RU124434U1 - MASS SPECTROMETER - Google Patents

Abstract

A mass spectrometer containing an ionization chamber arranged sequentially in a grounded vacuum chamber in the direction of propagation of the investigated plasma stream from its inlet, which is made with inlet and outlet axial openings, has a current lead and is equipped with a heated cathode, the terminals of which are connected to the glow unit, the focusing electrode with with a current lead, grounded extractor and output diaphragm, a collector to which a recording device is connected, in addition, a magnetic analyzer covering a vacuum chamber drain between the extractor and the output diaphragm, and a synchronized pulse generator, characterized in that it is equipped with a drift tube, which is made with end diaphragms and has a current lead, a grounded diaphragm, complex voltage pulse generators for controlling the drift tube, the ionization chamber and the heated cathode, a bias unit, which is connected to one of the terminals of the heated cathode, and the drift tube is placed in the vacuum chamber at its inlet, and the grounded diaphragm between at the drift tube and the ionization chamber, while the current leads of the drift tube and the ionization chamber and the glow cathode terminal connected to the bias unit are connected to the outputs of the corresponding voltage pulse generators of complex shape, in addition, a synchronized pulse generator that has independent channels in the number of voltage pulse generators of complex shape and is configured to generate voltage pulses at the output of an independent channel that is connected to the input of the voltage pulse generator

Description

The proposed device relates to the field of measurement technology and, in particular, to mass spectrum analyzers.

Known mass spectrometers, as a rule, consist of an ion source located in a vacuum chamber, forming an ion beam of optics, diaphragms, a magnetic analyzer and an ion detector. And often, such a device alone cannot be used to measure the mass spectra of both ions and neutrals.

Known mass spectrometer (JP 61233959 A, IPC: G01N 27/62; G01N 30/72; H01J 49/02; 49/10; 49/30, published 10/18/1986) - [1], which contains placed sequentially an ion source with a channel for entry from outside the test gas sample, focusing and accelerating electrodes, a magnetic analyzer, an output diaphragm, a collector and a synchronized pulse source for controlling the ion source and magnetic analyzer. The ion source is equipped with a heated electron emitter. The voltage in the ion source (accelerator) changes synchronously with the induction of the magnetic field, which ensures high sensitivity even to the small mass component of the ionized particles of the test gas sample. The mass spectrum is accurate even with a sharp change in sample flow rate or pressure.

The disadvantage of this mass spectrometer is the impossibility of studying the mass spectra of ions entering its input, since it does not provide for the possibility of turning off the heated emitter (cathode).

The closest in technical essence to the proposed technical solution and selected as a prototype is a magnetic mass spectrometer (US 3764803 A, IPC: H01J 49/34, published 09.10.1973) - [2], which contains sequentially placed in a vacuum chamber an ionization chamber with a heated electron emitter, a system of accelerating and focusing electrodes, an electrostatic analyzer in the form of a flat capacitor (deflecting electrode), an output diaphragm, a collector that is connected to the indicator, and a magnetic analyzer Covering the vacuum chamber region between the electrostatic analyzer (deflection electrode), and an output diaphragm, and the respective power sources.

In the prototype device, the test gas sample is fed into the ionization chamber, where it is ionized by accelerated electrons. Further, the obtained ions from the ionization chamber enter a magnetic analyzer, where ions with different mass-to-charge ratios are spatially separated, then they reach the collector and are recorded. A voltage is applied to the flat capacitor, the pulse of which is rectangular. When a positive pulse is applied to a flat capacitor (deflecting electrode), it deflects the ions into the monitoring detector, which allows you to track the current at the input to the magnetic analyzer, as well as obtain information about the concentration of particles with certain mass numbers, knowing the initial current and the current passed through collector.

