JPH0821363B2 - Method for sampling plasma into a vacuum chamber and apparatus with rf bias therefor - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a method and a method for sampling an inductively generated plasma into an interior of a vacuum chamber through an opening drilled towards the vacuum chamber. It relates to the device. Further, the invention relates to methods and apparatus for mass spectrometry using such sampling.

The present invention relates to a modification of the method and apparatus described in our US Pat. No. 4,501,965 and may be used with the method and apparatus shown in US Pat. No. 4,501,965. In particular, the invention is described with respect to mass spectrometry.

PRIOR ART As described in the above-referenced U.S. Pat. No. 4,501,965, there is often the desire to make an analysis of a sample by introducing it into a high temperature plasma. The plasma creates predominantly charged ions of the elements in the material. The ions are introduced from the plasma into a vacuum chamber provided with a mass spectrometer to detect the presence of trace material in the sample.

Problems to be Solved by the Invention However, by extracting a plasma sample from the plasma body,
Introduction into the vacuum chamber through a small opening has not been easy. U.S. Pat. No. 4,501,965 provides a method and apparatus for improving plasma sampling into a vacuum chamber by reducing the voltage swings present in the plasma. With this method, the problem of arcing at the opening was greatly reduced. Such arcing can cause corrosion of the aperture, sputtering of the aperture material that causes a background spectrum of the aperture material that interferes with the desired spectrum, generation of high levels of doubly charged ions, and UV photon noise. It causes the occurrence.

SUMMARY OF THE INVENTION The present invention provides a non-conventional means of providing an appropriate radio frequency (RF) bias to an aperture plate.
A method and apparatus for eliminating the arcing problem.

The present invention relates to an electric induction coil in which a coil is wound at least once between a first terminal and a second terminal, and a plasma generation space defined by the one-turn coil is provided in the coil, and the plasma. Generating means for generating a first RF voltage to be supplied to the coil for heating the space to generate a plasma, and an opening plate which itself is a partition wall. A vacuum chamber having an opening plate having one opening on the opening plate adjacent to the plasma generation space, and through the opening,
Sampling a part of the generated plasma into the vacuum chamber, a second generator for generating a second RF voltage having the same frequency and phase synchronization as the first RF voltage,
And means for connecting the aperture plate with a second generator so as to bias the aperture plate by the second RF voltage to increase the flow of ions in the plasma through the aperture. And a device for sampling ions in a plasma into a vacuum chamber.

Furthermore, the present invention complements the configuration disclosed in the above-mentioned US Pat. No. 4,501,965.

In the above-mentioned U.S. patents, a means of significantly reducing voltage swings in the plasma has been provided, but the voltage swings still remain due to the heating current in the plasma and other poorly understood factors. At least the voltage fluctuation due to the heating current cannot be reduced. Thus, this residual voltage swing can still be a cause of some residual arcing, particularly arcing in the portion of the vacuum chamber adjacent the inlet of the second vacuum chamber section, as shown in the U.S. patent. Has become.

The present invention combines the means for supplying an RF bias to the aperture plate in the second vacuum chamber section of the vacuum chamber according to the present invention with the invention of the above-mentioned US Pat. No. 4,501,965 to obtain an ion signal to the second vacuum chamber section. It is intended to further improve the transmission.

Therefore, in the present invention, in addition to the above configuration, the first terminal and the second terminal
An electrical induction coil having at least one winding between the terminals of the coil and having a plasma generation space defined by the one-turn coil in the coil, and heating the space to generate the plasma Generating means for generating a first RF voltage supplied to the coil for use in plasma, a vacuum chamber having a first vacuum chamber section and a second vacuum chamber section, the vacuum chamber comprising: A sampler plate having a sampler opening to form one outer wall and a skimmer plate having a skimmer opening, the sampler plate and the skimmer plate being separated from each other. And a second wall that forms the first vacuum chamber portion therebetween and is separated from the skimmer plate, and the second vacuum is provided between the second wall and the skimmer plate. Chi The vacuum chamber forming the chamber part, the sampler opening on the sampler plate and the skimmer opening on the skimmer plate refer to a part of the plasma through the sampler opening and the first vacuum chamber part. To a second sample through the skimmer opening.
To be sampled into the vacuum chamber of the device, and connected to an RF generator that produces a first RF bias voltage, due to an increase in ion flow through the skimmer opening, at least An apparatus for plasma sampling into a vacuum chamber is also provided which includes means for applying the RF bias voltage to the skimmer plate.

