Electric lamp and discharge devices: systems – Discharge device load with fluent material supply to the... – Plasma generating
Reexamination Certificate
1999-04-22
2001-05-01
Shingleton, Michael B (Department: 2817)
Electric lamp and discharge devices: systems
Discharge device load with fluent material supply to the...
Plasma generating
C219S121480
Reexamination Certificate
active
06225743
ABSTRACT:
The invention relates to a device for supplying voltage to a plasma producer.
In a known device of this kind, a plasma gas is blown substantially continuously through a chamber in which the anode-to-cathode gap is located. A fluctuating current flow is ensured by way of the arc gap through a control of the power supply. Usually, the current will fluctuate with a frequency of 1 to 10 Hz, with the maximum current usually being 7 to 15 times the minimum current.
The power supply is usually formed by a transformer with downstream rectifier. Furthermore, in the known methods the anode-to-cathode gap is charged with a voltage corresponding to the arc drop voltage of the arc, with a separate ignition pulse being provided for igniting the arc.
The relevant aspect in the known method is that the arc will burn continuously, even though its output will fluctuate.
This is problematic for various applications due to its continuous energy output.
Thus, a plasma will emit UV radiation to a considerable extent which could be used for the sterilisation of objects, for example. However, the simultaneous radiation of a considerable quantity of heat constitutes a problem.
It is the object of the present invention to avoid such disadvantages and to provide a a device for supplying voltage to a plasma producer, in which.
The proposed measures will lead to the advantage that plasma pulses of only a very short duration can be produced. Such plasma pulses, despite their very high temperature, can be tolerated by even relatively sensitive materials without causing any damage as a result of their short duration because the energy introduced over a longer period into the material to be treated can be kept below a harmful level.
It is not absolutely necessary to introduce a gas in the anode-to-cathode path. Metal vapours emerging from the surface of the anode and cathode occur as a result of the temperature of the arc, which metal vapours are ionised by the arc and form a plasma which flows out of an outlet opening of a chamber receiving the anode and the cathode.
Holding the voltage pulses to 10
−5
to 10
−3
seconds, and preferably the pauses between the voltage pulses to 10 to 100 times the duration of the voltage pulses, allows keeping at a low level the energy introduced by a plasma produced in accordance with the invention into a subject charged with said plasma, so that even sensitive subjects can be processed with such a plasma whose individual pulses have a high energy density.
The invention accomplishes these objects with a device for supplying voltage to a plasma producer comprising a chamber having an outflow opening, and an anode and a cathode arranged in the chamber, the anode and cathode defining a gap therebetween, the voltage supplying device comprising a charging circuit, a capacitor battery having an input connected to the charging circuit and an output connected to the anode and the cathode, and an ignition set supplying HF signals connected to the anode and the cathode, a maximum voltage supplied by the capacitor battery being smaller than an arc-over voltage of the anode-to-cathode gap.
The proposed measures lead to a very simple arrangement, whereby the pulse times can be determined very easily by a dimensioning of the capacitors and the resistance of the circuit comprising the anode-to-cathode gap as well as the charging circuit for determining the respective time constants.
Since a very rapid heating of the medium disposed in the interior of the chamber will occur during the ignition of the arc, it will expand very rapidly and will flow outwardly with a high kinetic energy through the outlet opening. In the following interpulse period, air can flow into the cooling chamber from the ambient environment, so that the same can be operated in a practically regenerative manner and no gas flow that permanently flows through the chamber needs to be forced.
Since the individual plasma pulses exit with a high speed, there will not be any mixture with the ambient atmosphere during their emergence and thus there will not be any divergence of the plasma jet. In this context, tests have shown that the produced plasma pulses have a behaviour similar to that of globular lightning. This also ensures a very high energy density on the subject to be treated.
The HF ignition set allows a very precise determination of the ignition of the arc while ensuring that the end of the voltage pulse or the arc duration is determined by the discharge of the capacitor battery to a voltage below the arc drop voltage. This ensures even in the case of the ignition of the arc by means of a separate striking voltage source that the arc will extinguish between the individual pulses and no static current will flow through the anode-to-cathode gap.
The HF ignition set also allows triggering the ignition of the arc even before reaching the arc-over voltage of the anode-to-cathode gap, as a result of which the duration of the arc and thus the duration of the plasma pulse can be kept extremely short without having to make any special efforts to ensure a particularly low-impedance arrangement of the discharge circuit of the capacitor battery.
In principal, it also possible to use a technical A.C. system or a voltage source supplying a high-frequency alternating current in connection with a phase-angle control unit instead of the capacitor battery as a power supply means. In the case of electrodes made from different materials, it must be ensured that similarly polarised half-waves are partly connected through only so that voltage pulses with the same polarity are always applied to the different electrodes and substantially the same ratios as in the supply of the plasma torch with d.c. voltage pulses, like from a capacitor battery for example, are obtained.
In electrodes made from the same materials, pulses with different polarity can be applied to each of the two electrodes.
As electrodes which are made of different materials for the purpose of achieving a longer service life are usually charged with the same polarity in plasma torches, the anode and cathode are referred to generally in the description and the claims.
In order to ensure the short pulses which are provided for according to the method of the invention, it will usually be appropriate to provide a through connection by means of the phase-angle control only in the falling branch of the respective half-wave, which also depends on the rigidity of the supplying voltage source. It can also be provided to block the phase-angle control after each through connection for a certain number of periods in order to reduce the repeat frequency of the plasma pulses to a desired level.
Preferably, the diameter of the outflow opening of the plasma producer is 10 &mgr;m to 100 &mgr;m. This has the advantage that the individual plasma pulses exit from the outlet opening of the chamber with a very high speed and impinge on the subject to be treated with a very high kinetic energy. Outgoing speeds of 1000 to 2000 m per second could be determined in experimental set-ups. In this way it is possible to manufacture very small bores in thin sheet metal or even weld points.
The application of a plasma produced in accordance with the invention is also provided in accordance with the invention for sterilising objects, in particular interior spaces of hollow objects or conduits.
In this process, any bacteria or viruses are killed rapidly and effectively, despite the short exposure time, by the high temperature of the individual plasma pulses, which are approx. 20,000 to 50,000° C., and are simultaneously removed from the surface of the object to be sterilised by the kinetic energy of the plasma pulses so that no “bacteria carcasses” remain.
As a result of the continued production of very short plasma pulses as provided for in accordance with the invention, they can also be used for surgical and dental purposes, e.g. instead of laser scalpels.
Plasma torches with a relatively small output, e.g. from 0.5 kW to 10 kW, can be used in both cases.
Furthermore, the plasma produced in acc
Collard & Roe P.C.
Inocon Technologie Gesellschaft m.b.H.
Shingleton Michael B
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