TU/e Eindhoven University of TechnologyA.J. Flikweert, E. Stoffels, W.W. Stoffels, E.J. Ridderhof, R.P. Dahiya, G.M.W. KroesenDept. of Applied Physics, Eindhoven University of Technology, P.O. Box 513, 5600 MB Eindhoven, The Netherlands

Non-thermal atmospheric discharge for biomedical purposes

1. Introduction

• Non-thermal plasmas: electrons and heavy particles are not in equilibrium. Electrons are hot (T~30,000-50,000K), gas at room temperature.• Non-thermal plasmas are readily created at low pressures• Non-thermal plasmas are non-destructive and therefore have many applications in material science• Various surface processing technologies: etching, deposition, surface cleaning• Refined surface processing is obtained (solar cells, microprocessor chips) in plasma reactors• Can we apply plasmas for refined surface treatment of organic materials/living tissues?• If so, plasma treatment has potentially many biomedical applications: local high precision surgery, like destroying of cancer cells or plaque in blood vessels, cleaning of bone surfaces and dental cavities• Problem: a suitable source must be developed

create a non-thermal plasma at atmospheric pressure• Possible solution: reduce the plasma size

2. Scheme of the micro plasma

• We used function generator and a 13,56 MHz amplifier• The RF is supplied to the matching network box• The transmitted and reflected power is measured and the matching network is adjusted to minimise the reflected power and to optimise the peak to peak voltage at the tip• The voltage at the tip is measured with a probe connected with a scope• We used a flow controller to regulate the flow of helium, argon and air supplied to the tip• The pin is isolated by ceramics, so to obtain plasma only at the tip. The tip diameter is about 1 mm. We test different shapes of the tip (pointed or flat)• Diagnostics: power meter, electrical probe to measure the RF voltage, optical multichannel analyser (OMA) to obtain emission spectra• The pin at which the plasma is obtained is isolated by ceramics. The pin is of stainless steel and has a diameter of about 1 mm• The size of the plasma ranges from sub-millimetre to a few millimetres

Function generator RF generator

Powermeter

Matchingnetwork

Scope

Helium

Argon

Flowcontroller

Flowcontroller

Coupler

Probe

3. Results

• We developed a small-size plasma source ("plasma needle") • It is stable and operates in helium • We test the plasma, to check whether it is safe for treatment of living beings.• We have measured the I-V characteristics for different needles (flat and sharp tips) and different flow rates of helium and argon.• In the near future we will determine the temperature of the plasma by determining the spectral properties by means of optical emission spectroscopy.

Sharp tip

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Vpp (Volt)

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plasma (He)

air (no plasma)

Flat tip

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Vpp (Volt)

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plasma (He)

air (no plasma)

Different flowrates He / air (total: 340 ml/min), flat tip

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Vpp (Volt)

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tt) 0‰ air

4.4‰ air

8.7‰ air

13.1‰ air

17.5‰ air

26.2‰ air

pure air (no plasma)

Plasma on/off/arc voltages at different He / air flowrates, flat tip

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Air flowrate (‰)

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arc

Plasma on/off/arc power at different He / air flowrates, flat tip

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plasma off

arc

•We have measured different I-V characteristics. We have used different tips and different flowrates of helium, argon and air.•The plasma at the flat point is more stable and homogeneous. At the sharp point, the plasma tends to creep along the pin.•Helium plasma is more stable than argon plasma. In argon the minimum voltage to obtain plasma lies higher than in helium. In argon arcs are created readily, and the voltage to obtain plasma lies near the voltage one at which gets an arc.•Low air flowrates influence the stability significantly. The voltage to obtain plasma rises much and that voltage lies near the voltage at which one gets an arc.

•The spectrum of a helium plasma (sharp tip) is also measured. We want to analyse the spectrum in the near future to obtain the electron temperature.•Paper exposed directly to the plasma displays blue fluorescence, but does not show any signs of thermal damage. We put organic materials (blades of grass, leafs) in the plasma to see what happens with it. The tissue is not damaged in the plasma and the colour of the tissue is not changed. Because of these results we expect that the temperature is low enough not to destroy tissues.

4. Conclusion

• We can generate an atmospheric non-thermal plasma • The plasma is stable in helium; operating voltages are 200-500V, power consumed by the plasma lies in the range of 100 mw - 5 W• Gas temperature is low• Future plans: analyse the spectra to obtain electron temperature (helium lines), vibration and rotation temperature (from N2/O2 bands of air admixture)• Determine gas temperature using thermocouples

Spectrum He plasma, sharp tip

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The lab

The pin at which the plasma is obtained

1 mm

Plasma at the tip Piece of paper in the plasma