ISPlasma 2012
(2012/3/6、Kasuga)
Design and application of a thermal probe
to an atomspheric pressure plasma jet
Radiation Research Center,
Osaka Prefecture University
Hiroto Matsuura
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.
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/o
b7704/cont7704.html
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 supply
LHV-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
Water temperature is monitored for He gas/plasma irradiation.
(22P039-P, plasma conference 2011, Kanazawa)
He gas
He plasma
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
Material: Cu, Mo
Electrically isolated
Heat flux determination
Type-T TC
Type-K TC
Temperature gradient method
Fitting/cut method
Easy to modify for
Q-V characteristic
Estimation of heat flux(Fitting)
12
dT
4
Target moved
decay time t
is obtained
by fitting.
0
Estimation with exponential fitting
Q（~dT/t) = 0.5 [W]
Heat flux depends upon measurement position.
0.5
0.17
Estimation of heat flux(Cut)
before
after
Estimation with discharge cut
Q（~jump of dT/dt) = 0.2 [W]
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 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).
Electron, ion, radical
heat flux
Heat loss
Its temperature is determined by heat
balance between plasma heat flux,
ohmic heating, heat loss.
Pt/W
ohm heating
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
V
Only an idea. But is it possible?
R0
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
HR2500E Chart
LF plasma(2011/12/22)
Temp.[deg.C]
30
20
10
0
During discharge, TC signal shows
large fluctuations inspit of large
thermal diffusion time.
electro-magnetic noise?
movement of jet column?
1000
2000
3000
time[s]
Data aqusition with NI9211 and averaging
Discharge control( flow, power, distance)
Relatively smooth TC signal is obtained.
Effect on TC raw data
of target bias
Target Temp.[deg.C]
LF plasma(2012/2/14)
20
At positive bias, traget current
becomes negative and TC signal
shows large fluctuation.
16
12
0
Al data is limited, TC
Although
Although
data
is limited
data
is limited
andand
signal though
seems to
depend
upon
bias voltage applied to target.
2000
4000
time[s]
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].