Thermal Plasmas - Fundamentals Tony Murphy Summer School, 21 st International Symposium on Plasma...

Thermal Plasmas - FundamentalsTony Murphy Summer School, 21st International Symposium on Plasma Chemistry1 August 2013MATERIALS SCIENCE AND ENGINEERING

Outline1. A brief introduction to plasmas2. Thermal plasma properties

Local thermodynamic equilibrium (LTE) Composition Thermodynamic and transport properties Radiative emission Deviations from LTE

3. Generation of thermal plasmas Transferred arcs Non-transferred arcs RF inductively-coupled plasma torches Types of plasma flow

4. Modelling of thermal plasmas Equations Turbulence, electrode sheaths, gas mixtures

5. Thermal plasma diagnostics Enthalpy probes Emission spectroscopy Laser scattering

Charged Species are Accelerated by the Electric Field

Ar+

Anode

Cathode

e

EAr+

Anode

Cathode

e

E

Collisions between Electrons and Heavy Species Transfer Little Energy

Ar+

Anode

Cathode

e

E

kin 2 e hE m mAr+

Anode

Cathode

Ee

Lots of Collisions between Electrons and Ions Transfer A Lot of Energy

Ar+

Anode

Cathode

e

E

Ar+

Ar+

Ar+

Ar+

Ar+ ee

ee

e

e

e

ee

Ar+

Anode

Cathode

E

Ar+

Ar+

Ar+

e

e

e6

5

For 15 000 K,

1 atm:

3 10 m ~

7 10 m/s ~ 5 ps

e e el v

Maxwellian Distribution

2 312 2 Bmv k T

Established for electrons, and for heavy speciesFor electron and heavy-species temperatures to be equal, need high collision rate

Effect of Pressure on Equilibrium

Increasing pressure increases the number density,and therefore the collision rate and the transfer of energyfrom electrons to heavy species

Industrial PlasmasLow-pressure plasmas

Arc weldingPlasma sprayingPlasma cuttingMineral processingWaste treatmentArc lampsNanoparticle production

Ozone productionElectrostatic precipitationPolymer treatmentSterilisationPlasma TVs

Semiconductor etchingFluorescent lightingThin-film deposition

Atmospheric-pressure non-equilibrium plasmas

Thermal plasmas

2. Thermal Plasma Properties

What is a Thermal Plasma?At or close to atmospheric pressure (at least 0.1 atm)Temperature ~ 1 to 2 eV (10 000 to 20 000 K) for electrons and heavy speciesFormed by dc or ac electric arcs, radio-frequency or microwave electromagnetic fieldsDominated by collisionsHighly ionised (typically 100%, at least 5%)High electron densities (~ 1023 m-3)Very widely used in manufacturing and other industries High power fluxes High fluxes of reactive species Strong radiative emission

Local Thermodynamic Equilibrium (LTE)

LTE exists if all species satisfy

• Maxwellian distribution for translational temperatures

• Boltzmann distribution for excitation temperatures

• Chemical equilibrium equations for reactions, e.g., ionisation

and all these temperatures are the same

LTE exists if the collision rate is much greater than the rates of diffusion and convection

It is generally valid in the bulk of the plasma (away from the edges and electrodes)

If LTE exists, then if we know (at a given point in the plasma)

• the pressure

• the temperature (or instead the density of any species)

• if there is a mixture of gases, the proportions of each gases

then we can fully describe the composition of the plasma at that point

This greatly simplifies modelling and diagnostics

0 5000 10000 15000 20000 25000 300001020

1021

1022

1023

1024

1025

1026

e-,Ar+

Ar3+

Ar2+

Num

ber

dens

ity (

m-3)

Temperature (K)

Ar

Ar+

e-

Why We Love LTE

Example:argon arcat 1 atm

Classification of PropertiesThermodynamic properties Mass density (kg/m3) Specific heat at constant pressure cp (J/kg/K) Specific enthalpy (J/kg)

Transport properties (transport coefficients) Viscosity (kg/m/s) Thermal conductivity (W/m/K) Electrical conductivity (S/m) Ordinary diffusion coefficient (m2/s) Thermal diffusion coefficient (kg/m/s)

Radiation properties Net emission coefficient (W/m3/sr)

Why Calculate Plasma Properties?1. They are needed for computational modelling

2

( ) 0

( )( )

where 2 , etc

5( )( )