Example Hereinafter, an example of the present invention will be described in detail with reference to the accompanying drawings.

Embodiment 1 FIG. 1 is a conceptual diagram showing an apparatus according to the first embodiment of the present invention.

In FIG. 1, a plasma cylinder 10 is an electric induction coil.
Covered by 12. A carrier gas such as argon, which is used for plasma formation, is supplied from a supply source 14 to the plasma tube 10 through a conduit 16. Further, another flow of the above carrier gas from the supply source 14 is discharged to the plasma tube 10 through the inner tube 18 in the plasma tube 10 from the flare end which has a fan-shaped cross section at the upstream portion of the induction coil 12. A sample gas containing the trace material to be analyzed is fed into the plasma tube 10 from a source 22 into a carrier gas, for example argon, coaxial with the inner tube 18 and through a conduit 24 provided therein. . In this way, the sample gas is released to the central region where the plasma is to be formed.

Usually, the coil 12 has a small number of turns, and is shown as four turns in the drawing. RF power is supplied to the coil 12 from an RF generator (radio frequency generator) 26 via an impedance matching network 28. The RF power supplied to coil 12 is adjusted in the approximate range of 200 watts to 10,000 watts depending on the nature of the desired plasma. The frequency of the RF power is as high as 27 megahertz (MHz). FIG. 1 shows the plasma 30 generated under the atmospheric pressure by the above-mentioned structure.

The plasma cylinder 10 is provided adjacent to the sampler plate 32 forming one side wall of the vacuum chamber 34,
This sampler plate 32 is water-cooled by means not shown. The generated plasma 30 passes through the opening 36 provided in the sampler plate 32, and is sampled into the first vacuum chamber 38 which is evacuated by the pump 42 through the duct 40. Usually, the sampling opening 36 is actually a "sampler".
It is said that the sampler plate 32 and the sampler plate 32 are processed as a separate member having good electrical conductivity. The remaining plasma gas other than the sampled gas is discharged from the gap 43 between the plasma cylinder 10 and the sampler plate 32.

The first vacuum chamber section 38 of the vacuum chamber 34 is separated from the second vacuum chamber section 44 by a skimmer plate 46 having a second opening 48. Usually, the skimmer opening 48 is also called a "skimmer", and is processed as a separate body having good electric conductivity from the skimmer plate 46. The second vacuum chamber section 44 is evacuated by a pump 50. Within this second vacuum chamber 44 is a mass spectrometer 52.
Is provided. The mass analyzer 52 is a type of quadrupole mass spectrometer having an analysis rod 54. Further, a conventional ion optical element 56 is provided between the analysis rod 54 and the skimmer opening 48. The ion optical element 56 is, for example,
Has a perforated quadrupole rod that is only supplied with non-DC RF power as shown in US Pat. No. 4,328,420 to JB French et al, or is supplied with such RF power. And analysis rod
It may have a standard vessel box lens between 54.

According to the present invention, one sample of the RF voltage is output as follows. The output from the RF generator 26 is phase adjusted in a phase adjustment network 60 via a lead 58 and an amplifier 62
The amplitude is adjusted by and is supplied to the sampler plate 32 via the lead 64. Insulating ring 66 for sampler plate 32 (for direct current)
It is electrically isolated from earth, but has a considerable capacitance to earth. No special device, such as that shown in U.S. Pat. No. 4,501,965, for reducing voltage fluctuations in plasma 24 is used in this embodiment.

