11

CRYOPLASMA IN HELIUM INDUCED BY CRYOPLASMA IN HELIUM INDUCED BY CORONA DISCHARGE CORONA DISCHARGE

N. Bonifaci, F. Aitken, G2Elab Grenoble, France

V Atrazhev, Joint Institute for High Temperatures, Russia

V.A. Shakhatov, Topchiev of Petrochemical Synthesis Institute, Russia

J. Eloranta Department of Chemistry,California State University, USA

K. von Haeften , Leicester University, Leicester, UK

G Vermeulen, Institut Néel Grenoble, France

2

Discharges in dense fluids (liquids or high-pressure gases :1-100 bar)

Motivation

2

Filamentary Streamers in Liquid N2

This process in dense fluids is very complex that involves

- electronic phenomena : electron injection, electron impact, excitation and ionization

- thermal phenomena: phase change

- hydrodynamic phenomena : formation of pressures waves, propagation of discharge channel.

Modeling

3

Cryoplasma in Helium

3

Discharge model in liquid model

µ-discharge Liquefied Helium

Condensed 4He

Interaction of atoms He*, molecules He2, and e- with helium in various thermodynamic phases and states

Gas liquid

300k 4.2k

nanoscopic probes

44

Corona discharge in dense heliumLiquide

Light emission

Transport zone : E ~ kV/cm µe and µ+

Ionization zone : Ep~ MV/cm

Densities of the plasma particles (Ne and Np), Temperature, etc

4

Crucial importance for the modelling of plasmas produced by electric discharges

I ~ 0.1-50µA, DC V ~ kV

Applied power : 0.5-100mW

gap distance~mm

Rp ~ 0.1-0.2µm

Gas pressure ~ 1-100 bar

CCD Camera picture

55

Electronic mobility

Ntr1021cm-3

0 50 100 150 200 2500,01

0,1

1

10

100

(c

m2 /V

.s)

N(1020cm-3)

T=6K T=7K T=10K

e- bubble

Transition

5

Electrons in condensed 4He

e- repulses surrounding atoms He

Repulsive interaction

Free e-

Electron bubbles are formed by excess electrons in condensed He

6

Optical Spectroscopic Investigation

Discharge in helium supercriticalat 300 K and 150 K

Discharge in helium liquidat 4.2 - 5.1KIn helium supercritical T<12K

He* lines, He2* excimers,

Impurities N2*, N2

+ ,H*, O*, OH

Continuum emission (400-1000 nm)

He* lines, He2*

7

Kinetic temperature of Discharge at 300K

Rovibrational spectra of molecules

Trotational =300K-320k ≈ Tk

He2

P=1-20barP=1-5 bar

(P=1-20Bar)

Cold plasmaTk

8

At 300K Hydrogen line : Electron density Ne

The lorentzian width of the H

profile is ascribed to stark broadening

485,7 486,0 486,3 486,6 486,9

1x106

1x106

2x106

2x106

2x106

2x106

2x106

2x106

I (a.

u.)

l (nm)

Ne~1015-1016 cm-3

He I : Stark Broadening

He Istark=0,08-0,2nm

Hydrogen Hnm

0,1 0,2 0,3 0,4 0,5 0,60

1x1015

2x1015

3x1015

4x1015

5x1015

6x1015

7x1015

8x1015

Ne c

m-3

Pressure MPa

Negative polarity Positive polarity

w

w

Stark width

9

At 300K Analysis of atomic He line 706.5 nm

696 698 700 702 704 706 708 710 712 7140,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1,0

Inte

nsity

nm

P=1MPa P=1.6MPa P=2.4MPa P=3.2MPa P=3.9MPa P=5.9MPa

“Blue” wing

Blue satellites

Main line disappears

700 702 704 706 708 710

P=0,1MPa

(nm)

