Generator for spectrometry

Abstract

The invention relates to a generator for spectrometry. An HF plasma generator for generating an inductively coupled plasma in spectrometry comprises: a voltage supply device having a DC voltage source; an oscillator circuit connected to the power supply device for generating HF power; and a load circuit coupled to the oscillator circuit for generating plasma, the load circuit having at least one induction coil and one capacitor connected in parallel to the induction coil. According to the invention, the HF plasma generator, in particular the voltage supply device, comprises at least one controllable voltage source arranged in a branch of the oscillator circuit, wherein the controllable voltage source is designed to set a voltage applied to the load circuit and / or at least one potential difference between the induction coil and a spectrometer, in particular a cone of the spectrometer. The invention also relates to a spectrometer having an HF plasma generator according to the invention.

Description

Technical Field

[0001] The invention relates to an HF plasma generator for generating an inductively coupled plasma in spectrometry and to a spectrometer having an HF plasma generator according to the invention.

[0002] Inductively coupled plasmas are widely used in the field of spectroscopy, for example to generate ions in mass spectrometry or to generate spectra in optical emission spectroscopy. Background Art

[0003] From the prior art, various HF plasma generators for generating inductively coupled plasmas, such as free-running or frequency-stabilized generators, as well as generators based on high-performance tubes and generators using semiconductors are known. In principle, a plasma generator generally comprises a voltage supply and an oscillator circuit, which is coupled to a load circuit for generating the plasma. For example, the oscillator circuit is a circuit according to Colpitts, Meienner or Huth-Kühn. However, the use of half-bridge circuits or full-bridge circuits is also known. Thus, an HF generator for spectroscopy based on the principle of a full-bridge circuit, in which semiconductor switching elements are used, has been disclosed in WO 2007 / 134363 A1.

[0004] A device for generating an inductively coupled plasma also includes one or more induction coils, which are arranged coaxially with a burner, into which a gas (usually argon) is introduced and heated. A strong alternating electromagnetic field is generated in the coil by a high frequency generator (HF generator), which provides the required energy for the plasma by inductive coupling. The typical temperature of the plasma is in the range of 3,000K (Kelvin)-10,000K. The frequency for generating the alternating magnetic field is in the range of MHz (megahertz) to GHz (gigahertz), and is often in the range of 10MHz-50MHz. In principle, the HF plasma generator must be able to provide enough power for generating and maintaining plasma. The power is usually in the range of 500W (watt)-3kW (kilowatt). In addition, high efficiency and high quality are desired.

[0005] Of particular importance is also the plasma shape, which depends in particular on the dominant potential in the vicinity of the plasma (e.g. the cone of a particular spectrometer), on the shape and mechanical design of the induction coil used and on various characteristics of the components used. In order to influence the shape of the plasma (in particular the plasma core) in a targeted manner, it is appropriate, for example, to move the dominant potential change to an analytically optimal value. In this regard, although different circuit concepts have been described (which actually establish conditions for an analytically optimal plasma shape), they are generally static and cannot be automatically adjusted to changing conditions. In order to achieve an optimal plasma shape, it is generally necessary to make complex adaptations to the components used and to the geometry of the plasma coil. Therefore, each plasma generator is unique and has a complex and expensive manufacturing process. In contrast, large-scale production of plasma generators that can generate analytically optimally shaped plasmas is very difficult to achieve. Summary of the invention

[0006] Against this background, it is an object of the present invention to provide a plasma generator with which an optimally shaped plasma can be generated in a simple manner.

[0007] This object is achieved by an HF plasma generator according to claim 1 and a spectrometer according to claim 8 .

[0008] With regard to an HF plasma generator, the object is achieved by an HF plasma generator for generating an inductively coupled plasma in spectrometry, the HF plasma generator comprising: a voltage supply in the form of a DC voltage source; an oscillator circuit connected to a power supply for generating HF power; and a load circuit coupled to the oscillator circuit for generating plasma, the load circuit having at least one induction coil and one capacitor connected in parallel to the induction coil. According to the invention, the HF plasma generator, in particular the voltage supply, comprises at least one controllable voltage source, which is arranged in a branch of the oscillator circuit, wherein the controllable voltage source is designed to set a voltage applied to the load circuit and / or at least one potential difference between the induction coil and a spectrometer, in particular a cone of the spectrometer, such as a sampler or skimmer.

[0009] Furthermore, in a possible embodiment, the plasma generator may comprise a computing unit for controlling the controllable voltage source.

[0010] Providing a controllable voltage source allows shaping of the plasma, in particular the plasma core, during continuous operation of the HF plasma generator. By purposefully varying the voltage applied to the load circuit and / or at least one potential difference between the induction coil and the cone of the spectrometer, the plasma, in particular the plasma core, can be purposefully compressed or stretched, or the distance to the cone of the spectrometer can also be varied. In this way, the plasma shape can be correspondingly continuously optimized and, for example, corrected with respect to analytical optimization. This enables controllable bundling of each generated ion beam.