In the device having the above configuration, the sampler 32
Arcing was observed between the plasma and the openings 36 in the sampler plate 32, whether RF bias was applied and whether the sampler plate 32 was grounded or insulated. The extinction of the arc was observed when a properly phased RF bias was applied to the sampler plate 32 via the lead 64. If the phase of the RF bias was reversed 180 °, the arc did not decrease, but rather increased. The reason for this is that the sampler plate 32, which has a large capacitance with the ground regardless of whether it is insulated or not, is always at or near the RF potential, so that the voltage difference with the plasma 30 is usually It causes the above arc. If the RF voltage applied to the sampler plate 32 is plasma
If it is in the same phase as the peak-to-peak voltage fluctuation of 30, the sampler plate
The voltage difference between 32 and the end of the plasma 30 closest to the sampler plate 32 is reduced and the arc is extinguished. Even if the phases are reversed, the potential difference does not decrease but actually increases. As a result, the arc does not disappear.

Furthermore, the plasma 30 generates an arc not only with the opening 36 of the sampler plate 32 but also with the opening 48 of the skimmer plate 46. Such an arc occurs when skimmer plate 46 and plasma 30 are in substantial electrical contact. In particular, it easily occurs when the sampler opening 36 has a large diameter. In addition, if the sampler plate 32 is RF-biased and the skimmer plate 46 is grounded, the RF bias itself causes a low voltage in the first vacuum chamber section 38 due to the RF voltage difference between the sampler plate 32 and the skimmer plate 46. The atmospheric pressure region causes the discharge. Such an electric discharge is generated by the plasma 30 and the sampler plate.
It has the same harmful effect as the discharge due to the voltage between 32 or the skimmer plate 46.

The arc between the opening 48 of the skimmer plate 46 and the plasma 30 or its adjacent element is controlled by the insulating ring 68.
Can be reduced or eliminated by isolating it from ground or by biasing the skimmer plate 46 with RF power. Such bias application is
As shown in FIG. 1, the other output from the RF generator 26 is extracted through a lead 69, passed through a phase adjustment network 70, an amplifier 72, and supplied to a skimmer plate 46 through a vacuum feedthrough 74 and a lead 75. Be seen.

FIG. 2 shows a device according to a second embodiment of the present invention, which is the same as the device shown in FIG.
In particular, components having a prime mechanism "'" added to the reference numbers are the same as those in FIG. The difference between FIG. 2 and FIG. 1 is that the sampler plate 32 'is not RF biased and one end of the coil 12' is not grounded. Instead, between the ends of the coil 12 ', similar to the configuration shown in U.S. Pat.No. 4,501,965 by the present inventors,
It is grounded at point 76 near the center of the coil. This extinguishes the arc between the plasma 30 'and the opening 36' of the sampler plate 32 ', and hence the RF to the sampler plate 32'.
It eliminates the need for bias supply. However, skimmer plate 46 'is still RF biased through phase adjustment network 70' and amplifier 72 '.

By using the apparatus of FIG. 2, significant improvements in both ion transfer and background noise levels are obtained when the RF bias applied to skimmer plate 46 'is of the correct phase and amplitude.