The disadvantage of the prototype device is the impossibility of studying the mass spectra of both neutral and ionized particles entering the mass spectrometer from a plasma or ion beam formed outside the vacuum chamber, since it does not provide the possibility of turning off the incandescent cathode similarly to the analog device. In addition, the ion-optical system used in the prototype device does not provide energy analysis of the incoming ion beam or ionized component of the plasma stream.

The basis of the proposed technical solution is the task of creating the design of a mass spectrometer, which allows the study of particles of ionized and neutral components that make up the plasma flows and ion beams formed outside the vacuum chamber of the mass spectrometer with minimal errors.

The technical effect of the implementation of the task is the possibility of implementing a non-inertia method for studying the mass spectrum of the plasma and ion flows of ionized and neutral particles by one device due to the expansion of its functional capabilities, which will allow constant monitoring of technological processes, for example, spraying, with high accuracy.

The solution of the problem and the corresponding technical result are achieved by the fact that the mass spectrometer containing sequentially placed in the grounded vacuum chamber in the direction of propagation of the investigated plasma flow from its inlet to the ionization chamber, which is made with input and output axial holes, has a current lead and is equipped with a heated cathode , the findings of which are connected to a glow unit, a focusing electrode with a current lead, a grounded extractor and an output diaphragm, a collector to which a recording device is connected, in addition, a magnetic analyzer, which covers the portion of the vacuum chamber between the extractor and the output diaphragm, and a synchronized pulse generator, is equipped with a drift tube that is made with end diaphragms and has a current lead, a grounded diaphragm, complex voltage pulse generators for controlling the tube the drift, the ionization chamber and the heated cathode, a bias unit that is connected to one of the terminals of the heated cathode, and the drift tube size it is located in the vacuum chamber at its inlet, and there is a grounded diaphragm between the drift tube and the ionization chamber, while the current leads of the drift tube and the ionization chamber and the output of the heated cathode connected to the output of the bias unit are connected to the outputs of the corresponding voltage pulse generators of complex shape, in addition, the generator synchronized pulses, which has independent channels in the number of voltage pulse generators of complex shape, is configured to generate voltage pulses at the output n independent channel, which is connected to the input of a voltage pulse generator of complex shape to control a heated cathode, with a time delay relative to voltage pulses at the output of its independent channel, which is connected to the input of a voltage pulse generator of complex shape to control a drift tube, not more than the sum of the time of flight of the ionic component plasma flow through the drift tube and the deionization time of the residual (space) charge of ions in the ionization chamber, and at the output of an independent channel that is connected to the input of a voltage pulse generator of complex shape to control the ionization chamber, with a time delay relative to voltage pulses at the output of its independent channel, which is connected to the input of a voltage pulse generator of complex shape to control a heated cathode equal to the ionization time of the neutral component of the plasma stream by electrons.

The introduction of a drift tube into the device is necessary to ensure:

- the possibility of braking the particles of the ionic component of the plasma stream and obtaining a time scan of the ions according to the mass (composition) of the spectrum;

- the possibility of locking ions in order to study the neutral component of the plasma flow;

- the possibility of accelerating ions of the plasma flow.

In addition, the drift tube in combination with a grounded diaphragm helps to reduce the loss of ions received in the ionization chamber from the neutral component of the plasma stream.

The introduction of complex voltage pulse generators into the device for controlling the drift tube, ionization chamber, and a heated cathode in combination with a heated cathode bias unit and the execution of a synchronized pulse generator with multichannel pulses and with the possibility of generating pulses for triggering complex voltage pulse generators with an appropriate time delay makes it possible to separate by the time of the processes of studying the ionic and neutral components of the plasma flow.

The listed set of distinctive features allows you to explore the parameters of the ionic and neutral components of the plasma flow using one device, which greatly simplifies, accelerates and cheapens the research process.

The presence of a set of features that distinguish the proposed technical solution from the prototype device and from other known sources of information, allows us to conclude that its criterion of "novelty".

Figure 1 schematically shows in cross section the proposed mass spectrometer.

