Design and application of a thermal probe to an atomspheric pressure plasma jet

Radiation Research Center, Osaka Prefecture University

Hiroto Matsuura

ISPlasma 2012(2012/3/6 、 Kasuga)

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 notis 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.

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?

Heat flux measurement

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

Conventional thermal probe

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

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

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?

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.

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 defference 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 of water vessel isolation sufficient?

Is temperature in water homogenious?

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

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

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.

Usage of Pt thermistorOxygen radicals recombine on platinum surface, which recieves more heat than other metal( ex, tangsten). 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 ohming 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?

Conclusion

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

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

• Pt thermistor type sensor would become an interesting tool to deduce radical contribution to heat flux.

Appendix

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 inspit 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.

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, traget 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?)

DC atmospheric plasma data

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