VUV-diagnostics of inelastic collision processes in low tem - PowerPoint Presentation

Slide1

VUV-diagnostics of inelastic collision processes in low temperature hydrogen plasmas

J. Komppula

&

JYFL

ion source

group

University of

Jyväskylä

Department

of

Physics

FinlandSlide2

Motivation

Diagnostics challenging

Experimental plasma parameters

Ri = ne nn <σ v>i∆Te = 1.5 eV → ∆Ri = ±1000%This presentationRi ∝ photon emission ∆Te = ±1.5 eV → ∆Ri = ±50%H- ion source vs. H+ ion source

∝ R

i τ

∝ ni

Ion beam Slide3

Hot electrons

Energy

exceeds

threshold ofIonization (>15 eV)Electronic excitation (>6-10 eV)photonH2(v>5), 2S, c3ΠdissociationSlide4

Where is VUV from?

Atom

Molecule

BalmerlinesLymanlines

H

2

+

H

+

H

2Slide5

Processes related to VUV emission

50% → H

2

(v>5)15% → 2 HIonizationLyman-bandMolecular continuum

~100% →

2 H

30% → H

2

(c

3

Π)

Proportional to

Proportional toSlide6

How to measure?

Spectrometer

Good

spectral resolutionDifficulties in calibration for absolute intensityGeometry!Diode + bandpass filttersLower spectral resolutionEasy to connect and use~15% accuracy for absolute valuesA. McPherson et al., Applied Optics, vol. 25, 1986, 298-310.Slide7

Our apparatus

10 cmSlide8

Measurement of reaction rates

Measure photodiode current

+ Simple equation → volumetric emission rate

in line of sight volume+ coefficient → volumetric reaction rate ne nn <σ v>ionz ne nn <σ v>Ly-Band= ~ constant

15-60 min!

Ionization 30%v>5 20%Dissociation (

singlet) 20%Dissociation (triplet) 50%

Metastable states 50%

Order

of magnitude

~20

%

~20

%

~50

%

~50

%

∆T

e

= 1.5

eV

T

e

= 3-25

eV

n

e

n

n

<

σ

v>

x10

x1000

Total uncertaintySlide9

There is a catch

Monitor optical elements

Check background signals

Optical elements unstable in VUV rangeSignificant background signal possiblee.g. filamentSlide10

Benchmarking of simulations

Diagnostics of the most

significant electron impact

processesIncluded in simulationsHigh statistical noise in PIC-MCC simulationsImportance of validation H. C. Kim e al., J. Phys. D, 38 (2005) R238 M. J. Kushner, J. Phys. D, 42 (2009) 194013 M. M. Tuner, Plasma Sources Sci. Technol., 24 (2015) 035027Slide11

New hybrid simulation?

Reaction rates of hot electrons from experiments

Dynamics of the cold (main) electron populations from

simulationPIC, fluid model, etcSlide12

Development of ion sources?

Diagnostics about ion production

Surface processes and diffusion are important but...

Feedback from mechanical modificationsApprove or exlude conclusionsH2, H+ and H- ions+Slide13

Studied ion sources

H

-

: filament driven multicusp arcH+: 2.45 GHz microwavePower: 1 kWPower: 1 kWSlide14

Results

H

2

HP(metal)~10%P(BN)~<<1%Filament arc superior driver for H- volume productionExtremely poor energy efficiency in microwave dischargeMicrowave discharge a good proton source

due to surface association

H

-

(filament arc)

H

+

(2.45 GHz)

H

2

ionization

7-15

0.15-2

x10

16

1/cm

3

s

v>5 production

7-8

1-2

x10

16

1/cm

3

s

Dissociation (singlet)

2

0.3

x10

16

1/cm

3

s

Dissociation (triplet)

2-4

3-6

x10

16

1/cm

3

s

Total photon

emission

>15-20%

<8%

of P

heat

Lyman-alpha/Lyman-band

<1

5

Singlet

/triplet

~4

~1

Reactions

per molecule

Several

tens

2-20Slide15

Read more

VUV diagnostics of electron impact processes in low temperature molecular hydrogen plasma

J. Komppula and O. Tarvainen 2015 Plasma Sources Sci. Technol. 24 045008VUV irradiance measurement of a 2.45 GHz microwave-driven hydrogen discharge J. Komppula et al 2015 J. Phys. D: Appl. Phys. 48 365201My PhD thesis will be published in DecemberPS. I need a job!(Contract will end in December)