Description

Plasma Source

Field of the invention

The invention relates to a plasma source, particularly for the disinfection of wounds, according to the preamble of claim 1.

Background of the invention

The use of non-equilibrium plasmas for the invivo sterilization of wounds has been discussed in Stoffels, E. ; Stoffels, W. : "The healing touch of a micro-plasma", published on http://www.phys.tue.nl. However, the invivo sterilization of wounds requires low temperatures of the plasma and a low electromagnetic irradiation, so that the conventional plasma sources are not suitable for the invivo sterilization of wounds .

Further, WO 2007/031250 Al discloses a plasma source which is suitable for the aforementioned invivo sterilization of wounds .

High-temperature plasma sources are disclosed, for example, in US 2007/0021748 Al, US 5 573 682, US 5 296 672, FR 1 376 216, US 6 114 649 and US 6 121 569. Other types of conventional plasma sources are disclosed in WO 2005/026650 A2 and US 3 692 431. However, these plasma sources are not suitable for the invivo sterilization of wounds which requires a low temperature plasma.

Summary of the invention

Therefore, it is a general object of the invention to improve the plasma generation within a plasma source which is suit- able for the invivo sterilization of wounds.

This object is achieved by a plasma source according to the invention as defined in claim 1.

According to the invention, a plasma source is provided comprising an ionization chamber in which a plasma is generated. Further, the plasma source comprises a conduit carrying a gas flow of a carrier gas (e.g. ambient air, argon or nitrogen). The plasma source according to the invention is characterized in that the ionization chamber is connected to the conduit, so that the gas flow in the conduit carries away gas particles (e.g. ions, electrons, atoms) out of the ionization chamber thereby reducing the pressure in the ionization chamber. The pressure reduction in the ionization chamber advan- tageously yields an improvement in the efficiency of the plasma generation since the ionizability of gases generally declines with a rising pressure. Therefore, it is easier and more efficient to generate a plasma in a gas having a low pressure .

In a preferred embodiment of the invention, the conduit carrying the gas flow comprises a nozzle, wherein the ionization chamber is connected to the conduit downstream the nozzle. In this embodiment, the pressure reduction within the ionization chamber is produced by the gas flow in the conduit downstream the nozzle.

Preferably, the nozzle is a Venturi nozzle or a Laval nozzle. When using a Laval nozzle, the nozzle generates a shock wave

within the carrier gas flow thereby increasing the flow speed of the carrier gas flow at the junction connecting the ionization chamber to the conduit, which in turn results in a pressure reduction. However, it should be noted that the in- vention is not restricted to the aforementioned types of nozzles.

However, it should be noted that the nozzle is preferably shaped in such way that the gas flow in the conduit comprises a subsonic flow speed (M<1) upstream the nozzle, a supersonic flow speed (M>1) downstream nozzle and/or a substantially sonic flow speed (M«l) in the nozzle. Such a distribution of the flow speeds along the conduit produces the desired pressure reduction in the supersonic gas flow in the conduit ac- cording to the well-known laws of Bernoulli.

In a preferred embodiment of the invention, the ionization chamber is ring-shaped and surrounds the conduit. In this embodiment, the nozzle and the surrounding ionization chamber can be arranged in the same cross sectional plain. Alternatively, it is possible that the ionization chamber is axially displaced with regard to the nozzle. Preferably, the ionization chamber is displaced axially in flow direction relative to the nozzle of the conduit carrying the gas flow. In other words, the ionization chamber is preferably arranged downstream then nozzle. Therefore, the junction of the ionization chamber and the conduit is located downstream the nozzle, where the pressure is reduced as explained above.