As a first experiment, the phase and amplitude of the RF bias supplied to the skimmer plate 46 'in the configuration shown in FIG. 2 was measured for the best signal using 1 microgram vanadium solution per milliliter. It was adjusted. With this special equipment and operating conditions, when the RF bias was adjusted to the optimum phase and amplitude, the ion signal was 89,000 counts per second and the background noise was 66 counts per second. Also, remove the RF bias, skimmer plate
Simply grounding the 46 'through the feedthrough 74', the ion signal dropped to 17,500 counts per second and the background noise increased to 427 counts per second. It was found that the signal to background noise ratio in the above two cases decreased by a factor of 35 when the optimal RF bias was deleted. However, it was subsequently discovered that the loss of signal-to-noise ratio due to switching the skimmer plate 46 'from RF bias to ground voltage caused the skimmer plate 46' to pass through the lead 75 'having a length of about 4 inches. Grounding directly in the vacuum system with the above configuration rather than grounding, for example, skimmer plate 4
The 6'can be reduced by bolting directly to the vacuum system. For example, the inductance of a 4-inch wire was abnormal, and it seemed to be enough to give an unnecessary voltage to the skimmer plate. Nevertheless, if the skimmer plate 46 'is optimally grounded, the correct RF bias may be applied to the skimmer plate 46' to reduce the S / S
The N ratio could be improved at a rate of about twice.

In the second experiment, changes in the ion signal due to changes in the phase and amplitude of the RF bias applied to the skimmer plate 46 'were carefully measured for different number phases and two aperture sizes,
Plotted on the graph. FIG. 3 is a graph obtained as a result. In the graph of FIG. 3, the skimmer plate 46 '
The voltage supplied to the, that is, the RF peak-to-peak voltage is scaled on the horizontal axis, and the ion signal transmitted to the vacuum chamber, that is, the number of ions per second detected by the mass spectrometer 52 'is scaled on the vertical axis. Has been.

In the graph of FIG. 3, a curve 80 with a phase angle of 0 ° and a phase angle 90
Four curves are shown, a curve 82 with a phase angle, a curve 84 with a phase angle of 180 degrees and a curve 86 with a phase angle of 270 degrees.

The phase angles shown in FIG. 3 are arbitrary and are the phase shift setpoints shown on the phase shift box used as the phase shift network 70 '.
The phase angle is not indicative of the phase difference between the RF voltage supplied to coil 12 'and the RF voltage supplied to skimmer plate 46' for the following reasons.

Thus, as a first reason, the RF generator 26 'used has several stages of power amplification, and the lead 69' has an RF generator.
It is connected before the final stage of power amplification of 26 '. It is expected that one phase shift will occur in such final stage. Secondly, the RF generator 26 'to the coil 12'
Since the lead length is about 3 meters, there is a shift in phase of about 1/3 wavelength or 120 ° between the RF voltage produced by the RF generator 26 'and the RF voltage supplied to the plasma 30. Thirdly, the amplifier 72 'and the amplifier 72'
A phase shift also occurs in the lead cable to the skimmer plate 46 '. In addition, the feedthrough 74 'has a resistor-capacitance network (not shown) to reduce the voltage from the amplifier to an optimum level, which introduces additional phase shift. There is also a phase shift due to the lead 69 'from the network 70' to the amplifier 72 'and from the amplifier 72' to the feedthrough 74 '. Therefore, it is not easy to directly measure the phase shift between the RF voltage in the plasma and the RF bias in the skimmer plate 46 '. Thus, the phases plotted in FIG. 3 only display the fact that some number phases produce much better results than others.

From Fig. 3, the optimum ion transfer phase setting is 270 ℃, RF
It turns out that it occurs at a peak-to-peak voltage of about 1.5 volts. The device used can reduce the bias voltage to 1 volt peak-to-peak. However, if a voltage lower than 1 volt is used, the above-mentioned first
Curve 86 will fall sharply at RF peak voltages of about 1 volt or less, as evidenced by the loss of signal in the previous experiment.

The graph in Figure 3 shows a sampler opening 3 with a diameter of 0.027 inches.
It was obtained using 6 '. This is a relatively small aperture diameter, and will
The diameter dimension of 36 'has a significant effect on the effect produced by the RF bias voltage applied to skimmer plate 46'.