Figure 2 shows the plot of the pulse voltage from the outputs of the independent channels of the synchronized pulse generator to start the pulse voltage generators of complex shape.

Figure 3 shows the diagrams of voltage pulses for controlling a drift tube, a heated cathode and an ionization chamber obtained from the corresponding generators of voltage pulses of complex shape and explaining the operation of the mass spectrometer.

The mass spectrometer shown in Fig. 1 has a vacuum chamber 1, which is grounded and made with an axial inlet 2. In the vacuum chamber 1 along the Z axis in the direction of propagation from the inlet 2 of the test stream are placed: an ionization chamber 3, which is made with the inlet and output axial holes and has a current lead; a heated cathode 4 placed in the ionization chamber 3; a glow unit 5 connected to the terminals of the heated cathode 4; a focusing electrode 6 with a current lead to which a positive potential is supplied, for example, from an autonomous power source (not shown); extractor 7, which is grounded; output diaphragm 8, which is grounded; collector 9; a recording device 10 connected to the collector 9.

Moreover, the proposed mass spectrometer is equipped with: a magnetic analyzer 11, which covers the portion of the vacuum chamber 1 between the extractor 7 and the output diaphragm 8; synchronized pulse generator 12.

In addition, the proposed device contains: a drift tube 13, which is made with end diaphragms, has a current lead and is placed in the vacuum chamber 1 along the Z axis coaxially with its inlet 2, as well as with the inlet and outlet openings of the ionization chamber 3, while one of the end is located at the inlet 2 of the vacuum chamber 1; a diaphragm 14. which is grounded and placed in a vacuum chamber 1 between the ionization chamber 3 and the other end of the drift tube 13; complex voltage generators 15, 16 and 17, the outputs of which are connected respectively to the current leads of the drift tube 13 and the ionization chamber 3 and one of the terminals of the heated cathode 4 in order to control them; a bias unit 18, the output of which is connected to the output of a heated cathode 4 connected to the output of a voltage pulse generator of complex shape 17.

In this case, in order to ensure synchronization of the start of voltage pulse generators of complex shapes 15, 17 and 16, the synchronized pulse generator 12 has independent channels 19, 20 and 21, configured to generate voltage pulses at the output of each of them, by the number of complex voltage pulse generators with a corresponding time offset relative to each other and connected to the inputs of the voltage pulse generators of complex shapes 15, 17 and 16, respectively. Moreover, the voltage pulse generator of complex shape 17, which controls the heated cathode 4, is triggered by channel 20 with a time delay relative to the channel 19 of the voltage pulse generator of complex shape 15 to start the drift tube 13 for no more than the sum of the time the ionic component of the plasma flow passes through the drift tube 13 and the deionization time the residual charge of ions in the ionization chamber 3. In this case, the voltage pulse generator of complex shape 16 is launched by an independent channel 21 to control the ionization chamber 3 from time to time second delay relative to the trigger generator 20 channel complex shape of the voltage pulses 17 with a delay time equal to the ionization electrons neutral plasma stream components.

To explain the operation of the proposed mass spectrometer in figure 2 shows plots having the same repetition period T pulses at the outputs of channels 19 (figa), 20 (fig.2b), 21 (fig.2c) of the synchronized pulse generator 12, while the fronts pulses at the outputs 20 and 21, which start the voltage pulse generators of complex shapes 17 and 16, respectively, have a time delay t _s1 and t _s2 relative to the front of the pulse at the output of channel 19 of the synchronized pulse generator 12, the pulse duration t _and significantly less than the period following them pulses T (t _and << T).

For the operation of the mass spectrometer, the heated cathode 4 is heated (turned on) from the filament block 5 to the emission temperature, which is kept constant for the time necessary to measure the mass spectra of both the ionized and neutral components of the plasma stream. Simultaneously with the inclusion of a heated cathode 4, a constant positive electron blocking voltage is supplied to its filament from the bias unit 18.

