SPIS multi time scale and multi physics capabilities:SPIS multi time scale and multi physics capabilities: development and

application to GEO charging and flashover modeling

ROUSSEL J.-F., DUFOUR G., MATEO-VELEZ J.-C. ONERATHIEBAULT B. ArtenumANDERSSON B SSCANDERSSON B. SSCRODGERS D., HILGERS A. ESAPAYAN D. CNES

Outline

Introduction

New modelling capabilities Multi time scale Multi time scale Multi physics

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Simulation cases Charging in GEO Flashover expansion

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Conclusions and perspectives

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SPIS context and project overview

SPINE (Spacecraft Plasma Interaction Network in Europe) community setup around year 2000 (A. Hilgers, J. Forest...): An idea was born: gather European efforts for SC-plasma interactions Exchange: knowledge, data, codes, results... Boost the development of a common simulation toolkit: ESA ITT in 2002 => SPIS

SPIS D l SPIS Development (Spacecraft Plasma Interaction Software) : Initial development: 2002 – 2005

ONERA-Artenum consortium ESA/ESTEC TRP contract

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ESA/ESTEC TRP contract Major solver enhancement: 2006 – 2009

Mostly ONERA ESTEC ARTES contract, French funding

this presentation

SPIS releases (open souce): - v4.0 July 2009 - v4.3 soon

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Others: Some community developments Some CNES-funded enhancements (EP, ESD) ESD t i i d lli l t l t d (ESA TRP)

next presentation (Pierre Sarrailh)

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ESD triggering modelling almost completed (ESA TRP) Next steps: EP integration (Astrium), SPIS-GEO (Artenum), SPIS-Science...

( )

Overall status of SPIS code SPIS-UI:

Real framework: task monitor, data management, script console (jython)… Interfacing with modeler/mesh-generator, postprocessing tools…

SPIS-Num: Plasma:

Matter models: PIC (leapfrog/exact (potential P1)), Boltzmann distribution, multi physics E field solver: Poisson, non linear Poisson, singularities (wires, plates) Volume interaction: CEX (MCC)

Spacecraft: Material properties: secondary emission (under electron/proton/UV), conductivities

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Material properties: secondary emission (under electron/proton/UV), conductivities (surface/volume, intrinsic/RIC), field effect, sputtering (recession rate, products generation and transport)

Equivalent circuit: coatings (RLC) + user-defined discrete components (RCV), implicit solver Sources: Maxwellian Axisymmetric two axes

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Specific features: Time integration: control at each level (population, plasma, simulation) Numerical times: integrate fast processes over a smaller duration (electrons/ions, plasma/SC…)

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Multiscale capabilities: cell = box / 100,000 Modularity: OO (Java), “plug-in” classes (Java introspection)

Outline

Introduction

New modelling capabilities Multi time scale Multi time scale Multi physics

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Simulation cases Charging in GEO Flashover expansion

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Conclusions and perspectives

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Multi time scale: requirements

Examples of modelling requirements: Charging in GEO: fast absolute charging (ms) / slow relative charging (mn) ESD triggering: slow precharge (mn) / very fast electron avalanche (ns!) + gg g p g ( ) y ( )

steep field emission

Surface potentials => SC circuit: Plasma

New SW requirements:spacecraft ground (node 0) Electric super node 1 Electric super node 2

C0 = Csat A0/Atot C1 = Csat A1/Atot C2 = Csat A2/Atot

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New SW requirements: Circuit:

Inductances " C " ( h i h h G h ) i d f d fi d

0 sat 0 tot 1 sat 1 tot 2 sat 2 totIf CSat >0

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Csat

Circuit solver: I li i

Newton type solver with: - dI/dV predictor (a matrix) with validity control

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ImplicitVariable, automatic time step

dI/dV predictor (a matrix) with validity control - automatic time steps (saturating validity)

The circuit solver: a test case0

Implicit solver / automatic time step: An example (GEO charging with -4000

-3000

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-10000 20 40 60 80 100

elecNode0ground elecNode1surface elecNode3surface

very large electron flux) Quite large range of time scales

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elecNode0ground elecNode1surface elecNode3surface

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elecNode0ground elecNode1surface elecNode3surface

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-4000

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elecNode1surface elecNode3surface

-3000

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-4000 elecNode0ground elecNode1surface elecNode3surface

Outline

Introduction

New modelling capabilities Multi time scale Multi time scale Multi physics

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Simulation cases Charging in GEO Flashover expansion

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Conclusions and perspectives

