recent state and progress in negative ion modeling by means onix code

Mochalskyy Serhiy NI modeling workshop, Chiba, Japan, 2013

Recent state and progress in negative ion modeling by means ONIX code

Mochalskyy Serhiy1, Dirk Wünderlich1, Benjamin Ruf1, Peter Franzen1 Ursel Fanz1 and Tiberiu Minea2

1Max-Planck-Institut fuer Plasmaphysik

EURATOM Association

Boltzmannstr. 2,D-85748 Garching

2LPGP, Univerisity Paris-Sud, CNRS

F-91405 Orsay, France


Outline

• Introduction

• Code improvement

• Code validation

• Code benchmarking

• Realistic parameters

• Results

• Conclusions and future plans2/32


Introduction: Negative ion plasma source system

Driver Expansion region Extraction region

NI surface and volume production

The goal is to produce negative ion 48A H- (40A D-) (j~20mA/cm2) beam with INI/Ie~1 at low pressure 0.6pa during continuous 1 hour operation.

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Introduction: ONIX (Orsay Negative Ions eXtraction) code

3D Particle-in-Cell Monte Carlo Collision electrostatic code specially developed for modeling NI production and following extraction from ITER NBI plasma source.

Fully paralellized via MPI using domain and particle decomposition techniques. Able to deal with complex geometries as in the case of the extraction aperture.

Simulation domain

19 mm

14 mm

14 mm

Plasma

grid

Extraction

grid

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Code improvement: Second order charge and E field assignment routine (1)

First order

Potential distribution

Second order

Potential distribution

E(x) distribution E(x) distribution

P (V)

P (V)

P (V)

P (V)

Ex (V/cm)

Ex (V/cm)Ex (V/cm)

Ex (V/cm)

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x (mm)

y (mm)


Code improvement: Second order charge and E field assignment routine (2)

First order Second order

E(z) distribution E(z) distribution

Ex (

E(y) distribution E(y) distribution

Ey (V/cm)

Ey (V/cm) Ey (V/cm)Ey (V/cm)

Ez (V/cm)

Ez (V/cm) Ez (V/cm)Ez (V/cm)

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x (mm)

x (mm)

y (mm)

y (mm)


Code improvement: NI flux from PG (1) – injection method

Trajectories of NI Flux at the given x plane

Z (

mm

)

y (m

m)

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Code improvement: NI flux from PG (2) – extracted electron and NI current

Extracted NI current Extracted e current

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Code improvement: NI flux from PG (3) – potential well in vicinity to PG

Old routine

(normal injection, 1eV)

New routine

(random injection, 1eV)

New routine

(random injection, random energy 0.01 - 1eV)

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X (mm)

PG PG PG

X (mm) X (mm)

y (

mm

)

y (

mm

)

y (

mm

)

Potential (V) Potential (V) Potential (V)


Code improvement: Addition to the simulation H3+ ion and H-

in the volumeH3

+ density

y (m

m)

H- from volume density Y

(m

m)

Y (

mm

)

nH3+ (m-3)Extracted electron and

NI current

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nH3+ (m-3)

PG

PG

PG

PG


Code validation: Potential well test in simplified model

Potential well test Potential sheath test

X (mm)

Po

ten

tia

l (V

)

X (mm)

De

ns

ity

(m

-3)

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0V

-5V

-10V

0V

FIG. 10. Schematic of possible steady-state plasma potential profiles near a

positively biased plate. Curve A corresponds to a large plate. Curve B corresponds

to a small plate. Noah Hershkowitzb, Phys. Of Plasma (2005) 055502

Code validation: Potential well test in simplified model (2)

Negative bias

0V

5V

10V

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Po

ten

tia

l (V

)

Po

ten

tia

l (V

)

Potential (V)

Potential (V)

x (mm)

x (mm)

Positive bias


Code validation: different mesh size (real domain)

Ele

ctr

on

s c

urr

en

t

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PG PG

PG

x (mm)

x (mm)

x (mm)

y (m

m)

y (m

m)

y (m

m)

Potential (V)Potential (V)

Potential (V)


Code benchmark: ONIX vs KOBRA3D

2 completely different codes with different approaches:

1) ONIX – uses plasma parameters (density, temperature,…) to calculate the extraction current and meniscus shape;

2) KOBRA 3D –uses the extraction current to calculate the potential and meniscus shape

PI extraction test (2 runs)