700 702 704 706 708 710

P=1,4MPa

P=2,3MPa

700 702 704 706 708 710

P

10

Results for He line 706 nm (3S-3P) at 300K

Np=3.8 1020 cm3

P= 16 bar

Np=2.4 1020 cm3

P=10 bar

Np=4.8 1020 cm3

P= 20 bar

Comparison between experiment and theory

Np ≈ N

perturber density

N ALLARD, et al EPL 88 (2009) 53002

N ALLARD, et al EPJ D 61 (2011) 365-372

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Ionization zoneTransport zone

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NPlasma~ NNe 1015-1016cm-3

Tkinetic~ 300-320K

NT= 300 K

Nplasma and Tkinetic at T = 300 K

Discharge in helium gas at 300 K

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Discharge in liquid helium at 4.2 K

Discrepancy between the rotational temperature of He2(d3u+-b3g)

and He2(D1u+- B1g) Tkinetic

He2(d3u+-b3g)

He2(D1u+- B1g) Tr=700K

Tr=220K

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Discharge in liquid helium at 4.2 KShape of Line 706 nm in Liquid He at 4.2K.

685 690 695 700 705 710 715 720-0,2

0,0

0,2

0,4

0,6

0,8

1,0

1,2

1,4

Inte

nsi

ty

nm

P=0.1MPa P=0.6MPa P=1.6MPa P=3.5MPa

696 698 700 702 704 706 708 710 712 7140,0

0,2

0,4

0,6

0,8

1,0

Inte

nsi

ty

(nm)

P=0.5MPa P=1.3MPa P=2.6MPa P=4.7MPa P=5.7MPa

Strongly Blueshifted

Gas

300 K

706 nm line (3S-3P)

observed

in liquid helium

symmetrical Gaussian profile

696 698 700 702 704 706 708 710 712 7140,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1,0

Inte

nsity

nm

P=1MPa N=2.40 1020

P=1.6MPa N=3.83 1020

P=2.4MPa N=5.73 1020

P=3.2MPa N=7.61 1020

P=3.9MPa N= 9.25 1020

P=5.9MPa N=1.38 1021

Gas

150 K

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New Autocorrelation function liquid helium

rdrtrVi

ei

fi

3

/1exp

is the liquid density in the electronic ground state around 3s calculated using Bosonic Density Functional Theory DFT

i

He*(3s)

Ab initio potentials of the excited state He(3 3S)-He

In Analogy to electron bubbleRepulsion between excited atom (Rydberg e-) and surrounding atoms in the ground state forms bubble Atomic bubble

He* fluorescence lines originate from outside the discharge region

Bulk helium

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Liquid density around He*(3s)

Bubble Radius Rb depends on applied pressure P.

Liquid density around 3s3S excited state calculated using Density Functional Theory (DFT) 1 bar

6 bar

16 bar

LHe3s

35 bar

Empty cavity aroundexcited atom (radiator).

Bulkliquid

16

706.5 nm He* line (3S-3P)

Experimental (continuous) vs theoretical (dashed)

wth≈wexp

e-+He ->He*+e-+heat

the increased local temperature

3s

Electron impact excitation

« Local heating »

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Shape of Line 706 nm in Fluid He at 11 K.

Fixed temperatures 11 K, different pressures, the increasing density.the line has symmetrical Gaussian profile with shift and width dependent on Pressure

0 1 2 3 4 5 6

0

20

40

60

80

100

120

140

160

180

4.2 K 5.1 K 11 K 150 K 300 K

line

shift

cm

-1

P MPa

300K

150 K

4.2-11K

the same slopes at 4.2 and 11 K

Line shift

Empty cavity around excited atom (radiator).

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Conclusions

Discharge in helium gasat 300 K

Discharge in helium at 4.2 K-T= 11K

NPlasma~ N

Ne 1015-1016cm-3

Tkinetic~ 300-320K

He line 706,5nmLarge blue shiftGaussian Line ShapeThe line profile have been interpreted in terms of « bubble model » over extended temperature range

He* fluorescence lines originate from outside the discharge region

inhomogeneous structure

He Line 706.5 nm

Small blue shift

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CRYOPLASMA IN HELIUM INDUCED BY CORONA CRYOPLASMA IN HELIUM INDUCED BY CORONA DISCHARGE DISCHARGE

Thank you !