Then, control signals with the algorithm for measuring the time delay of the voltage pulse front on the heated cathode 4 relative to the front of the voltage pulse on the drift tube 13 are supplied from the outputs of the voltage pulse generators of complex form 15, 16, and 17 to the drift tube 13, the ionization chamber 3, and the heated cathode 4; equal to t _s1 (Fig.3b) and the time delay of the front of the voltage pulse on the ionization chamber 3 relative to the front of the voltage pulse on the heated cathode 4 is equal to t _s2 -t _s1 = t ₁ (Fig.3c).

Figure 3 shows the three time dependence of the pulse voltage at the outputs of the pulse voltage generators of complex shape 15, 17 and 16, reflecting the operating modes of the main structural elements of the device:

a) a change in the pulse voltage at the drift tube 13;

b) a change in the pulse voltage at the heated cathode 4;

c) a change in the pulse voltage on the ionization chamber 3.

The triggering of voltage pulse generators of complex shape 15, 17 and 16 by the synchronized pulse generator 12 can be either single or frequency-pulse, with a given pulse repetition period T. The initial pulse is fed by a voltage pulse generator of complex shape 15 to the drift tube 13.

We consider 7 points of change in the modes of operation of the mass spectrometer.

From point 0 to point 1 over time t _f (front duration), the voltage at the drift tube 13 (Fig. 3a) increases linearly from zero potential to a maximum value of U _a sufficient to completely block the ion component of the plasma stream. The duration of the front t _{f of the} pulse with a maximum value of U _a is selected no more than the time of flight of the ion component of the plasma stream through the drift tube 13 of length 1:

,

,

where: M _l is the mass of the lightest ions of the plasma stream;

W _i is the ion energy at the input of the mass spectrometer;

q is the ion charge.

At the same time, a constant voltage equal to U _b1 is applied to the heated cathode 4 (Fig.3b) from the bias unit 18, which is necessary for locking electrons from the filament of the heated cathode 4, and the zero potential is maintained on the ionization chamber 3 (Fig.3c) (U.к. = 0).

From point 1 to point 2, during the Δt time (Fig. 3a), when the ions of the ionic component are locked, complete deionization (resorption) of the volume (residual) charge of ions occurs in the ionization chamber 3, at which the zero potential is maintained. The period of deionization of the residual charge is necessary to eliminate the charge formed in the ionization chamber 3 after the moment of complete braking of the ions, to eliminate the measurement error. To estimate the time Δt, the following relation is used:

,

,

where: L _i is the size of the ionization chamber 3;

M _h is the mass of the heaviest ion in the stream.

Then at point 2 with a time delay equal to t _s1 (Fig.2b) of the pulse front from the output of channel 20 relative to the front of the pulse from the output of channel 19 of the synchronized pulse generator 12, a negative potential equal to U _b1 + | U _b2 | (fig.3b), which is maintained for a time t _ion and accelerates electrons in the direction of the ionization chamber 3, while the potential U _a remains constant on the drift tube 13 (Fig. 3a) and the zero potential on the ionization chamber 3 (Fig. 3c) .

From point 2 to point 3, in a time equal to t ₁ , the particles of the neutral component (neutrals) of the plasma flow in the ionization chamber 3 are ionized by electrons from the glowing cathode 3. At point 3, with t _z2 = t _f + Δt + t _{1, there is a} time delay relative to the front the pulse at the output of channel 19 by the pulse from the output of channel 21 (Fig. 2c), the voltage at the ionization chamber 3 is turned on to draw out from its output hole a beam of ions obtained from neutrals through the extractor 7 in the direction of the magnetic analyzer 11, which separates from the masses. Next, a beam of ions with a certain mass is cut out by the output diaphragm 8, which enters the collector 9 and generates a current in its circuit, which is recorded by the device 10. In addition, the grounded diaphragm 14 located between the drift tube 13 and the ionization chamber 3 provides a reduction in the losses of ions received in the ionization chamber 3, so that ions propagating from the ionization chamber 3 in the direction of the drift tube 13 are deployed, pass through the ionization chamber 3 and fall into the magnetic field of the analyzer 11.