In another embodiment of the invention, the ionization chamber is cup-shaped and open in flow direction, wherein the ionization chamber is disposed within the conduit, particularly within the nozzle. In this embodiment, the cup-shaped ionization chamber and the surrounding conduit (e.g. the noz-

zle) are preferably arranged coaxially, so that the gas flow in the conduit flows in the ring-shaped gap between the inner wall of the nozzle and the outer surface of the cup-shaped ionization chamber. Then, the gas flow in the ring-shaped gap passes the ionization chamber and carries away gas particles out of the interior of the ionization chamber thereby reducing the pressure within the ionization chamber.

In the aforementioned embodiment, the cup-shaped ionization chamber preferably touches the inner surface of the nozzle at the downstream end of the ionization chamber thereby closing the aforementioned ring-shaped gap between the inner surface of the nozzle and the outer surface of the cup-shaped ionization chamber. However, the cup-shaped ionization chamber preferably comprises axially arranged notches at the ring- shaped contact point between the ionization chamber and the nozzle, so that the gas flow in the ring-shaped gap between the inner surface of the nozzle and the outer surface of the ionization chamber can flow through these notches.

Further, the cup-shaped ionization chamber preferably comprises an axial position, which is adjustable in axial direction, i.e. the cup-shaped ionization chamber can be adjusted axially relative to the surrounding conduit.

Further, the plasma source according to the invention preferably comprises a first electrode and a second electrode for generating the plasma in the ionization chamber. However, the invention is not restricted to electrode arrangements com- prising two electrodes for plasma generation. It is also possible to use electrode arrangements comprising more than two electrodes as disclosed in WO 2007/031250 Al, which is therefore incorporated by a reference herein.

In a preferred embodiment of the invention, the first electrode is formed by the nozzle, whereas the second electrode is formed by a conic part of the conduit, wherein the conic part of the conduit is tapering in flow direction and sur- rounding the nozzle as already mentioned above. In this embodiment of the invention, the nozzle empties into the funnel-shaped conic part of the conduit.

In another embodiment of the invention, the first electrode and the second electrode are both disposed within the ionization chamber. Such an electrode arrangement is preferred in the aforementioned embodiment comprising a cup-shaped ionization chamber.

In yet another embodiment of the invention, the first electrode is formed by the conduit, particularly by the nozzle, whereas the second electrode is disposed alone within the ionization chamber. In this embodiment, electrical discharges take place between the inner surface of the conduit on the one hand and the second electrode in the ionization chamber on the other hand. Therefore, different electrical potentials are applied to the conduit on the one hand and to the second electrode in the ionization chamber on the other hand. For example, the conduit can be electrically grounded, whereas a positive or negative high voltage potential is applied to the second electrode in the ionization chamber.

The plasma generation within the ionization chamber generally produces radio frequency (RF) radiation or microwaves, which can be shielded by the walls of the ionization chamber or by the walls of the surrounding conduit in order to reduce RF or microwave irradiation of the plasma source. Further, it is possible to encase the plasma source by a housing made from

an electrically conductive material in order to reduce the RF or microwave irradiation.

Further, the plasma source according to the invention can be configured in such a way that there is no direct radiation path from the inside of the ionization chamber into the conduit carrying the gas flow and through the outlet of the conduit, so that the plasma source is substantially free of plasma generated electro magnetic irradiation, e.g. ultravio- let irradiation.

However, in some applications of a plasma source ultraviolet irradiation might be desirable, e.g. for sterilization of wounds or for decontamination of surfaces. Therefore, it is also possible that the plasma source according to the invention is configured in such a way that there is a direct radiation path from the inside of the ionization chamber into the conduit carrying the gas flow and through the outlet of the conduit, so that the plasma source emits plasma generated electromagnetic irradiation.

Further, the ionization chamber may comprise walls, which are at least partially transparent thereby enabling a visual control of the plasma generation within the ionization chamber. For example, a window can be disposed in the walls of the ionization chamber and/or in the walls of the surrounding conduits so that the plasma generation in the ionization chamber can be visually monitored through the window, which is therefore preferably transparent for visible light and in- transparent for ultraviolet light. Further, a photo diode, a CCD camera (CCD: Charge c_oupled device) or any other optical sensor can be used for monitoring the plasma generation through the window.

