Electric lamp and discharge devices: systems – Discharge device load with fluent material supply to the... – Plasma generating
Utility Patent
1999-09-03
2001-01-02
Bettendorf, Justin P. (Department: 2817)
Electric lamp and discharge devices: systems
Discharge device load with fluent material supply to the...
Plasma generating
C315S111310, C219S121360, C313S231310
Utility Patent
active
06169370
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing an RF/HF induced, low-energy plasma, in particular noble gas plasma, and a device for producing an RF/HF induced, low-energy plasma, in particular noble gas plasma, comprising a generator and a supply element for the plasma gas.
Methods and devices for producing a plasma, in particular noble gas plasma, are known in various embodiments, wherein such a plasma can be used for example as radiation source, in particular in emission spectrometry. By providing for a sample in the plasma, further possible applications of such a plasma are for example in the field of investigations relating to atomic emission, chemiluminescence, ion mobility, and as ion source for mass spectrometry. Without providing for a sample such a plasma can for example be used as a source for slow, thermalized electrons. In the field of ionization techniques for mass spectrometry such an electric discharge can be used instead of the commonly used corona discharge to ionize a component: of the gas, whereby this component in turn ionizes the sample molecule. In the context of a photoionization detector such a plasma can be used as a point-source for VUV radiation. In the context of ozone production a microplasma can be employed when in certain applications the total gas flow during ozone production has to be very low, for example when the ozone is to be introduced into the vacuum chamber of an analytical instrument. Furthermore such a plasma can for example generally be used for the production of redox-reagents to be introduced in small amounts into gaseous or liquid systems. Further possible applications of such a plasma comprise the use as VUV light source for the treatment of surfaces, in particular at atmospheric pressure.
For the production of plasmas various methods are known. Besides the possibility to form plasmas by means of an electric arc, preferably methods and devices are used, in which the energy necessary for plasma formation and maintenance is coupled to the gas by electromagnetic waves. Such a method and apparatus for the production of an HF-induced noble gas plasma can be found for example in DE-OS 36 38 880, wherein the energy should be coupled into the plasma capacitively. Relating to a microwave-induced noble gas plasma EP-A 0 184 912 can serve as an example, wherein in that known embodiment the microwave-induced plasma is subsequently to be employed for photoionization detection.
Problematic in such known methods and devices is on the one hand the coupling of the electromagnetic energy into the plasma gas, wherein in the known methods the employed power is in the range of approximately hundred watts. Therefore the power to be coupled is very high, wherein in addition to that of course adequate heat dissipation has to be provided in immediate vicinity of the produced plasma, to avoid damage to parts of the apparatus. For this purpose for example tubes made of an electrically non-conducting, high-temperature resistant material are used to separate the gas or plasma from the remaining parts of the apparatus, wherein it is immediately apparent that by providing such enclosing elements for the plasma, there is in addition increased need for adequate cooling devices, which renders the production of a plasma of low spatial spread, and preferably of a plasma which can be termed essentially and idealized as point-like, more difficult or even impossible. Such a device is known for example from U.S. Pat. No. 4,654,504.
In addition to that a plasma panel has been known from DE-A 26 46 785, wherein a discharge path is confined by layers of insulating material, and for the production of the plasma there are provided ring electrodes, which are supplied by direct current.
Furthermore devices are known, which use a plasma for either etching or coating of surfaces, for which EP-A 303 508 or JP-A 8274069 give examples. A plasma machining apparatus can for example be found in JP-A 8273894.
In addition to the possible applications for a low-power plasma, as discussed in detail above, plasma-arc torches can be found for example in DE-A 38 14 330 or DE-OS 25 25 939, which due to their high-energetic plasmas are not directly comparable with applications in the low-energy range.
SUMMARY OF THE INVENTION
Starting from the state of the art mentioned at the outset, the present invention aims at providing a method and device for the production of a low-energy plasma, by which, from a process-engineering point of view, a simple and stable way of producing a low-energy plasma is provided. With this it is in particular aimed at providing a plasma of low spatial spread with simultaneously simplified heat dissipation.
To solve these objects, the process of the subject invention for producing a RF/HF induced low-energy plasma, in particular noble gas plasma, is essentially wherein the energy is supplied through two parallel, interspaced, in particular ring- or disk-shaped electrodes, each having at least one through-opening, that said plasma is confined by at least one isolator, positioned between said electrodes, having at least one particularly circular through-opening assigned to the through-opening of said electrode, and that the pressure of the plasma gas is selected to be at least 0.01 bars, preferably between 0.1 and 5 bars. By confining said plasma, according to the present invention, with at least one isolator, which is positioned between parallel interspaced, in particular ring- or disk-shaped electrodes, the definition of the desired dimensions of the plasma, which can be selected according to the requirements, is successfully achieved. Furthermore it is possible to achieve through said isolator, in the particularly circular through-opening of which said plasma is produced and maintained, in a simple way and without the provision of additional confining elements, such as tubes in known embodiments, safe confinement of said plasma and simultaneously securing heat dissipation from the immediate vicinity of said plasma. By the particularly ring- or disk-shaped electrodes, which are positioned at both sides of said isolator and the through-openings of which are aligned with respect to each other, the supply of the energy necessary for the ignition and maintenance of said plasma is successfully achieved in a very small volume, so that overall a simple method for the production of such a low-power plasma, in particular noble gas plasma, can be provided at low power uptake and low gas consumption.
In accordance with a preferred embodiment it is proposed that said plasma is produced at atmospheric pressure, so that a further simplification in the implementation of the method for producing a low-energy plasma at low gas consumption can be achieved.
In accordance with a further preferred embodiment it is proposed to select the power of said plasma below 30 preferably below 10 W, so that with simple means a safe and sufficient heat dissipation can be achieved without the provision of costly cooling devices, wherein in the case of an array of plasma discharges said power can be achieved for each single discharge.
Within the scope of the method of the present invention it is furthermore proposed to preferably select the operating frequency higher than 5 kHz, preferably in the range of 50 kHz to 5 GHz, more preferably higher than 10 MHz, wherein the upper limit is essentially given by the requirement that the electromagnetic energy has to be produced by discrete components and transmitted along leads. Particularly preferable are for example the frequency ranges from 25 MHz to 45 MHz, as well as beyond 1000 MHz, in particular at approximately 2450 MHz, where simple and economic electronic components are available.
According to another preferred embodiment of the method of the present invention it is proposed, that the plasma gas is selected from helium or argon, wherein in particular helium is preferred as plasma gas due to its low atomic mass, as it causes almost no erosion at the electrodes. Moreover helium provides the best excitation conditio
Bettendorf Justin P.
Jacobson Price Holman & Stern PLLC
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