2

where is a function of

0

rr r

p

B

pc c

h

t

Pt

v r

khh h h

t e

T

Uκ

v

vvv τ

v

j B g

jj

Why Calculate Plasma Properties?2. Measurements are inaccurate and inadequate

0 5000 10000 15000 20000 25000 300000

1

2

3

4

5

6

Nitrogen, 1 atm

Temperature (K)

The

rmal

con

duct

ivity

(W

m-2

K-1

)

Calculated (Murphy) Measured (Hermann & Schade) Measured (Plantikow)

0 5000 10000 15000 20000 25000 300000.00000

0.00005

0.00010

0.00015

0.00020

0.00025

Nitrogen, 1 atm

Temperature (K)V

isco

sity

(kg

m-1

s-1)

Calculated (Murphy) Measured (Guevara et al.)

Relation between Basic Data and Material Properties

Species t hermo - d ynamic d ata

Binary collision integrals

Composition

Thermodynamic properties

Transport properties

Fluid dynamic equations

Basic data

Properties

Plasma Composition

Use either: Saha equations for ionisation reactions & Guldberg-Waage

equations for dissociation reactions– Solve simultaneously (one equation for each reaction)

Minimisation of Gibbs free energy G = H – TS (H = enthalpy, S = entropy)– Restrictions: chemical elements conserved, charge neutrality– Input data (specific heat of each species / partition functions for

each species) can be calculated from spectral data, or taken from tables

Examples

0 5000 10000 15000 20000 25000 300001020

1021

1022

1023

1024

1025

1026

e-,Ar+

Ar3+

Ar2+

Num

ber

dens

ity (

m-3)

Temperature (K)

Ar

Ar+

e-

0 5000 10000 15000 20000 25000 300001020

1021

1022

1023

1024

1025

Ar3+

N2+

Ar2+

Nu

mb

er

de

nsi

ty (

m-3)

Temperature (K)

e-

Ar, N2

N

N2

Ar+N+

Argon, 1 atm

50% Argon, 50% Nitrogen, 1 atm

Sulfur hexafluoride, 1 atm

Thermodynamic Properties

These are easily calculated once the plasma composition is known

3

1

1

1

1 1

Density (kg m )

1Enthalpy (J kg ) (+ correction term at high pressures)

Specific heat (J kg K )

N

i ii

N

i i ii

pP

n m

h n m h

hC

T

Specific Heat for Various Plasmas

0 5000 10000 15000 20000 25000 300000

50

100

150

200

250

300 Argon Nitrogen Oxygen Helium Hydrogen

Sp

eci

fic H

ea

t (k

J kg

-1K

-1)

Temperature (K)

Enthalpy for Various Plasmas

0 5000 10000 15000 20000 25000 300000

200

400

600

800

1000

1200

1400

1600

1800


En

tha

lpy

(MJ

kg-1)

Temperature (K)

Transport Coefficients

References for transport coefficient calculations:J. O. Hirschfelder, C. J. Curtiss and R. B. Bird ‘Molecular Theory of Gases and Liquids,2nd edn (Wiley: New York, 1964)M. I. Boulos, P. Fauchais and E. Pfender ‘Thermal Plasmas: Fundamentals and Applications’ Vol. 1 (Plenum: New York, 1994)A. B. Murphy and C. J. Arundell Plasma Chem. Plasma Process. 14 (1994) 451

• Viscosity: transport of momentum perpendicular to flow• Thermal conductivity: transport of heat• Electrical conductivity: transport of charge• Diffusion coefficients: transport of mass

Determined by collision cross-sections (mean free paths) of all species usingformulas derived from Boltzmann equation (Chapman-Enskog method)

flux density (transport coefficient) (driving force)

Viscosity

102

000

1

002

1

(1,1) (2,2)32

To first order:

where 5

163

5

B j jj

qij j i

j

qi i k k

ijkj i k

j ij jk k ij jkik ik

k T n b

Q b n

n m n mQ

m m m

m m

Collision Integrals are Calculated from the Intermolecular Potentials

( , ) ( )2 2 3

0

exp where 2 2

ijl s lsij ij ij ij ijij ij

ij

kTT Q g d g

kT

0

( ) 2 1 cosl lijQ g bdb

are averages over a Maxwellian distribution of the gas kinetic cross-section

02

2 2 212

( , ) 2(1 )

mrr

dr rb g b

g b r

intermolecular potential (r) reduced mass initial relative speed g impact parameter b

where the angle of deflection is

Four Types of Interaction Have to be Considered in a Thermal Plasmao Neutral-neutral Calculated by integrating the intermolecular potential

o Ion-neutral Elastic collisions calculated by integrating the intermolecular potential Inelastic (charge-exchange) collisions obtained by integrating measured or

calculated cross-sections

o Electron-neutral Calculated by integrating the momentum transfer cross-section

o Charged particle-charged particles Calculated by integrating the intermolecular potential (screened Coulomb

potential)