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Multi physics modelling requirement

Typically simulate in a single simulation: Dense quasi-neutral regions Low density, space charge regions

low density, space charge

Low density, space charge regions

Examples: Ambient plasma

positively biased surface

space charge region (sheath)at rest / sheath:

Expanding plasma /

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low density, space charge region

p g pfast electrons ahead of the plasma front (ESD, EP i iti )

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cathode spot, plasma source

EP ignition…):

Method:

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multi-zone, interface handling at sheath edge or plasma bubble edge

The physics at the boundary

Child-Langmuir theory: The current emitted at the boundary is the maximum allowed by space charge

(space charge limitation): E = 0 in the emission plane (Te = 0) Case 1D analytical: jCL ~ V 3/2 / d 2

ideal Child Langmuir situation (Te=0, no ions)ideal Child Langmuir situation (Te=0, no ions)ideal Child Langmuir situation (Te=0, no ions)V,

collecting

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xelectron source (dense

plasma in

collecting electrode

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potential (x 4̂/3)potential (x 4̂/3)charge density (~x^ 2/3)

potential (x 4̂/3)charge density (~x -̂2/3)potential due to larger charge

plasma in pour case)

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potential (x 4/3)charge density (~x -̂2/3)

charge density (~x -̂2/3)potential due to larger chargelarger charge (larger current)

potential due to larger chargelarger charge (larger current)potential due to smaller chargesmaller charge (smaller current)

Algorithm

Multi-physics solver design:

Loop 1: l

3. In case of "artificial source", electron balance for the expanding plasma bubble

plasma dynamics

2. Coupling of quasi-neutral region and space charge region (Child-Langmuir 3D)

Define n0 and Te in Boltzmann distribution n0exp(e/Te) for electrons in dense quasi-neutral region

Loop 2: CL

Modify local parameter defining jCL-3D = jCL-1D , itself defining boundary where jth = jCL-3D

2. Coupling of quasi neutral region and space charge region (Child Langmuir 3D)

no

electron b l

condition

Loop 3: "floating

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Particle dynamics (PIC electrons)

1. Vlasov-Poisson solving

no

noyes

CL condition:En = 0 on

yes

balance ok?potential" of

the plasma bubble (i l di

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yes Poisson equationStationary?

or given loop

number

(including cathode spot), still lacks

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lacks stability

Test case 1 – bubble LD T t l b bbl

total

Test case: plasma bubble expansion

Electron density:y composed of Boltzmann

electrons in dense ion zone (quasi neutral)(q )

and PIC electrons in low density zone (non neutral)

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Boltzmann PIC

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Test case 1 – bubble LD S

ep. 2

010

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Test case 2 – bubble HD

Test case2: plasma bubble expansion

Higher electron density (x 100)

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Boltzmann PIC

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Test case 2 – bubble HD S

ep. 2

010

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Test case 3 – Child-Langmuir test case

1D test case, close to ideal CL 1 case

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SPIS current density = 0.35 A/m2

CL theory at Te = 0:jCL = 0 233 A/m2

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- jCL = 0.233 A/m2

- fine, as much as can be checked

Specific difficulties encountered

Some extra instabilities were discovered and had to be handled (with specific algorithms):

CL condition feed back loop can be unstable (Bohm type instability) if too small ion gradient: extracting electric field can be due to a positive space charge in the space charge

zone, and increasing the electron emission is not necessarily an improvement! stability condition (li / d) (es / kTe) < 1, with: li the typical scale of ion density

variation (fixed at electron time scale), d the sheath size, s the sheath potential drop and Te the electron temperature

=> need to consider a possible positive space charge in the space charge zone to

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=> need to consider a possible positive space charge in the space charge zone to improve the algorithm

Bi-stable behaviour: A region can be consistently considered as:

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either in quasi-neutral zone (high density) or in the space charge zone (smaller density) (appeared when considering Ne not strictly = Ni in quasi-neutral)

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(appeared when considering Ne not strictly Ni in quasi neutral)

=> control of non neutrality w.r.t. cell size / Debye length ratio

…

Outline

Introduction

New modelling capabilities Multi time scale Multi time scale Multi physics

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Simulation cases Charging in GEO Flashover expansion

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Conclusions and perspectives

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Modelling charging in GEO

Plasma dynamics : Blocking of photo/secondary Blocking of photo/secondary

emission by the barrier (small barrier height compared to potentials involved)