Curve 88 in FIG. 4 was obtained using the same data used to create the graph in FIG. In FIG. 4, the vertical axis indicates the ion count number (ion transmission), and the horizontal axis indicates the phase angle. In addition, a sampler opening with the same diameter as in FIG. 3 is used. However, a constant RF bias voltage of 2.32 volts peak-to-peak is supplied to skimmer plate 46 '. It is clear from the graph of FIG. 4 that optimum ion transfer occurs at a phase angle of about 290 °, and the maximum and minimum ion transfer ratios are about 2.5 at the above working voltage.

The graph in Fig. 5 is similar to the graph shown in Fig. 3, but the curve 90 and the phase angle are 27 when the phase angle is set to 0 °.
Only two of the curves 92 when setting 0 ° are graphed. The 90 ° and 180 ° phase angle shifts did not result in substantial ion transfer. The graph in Figure 5 is
The result is the use of a larger opening 36 'with a diameter of 0.034 inches. As is evident from this graph, maximum ion transfer occurs at the higher skimmer bias voltage of RF peak-to-peak voltage of about 5.4 volts. The ion transfer ratio between the phase angle 0 ° and 270 ° at this voltage is about 1.5.

The phase angle setting in FIG. 5 cannot be simply compared with the phase angle setting in FIG. This is because to obtain the graph of FIG. 5, a slightly different voltage drop network (not shown) is used adjacent the feedthrough 74, which makes a difference in the phase shift.

FIG. 6 is a graph similar to that of FIG. 4, but similar to the data for creating the graph of FIG.
6 is a graph made using a 0.034 inch sampler opening and an RF bias voltage of 5.4 volts peak-to-peak.
As is clear from the graph, maximum ion transfer occurs when the phase angle is 0 ° or 360 °. Phase angle 90 ° to 2
Up to 70 °, there is virtually no ion transfer.

Although the above mechanism is complicated and may not be fully understood, as is clear from the above experiment, if the skimmer plate 46 'is supplied with the RF bias of the correct phase and amplitude, the ion transfer is not possible. Optimally done. In addition, the change in ion transfer by changing the phase and amplitude of the RF bias can result in sampler openings 36 'with larger aperture diameters.
In the case of a sampler aperture with a larger aperture diameter and a larger aperture diameter, a higher RF bias voltage is required.

Larger diameter sampler opening 3 for the following reasons:
With 6 ', the supply bias signal to skimmer plate 46' has a greater effect. As mentioned above, the heating current in the plasma 30 cannot be reduced. Therefore, coil 1
When the 2'is center tapped, there is always an RF voltage swing in the plasma, typically up to about 10 volts. If the sampler opening 36 'has a small diameter,
The insulation of the skimmer plate 46 'against the plasma 30' is better. Under such circumstances, the sampler plate 32 '
There is a tendency to form a kind of cooling boundary layer on top of this cooling boundary layer, together with the small opening 36 ', the RF in the plasma.
Isolates the skimmer plate 46 'from voltage. If the opening
If the aperture diameter of 36 'is large, the above effect of this cooling boundary layer is smaller, and in addition, the skimmer plate 46' has a plasma 30 '.
It makes a better electrical connection with and therefore cannot draw out the action of the cooling boundary layer.

If the skimmer plate 46 'is simply grounded, RF
Approximately one-half of the cycle, it is expected that the plasma 30 'will have a negative potential with respect to the skimmer plate 46', thus preventing the formation of positive ions from the plasma 30 'through the skimmer opening 48'. It If supplied to the skimmer plate 46 '
If the RF bias is always negative with respect to the plasma, ion extraction is easily done over the entire RF cycle rather than half of the above RF cycle. This is when it is grounded
It explains the reason for the doubling in and out of being RF biased.

