First eLISA Consortium Meeting - APC, Paris 22nd October 2012 Charge Management T J Sumner Charging Effects Charging Processes Charge Control Technology.

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


Charging Effects

Time dependent forces*

For interplanetary fields shielding from electrode housing and vacuum housing – limited by access holes η ~ 0.01

*Assumes VT = 0

BvtQFl )( HallEQMetallic

Enclosure(Blaser)

BvQFl

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


Charging Effects

Time dependent forces*

n

i

ii k

CV

C

tQ

k

C

C

tQ

12

2

2

232

2 4

2 d

Ad

d

A

C

tQ Common-mode voltage effects disappear to first order in force

Differential-mode voltages used for charge measurement

*Assumes VT = 0

32

2 2

d

A

C

Qk

2

2

2 k

CV

C

Q

k

CV

k

C

C

Qk r

cmr


Charging Effects

Time dependent forces

32

2 2

d

A

C

Qk

100mV

30pC

charges 102%10 7

Qk

k


Charging Effects

Acceleration noise

2

32

2

2

332

22 442

14

2

d

d

A

mC

QQdd

d

A

Cd

A

mC

Qa n

nn

2

2

2

2

2

222

nr

cmr

rn

rnn

kk

CV

mC

Q

k

CV

k

C

mC

Q

k

CV

mC

Q

k

CV

mC

Qa

222 vBQBQva nnn


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


Charging Processes

primary solar GCR flux timeline

particle

activity , /s/cm2 , % N0 (x106

)

CPU, days T, s N0/NQ

protons 4.29 92.0 121.1 150 200 2189

He-4 min 0.315 6.8 14.4 12 321 1002

He-3 0.0591 1.3 14.1 12168

3 1073

Total 4.66 100 149.6 174 − 419

protons 1.89 91.9 53.3 70 200 1889

He-4 max 0.142 6.9 9.3 11 462 849

He-3 0.0236 1.1 8.0 10240

2 928

Total 2.06 100 70.6 91 − 359Solar minimumR~100 +e/sSR=34.6 +e/s/Hz1/2

Includes estimate for

additional low-energy

processes

primary solar TM 0 TM 1

particle

activity R, e/s sM, e/s

SR,e/s/√Hz R, e/s sM, e/s

SR,e/s/√Hz

protons 79.5 1.6 30.0 82.3 1.6 30.4

He-4 min 14.5 0.6 14.9 15.3 0.6 15.5

He-3 2.15 0.1 5.6 2.07 0.1 5.7

Total 96.2 1.7 34.0 99.7 1.7 34.6

protons 35.6 1.2 23.8 39.4 1.3 25.4

He-4 max 7.1 0.4 12.4 7.0 0.4 12.8

He-3 0.90 0.06 3.9 0.89 0.06 4.0

Total 43.6 1.3 27.1 47.3 1.4 28.7

Charge Spectrogram


Charging Processes

FLUKA

cr protons +37 /s at solar minimum cf +41 /s


Charging Processes

See also Mulligan et al. JGR, Evidence for relevant non-Gaussian events


Charging Processes

Solar Energetic Particles


Charge Control

Design – trade-off within gravitational reference sensor designInitialisation – 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 UVScience data – slow continuous closed loop feedback to:

Reduce coherent artefacts in science data due to cyclic force build-upSuppress low-frequency 1/fn (n≥1) acceleration noise

Charge measurement, timed differential exposure to UVRadiation monitor assistance for pre-emptive strike

Recovery – rapid response to occasional large excursionsCharge measurement, timed exposure to UV (with bias voltage boost)

Caging mechanism assistance?[Data processing – removal of artefacts from science data]

Instrument historyRadiation monitor dataOther solar activity dataScience data


Technology (eLISA and LISAPF)

HardwareUV sourceOptical harnessSensor interface couplingActuation/sensing electronics – [Front-end electronics]Radiation MonitorElectrode/Housing surfacesTest-mass surfaces

On-board softwareCharge measurementCommandingClosed-loop feedback

Data ProcessingIdentification/removal of artefactsQuality flagsModelling/Simulation toolsLaboratory test-bed(s)


Technology (LISAPF)

LISAPF solution:


Technology (LISAPF)

LISAPF hardware:

ULU (UV Lamp Unit)

ISUK

FOH


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

Bias voltage on TM (V) vs time (s)

-10

-8

-6

-4

-2

0

2

4

-100 100 300 500

Time (s)

Bia

s vo

ltag

e o

n T

M (

V)

18/06/02

24/06/02

Au

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


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


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)


ISUK Modification


Render of final design after iteration with CGS

ISUK Modification


• ISUK mirrors before coating

• Prior to final iteration

• Coating trials at Selex Galileo optical coatings

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


ESA Technology Study AO/1-6482/10/NL/HB - LISA CHARGE MANAGEMENT SYSTEM


Facility for longer term

AO/1-6482/10/NL/HB - LISA CHARGE MANAGEMENT SYSTEM


Phase 2Phase 1

Some progress


SRIS

Some progress


UVDM

UV Light Sources


UV LEDSSETICRYSTAL-IS

Tripling a red laser with BBO 212nm

UV Light Sources – A/C synchronisation?


Complicated by additional AC


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


Way Forward

Item LISAPF eLISA Next step

Comment Desirability

UV type Hg LED/Laser EBB/EM Simpler, less aging, wider temp range, flexibility

Very High

Mode DC AC or DC EM/EBB Increased 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 noise Very high

Model ASD ICL Update model

Payload independence

High

GRS LTP LTP+ Review Avoid caging, dis-charge electrode?

Medium

First eLISA Consortium Meeting - APC, Paris 22nd October 2012 Charge Management T J Sumner Charging Effects Charging Processes Charge Control Technology.

Documents

elisa slide

elisa consortium meeting

s slide

charge spectrogram slide

testmass charge measurement

unknown charge residual

solar minimum r

eshz protons