Analysis of Discharge Parameters and Spectroscopic ......Jan 24, 2012 · Typical dielectric barrier discharge configurations (i). Volume discharge, (ii). Surface discharge (iii)

Analysis of Discharge Parameters and

Spectroscopic Diagnostic of DBDs

Joint ICTP-IAEA Workshop on Fusion Plasma Modelling using Atomic and Molecular

Data, Trieste - Italy

Pooja Gulati

Plasma Device Technology, Microwave Tubes Division

CSIR-Central Electronics Engineering Research Institute (CSIR-CEERI) Pilani Rajasthan-

333031

CSIR-Central Electronics Engineering Research Institute (CSIR-CEERI), Pilani

Foundation was laid on 1953.Around 450 Employees

� Leading Research Institute in India in the field of Electronics Devices

3.Semiconductor

• Hybrid Microcircuits

• IC Design

• MEMS and Microsensors

• Nanotechnology & Devices

1.Microwave Tubes

• Gyrotron

• Klystron

• Magnetron

• TWT

2.Electronic Systems

• Agri-Electronics

• Embedded System

• Digital System

• Power Electronics

Major Research Areas at CSIR-CEERI Pilani

• Nanotechnology & Devices

• Photonics & optoelectronics

• Semiconductor Material & Tech.

• TWT

• Plasma Devices Technology

• Power Electronics

Activities in Plasma Devices Group

• High Power Plasma Switches:Thyratrons & Pseudospark

• VUV/UV Excimer Sources based on DBD: Biomedical ApplicationsSurface TreatmentWater Purification (jointly with NEERI)

• Plasma Cathode Electron Gun:• Plasma Cathode Electron Gun:Electron and Ion Source

• Plasma Assisted Microwave Sources:Plasma TWT, Pasotron

• Penning Discharge DevicesIon Sources and VUV Spectroscopy

Motivation and objectives of the work.

Introduction

What is Dielectric Barrier Discharges (DBDs)?

Advantages and open areas of research and applications

of DBDs.

Experiments

Organization of Presentation

Experiments

Experimental Setup and testing

Results and discussions.

Conclusion

Joint ICTP-IAEA Workshop on Fusion Plasma Modelling using Atomic and Molecular Data, Trieste - Italy

In recent time it has been observed that Dielectric Barrier

Discharge (DBD) based micro-discharges and micro-array-

discharge plasmas can produce ultraviolet radiation in

germicidal wavelength range UV-C (200-280nm) and VUV(100-

200nm), UV-B(280-315nm), UV-A (315-400nm) that can

effectively treat impure water, and also can be used for

Motivation

effectively treat impure water, and also can be used for

medical and other industrial applications. Our group is

working in this area and I am motivated in the spectroscopic

studies related to this technology which can in future transit

me for large scale plasma related spectroscopic analysis.


Objectives

To investigate and analyze the characteristics of discharge

patterns occurring in the volume discharge (VD)

configuration of DBDs filled with inert gases.

The traditional metallic diagnostic technique is not useful

in the very small geometry of the proposed DBD

configuration. Hence to derive the internal electrical and


configuration. Hence to derive the internal electrical and

plasma parameters with the help of electrical analysis and

spectroscopic diagnostics is the key component of the

objectives.

Dielectric barrier discharges (DBDs), also known as silent discharges or

barrier discharges, are generated in discharge configurations with at least

one dielectric barrier between the electrodes.

Introduction

What is Dielectric Barrier Discharge(DBDs)?


Role of Dielectric layers:

It acts as current limiter and limits the discharge transition from glow to arc.

Possible DBD Geometries

Typical dielectric barrier discharge configurations

(i). Volume discharge, (ii). Surface discharge (iii). Coplanar discharge


Fabricated Geometries


Cg

Cd1

Cd2

Geometrical Design and Parameters

• Dielectric Thickness= 1 mm• Electrode diameter =36 mm• Electrode Thickness = 1mm• Gas gap = 2 mm• Dielectric Material Used= Quartz• Pressure of Gas=100mbar• Gas Used = Helium

Dielectric barrier capacitance Cd1 = Cd2 = 20.48 pF


�Base pressure=1x10-4 mbar

�Gas filling assembly is usedto fill gas at differentpressures.