It should further be noted that the ionization chamber may comprise a connection for connecting a vacuum meter or the like.

In another embodiment of the invention, the plasma source comprises a magnet generating a magnetic field in the ionization chamber and/or downstream the ionization chamber in a conduit, wherein the magnetic field enhances the plasma generation. This is reasonable if the mean free path of the charge carriers (i.e. electrons) of the plasma is sufficient to produce a significant effect of the magnetic field on the charge carriers due to the Lorentz force.

It should further be mentioned that the conduit carrying the carrier gas flow comprises an inlet for introducing the gas flow into the conduit and an outlet for dispensing the gas flow with the intermixed plasma onto an object, which is to be treated with the plasma.

Further, the vacuum in the ionization chamber is preferably in the range between 5mbar to 900mbar and more preferably in the range between 400mbar to βOOmbar. However, the invention is not restricted to the aforementioned pressure range.

Moreover, it should be noted that the gas flow introduced into the conduit preferably consists of ambient air, nitrogen, noble gas (e.g. argon) or one of the aforementioned gases with additives, particularly with carbon dioxide.

Further, the gas flow in the conduit preferably amounts to less than 501/min., 401/min., 301/min., 201/min. , or even to less than 101/min. However, the invention is not restricted to the aforementioned limits for the gas flow in the conduit.

Further, the plasma source according to the invention preferably comprises a plasma generator driving the electrodes within the ionization chamber. In one embodiment of the invention the plasma generator produces a direct current (DC) excitation in the ionization chamber. In another embodiment, the plasma generator produces an alternating current (AC) excitation in the ionization chamber, particularly a radio frequency (RF) excitation.

It should further be noted that the plasma source according to the invention preferably generates a non-thermal plasma having a low temperature, so that the plasma can be used to treat wounds or other temperature sensitive surfaces. Therefore, the plasma generated by the plasma source preferably has a temperature of less than 100 ⁰ C, 75°C, 50 ⁰ C, 40°C or even less than 30 ⁰ C measured at the outlet of the plasma source .

It has already been mentioned that the gas flow in the con- duit carries away gas particles out of the ionization chamber thereby reducing the pressure within the ionization chamber. In the preferred embodiment of the invention, different types of gas particles are carried away out of the ionization chamber, e.g. gas molecules, gas atoms, gas ions and/or elec- trons.

It should further be noted that the invention is also directed to a medical device comprising a plasma source as mentioned above. For example, sterilizers or cauterizers may be equipped with the plasma source according to the invention.

Moreover, the invention is directed to a method of non- therapeutic use of a plasma source according to the invention

for treatment of an object, which can be sterilized or decontaminated by the plasma.

The non-destructive decontamination of objects may be of interest in astronautics, e.g. when parts of a space craft shall be decontaminated after return to earth. Therefore, the plasma source according to the invention can be used to decontaminate electronic circuits, electric or electronic components, subassemblies of a space craft or the surface of a space-suit.

The invention and its particular features and advantages will become more apparent from the following detailed description considered with reference to the accompanying drawings.

Brief description of the drawings

Figure 1 is a sectional view of a plasma source according to the invention comprising a Laval nozzle and a funnel-shaped counter electrode,

Figure 2 is a cross sectional view of another embodiment of a plasma source according to the invention comprising a nozzle and a cup-shape ionization chamber within the nozzle.

Figure 3 is a modification of the embodiment according to figure 3, wherein the nozzle comprises a conically widening outlet.

Figure 4 is a sectional view of a modification of figure 3, wherein a single electrode is disposed within the ionization chamber.

Figure 5 is a sectional view of a modification of the embodiment according to figure 4, wherein the nozzle comprises a conically widening outlet.

Figure 6 is a sectional view of a modification of the embodiment according to figure 4, wherein a magnet is surrounding the nozzle generating a magnetic field within the nozzle.

