KIT – University of the State of Baden-Württemberg andNational Large-scale Research Center of the Helmholtz Association

Light Technology Institute, University Karlsruhe, Germany

www.kit.edu

Plasma Efficiency and Losses for pulsed Xe Excimer DBDs at high Power DensitiesMark Paravia, Michael Meisser, Wolfgang HeeringGEC, Saratoga Springs 2009

Mark Paravia – Plasma Efficiency and Losses for pulsed Xe Excimer DBDs at high Power Densities Light Technology InstituteUniversity Karlsruhe

2/ 21.10.2009

Dielectric Barrier Discharges

Non-equilibrium plasma Xenon excimer Radiation around 172 nmPlasma efficiency up to 65 % [1]

Phosphor coated lamps forUV water disinfectionAdvanced oxidation processes

[1] Vollkommer, Hitzschke, US000005604410A (1994)

Mark Paravia – Plasma Efficiency and Losses for pulsed Xe Excimer DBDs at high Power Densities Light Technology InstituteUniversity Karlsruhe

3/ 21.10.2009

Experimental setupLamp overview

barrier: fused silicagas gap: 4,5 - 5,5 mmxenon: 210 - 400 mbarfrequency: 20 - 200 kHz

Investigation:radiation fluxoptical lossesplasma efficiency estimation

gas gap spacer

glass solder

electrode

glass plate

barrier: glassgas gap: 2 mmxenon: 50 - 350 mbarfrequency: 20 - 200 kHz

Investigation :luminanceinner electrical valuesNIR (823 nm, 828 nm)

Mark Paravia – Plasma Efficiency and Losses for pulsed Xe Excimer DBDs at high Power Densities Light Technology InstituteUniversity Karlsruhe

4/ 21.10.2009

Experimental setupVUV goniometer

wavelength range from 115 nm < λ< 1700 nmabsolute calibration from VUV to NIRphotometric distance = 120 cm (max lamp size = 12cm)ability to measure angular distribution of radiant intensity

Mark Paravia – Plasma Efficiency and Losses for pulsed Xe Excimer DBDs at high Power Densities Light Technology InstituteUniversity Karlsruhe

5/ 21.10.2009

angular distribution of radiant intensity (ARI) shows optical thin plasmaXe2

* spectra is overlapped with transmission edge of fused silica (~155 nm)

Results for silica lamps:angular distribution and spectra

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

150 160 170 180 190 200 210 220wavelength [nm]

spec

tal

radi

atio

n in

tens

ity [µ

W/(s

r nm

)]

pXe = 210 mbarλ = 172 nm

Mark Paravia – Plasma Efficiency and Losses for pulsed Xe Excimer DBDs at high Power Densities Light Technology InstituteUniversity Karlsruhe

6/ 21.10.2009

Results for silica lamps:Calculation of plasma efficiency

light flux:

extraction efficiency Teff:transmission of silica net-shaped electrodeabsorption of inner barrier

plasma efficiency:isotropic emission of Xe2

* (4π)

155 160 165 170 175 180 185 190 1950

20

40

60

80

100

0

20

40

60

80

100

kl

Shl

äk

[]

T = 20 °CT = 100 °CT = 180 °CXe2*

Plasmaeff

Φη =ARI T P⋅ ⋅

14 ( , )

Mess

n

i ji

ARI Iλ

ϕπ λ λ ϕ ==

Φ = ⋅ ⋅∆ ⋅∑

2

1

2

0 0

( , , ) sin( )I d d dΦ = ∫ ∫ ∫λ π π

λ

λ ϕ γ γ λ γ ϕ

wavelength [nm]

trans

mis

sion

[%]

spec

tral r

adia

nce

inte

nsity

[a.u

.]

Mark Paravia – Plasma Efficiency and Losses for pulsed Xe Excimer DBDs at high Power Densities Light Technology InstituteUniversity Karlsruhe

7/ 21.10.2009

maximum optical power density: PVUV = 0,12 W/cm² at pXe = 300 mbarpower density rises with pressure, but …transition of homogeneous into filamented discharge(pressure depended)

Results for silica lamps:efficiency

Variation of repetition rate:

f [kHz]

PV

UV

[W/c

m2 ]

0,00

0,02

0,04

0,06

0,08

0,10

0,12

0,14

0 25 50 75 100 125 150 175

210 mbar300 mbar400 mbar

Mark Paravia – Plasma Efficiency and Losses for pulsed Xe Excimer DBDs at high Power Densities Light Technology InstituteUniversity Karlsruhe

8/ 21.10.2009

0,00

0,02

0,04

0,06

0,08

0,10

0,12

0,14

0,0 0,2 0,4 0,6 0,8 1,0

Pel [W/cm²]

210 mbar

300 mbar

400 mbar

Results for silica lamps:efficiency

maximum plasma efficiency ~ 52 % (at Pel = 0,07 W/cm²)

plasma efficiency declines to ~ 34 % (at Pel = 0,8 Wcm²)

why is the efficiency declining?