[0011] An advantage of the invention is that it is possible to deform the plasma with the plasma generator according to the invention without intervening in the components of the generator. This electronic adjustment option allows to significantly reduce the costs and production time of a particular generator and to optimize the analytical performance of a particular device during ongoing operation.

[0012] In one embodiment, the oscillator circuit of the HF plasma generator comprises a bridge circuit, in particular a half-bridge circuit or a full-bridge circuit.

[0013] In this respect, it is advantageous if the bridge circuit is a full bridge circuit with four transistors arranged in four branches, wherein each transistor has a gate electrode via which a gate control voltage can be applied to each transistor, and wherein the transistors are switched in an alternating manner to generate HF power.

[0014] It is further advantageous if the HF plasma generator comprises a gate control circuit for generating a gate control voltage for switching the transistor.

[0015] Finally, it is advantageous with respect to the gate control circuit that it is designed to set a predeterminable value of the plasma oscillation frequency of the load oscillation circuit. The gate control circuit can preferably set the plasma oscillation frequency by using the timing of the gate control voltage, for example the gate control voltage can be a time period signal (in particular a square wave signal), by which the transistor can be switched on and off in an appropriate manner. This targeted control of the gate control voltage advantageously allows compensation of varying plasma loads and compensation of specific component characteristics. Thus, a reliable plasma that can be used for analysis can be provided in a simple manner by the HF plasma generator according to the invention. In this regard, reference is made to the previously unpublished German patent application with application number 102020106692.9, which is fully referenced in the context of the present application.

[0016] In a further embodiment, the HF plasma generator comprises at least two controllable voltage sources, which are arranged in two different branches of the oscillator circuit.

[0017] In a further embodiment, the HF plasma generator comprises at least four controllable voltage sources which are arranged in four different branches of the oscillator circuit. This embodiment is particularly advantageous in combination with an oscillator circuit designed in the form of a full-bridge circuit. In this case, targeted adjustment options of the potentials in all four quadrants are produced.

[0018] The use of a plurality of, in particular structurally identical, controllable voltage sources allows a specific adjustment of the voltage applied to the load circuit and / or of at least one potential difference between the induction coil and the cone of the spectrometer.

[0019] The object of the invention is also achieved by a spectrometer comprising an HF plasma generator according to the invention according to at least one of the described embodiments.

[0020] In this case, it is advantageous if the spectrometer is a mass spectrometer or a light emission spectrometer.

[0021] It should be noted that the embodiments described in connection with the HF plasma generator according to the invention are also applicable mutatis mutandis to the spectrometer according to the invention and vice versa. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Further details of the present invention are explained with reference to the following drawings. They are shown as follows:

[0023] Figure 1 is a schematic diagram of a HF plasma generator with a controllable voltage source,

[0024] Figure 2 is a schematic diagram of the operating mode of the controllable voltage source,

[0025] Figure 3 is a circuit diagram of a possible oscillator circuit in the form of a full-bridge circuit with four transistors and an additional inductive element, and

[0026] Figure 4 is based on Figure 3 and circuit diagram of a possible oscillator circuit with four controllable voltage sources.

[0027] In the drawings, the same elements are denoted by the same reference numerals. DETAILED DESCRIPTION

[0028] Figure 1 1 shows a schematic block diagram of an HF plasma generator 1 according to the invention. The generator 1 comprises a voltage supply 2 in the form of a DC voltage source, by means of which an oscillator circuit 3 is supplied with power. The required high frequency power is generated by the oscillator circuit 3. The oscillator circuit 3 is correspondingly coupled to a load circuit 4 for generating plasma, the load circuit 4 having an induction coil L P(not shown separately here) and capacitor C P , the capacitor C P Connect in parallel to the induction coil.

[0029] The HF plasma generator 1, in particular the voltage supply 2, further comprises a controllable voltage source 5, which is arranged in a branch of the oscillator circuit 3 and is designed to set a voltage applied to the load circuit 4 and / or at least one potential difference between an induction coil (not shown here) and a spectrometer (also not shown), in particular the cone of the spectrometer.

[0030] Figure 2 The operating mode of the controllable voltage source 5 is schematically depicted. The shape of the plasma P generated in each case (in particular the plasma core shown here) depends decisively on the plasma coil L. P The potentials U1, U2 between the cone 7 (such as a sampler) of the spectrometer 6 (with which the plasma generator 1 can be used) and also depend on the voltage U applied to the load circuit 4 L Thus, the plasma shape can be specifically influenced by a particular setting of one or more of these potentials. In particular, the plasma shape can even be dynamically adapted during ongoing operation.

