Advanced Probe Measurement for Atmospheric Pressure Discharge Plasma

Radiation Research Center, Osaka Prefecture University

Hiroto Matsuura

Graduate School of Engineering,

Osaka Prefecture University

Ken Nakano and Taku Kiriishi

APSPT7(2012/4/15 、 Taipei)

Contents of this presentation

• Introduction of Radiation Research Center and a new division of OPU.

• Background of atmospheric plasma• DC discharge plasma parameters obtaine

d with the probe method• Heat flux of Dielectric Barrier Plasma Jet• Conclusion

Largest tomb of ancient emperor

1959: Establishment of RCOP　　　　　1962: Installation of the electron linear accelerator (linac)1990: merged in OPU and reorganized2011: reorganized to RRC in Research Organization for University-Community Collaborations

Outline of Radiation Research Center

2013 new Division will startthe Division of Quantum and Radiation Engineering

RadiationLaserBeamPlasma

PhysicsChemistryBiology

We can provide your students with the basic and practical education.

The irradiation rooms and the accelerator rooms.

Division of Quantum and Radiation Engineering (Apr. 2013)

• A new division of graduate school of engineering of our university will start next year.( 我們大學工程研究生院的一個新部門將於明年啟動。 )

• We will accept students from all of the world.( 我們將接受來自世界各地的學生。 )

• http://www.eng.osakafu-u.ac.jp/English/02senko/senko.htm

Background

Atmospheric pressure plasma is now attractive for decontamination of environmental waste and medical technology, because of

low cast without vacuum pumping systemapplicability for biomaterial that does not less tolerate vacuumlarge process speed

Although many production methods have been proposed, parameters of plasma produced with them are not well studied.

Electro static probe method has been widely used for low pressure discharge plasma. And even for Atmospheric pressure plasma, some literature reported its application as following.

O.Sakai et al.: J.Phys. D: Appl. Phys, 38, 431(2005).M.R.Talukder et al.: J.Appl.phys., 91, 9529(2002).H.Matsuura, et al.:AIP conf. Proc., 1084, 871(2008).

Key issue is the choice of probe tip material which tolerate plasma heat loadand analysis of I-V characteristic with collisional sheath effect.

DC atmospheric discharge device

Ip

Cathode

Probe

Idis

Vp

Air plasma and He plasma

（ 1 ） Air(w/o flow) （ 2 ） He flow

Ar plasma

（ 3 ） Ar （ high) （４） Ar （ low)

DC plasma parameters Comparison of plasma parameters in air/He/Ar plasma( Normal )

Parameter Working gas

Air He Ar(high) a Ar(low)

Idis(mA) 70 58 85 68

Iis(mA) 0.02 0.7 0.2 0.4

Ies(mA) 0.8 1.2 0.9 1.3

Vs(V) 100 250 35 200

Te(eV) 9 10 9 8

Ne(10 17 m -3 ) 1.6 2.3 1.2 2.7

a. Data from previous work

Space potential varies with gas spicis.Ion current for He/Ar plasma is too large.(metastable and 2nd electron?)

How about heat flux measurement?

http://www.jsap.or.jp/ap/2008/ob7704/cont7704.html

http://www.maximizingprogress.org/2010/02/plasma-medicine-disinfection.html

http://www.drexel.edu/research/img/mri_plasma.jpg

New J. Phys. 11 (2009) 115012

Are these guys insensitive?

Yambe's work on calorimetry

He gas He plasma

Water temperature is monitored for He gas/plasma irradiation.(22P039-P, plasma conference 2011, Kanazawa)

The difference of two case corresponds to plasma heat flux.

They said 3.81E-5[J] energy was carried by 13[kHz] micro pulse, which consists plasma jet. Average heat flux is 0.5[W].

Is the thermal isolation of water vessel sufficient?

Is temperature in water homogeneous?

Atmospheric Pressure Plasma Jet

Power supplyLHV-13AC(Logy Electric Co.LTD.) Input AC100V/2A Output 10KV/120mA RMS 9 ～ 12KHz Size 140×92×175 Weight 1.4kg

Heat flux measurement with a metal target

Heat flux determination

Type-T TC Temperature gradient methodType-K TC Fitting/cut method

Electrically isolated

Easy to modify for Q-V characteristic

Material: Cu, Mo

This target was provided by Dr. Osakabe(NIFS).

First result of target temperature

This data gives us heat flux of about 2(kW/m2) or 0.15(W) as a whole.

Estimation of heat flux(Fitting)

0

4

8

12

16

20

1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000

TC(center)

time[s]

TC[deg.]

Estimation with exponential fitting Q （ ~dT/t) = 0.5 [W]

12

4

0

0.5 0.17

Target moved

Heat flux depends upon measurement position.

dTdecay time t is obtained by fitting.

Estimation of heat flux(Cut)

0

2

4

6

0 500 1000 1500 2000 2500 3000

TC(center)

t ime[s]

TC[deg.]