In addition, the ion optics system 56 'has a skimmer plate
If the 46 'has a constant potential difference with respect to the plasma 30', it seems that the ion beam can be more easily received. Ion optical transfer depends on the ion energy, which depends in part on the voltage of the skimmer plate 46 'and in part on the voltage in the plasma. If skimmer plate 46 'and plasma 3
If the potential difference between 0 'and 0'is kept constant, the ion optics system 56' will consistently maintain a considerable number of incoming ions throughout, as opposed to a steady change in the voltage. Can communicate. Furthermore, if the skimmer plate 46 'has a negative or positive voltage of several volts with respect to the plasma, the actual ion optic lens system will easily accept the ion beam. Thus, a suitable RF bias is desired for proper ion transfer through the ion optic lens system 56.

Furthermore, the background noise level changes with RF bias (but is relatively low in all cases). The reason for this effect is not clear, but there are two possibilities. The first possibility is that the voltage fluctuations remaining in the plasma are considered sufficient to cause a very weak discharge in the first vacuum chamber 38 'of the vacuum chamber. This first vacuum chamber is at most about 10 times larger than the second vacuum chamber.
It is about 1 torr compared to ^-5 torr. Correctly biasing the skimmer plate reduces or eliminates this discharge while reducing noise.

Alternatively, the skimmer plate and the first part close to the root of the skimmer plate
There is a risk of destruction with the ion optical element. This is because the first ion optical element has a relatively high voltage, and because of the gas jet from the skimmer opening 48 ', the first ion optical element is located in a fairly high density region. . The discharge from the first ion optics to the skimmer plate is initiated by the first free electrons from the plasma 30 '. If the skimmer plate is biased to create an ion beam of plasma over the entire cycle,
Free electrons from the plasma are blocked and the destruction of the first lens element is reduced.

Improvements in the ion transfer signal, as well as noise reduction, a factor of two in this experiment, can be achieved at the lowest price of just a few inexpensive electronic components.

The fact that lower voltages are more appropriate for smaller sampler apertures than larger sampler apertures means that the improved ion transfer effect is correctly associated with the potential difference between plasma and skimmer and is not just an ion optic effect. Is confirmed.

The bias voltage or voltage is shown as being drawn from the generator 26 or 26 'and is therefore phase-locked with the RF voltage supplied to the coil 12 or 12',
Other bias voltage generators that are phase locked with the generator 26 or 26 'may be used in the present invention.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a mass spectrometer of the first embodiment according to the present invention, FIG. 2 is a schematic diagram of a mass spectrometer of the second embodiment of the present invention, and FIG. , Supply to skimmer plate with specific opening diameter
FIG. 4 is a graph plotting the number of ions transferred into the second vacuum chamber at several phase angles of the RF bias voltage with respect to the RF peak-to-peak voltage. FIG. 4 was used to create the graph in FIG. FIG. 5 is a graph plotting the ion transfer number into the second vacuum chamber with respect to the phase angle of the RF bias voltage at the same opening diameter, and FIG. 5 is similar to the third graph when only the opening diameter is different. Figure 6 is a graph similar to Figure 4, but for the openings used to create the graph of Figure 5; (Main reference numbers) 10 …… Plasma cylinder, 12 …… Coil, 14 …… Carrier gas supply source, 22 …… Sample gas supply source, 26 …… RF generator, 30 …… Plasma, 32 …… Sampler plate , 36 …… Opening part, 46 …… Skimmer plate, 48 …… Opening part, 38 …… First vacuum chamber part, 44 …… Second vacuum chamber part

Claims (19)