Figure 7 is a modification of the embodiment according to figure 6, wherein the nozzle comprises a conically widening outlet.

Figure 8 is a modification of the embodiment according to figure 6 comprising a hollow cathode for plasma generation.

Figure 9 is a cross sectional view of a modification of the embodiment according to figure 8, wherein the nozzle comprises a conically widening outlet.

Figure 10 is an enlarged cross sectional view of the hollow cathode for plasma generation.

Figure 11 is a cross sectional view of the ionization chamber along the line A-A in figure 2.

Figure 12 is a schematic view of a medical device for treatment of a patient with plasma.

Figure 13 is a schematical view showing a surgeon using the plasma source as a cauterizer.

Figure 14 is a schematical view showing a plasma source similar to the one of Figure 1 but with a different electrode arrangement.

Figure 15 is a modification of the embodiment of figure 14 comprising two DC sources for generating the plasma.

Figure 16 is a modification of the embodiment of figure 14 comprising a free-running pulsed plasma excitation.

Figure 17 is a schematical view showing a plasma source similar to the one of Figure 15 but with an additional magnet .

Figure 18 is a modification of the embodiment of figure 17 comprising two DC sources for generating the plasma .

Figure 19 is a modification of the embodiment of figure 17 comprising a free-running pulsed plasma excitation.

Detailed description of the drawings

Figure 1 shows a sectional view of an embodiment of a plasma source 1 according to the invention, which can be used for plasma treatment of an object 2, e.g. a wound, which is to be sterilized.

The plasma source 1 comprises a conduit carrying a gas flow, wherein the conduit consists of a modified Laval nozzle 3 and a conduit pipe 4.

The Laval nozzle 3 is arranged upstream and comprises an inlet 5 for introducing a carrier gas flow into the plasma source 1. Further, the Laval nozzle 3 comprises an inner wall 6 which is shaped in such a way that the carrier gas flow within the Laval nozzle 3 comprises a subsonic flow speed (M<1) at the inlet 5, a supersonic flow speed (M>1) at an outlet 7 of the Laval nozzle 3 and a substantially sonic flow speed (MwI) at a bottleneck within the Laval nozzle 3. Therefore, the gas pressure at the outlet 7 of the Laval nozzle 3 is reduced, which enhances the plasma generation, which will be described in detail later.

The conduit pipe 4 is disposed downstream behind the Laval nozzle 3 and comprises a funnel-shaped upstream portion and a cylindrically shaped downstream portion and an outlet 8 for applying the plasma to the surface of the object 2.

It should further be noted that there is an axial displacement between the Laval nozzle 3 and the conduit pipe 4, so that there is a gap between the Laval nozzle 3 and the conduit pipe 4, whereas the gas jet is flowing freely in the gap thereby generating a vacuum.

Further, the Laval nozzle 3 and the conduit pipe 4 are en- cased by a housing 9 defining an ionization chamber 10 between the Laval nozzle 3 and the conduit pipe 4 on the inside and the walls of the housing 9 on the outside.

The Laval nozzle 3 comprises an external thread, which is screwed with an internal thread of the housing 9.

Further, the cylindrical downstream portion of the conduit pipe 4 comprises an external thread, which is screwed with an internal thread of the housing 9.

In this embodiment, both the Laval nozzle 3 and the conduit pipe 4 consist of an electrically conductive material, whereas the housing 9 consists of an electrically non- conductive material.

The plasma source 1 further comprises a plasma generator 11, which can be an AC-source, a DC-source or an RF-source depending on the excitation mechanism used for plasma genera- tion. The plasma generator 11 is connected to the Laval nozzle 3 and to the conduit pipe 4, so that electrical discharges take place in the ionization chamber 10 between the downstream end of the Laval nozzle 3 and the upstream end of the conduit pipe 4, which is illustrated in the drawings by arrows.