Viscosity for Various Plasmas

0 5000 10000 15000 20000 25000 300000.0000

0.0001

0.0002

0.0003

0.0004

Argon Nitrogen Oxygen Helium Hydrogen

Vis

cosi

ty (

kg m

-1s-1

)

Temperature (K)

Viscosity describes relationship between shear stress and velocity gradient

, is collis~ ion cross e n s ctio

x

i

dvF

dy

mT

Thermal Conductivity for Various Plasmas

0 5000 10000 15000 20000 25000 300000

2

4

6

8

10

12


Th

erm

al C

on

du

ctiv

ity (

W m

-1K

-1)

Temperature (K)

Thermal conductivity describes relationship between heat flux density an

~

d temperature gradient

, is collision cross-secti onp i

i

dTk q k

dxC T

km

Components of Thermal Conductivity for Nitrogen

0 5000 10000 15000 20000 25000 300000

1

2

3

4

5

6 Total Heavy species Reaction Electron Internal

Th

erm

al C

on

du

ctiv

ity (

W m

-1K

-1)

Temperature (K)

Electrical Conductivity for Various Plasmas

0 5000 10000 15000 20000 25000 300000

2000

4000

6000

8000

10000

12000

14000

16000

Argon Nitrogen Oxygen Helium Hydrogen

Ele

ctri

cal C

on

du

ctiv

ity (

S m

-1)

Temperature (K)

Electrical conductivity describes relationship between current density and voltage gradient

, is electron density, is density of other species, is collision cross sectio n~ ee

dVj

dxn

n nTn

Radiative EmissionImportant in thermal plasmasA full treatment is difficult: Determine emission and absorption at

every volume element A large number of wavelength intervals

required to cover line and continuum radiation

Net emission coefficients are a very successful approximation For a given temperature, integrate

emission over all wavelengths Take into account absorption in a sphere

of a given radius

For applications in which radiation flux at boundary is important, need more complex treatments

J. J. Lowke J Quant Spectrosc. Radiat. Transf. 16 (1974) 111A. Gleizes et al. J. Phys. D: Appl. Phys. 26 (1993) 1921

Net Emission Coefficients for Argon at 1 atm

L is the radius of the absorbing sphere

J. A. Menart PhD Thesis Uni. of Minneapolis (1996)

Deviations from LTELarge density and temperature gradients Diffusion is faster than equilibration Important at arc fringes and near surfacesHigh flow velocities Flow is faster than equilibration (‘frozen flow conditions’) Important in high velocity jets and near cathode in arcsHigh electric fields Electrons acquire energy faster than they can equilibrate Important at low pressuresRadiative effects Atoms excited by radiative absorption faster than they can equilibrate Important in fringes of plasma

Most important deviations Electron temperature greater than heavy species temperature Frozen recombination reactions (e.g., H instead of H2 at low temperatures) Overpopulated excited states

3. Generation of Thermal Plasmas

Electric arcs Requires electrodes Relatively inexpensive The most widely-used method Transferred or non-transferred arcs Usually DC, but can be AC

Radiofrequency inductively-coupled discharges No electrodes required More expensive Generates a larger, more uniform, plasma volume Lower efficiency More sensitive to process variations

Microwave discharges No electrodes required Relatively small-scale and expensive Usually Te > Th

Electric Arcs: Transferred Arcs

Arc between one electrode (usually cathode) and metal or conducting workpiece

High energy transfer efficiency to workpiece

Low gas flow

High peak temperature, narrow distribution

Used in welding, plasma cutting, electric arc furnaces, arc lamps, waste destruction, etc.