0

2

4

6

2100 2200 2300 2400 2500 2600 2700 2800 2900 3000

TC(center)

time[s ]

TC[deg.]

Estimation with discharge cut Q （ ~jump of dT/dt) = 0.2 [W]

before

after

Plasma heat flux• Electron

positive bias• Ion

Negative bias• Metastable atom

Atmospheric He/Ar• Radical

Atmospheric N2/O2

• Surface recombination• Surface condensation

Is it possible to decompose these contribution? with bias? Tip material?

Effect on TC raw data of target bias

0 2000 400012

16

20

LF plasma(2012/2/14)

time[s]

Tar

get T

emp.

[deg

.C]

Although data is limited andAlthough data is limited and

Although data is limited, TC signal seems to depend upon bias voltage applied to target.

At positive bias, target current becomes negative and TC signal shows large fluctuation.

Although discharge itself might be changed with biasing, positive bias seems to reduce heat flux.(Ion, surface reaction?)

Consideration

• If heat flux of 0.5W is composited only electron and ion contribution, particle flux ( equivalently 50mA ) must be flowed into the target depending on bias voltage. But by now, such a large current has not been observed.

• For previous work on DC discharge, electron saturation current of 1mA was observed with a small probe.

Consideration 2

• Heat from atmospheric plasma seems to be carried by mainly metastable or radical.( Different Q-V curve ?)

• To confirm this, plasma current must be measured preciously. But, since plasma jet is composed of so many micro plasma bullet, current measurement needs to some integration procedure to compare with heat flux measurement.

Conclusion

• Probe measurement of atmospheric pressure plasma requires the heat conduction estimate for tip materials and careful analysis of I-V curve with collisional sheath theory.

• It gives us valuable information of plasma parameter, which depends on discharge device, gas spices, and so on.

• Heat flux of atmospheric plasma jet is measured with target TC data and thermal probe analysis, as like as for low pressure plasma.

• Obtained flux agrees well with Yambe's estimation. But by considering heat flux response to bias voltage, heat flux contribution from charged particles seems small.

• Comparison of Langmuire/thermal probe data would be interesting and left for future work.

Thank you for kind attention.多謝你的親切關懷。Is there any questions?有任何問題嗎？

Appendix

• DC atmospheric pressure plasma• Ion current abnormality• Thermal probe

DC atmospheric plasma data

With J.S.Chang's procedure, plasma density is about 1e17[m-3] for Ies=1[mA].

Discharge polarityNormal

Reverse Air plasma

(-)

(-)

(+)

(+)

Ip-Vp 特性

Ion current istoo large.

Secondary electron currentfrom probe surface,which can not be

distinguished from ion's.

Ip Vp

Reverse polarity discharge

Air(wo flow) He flowAr flow

No anonymity in ion current

No transition in Ar plasma

DC plasma parametersNormal Reverse

Air Ar （＊） He Air Ar He

Dis. curr.[mA] 70 68 58 40 65 58

Float. pot.Vf[V] 30 190 245 395 225 180

Space Pot.Vs[V] 100 200 250 440 310 200

Ele. temp.Te[eV] 9 8 10 8 9 10

Ele. sat.curr.Ies[mA] -0.8 -1.3 -1.2 ? -1.1 -0.90

Ion sat.curr.Iis[mA] 0.02 0.4 0.7 0.055 0.1 0.15

Ele.den.ne×1017[m-3] 1.6 2.7 2.3 1.3 2.2 1.7

＊ low current mode

Ar ion saturation current

This metastable density would produce secondary electron current, which is the same order as the observed ion current.

Conventional thermal probe

Probe tip size, material, thermometer, and so on must be optimized for target plasma.

Heat flux measurement

Various design of thermal probe tips for discharge plasma and divertor plasma

Requirement of design

• tip size smaller than the plasma size larger to smooth out plasma movement• tip material depends on expected flux and method• thermometer thermocouple is experienced Pt thermistor is attractive(?)

Trial measurement of heat flux is necessary.

Usage of Pt thermistorOxygen radicals recombine on platinum surface, which receive more heat than other metal( ex, tungsten). N.Haraki et al. EEJ 149(2004)14.

Pt/W

Electron, ion, radical heat flux

Pt/W temperature can be estimated from its resistance(=V/I-R0).

Its temperature is determined by heat balance between plasma heat flux, ohmic heating, heat loss.

If Pt and W temperature can be set equal by adjusting R0 or V, excess of ohmic heating is equal to radical contribution to Pt sensor, which can be measure of radical flux( or density).

I

R0

V

Heat loss

ohm heating

Only an idea. But is it possible?

Reduction of TC noise

0 1000 2000 300010

20

30LF plasma(2011/12/22)

time[s]

Tem

p.[d

eg.C

]

During discharge, TC signal shows large fluctuations in spite of large thermal diffusion time. electro-magnetic noise? movement of jet column?

HR2500E Chart

Data aqusition with NI9211 and averagingDischarge control( flow, power, distance)

Relatively smooth TC signal is obtained.