR fluxtimeline particle activity , /s/cm 2 , % N 0 (x10 6 ) CPU, daysT, sN 0 /N Q protons 4.2992.0121.11502002189 He-4min0.3156.814.4123211002 He-3 0.05911.314.11216831073 Total4.66100149.6174−419 protons 1.8991.953.3702001889 He-4max0.1426.99.311462849 He-3 0.02361.18.0102402928 Total2.0610070.691−359 Solar minimum R~100 +e/s S R =34.6 +e/s/Hz 1/2 Includes estimate for additional low-energy processes primary solar TM 0 TM 1 particle activityR, e/ss M, e/sS R,e/s/√HzR, e/ss M, e/sS R,e/s/√Hz protons 79.51.630.082.31.630.4 He-4min14.50.614.915.30.615.5 He-3 2.150.15.62.070.15.7 Total96.21.734.099.71.734.6 protons 35.61.223.839.41.325.4 He-4max7.10.412.47.00.412.8 He-3 0.900.063.90.890.064.0 Total43.61.327.147.31.428.7 Charge Spectrogram

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

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

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

11. First eLISA Consortium Meeting - APC, Paris 22nd October 2012 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/f n (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

12. First eLISA Consortium Meeting - APC, Paris 22nd October 2012 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)

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

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

15. First eLISA Consortium Meeting - APC, Paris 22nd October 2012 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

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

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

21. Technology (eLISA) 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 Tripling a red laser with BBO  212nm First eLISA Consortium Meeting - APC, Paris 22nd October 2012

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

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

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

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

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

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

28. First eLISA Consortium Meeting - APC, Paris 22nd October 2012 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

29. First eLISA Consortium Meeting - APC, Paris 22nd October 2012 Way Forward ItemLISAPFeLISANext step CommentDesirability UV typeHgLED/LaserEBB/EMSimpler, less aging, wider temp range, flexibility Very High ModeDCAC or DCEM/EBBIncreased safety margin High Surface study As supplied End-to- end spec. Test Facility Better surface control High Control loop Sigma- delta – 2 lamps PWM 1 lamp Test facility Lower noiseVery high ModelASDICLUpdate model Payload independence High GRSLTPLTP+ReviewAvoid caging, dis- charge electrode? Medium