0

0,1

0,2

0,3

0,4

0,5

0,6

0,0 0,2 0,4 0,6 0,8 1,0Pel [W/cm²]

210 mbar300 mbar

400 mbar

f

f

Pel [W/cm²] Pel [W/cm²]

PV

UV

[W/c

m2 ]

Pla

sma

effic

ienc

y

Mark Paravia – Plasma Efficiency and Losses for pulsed Xe Excimer DBDs at high Power Densities Light Technology InstituteUniversity Karlsruhe

9/ 21.10.2009

Results for flat lamp:power and efficiency

comparable results for flat lamp as for silica lampsabove p = 200 mbar slight pressure dependency when repetition rate is adjusted

Pel [mW/cm²] Pel [mW/cm²]

Lum

inan

ce [c

d/m

²]

Lam

p ef

ficie

ncy

[lm/W

]

0

5000

10000

15000

20000

25000

0 200 400 600 800 1000

350 mbar250 mbar150 mbar100 mbar50 mbar

f0

5

10

15

20

25

0 200 400 600 800 1000

350 mbar

250 mbar

150 mbar

100 mbar

50 mbar

f

Mark Paravia – Plasma Efficiency and Losses for pulsed Xe Excimer DBDs at high Power Densities Light Technology InstituteUniversity Karlsruhe

10/ 21.10.2009

Lam

p vo

ltage

[V]

NIR

[a.u

.]

Results for flat lamp:voltage and IR

pulse shape matched for double ignitionfor f = 200 kHz no ignition in first positive half-wave, despite voltage excite ignition voltage

time [ns] time [ns]

-2000

-1500

-1000

-500

0

500

1000

1500

2000

2500

0 500 1000 1500 2000

f = 20 kHz

f = 200 kHz

-0,2

0

0,2

0,4

0,6

0,8

1

1,2

0 500 1000 1500 2000

f = 20 kHz

f = 200 kHz

Mark Paravia – Plasma Efficiency and Losses for pulsed Xe Excimer DBDs at high Power Densities Light Technology InstituteUniversity Karlsruhe

11/ 21.10.2009

Results for flat lamp:pre ignition current and gap voltage

Due to high frequency increasing plasma current density before ignition, that separates the remaining charges and lowers the gas gap voltage.Plasma becomes a glow discharge.

plas

ma

curr

ent d

ensi

ty [m

A/c

m²]

time [ns]

-20

-15

-10

-5

0

5

10

15

0 500 1000 1500 2000

f = 20 kHz

f = 200 kHz

-800

-600

-400

-200

0

200

400

600

800

1000

1200

0 500 1000 1500 2000

f = 20 kHz

f = 200 kHz

time [ns]

gap

volta

ge [V

]

Mark Paravia – Plasma Efficiency and Losses for pulsed Xe Excimer DBDs at high Power Densities Light Technology InstituteUniversity Karlsruhe

12/ 21.10.2009

Summary

VUV goniometer to measure the total radiance of a lamp between 115 nm and 1700 nm

Measurements of power density and efficiency for high power Xe2

* DBDs

Limiting factors:Transition into filamented dischargeRemaining charges and plasma current density

Mark Paravia – Plasma Efficiency and Losses for pulsed Xe Excimer DBDs at high Power Densities Light Technology InstituteUniversity Karlsruhe

13/ 21.10.2009

GEC 2009, Saratoga Springs

Thank you for your attention.

Mark Paravia – Plasma Efficiency and Losses for pulsed Xe Excimer DBDs at high Power Densities Light Technology InstituteUniversity Karlsruhe

14/ 21.10.2009

Electrical excitation / measurementresonant pulse ECG as current sourcemeasurement of plasma current iplasma

measurement of gap voltage ugap

Experimental setupECG

Roth, M., Neiger, M., 21. IDRC, Nagoya, 2001, p. 893-896

UL

S1

S2

DBD

C

D1 D2

D3D4

-2000

-1000

0

1000

2000

0 5 10 15 20 25time/µs

lam

p vo

ltage

/V

T periode = 25 µs