246810Radial distance (mm)

0

2

4

6

8

10

12

-2

-4

-6A

xial

dis

tanc

e (m

m)

Max. 217 m/s

0 2 4 6 8 10

0 2 4 6 8 10

Ar 150 A, 10.8 V

246810

Water cooled Cu

0

2

4

6

8

10

12

-2

-4

-6

Radial distance (mm)

3000 K, Interval 2000 K

17000 K

3300 K



600 K

Electric Arcs: Non-transferred Arcs

Arc is confined within plasma torchHigh efficiency heating of bulk gas (“arc heater”)High gas flowBroader heat flux distribution, lower peak temperatureUsed in plasma spraying, waste destruction, etc.

400 A, 10 kW argon plasma jet

Solid line: calculations for jet into air

Dotted line: calculations for jet into argon

Circles: measurements for jet into air

A. B. Murphy and P. Kovitya, J. Appl. Phys. 73 (1993) 4759

RF Inductively-Coupled Plasma

No electrodes, so low contaminationLow gradientsUsed for powder processing (densification, spheroidisation), nanoparticle production, etc.

Types of Plasma Flow

Gravity-driven flow Low current (< 20 A) arcs Flow driven by buoyancy Arc lamps

Flow driven by j x B forces Higher current (> 30 A) arcs Pressure gradient = j x B (the

magnetic pinch effect) Maximum velocities from

100 to 1000 m/s Arcs for welding, plasma

cutting, etc

246810Radial distance (mm)

0

2

4

6

8

10

12

-2

-4

-6

Axi

al d

ista

nce

(mm

)

Max. 217 m/s

0 2 4 6 8 10

0 2 4 6 8 10

Ar 150 A, 10.8 V

246810

Water cooled Cu

0

2

4

6

8

10

12

-2

-4

-6

Radial distance (mm)


17000 K

3300 K



600 K

j

Magnetic Pinch (Lorentz or j x B) Force

B

F

Types of Plasma FlowFlows driven by imposed pressure Gas blast circuit breakers use

stored high-pressure gas or a piston to extinguish high current arcs with a rapid flow of gas (usually SF6)

Flows driven by thermal expansion In plasma torches, the arc occurs

in a confined region, causing the pressure to rise

Supersonic velocities (over 2000 m/s) typically achieved

Arc stabilised by high gas flow and often swirl of gas

Typical in plasma spraying Shock diamonds indicating supersonic flow

4. Modelling of Thermal Plasmas• Use computational fluid dynamic equations for viscous flow• Can often assume incompressible flow (except for Mach number

> 0.3 – plasma jets)• A conservation of energy equation is required because the

temperature is not constant• Maxwell’s equations are used to describe current continuity

(charge conservation) and magnetic fields• Additional terms describing ‘plasma’ effects are included (ohmic

heating, radiative emission, magnetic pinch effect, electron diffusion)

• The equation of state is implicit in the dependence of thermophysical properties on temperature

• Modifications required for electrode regions, turbulent flows, departures from LTE, etc.

Conservation Equations: Single Gas

2

20

( ) 0

( )( )

2where 2 , ,

3

5( )( )

2

0

ji iii ij

i j

p p

i

B

t

Pt

vv vi j

x x x

khh

κh h

cU

t ce

v

vvv τ j B g

v

jv j

A j

Conservation of:

Mass

Momentum

Energy

Charge

Nomenclature

temperature

velocity

stress tensor

pressure

current density

magnetic field strength

vector (magnetic) potential

electric potential

T

P

v

j

B

A

3

1 1

1

1 1

1 1

mass density (kg m )

specific heat at constant pressure (J kg K )

specific enthalpy (J kg )

thermal conductivity (W m K )

viscosity (kg m s )

net radiative emission coefficient

pC

h

k

U

3

1

(W m )

electrical conductivity (S m )

electronic charge

Boltzmann's constant

gravitational accelerationB

e

k

g

Complications: Turbulence

Many thermal plasma flows are turbulent Plasma jets (e.g., for plasma spraying) Plasma cutting arcsDifferent approaches Direct numerical simulation (DNS)

– Solves all the scales of flow– Very expensive, and unfeasible for industrial problems

Large eddy simulation (LES)– Solves for large scales and models small scales of the flow– Turbulence model needed to approximate the small scales

Reynolds-averaged Navier-Stokes (RANS)– Models all scales of the flow– The most common approach for industrial problems– Include:

– 0 equations: Prandtl mixing length– 1 equation: Spalart-Allmaras– 2 equations: K-ε, K-ε RNG, K-ω