Sun side Equipotential at-3100 V

Saddle point at– 3010 V

Accuracy of (collected) currents: small object in a large computation box (noisy) => backtracking

d d ( b f l f d

-4500 V (S/C ground)

-3000 V S/C solar array

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needed (can be useful for detector also e.g.) Shade side

-3500 V

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Multi-time scale modelling Implicit SC circuit solver

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Comparison with NASCAP modelling

Published model (Davis et al) Published model (Davis et al)

"Validation of NASCAP-2K spacecraft-environment interactions calculations", V. A. Davis, M. J. Mandell, B. M. Gardner, I. G. Mikellides, L. F. Neergaard, D. L. Cooke and J. Minor, 8th Spacecraft Charging Technology Conference, Huntsville, Alabama, USA, 20-24 oct. 2003

Similar model with SPIS (B. Andersson, SSC)

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Similar model with SPIS (B. Andersson, SSC)

Comparison of potential maps and time variation

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Potential maps (t=1000s)

Comparison with NASCAP Globally good agreement Small local differences (OSR e.g.) Small local differences (OSR e.g.) Often smaller gradient

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Without SEE

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Time evolution

Comparison with NASCAP: falls within NASCAP-series code

results

Node potentials vs Time

-2000

00 100 200 300 400 500 600 700 800 900 1000

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-6000

-4000

entia

l [V]

elecNode0ground elecNode0surface elecNode1surface elecNode2surface elecNode3surface

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-12000

-10000

-8000

Pote elecNode4surface

elecNode5surface elecNode6surface elecNode7surface

SC ground

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-14000

Time [s]

SC ground (the one to be compared)

-Part of the

/Chas

i

PVSA (shadow

id ) OSR

PVSA (solar

id )Main SC

t tTop

A t

Circular anten

- -

s/c si side) OSR side) structure Antenna nae

Material

Black kapton Kapton OSR Solar Cells Teflon

Non-conducting paint

Graphite

Absolute Charging (kV)

NASCAP/GEO -10.0 -8.2 to -13.1-8.23 to -

10.7-5.2 to -

7.68 -7.5 to -12.7-8.3 to -

10.3 N/A

SEE None in -7.5 to -SEE Handbook -8.6

None in model -7.3 to -9.6 -3.6 to -5.7 -6.8 to -11.3

7.5 to 11.3 N/A

Nascap-2k -12.0 -11.5 to -14.4-10.0 to -

13.7-7.2 to -

10.8 -7.9 to -14.0-7.9 to -

14.0 N/A

SPIS 10 9 12 9 11 7 6 1 9 8 9 7 10 9

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SPIS -10.9 -12.9 (-10.9 to -

13.9)

-11.7 -6.1(-5.8 to -

6.4)

-9.8(-7.9 to -11.6)

-9.7(-9.6 to -

9.8)

-10.9

Differential charging (kV)

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SEE Handbook

None in model 1.3 to -1.0 5 to 2.9 1.8 to -2.7 1.1 to -0.3 N/A

Nascap-2k 0 5 to -2 4 2 to -1 7 4 8 to 1 2 4 1 to -2 2 to -0 2 N/A

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Nascap 2k 0.5 to 2.4 2 to 1.7 4.8 to 1.2 4.1 to 2 2 to 0.2 N/A

SPIS -2.0(0 to -3.0)

-0.8 4.8(5.1 to 4.5)

1.1(3 to -0.7)

1.2(1.1 to 1.3)

0

Outline

Introduction

New modelling capabilities Multi time scale Multi time scale Multi physics

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Simulation cases Charging in GEO Flashover expansion

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Conclusions and perspectives

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Flashover experiment: the setup Inverted Potential Gradient charging

of a large coupon (CNES R&T) In JONAS plasma tank

(ONERA/DESP) Monitoring of flashover current

individually on some of the strings

canon à électrons

Large PVSA coupon: 1.33 x 0.6 m, 19 strings

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source à plasma

feuille de diffusion (V=+10 kV)

caméra reliée à un magnétoscope

distanceréglable

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Arcoupon de GS

réglable

trajectoire de la sonde de potentielsonde de potentiel

plateau support

More positive potential (SEE or plasma neutralisation)

Initially positive (global potential rise, BO), then progressive neutralisation (FO)

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cage de Faraday cellules du GS

negative potential (bias)~ zero potential (e- emission, BO)

Flashover experiment: the measurements

Individual currents on intermediate string (9 to 13) + others together

This ESD (No 16) on string 15

ESD n°16, initiated on string 15

0,2

0,4

rrent

s (A

) Delay of flashover on successive strings consistent with plasma

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-0,2

0,00,0E+00 5,0E-05 1,0E-04 1,5E-04Time (s)