Density 0.8, 1.6,*1017 m-3 , e:100%, H+:100%; Te=2eV, TPI=1eV

Extraction potential: -5kV; B field is switch off, no collisions

PG aperture 8 mm diameter

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Code benchmark: ONIX vs KOBRA3D (2)

PI extraction test (4 runs)

Density 0.8, 1.6, 2.4, 3.2*1017 m-3 , e:100%, H+:100%;

Te=2eV, TPI=1eV

Extraction potential: -5kV; B field is switch off, no collisions

PG aperture 8 mm diameter and 4mm length (2mm to PG knife

and 2 mm after)

ONIX

KOBRA3D

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Realistic parameters: Magnetic field map

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Filter field

Deflecting field

axial x directionve

rtic

al

z d

irect

ion



Complete 3D magnetic field structure and thus 3D model is necessary to perform realistic simulation of NI extraction.

Filter field

Deflecting field

axial x direction

vert

ical

z

dire

ctio

n

Bx

PG

Bz

PG

PG

PG

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By

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Filter field

Deflecting field

axial x direction

vert

ical

z

dire

ctio

n



By

Bz

Bx

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Realistic parameters: Plasma parameters in ONIX simulations

Probe measurements

ONIX

NI emission rate

BACON

Full 3D magnetic field map

3D field simulation

Geometry of the plasma grid

Engineering specification

OES

CRDS

n=3*1017m-3

ne=90%; nNI=10%,

nH+=40%, nH2+=40%, nH3+=20%

Te=2, TH-=0.1,TH+=0.8, TH2+=0.1, TH3+=0.1 (eV)

jNI,PG=660A/m2

nH=1*1019m-3, TH=0.8eV

nH2=4*1019, TH2=0.1eV

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Typical evolution of extracted NI currents

NI from the surface is dominant;

NI current from the inner surface of the PG is higher than one from outer side;

Co-extracted electron current ~3.5 times higher than total NI current in no PG bias test.

Conical PG surface

flat PG surface PG

ONIX results BATMAN results

(no PG bias)

29.16~ cmmAjNI

15.4~ NIe II 3~NIe II

214~ cmmAjNI

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Results: Limitation of the NI extraction

Potential distributionin vicinity to PG

PG

Potential (V)

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x (mm)

y (m

m)


Results: Potential at the wall

Emission rate ~250A/m2 (~-3V)



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x (mm)

PG

PG

x (mm)y

(m

m)

y (

mm

)

Potential (V)

Potential (V)


Limitation of the NI extraction

NI density produced from the conical surface of PG

NI density produced from the flat surface of PG

NI density produced at the volume

Results:

Total NI density along domain

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x (mm)

x (mm) x (mm)

x (mm)

y (m

m)

y (m

m)

y (m

m)

y (m

m)

Density (m-3)

Density (m-3)

Density (m-3)

Density (m-3)

PG

PG

PG

PG

PG

PG


Results: Ion –Ion plasma calculation (NI current)

No B field With B field

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z ve

rtic

al d

irec

tion

z ve

rtic

al d

irec

tion

y horizontal direction y horizontal direction

curr

ent

(mA

)

curr

ent

(mA

)


Results: Ion –Ion plasma calculation (NI density distribution)


x (mm) x (mm)

x (mm) x (mm)

y (

mm

)y

(m

m)

y (

mm

)y

(m

m)

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Density (m-3)

Density (m-3)Density (m-3)

Density (m-3)


Results: Ion –Ion plasma calculation (e current)


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z ve

rtic

al d

irec

tion

y horizontal direction

z ve

rtic

al d

irec

tion

y horizontal direction

curr

ent

(mA

)

curr

ent

(mA

)


Results: Ion –Ion plasma calculation (e density distribution)


x (mm) x (mm)

y (

mm

)

y (

mm

)

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Density (m-3) Density (m-3)


Results: Ion –Ion plasma calculation (H+ density distribution - meniscus)


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x (mm) x (mm)

y (m

m)

y (m

m)

Density (m-3)Density (m-3)


Results: Ion-ion plasma simulations (5 runs)

e current densityNI current density

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Results: Meniscus shape for several ion-ion plasmas (5 runs)

H+ density95:5=e:NI (%)

75:25

50:50

25:75

5:95

PG

PG

PG

PG

PG

PG

PG

PG

PG

PG

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Thank you for your attention

Project is supported by

the Alexander von Humboldt foundation

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recent state and progress in negative ion modeling by means onix code

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