The K-ε ModelTurbulence is modelled as an additional diffusion mechanism

Solve additional transport equations for K (turbulence kinetic energy) and ε (turbulence energy dissipation), which then give viscosity and thermal conductivity

2

1 2

2

2

1

( )( ) 2

( )( ) 2

2

is turbulent viscosity, is turbulent thermal conductivityPr

, , ,

t

K

t

Tt

t pt t

t

K

KK K G

t S

C G Ct S K K

G

CKC

S S C

v

v

v v

2 , Pr are constantstC

Effect of Turbulence

Mass fraction of air for argon plasma jet discharging into air


Laminar

Turbulent

Argon

Air

Argon

Air

Effect of Turbulence

Temperature (1000 K) of argon plasma jet discharging into air


Laminar

Turbulent

Complications: Electrode Sheath Regions

10-1 mm 10-5 mm

Te > Th ne ≠ ni

Anode Treatments

*2 * 30 0

the temperature adjacent to the anode is low,

so if assume LTE, then 0 0

Add electron diffusion term (Sansonnens et al.)

0

and ar

Problem:

Approach

el

1:

e

e

a e e e e

e

e a

e

n

D

e

n n n n n n

D

D n

D

j

ectron and ambipolar diffusion coefficients

is three-body recombination coefficient, * indicates LTE value

"LTE-diffusion approximation" (Lowke and Tanaka)

Set mesh size near ano

App

de

roach

to

2:

width

of region in which

electron diffusion dominates ( 0.1 mm).

Then use LTE everywhere.Bk T eE

L. Sansonnens, J. J. Lowke and J. Haidar J. Phys. D: Appl. Phys. 33 (2000) 148J. J. Lowke and M. Tanaka J. Phys. D: Appl. Phys. 39 (2006) 3634

Comparison of Approaches 1 and 2

(Sansonnens et al)

(Lowke & Tanaka)

Anode

Thermionic Cathode Treatment

• Applies to high melting point materials e.g., W, C, Mo, Zr• Electrons emitted from cathode• Cathode heated through ion bombardment• Current densities around 100 A/mm2

2

5 2 2

Richardson equation

6 10 A mm K for most metals

(work function) 4.5 V for W

exp

2.5 V for W(Th)

w B

w

j AT k

A

e T

Thermionic Current Density vs Temperature

Decreasing work function by 2 V reduces the cathode temperature by 1700 K (for 100 A mm-2) Metals that don’t have high melting points (Cu, Al, Fe etc) cannot be thermionic emitters

0 1000 2000 3000 4000 500010-6

10-4

10-2

100

102

104

106

Cur

rent

den

sity

(A

mm

-2)

Temperature (K)

w = 4.5 V

w = 2.5 V

Example: Modelling of Arc Welding, including Cathode, Arc and Weld Pool (Anode)

Complications: Plasmas in Gas MixturesIf more than one gas present, these gases can mix or demix

Even in LTE, need to know their relative fractions

For each species i

2

1

: mass fraction : reaction source term

: diffusion mass flux

: ordinary diffusion coefficient

: thermal diffusion coefficient

: mass

l

f

n

r

i i i i

qTi

i j

i i

i

ij

Ti

i

i

j j ij

Y dt Y r

n mm

Y

D

D

x

T

D

D

r

x

v J

J

J

action

A. B. Murphy J. Phys. D: Appl. Phys. 34 (2001) R151

Combined Diffusion Coefficients

Group species into gases

E.g., for Ar-He arc argon gas = Ar, Ar+, Ar2+, Ar3+, e-

helium gas = He, He+, He2+, e-

Model diffusion of helium gas through argon gas

Typically 50 ordinary and thermal diffusion coefficients replaced by two combined diffusion coefficients

Exact for homonuclear gases that do not react for plasmas in LTE

Gas Conservation Equation

Species conservation equations for each species (Ar, Ar+,

Ar2+, Ar3+, He, He+, He2+, e-)

i i iY r v J

replaced by a single gas conservation equation

Ar Ar Ar

2Ar Ar He Ar,He He Ar/ lnx T

Y t Y

n m m D x D T

v J

J

The overbarred quantities are averaged over all species

A. B. Murphy Phys. Rev. E 48 (1993) 3594

Example: Demixing in an Argon-Helium Arc

A. B. Murphy Phys. Rev. E 55 (1997) 7473

5. Thermal Plasma Diagnostics

Probes Langmuir probes Enthalpy probes

Spectroscopy Emission spectroscopy Absorption spectroscopy

Laser scattering Elastic scattering

– Rayleigh scattering– Thomson scattering– Raman scattering

Inelastic– LIF (laser-induced fluorescence)– Two-photon LIF– CARS (coherent anti-Stokes Raman scattering)

