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

1. Design and application of a thermal probe to an atomspheric pressure plasma jet ISPlasma 2012 (2012/3/6、Kasuga) Radiation Research Center, Osaka Prefecture University Hiroto Matsuura

2. Background Atmospheric pressure plasma is now attractive for decontamination of environmental waste and medical technology, because of low cast without vacuum pumping system applicability for biomaterial that does notis less tolerate vacuum large 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 load and analysis of I-V characteristic with collisional sheath effect.

3. How about heat flux measurement? New J. Phys. 11 (2009) 115012 Are these guys insensitive? http://www.drexel.edu/research/img/mri_plasma.jpg http://www.maximizingprogress.org/2010/02/plasma-medicine-disinfection.html http://www.jsap.or.jp/ap/2008/ob7704/cont7704.html

4. Heat flux measurement

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

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

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

8. 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?

9. 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.

10. Yambe's work on calorimetry 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]. He plasma He gas Is the thermal of water vessel isolation sufficient? Is temperature in water homogenious?

11. Heat flux measurement with a metal target Material: Cu, Mo Electrically isolated Easy to modify for Q-V characteristic Heat flux determination Type-T TC Temperature gradient method Type-K TC Fitting/cut method

12. Estimation of heat flux(Fitting) 12 4 0 dT decay time t is obtained by fitting. Target moved 0.5 0.17 Estimation with exponential fitting Q（~dT/t) = 0.5 [W] Heat flux depends upon measurement position.

13. Estimation of heat flux(Cut) before after Estimation with discharge cut Q（~jump of dT/dt) = 0.2 [W]

14. 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.

15. 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.

16. Usage of Pt thermistor Oxygen radicals recombine on platinum surface, which recieves more heat than other metal( ex, tangsten). N.Haraki et al. EEJ 149(2004)14. 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). Electron, ion, radical heat flux Heat loss Pt/W ohm heating I V Only an idea. But is it possible? R0

17. 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.

18. Appendix

19. Reduction of TC noise HR2500E Chart During discharge, TC signal shows large fluctuations inspit of large thermal diffusion time. electro-magnetic noise? movement of jet column? Data aqusition with NI9211 and averaging Discharge control( flow, power, distance) Relatively smooth TC signal is obtained.

20. Effect on TC raw data of target bias Al though data is limited and Although data is limited, TC signal seems to depend upon bias voltage applied to target. Although data is limited and 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?)

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