�Working Pressure~100 mbar

�Sinusoidal voltage supply upto 2kV peak with frequenciesfrom 30 to 90 kHz has been

Experimental Setup

Schematic View of experimental setup

from 30 to 90 kHz has beenused.

�Applied voltage and the totalcurrent are measured usinghigh voltage probe andRogowski-type currenttransformer.

�Oscilloscope and visiblespectrometer are interfacedwith computer.


600 Va0.03

Testing & Characterization of He DBD

Experimental Setup for the DBD Source

10 15 20 25 30 35 40 45

-600

-400

-200

0

200

400

600 Va It

Time(u sec)

Va(

V)

-0.03

-0.02

-0.01

0.00

0.01

0.02

It(m

A)

�At breakdown voltage, the discharge begins with

some filaments distributed on the dielectric wall.

�Increasing the applied voltage little bit, number of

filaments increases and for further increase in

voltage, the discharge finally get diffused.


dt

tdVCtI d

ddbd

)()( =

dt

tdVCtI g

gdg

)()( =

)(

)())()((

1)(

tC

tItItI

Cdt

tdV

d

dbddisdbd

g

a +−=

tdVCg )(−+=

Total current through DBD and displacement current through gap

(4) (5)

(6)

Diff. (1) with respect to time and replacing (4) and (4) in (1),

Rearranging (6), we will get

)()()( tVtVtV gda += )()()( tItItI scdbdtc += )()()( tItItI dgdisdbd +=(1)

Using Kirchoff’s theorem for the model, we obtain the following equations

(2) (3)

Equivalent electrical circuit of DBDs

dt

tdVCtI

C

CtI a

gdbdd

gdis

)()()1()( −+=

0)(1

)( mdbdd

d VdttIC

tV += ∫

0)(1

)()( mdbdd

ag VdttIC

tVtV −−= ∫

∫−=2/

0

0 )(2

1 T

dbdd

m dttIC

V

(7)

The values of dielectric and gas gap voltages are,

Where Vm0 is memory voltages, ( In case of sinusoidal excitation)

(10)

(9)

(8)

� In case of sinusoidal excitationU N Pal et al, J. Phys. D: Appl. Phys.vol. 42, 045213 (8pp), 2009. U N Pal et al, J. Phys.: Confe. Ser.208, 012142, 2010.


0

7

14

-400

-200

0

200

400

Cur

rent

(m

A)

It Idbd Idis.

Vol

atag

e (V

)

Va Vd Vg Vm

Input Parameters:Gap capacitance Cg (11.30 pf) Dielectric barrier capacitance Cd (20.48 pF)

Equations are used from references:U N Pal et al, J. Phys. D: Appl. Phys.vol. 42, 045213 (8pp), 2009.

Results and discussionsResults and discussions

-14

-7

15 20 25 30 35 40-2

0

2

4

Cur

rent

(m

A)

Time (µs)

Pow

er (

W)

Psup. Pdis.

Experimental waveforms of dynamicprocesses occurring in gap (gas: Helium atf= 34.5 kHz) for the Parallel plate DBDGeometry. at 100 mbar.

(8pp), 2009. U N Pal et al, J. Phys.: Confe. Ser.208, 012142, 2010.


2.0x10 3

2.5x10 3

3.0x10 3

3.5x10 3

4.0x10 3

4.5x10 3

HeII 6559.7Å HeI 4921.9 Å

HeI 5875.6 ÅInte

nsity

(a.u

)

HeI 6678.1Å

HeI 7065.1Å

Spectroscopic ResultsSpectroscopic Results

3000 4000 5000 6000 7000 80005.0x10 2

1.0x10 3

1.5x10 3

HeI 4921.9 Å

HeI 5015.6ÅHeI 5875.6 ÅIn

tens

ity(a

.u)

Wavelength (Å)

HeI 3888.6Å

HeI 6678.1Å

HeI 7281.3Å

He I 3888.6 Å (23S-33P)He I 4921.9 Å (21P-41D)


He I 5015.6 Å (21S-31P)He I 5875.6 Å (23P-33D)

He I 6678.1 Å (21P-31D) He I 7065.1 Å (23P-33S)He I 7281.3 Å (21P-31S)

Neutral Helium Lines:

Intensities of the He I lines are calculated using collisional-radiative (CR) model based ADAS code[H. P. Summers, ADAS

users manual,JET –IR 06 (Abingdon: JET Jointundertaking) (1994)].Withan assumption that the average electron density and temperaturein an emission length x, the photon intensity I (λul ) of a spectralline can be written fromthe CR-model as,

)~

(~

)~

(~

)(~

xNNCPExNNCPEI +=λ

Collisional-Radiative (CR) Model

)~

(~

)~

(~

)(~

xNNCPExNNCPEI geexcitationiegrecombininul +=λ

FromCR-model the ground state populations of atoms and ionsis given by,

egCReiCRig NNSNN

dt

dN

dt

dN−=−= α

Under steady-state approximation,

g

i

CR

CR

N

NS=

α


Under equilibrium condition 0=− egCReiCR NNSNNα and CR

CR

g

i S

N

N

α=

So, the condition

For ionizing plasma is 1>>CR

CRS

α and for recombining plasma is 1<<

CR

CRS

α

In true sense the ionizing plasma

Purely Ionizing Condition

HeI

ionizing plasma condition holds well when Ni/Ng << SCR/ CRα [Fujimoto T. and Sawada K., NIFS-DATA-39 (1997)].


Under ionizing condition the term is taken tobe negligibly small and the line intensity for a transitionfrom level u to level l is expressed as,

The significance of the line ratio technique is that theexperimentallyobservableintensity ratio of two lines (which

)~

(~

xNNCPE iegrecombinin

)( ulI λ

)~

(~

)(~

xNNCPEI geexcitationul =λ

Intensity line ratios

experimentallyobservableintensity ratio of two lines (whichis not directly dependent on , and ) can be easilyobtained fromthe code as the ratio of corresponding photonemission rate coefficients is given by,

iN gN eN

),(

),(

2

1

2

1

ee

ee

TNPEC

TNPEC

I

I=


Temp. Sensitive Intensity Ratios: 7281.3/ 7065.7, 5049/ 4713.1

Density Sensitive Intensity Ratios: 6678.1/ 7281.3, 4921.9/ 5047.7

Temperature & Density CalculationTemperature & Density Calculation

Calculated Values: Electron Temp. = (6.5±0.5) eV, Density = (3.5±1.5) х1011 cm-3

Ref. Summers H P 1994 ADAS Users Manual JET–IR 06(Abingdon: JET Joint Undertaking).R. Prakash, et alJ. Appl. Phys. vol. 97, no.4, p.043301, 2005.


1.50x1011

3.00x1011

4.50x1011

6.00x1011

Ne(

cm-3

)

120nsec 105ns 95ns

Simulated results of the electron Density using Simulated results of the electron Density using

OOPIC-Pro

0 5 10 15 20 25 30 35 400.00

Diameter of the electrode (mm)

The statistical mechanics have shown that the many small perturbation (errors)

that affect a physical system almost always force the measurement to follow the

Gaussian distribution. It is usually referred to as simply the “normal distribution”.

Based on this, the average distribution of electron plasma density is derived for

entire system geometry using OOPIC-Pro simulation code and if we take line average of the saturated density it would give nearly similar results to the spectroscopic diagnostic measurements, which are in agreement to each other.


The homogeneous type of discharge has been observed at 100mbaroperating pressure for a fixed frequency 34.5 kHz in parallel plateDBD cell filled with helium gas.

The dynamic evolution of the process in the gap provides the usefulinformation about the electrical characterization of the DBD source.

The electron plasma temperatures and electron plasma density

Conclusion

The electron plasma temperatures and electron plasma densityobtained for present configuration at 100mbar gas pressure aretypically (6.5±0.5) eV and (3.5±1.5) х1011cm-3 respectively.

The existence of such density and temperature in this source is usefulfor existence of higher metastable states which needs to be furtherinvestigated.


Dr. Ram Prakash, CSIR-CEERI, Pilani

Mr. U.N Pal, CSIR-CEERI, Pilani

and all other group members

Acknowledgement

and all other group members


Thank YouThank YouThank YouThank YouThank YouThank YouThank YouThank You


Documents

Analysis of Discharge Parameters and Spectroscopic ......Jan 24, 2012 · Typical dielectric barrier discharge configurations (i). Volume discharge, (ii). Surface discharge (iii)