Enthalpy Probes Shut-off valve

Coolant in

Coolant out

stagnation atm

water gas flow no gas flow

2

Enthalpy Flow velocity

is cooling water mass flow rate

is gas sampl

ing w

w

g

pg

P Pmh

m

T v

m

C Tm T

mass flow rate

Can also measure composition using gas analyser

Enthalpy Probe Results

Entrained air %, temperature (K) andvelocity (m/s) for enthalpy probe (●)and laser scattering (Δ)

Plasma torch, 900 A, argon, 2 mm downstream from orifice

J. C. Fincke, S. C. Snyder, W. D. Swank,Rev. Sci. Instrum. 64 (1993) 711

Optical Emission Spectroscopy

x

Arc

Emission Spectroscopy: Abel Inversion

Arc

0

0

2 2

Emission is captured along a line through the arc

1Abel inversion gives radial dependence of emission coeff't:

(assumes arc is axially symmetric)

y

yR

r

I x r dy

I xr dx

x r

x

yArc scannedin x direction

Optical axisin y direction

Emission Spectroscopy: Determining the Temperature

Intensity exp

is energy of upper level

is transition probability

is statistical weight of upper level

is transition frequency

is number density of species (e.g.

mmn m mn

B

m

mn

m

mn

n T ES T A g h

Z T k T

E

A

g

n

Ar atoms)

is partition function of speciesZ

The measurement system has to be calibrated

Three standard methods:1. Use a calibrated radiation source2. Use ratio of intensity of two or more lines3. Fowler-Milne method

m

n

hνmn

Emission Spectroscopy: Fowler-Milne Method

Intensity exp mmn m mn

B

n T ES T A g h

Z T k T

0 5000 10000 15000 20000 25000 300001020

1021

1022

1023

1024

1025

1026

e-,Ar+

Ar3+

Ar2+

Num

ber

dens

ity (

m-3)

Temperature (K)

Ar

Ar+

e-

S(T) has a maximum value (at around 15 000 K) because

(1) n decreases as T increases (2) exp(-E/kT) increases as T increases

0.00E+00

5.00E-02

1.00E-01

1.50E-01

2.00E-01

2.50E-01

3.00E-01

0 5000 10000 15000 20000

T (K)

exp

(-E

/kT

)

Emission Spectroscopy: Fowler-Milne Method

Calculated S(T)

has maximum value at 15 000 K

The maximum value of measured S(r)

occurs at r = 1.1 mm

Therefore T = 15 000 Kat r = 1.1 mm.T(r) can be found from the dependence of intensity on temperature

Laser Scattering

Local (point) data is obtained

Scattering of Laser Light Occurs from Electrons – Both Bound (to Atoms or Ions) and Free

scattered laser

laser transition

laser transition

Elastic scattering:

Inelastic scattering:

Rayleigh scattering: elastic scattering from bound electronsThomson scattering: elastic scattering from free electronsResonance scattering: inelastic scattering from bound electrons

scattered laser Laser-induced fluorescence: inelastic scattering from bound electrons

Thomson Scattering

Spectrum of scatteredlight depends on T and ne

Approach 1. Integrated scattering:No wavelength resolutionAccept all light in a given range of wavelengths around laser wavelength

Approach 2. Wavelength-resolved scattering: Measure scattered light as a function of wavelength –Need a high power laser, which heats the plasma, so not recommended for Te (OK for ne, Th)

Laser Scattering: Integrated ScatteringRayleigh scattering (elastic scattering from atoms/ions)Thomson scattering (elastic scattering from free electrons)Resonance scattering (inelastic scattering from atoms/ions)

100 A argon arc: T vs r

Spectroscopy

Laserscatt.

A. B. Murphy and A. J. D. Farmer, J. Phys. D: Appl. Phys. 25 (1992) 634

Ar ion laser – 514.5 nm

Thank youCSIRO Materials Science and EngineeringTony MurphyChief Research Scientistt +61 2 9413 7150e [email protected] www.csiro.au/CMSE

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