[0031] Figure 3 An exemplary embodiment of an oscillator circuit 3 is depicted in FIG. The oscillator circuit 3 comprises a full bridge circuit consisting of four transistors T1 - T4 , wherein each transistor has a gate electrode E1 - E4 via which a gate control voltage U can be applied to the transistor. G The transistors T1-T4 are switched in an alternating manner so as to provide a current source having an induction coil L P and capacitor C P The load circuit 4 generates HF power. The inductive elements L1-L4 are optionally connected in series to each transistor T1-T4. The inductive elements L1-L4 then each form a series resonant circuit with the output capacitors C1-C4 of the transistors T1-T4.

[0032] Figure 4 By way of example, a preferred variant of the invention is shown in which four controllable voltage sources 5a-5d are used. This can be advantageous, for example, when using an oscillator circuit 3 designed as a full-bridge circuit. The design of the oscillator circuit 3 shown here is similar to that of Figure 3 Each of the four branches a, b, c, d comprises a transistor T1-T4 and a controllable voltage source 5a-5d for generating a voltage U s Ua s d. Optionally, it is also conceivable that Figure 4 In the case of use Figure 3 case of additional series inductors L1-L4.

[0033] Plasma coil L P The potentials U1 and U2 between the cone 7 and the voltage U applied to the load circuit 4 L The controllable voltage source 5a-5d or the voltage U s Ua s d. This in turn allows the plasma shape (particularly the plasma core) to be controlled by the coil L. P Influencing in a targeted manner, for example parallel to and / or perpendicular to the longitudinal axis l (see Figure 2 ) stretching or compression. All this can be done without changing the other components used and without changing the coil geometry. In addition, the distance from the plasma core to the cone 7 of the spectrometer 6 can be appropriately adjusted. In summary, therefore, by using the voltage sources 5a-5d, the bundling of the generated ion beam can also be controlled in a targeted manner.

[0034] In other embodiments, a different number of controllable voltage sources 5 may also be provided. Advantageously (but by no means absolutely necessary) the number of branches of the oscillator circuit 3 corresponds to the number of controllable voltage sources 5 used.

[0035] Reference Mark

[0036] 1 HF plasma generator

[0037] 2 Voltage supply device

[0038] 3 Oscillator circuit

[0039] 4 Load circuit

[0040] 5, 5a-5d Controllable voltage source

[0041] 6 Spectrometer

[0042] 7 Cone

[0043] T1-T4 transistors

[0044] E1-E4 Gate electrode

[0045] L P Induction coil

[0046] C P capacitance

[0047] L1-L4 Inductor components

[0048] C1-C4 Output capacitors

[0049] U s Uas d Voltage of the controllable voltage source

[0050] U1, U2 Potential between the induction coil and the cone

[0051] P plasma, plasma core

[0052] Vertical axis

Claims

1. A HF plasma generator (1) for generating an inductively coupled plasma (P) in spectrometry, comprising: A voltage supply device (2), the voltage supply device (2) having a DC voltage source, an oscillator circuit (3) connected to the voltage supply (2) for generating HF power, and A load circuit (4) coupled to the oscillator circuit (3) for generating the plasma (P), the load circuit (4) having at least one induction coil (L P ) and capacitor (C P ), the capacitor (C P ) is connected in parallel to the induction coil (L P ), It is characterized in that The voltage supply device (2) comprises at least four controllable voltage sources (5a-5d), the at least four controllable voltage sources (5a-5d) being arranged in four different branches (ad) of the oscillator circuit (3), and The four controllable voltage sources (5a-5d) are designed to set the voltage (U L ) and / or the induction coil (L P ) and at least one potential difference (U1, U2) between the spectrometer (6), Wherein, the oscillator circuit (3) comprises a bridge circuit, wherein the bridge circuit is a full-bridge circuit having four transistors (T1-T4) arranged in the four different branches (ad) of the oscillator circuit (3), Each of the transistors (T1-T4) has a gate electrode (E1-E4), through which a gate control voltage can be applied to each of the transistors (T1-T4), wherein the transistors (T1-T4) are switched in an alternating manner to generate the HF power, and Therein, the HF plasma generator (1) comprises a gate control circuit for generating the gate control voltage for switching the transistor.

2. HF plasma generator (1) according to claim 1, in, The controllable voltage sources (5a-5d) are designed to set the voltage (U L ) and / or the induction coil (L P ) and at least one potential difference (U1, U2) between the cone (7) of the spectrometer (6).

3. HF plasma generator (1) according to claim 1 or 2, in, The gate control circuit is designed to set a predeterminable value for the plasma oscillation frequency of the load oscillating circuit.

4. A spectrometer (6) comprising the HF plasma generator (1) according to any one of claims 1 to 3.

5. The spectrometer (6) according to claim 4, in, The spectrometer (6) is a mass spectrometer or an optical emission spectrometer.

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