It has already been mentioned above that the supersonic flow speed (M>1) of the carrier gas flow at the outlet 7 of the Laval nozzle 3 results in a reduced gas pressure at the out- let 7 of the Laval nozzle 3. Therefore, the carrier gas flow carries away gas particles (i.e. ions, electrons, molecules) out of the ionization chamber 10, so that the gas pressure in the ionization chamber 10 is reduced thereby enhancing the efficiency of the plasma generation.

Further, the housing 9 comprises a connection 12 for connecting a vacuum meter or the like.

Figure 2 shows a cross section of another embodiment of a plasma source 13 according to the invention.

The plasma source 13 comprises a Laval nozzle 14 and a cup- shaped ionization chamber 15, which is disposed coaxially within the Laval nozzle 14.

Further, the plasma source 13 comprises a cover plate 16, which is screwed on the upper front side of the Laval nozzle 14. In the cover plate 16, there are ducts for high voltage contacts 17, 18, which can be connected to a plasma generator. Further, the' cover plate 16 comprises a duct for a rod 19 supporting the ionization chamber 15. The rod 19 is fixed by a screw, so that the rod 19 can be adjusted axially in the direction of the arrow in order to adjust the axial position of the ionization chamber 15 within the Laval nozzle 14.

Further, the Laval nozzle 14 comprises an inlet 20 for introducing a carrier gas flow into the Laval nozzle 14.

The carrier gas flows within a ring-shaped gap between the outer wall of the ionization chamber 15 and the inner wall of the Laval nozzle 14 up to the downstream end of the ionization chamber 15, where the ionization chamber touches the inner wall of the Laval nozzle 14.

Therefore, the ionization chamber 15 comprises notches 21-24 (see figure 11), which are arranged in the outer wall of the ionization chamber 15 at the downstream end of the ionization chamber 15, so that the carrier gas can flow through the notches 21-24.

Further, the ionization chamber 15 comprises two electrodes 25, 26, which are connected to the high voltage contacts 17, 18, so that an excitation takes place between the electrodes 25, 26, which is illustrated by the arrow.

It should further be noted that the carrier gas flowing through the notches 21-24 produces a pressure reduction at the downstream end of the ionization chamber 15, so that the

carrier gas flow carries away gas particles out of the inside of the ionization chamber 15 thereby reducing the gas pressure within the ionization chamber 15, which enhances the plasma efficiency.

Further, the plasma source 13 comprises an outlet 27 at its downstream end for applying the plasma to the surface of the object 2.

Figure 3 shows a modification of the plasma source 13 comprising a conduit pipe 14' instead of the Laval nozzle 14. The conduit pipe 14' comprises a cylindrical upstream portion, a conically widening downstream portion and a tapering middle portion.

Figure 4 shows a modification of the embodiment of figure 2, which is characterized in that there is only the single electrode 25 in the ionization chamber 15, whereas the Laval nozzle 14 acts as a counter electrode and is therefore made of an electrically conductive material.

It should further be noted that the plasma is generated within the ionization chamber 15.

Figure 5 is a modification of the embodiment of figure 4, which is characterized in that the Laval nozzle 14 is replaced by the conduit pipe 14' as in figure 3.

Figure 6 is a modification of the embodiment according to figure 5, which is characterized in that the Laval nozzle 14 is surrounded by a magnet 28, which is generating a coaxially aligned magnetic field within the bottleneck of the Laval nozzle 14 thereby enhancing the plasma generation.

Figure 7 is a modification of the embodiment according to figure 6, which is characterized in that the Laval nozzle 14 is replaced by the conduit pipe 14' as mentioned above.

Figure 8 is a modification of the embodiment according to figure 6, which is characterized in that there is a single hollow cathode 29 disposed within the ionization chamber 15, which enhances the plasma generation.

Figure 9 is a modification of the embodiment of figure 8, which is characterized in that the outlet is conically widening .