[Claims] 1. An apparatus for sampling ions in a plasma into a vacuum chamber, the apparatus comprising: an electrical induction coil including at least one wound coil defining a plasma generation space; and the plasma. A plasma generating means including first generating means for generating a first RF voltage applied to the coil to heat the generating space to generate plasma; and an opening plate which itself constitutes one of the partition walls. A vacuum chamber, and the opening plate has an opening adjacent to the plasma generation space, and one of the plasma generated in the plasma generation space is provided.
A second RF voltage having a frequency that is the same as the first RF voltage and is phase-synchronized with the first RF voltage, the apparatus being configured to extract a portion through the opening into the vacuum chamber. A second generating means for generating the second RF voltage, and a coupling means for coupling the opening plate and the second generating means for biasing the opening plate by the second RF voltage to increase the flow rate of ions flowing through the opening. An apparatus for sampling ions in a plasma into a vacuum chamber, which is characterized by comprising. 2. The apparatus according to claim 1, wherein the first generating means includes the second generating means. 3. An apparatus according to claim 2 including means for adjusting the phase of the second RF voltage. 4. A device according to any one of claims 1 to 3, characterized in that it comprises means for adjusting the amplitude of the second RF voltage. 5. An apparatus for sampling ions in a plasma into a vacuum chamber, the apparatus comprising: an electrical induction coil including a coil wound at least once to define a plasma generation space; and the plasma. Plasma generating means including first generating means for generating a first RF voltage applied to the coil to heat the generating space to generate plasma; and a vacuum having a first vacuum chamber section and a second vacuum chamber section. And a chamber, the vacuum chamber being one outer wall of the vacuum chamber itself and having a sampler opening, and a skimmer plate provided inside the vacuum chamber and having a skimmer opening. And the first vacuum chamber section is defined between the sampler plate and the skimmer plate that are spaced apart from each other, and the first vacuum chamber part is installed separately from the skimmer plate. The second vacuum chamber section is formed between the other outer wall of the vacuum chamber and the skimmer plate, and the plasma generated in the plasma generating space is passed through the sampler opening section of the sampler plate. It is arranged so as to extract to the first vacuum chamber section and further to the second vacuum chamber section through the skimmer opening of the skimmer plate, and further by connecting to the first generating means. An apparatus for sampling ions in a plasma into a vacuum chamber, comprising means for applying the first RF voltage to the skimmer plate to increase the flow rate of ions passing through the skimmer opening. 6. A means for increasing the flow rate of ions passing through the sampler opening by applying a second RF voltage to the sampler plate by connecting to the first generating means. An apparatus according to claim 5 in the range. 7. A device according to claim 6 including means for adjusting the phase of the second RF voltage. 8. The apparatus of claim 7 including means for adjusting the amplitude of the second RF voltage. 9. The apparatus of claim 6 including means for independently adjusting the phase of each of the first RF voltage and the second RF voltage. 10. The apparatus of claim 7 including means for independently adjusting the amplitude of each of the first RF voltage and the second RF voltage. 11. The apparatus according to claim 5, further comprising a circuit connected to the coil to reduce peak-to-peak voltage fluctuations in the plasma. 12. The apparatus of claim 11 including means for adjusting the phase of the first RF voltage. 13. A device according to claim 12 including means for adjusting the amplitude of the first RF voltage. 14. The vacuum chamber comprises a mass spectrometer, claims 5, 9, and 10.
Item 10. The device according to any one of item 10. 15. Apparatus according to any one of claims 11 to 13, characterized in that the vacuum chamber comprises a mass spectrometer. 16. The vacuum chamber of claim 5, further comprising a mass spectrometer including a quadrupole spectrometer in the second vacuum chamber section. The apparatus according to claim 1. 17. A high-frequency current is applied to a coil to generate plasma in the coil, and a point between both ends of the coil is connected to a constant potential to limit voltage fluctuations in the coil. The peak-to-peak voltage change in the plasma is reduced, a part of the plasma is introduced into the first vacuum chamber section of the vacuum chamber through the sampler opening, and further the second vacuum chamber section of the vacuum chamber is introduced through the skimmer opening. And applying an RF bias voltage of the same frequency as the current to the skimmer opening to increase ion transfer through the opening. How to sample. 18. The method of claim 17, wherein the ion transfer is optimized by adjusting the phase and amplitude of the RF bias voltage. 19. The method of claim 18 including analyzing ions that have entered a second vacuum chamber section of the vacuum chamber.