Cu

Blow Off

consistent with plasma expansion at 104 m/s

Ahead of the plasma

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-0,6

-0,4

Blow-Off

string 9

string 10

string 11

t i 12

front, smaller current thought to be carried by electrons only (limited by space

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-0,8string 12

string 13

other strings

(limited by space charge)

FO modelling: the challenge

Multi physics: dense zone (plasma expansion) low density with positive potential low density with positive potential

Multi time scale Large currents in dense plasma

S ll t t f th l ( l t ) Small currents out of the plasma (electrons)

Difficult of coupling of both: Propagation of the plasma edge on the PVSA

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=> brutal variation of current expected on the cells Moving singular point

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in expansion

~ +1000 V ~ 0 V

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PVSA

~ 0 V

FO modelling

Initial conditions After the blow off PVSA ground already g y

back to ~ 0 Reason: loop 3 of

multiphysical model is needed to model that ("floating potential of the plasma bubble)

ESD model

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ESD model Ion source on a 5x5 cm

patch (Maxwellian, 10 mA – 1A range, 10-100 eV)

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Electron: Boltzmann distribution (10 eV, n0 = 1016 m-3) in the dense one + PIC in the space

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zone + PIC in the space charge zone

FO modelling: plasma expansion / ion density

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FO modelling: plasma expansion / ion density + zone boundary

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FO modelling: plasma expansion / electron density

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FO modelling: plasma expansion / electron density + isocontours

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FO modelling: potential

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FO modelling: current collectionESD n°16, initiated on string 15

0,2

0,4

urre

nts

(A)

Reaches all strings successively, but not the whole panel Expansion speed somewhat too fast Electron current ahead of the plasma correct

0 6

-0,4

-0,2

0,00,0E+00 5,0E-05 1,0E-04 Time (s)

Cu

Blow-Off

string 9

string 10

In presence of plasma, the plotted current is too large due to faster neutralisation and potprocessing artefact (current x 3 here due to an absence of current update in th i li it l I > I + dI/dV V)

-1,0

-0,8

-0,6 string 11

string 12

string 13

other string

the implicit solver I => I + dI/dV V)

0

0,E+00 1,E‐05 2,E‐05 3,E‐05time [s]

0 05

0,00

0,E+00 1,E‐05 2,E‐0

zoom on current y-axis

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‐5

t [A]

other strings (ESD side) ‐0,20

‐0,15

‐0,10

‐0,05

t [A]

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curren string 13

string 12string 11string 10string 9 ‐0,40

‐0,35

‐0,30

‐0,25

current

other strings (ESD side)string 13string 12string 11string 10

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‐30

‐25 string 9other strings (other side)

‐0,50

‐0,45

, string 10string 9other strings (other side)

Conclusions on FO simulation capabilities

Plasma expansion in volume with dynamical adjustment of the zone boundary: Operational Robustness could be improved: Robustness could be improved:

Several instabilities were identified (with respect to the ideal CL approach) Stabilisation schemes were proposed and tested => ok, sometimes needing manual tuning (UI-

accessible parameters) Improved schemes could be developed:

Improved feed back function (non linear…) Theoretically proven

Plasma expansion on S/C surfaces: interaction of zone boundary with surfaces

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Plasma expansion on S/C surfaces: interaction of zone boundary with surfaces Expansion certainly less favourable than in reality:

Total neutralisation of PVSA not demonstrated in SPIS, although exists in experiments Stopped expansions exist in experiments but are thought to be more related to cathode spot

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phenomena

Difficulty = presence of a singular point (line) where zone boundary crosses panel No specific handling => steps/peaks in current when boundary reaches a new node

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p g p p y => detailed study of this singular region needed (in particular centring of all quantities)

Conclusions and perspectives

Major solver improvements for SPIS: multi-physics, multi time scale Very ambitious Achievements:

Most features operational, not bad given the difficulties Still a lack of robustness of some points

Many applications: ESD triggering (electron avalanche), cf. next presentation: mn scale (charging) to ns scale

(electron avalanche)

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Positive biasing in a dense plasma (probes on SC, connectors on PVSA…)…

Perspectives

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Revisit some of the control features: to improve robustness To simplify the control parameters (more sophisticated automation)

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Complete (stabilise indeed) the external loop for multi physics ("floating potential" of the plasma bubble)