Figure 10 shows a cross sectional view of another embodiment of an ionization chamber 30 forming a hollow cathode. The ionization chamber 30 consists of an electrically conductive material and comprises an electrically insulating housing 31.

Figure 11 shows a cross section of the ionization chamber 15 along the line A-A as shown in the afore-mentioned figures. It is illustrated that the ionization chamber 15 comprises notches 21-24 at its downstream end.

Figure 12 shows a medical device 32 for treatment of a pa- tient 33 with non-thermal plasma. In this embodiment, there are several plasma sources arranged around the patient 33, so that the plasma is applied to the patient 33 from different sides.

Further, figure 13 shows a surgeon 34 handling a cauterizer 35 for cauterising tissue in an operating field 36. In this embodiment, the cauterizer 35 comprises a plasma source as described above.

Figure 14 is a modification of the embodiment of figure 1 so that reference is made to the above description relating to figure 1.

However, the Laval nozzle 3 and the conduit pipe 4 are not connected to the plasma generator 11. Instead, there are two electrodes 37, 38 for the excitation of the plasma in the ionization chamber 10.

The electrodes 37, 38 are radially aligned and arranged in a plane perpendicular to the gas flow between the Laval nozzle 3 and the conduit pipe 4.

The electrode 37 is connected to ground and the electrode 38 is connected to the plasma generator 11, which is an AC/DC source .

Figure 15 is a modification of the embodiment of figure 14 so that reference is made to the above description relating to figure 14.

However, there are two plasma generators 11 in the form of DC sources, which are connected to the electrodes 37, 38.

Figure 16 is a modification of the embodiment of figure 14 so that reference is made to the above description relating to figure 14.

However, there is a free-running pulsed plasma excitation. Therefore, the plasma generator 11 in the form of a DC source is connected to the electrode 38 via two resistors Rvl«lMω, Rv2«lω-100kω and a capacitor C=InF which is connected to ground. The plasma generator 11 generates a high voltage of

about U«6kV resulting in a charge time X _CHARGE ^IπIS , a discharge frequency foisc _HARGE ∞lkHz and pulse duration τ _PUL s _E ~lns-10ms .

Figure 17 is a modification of the embodiment of figure 14 so that reference is made to the above description relating to figure 14.

One distinct feature of this embodiment is that there are permanent magnets 39, 40 being integrated into the electrodes 37, 38. The permanent magnets 39, 40 generate a magnetic field in the ionization chamber 10 thereby improving the plasma generation.

Figure 18 is a modification of the embodiment of figure 17 so that reference is made to the above description relating to figure 17.

However, there are two plasma generators 11 in the form of DC source, which are connected to the electrodes 37, 38.

Finally, figure 19 is a modification of the embodiment of figure 17 so that reference is made to the above description relating to figure 17.

However, there is a free-running pulsed plasma excitation.

Therefore, the plasma generator 11 in the form of a DC source is connected to the electrode 38 via two resistors RvI, Rv2 and a capacitor C which is connected to ground.

Although the invention has been described with reference to the particular arrangement of parts, features and the like, these are not intended to exhaust all possible arrangements of features, and indeed many other modifications and variations will be ascertainable to those of skill in the art.

List of reference numerals:

1 Plasma source

2 Object

3 Laval nozzle

4 Conduit pipe

5 Inlet

6 Inner wall

7 Outlet

8 Outlet

9 Housing

10 Ionization chamber

11 Plasma generator

12 Connection

13 Plasma source

14 Laval nozzle

14' Conduit pipe

15 Ionization chamber

16 Cover plate

17, 18 High voltage contacts

19 Rod

20 Inlet

21-24 Notches

25, 26 Electrodes

27 Outlet

28 Magnet

29 Hollow cathode

30 Ionization chamber

31 Housing

32 Medical device

33 Patient

34 Surgeon

35 Cauterizer

36 Operating field

37 Electrode

Electrode Permanent magnet Permanent magnet

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