In this case, the positive potential U _a on the drift tube 13 for locking the ion component and the negative potential U _b2 on the heated cathode 4 with the aim of the entry of electrons into the ionization chamber 3 remain the same.

From point 3 to point 4, the voltage across the ionization chamber 3 increases linearly to expand the mass spectrum of the ions from the neutral component.

Once in the transverse magnetic field of the magnetic analyzer 11, the ions are separated by mass. The radius of the trajectory r of the ion in a magnetic field is determined by the well-known mathematical expression:

,

,

where: B is the magnitude of the magnetic field induction in the magnetic analyzer 11.

Since the accelerating voltage and magnetic field are the same for all particles, knowing the radius of the particle’s trajectory of motion r, we can determine its mass.

Then, at point 4, the voltage on the ionization chamber 3 takes a zero value, and a blocking voltage P _{b1 is} supplied to the filament of the cathode 4. In this case, the positive potential U _a on the drift tube 13 for locking the ion component remains the same.

From point 4 to point 5, deionization of the charge of ions obtained from the neutral component occurs in the ionization chamber 3 during the relaxation time of the heaviest ion component in the ionization chamber 3.

From point 5 to point 6, the voltage at the drift tube 13 linearly decreases over time t _c = t _f from the maximum (U _a ) to zero (Fig. 3a) and the ion flux (ionic component of the plasma flow) passes from the drift tube 13 in the magnetic direction analyzer 11 and collector 9, and then registered by the device 10 to study its mass spectrum.

At the same time, on the filament of the glowing cathode 4, the bias unit 18 maintains a constant electron-blocking voltage U _b1 (Fig. 3b), and a zero potential is maintained on the ionization chamber 3 (Fig. 3c).

The time interval from point 6 to the end of the pulse repetition period (point 7) from the output of a voltage pulse generator of complex shape 15 (Fig. 3a) may vary depending on the research program.

From the description of the operation of the proposed device, it is seen that the periods of study of the mass spectra of the ionic and neutral components of the plasma stream are separated in time due to the synchronized pulse generators 12, 12, and 21 generated by the independent channels 12 time delays of switching on the voltage pulse generators of complex shapes 17 and 16, controlling respectively the heated cathode 4 and the ionization chamber 3, relative to the moment of switching on the voltage pulse generator of complex shape 15, which controls the drift tube 13.

Claims (1)

A mass spectrometer containing an ionization chamber arranged sequentially in a grounded vacuum chamber in the direction of propagation of the investigated plasma stream from its inlet, which is made with inlet and outlet axial openings, has a current lead and is equipped with a heated cathode, the terminals of which are connected to the glow unit, the focusing electrode with with a current lead, grounded extractor and output diaphragm, a collector to which a recording device is connected, in addition, a magnetic analyzer covering a vacuum chamber drain between the extractor and the output diaphragm, and a synchronized pulse generator, characterized in that it is equipped with a drift tube, which is made with end diaphragms and has a current lead, a grounded diaphragm, complex voltage pulse generators for controlling the drift tube, the ionization chamber and the heated cathode, a bias unit, which is connected to one of the terminals of the heated cathode, and the drift tube is placed in the vacuum chamber at its inlet, and the grounded diaphragm between at the drift tube and the ionization chamber, while the current leads of the drift tube and the ionization chamber and the glow cathode terminal connected to the bias unit are connected to the outputs of the corresponding voltage pulse generators of complex shape, in addition, a synchronized pulse generator that has independent channels in the number of voltage pulse generators of complex shape and made with the possibility of forming voltage pulses at the output of an independent channel, which is connected to the input of the voltage pulse generator a false form for controlling a heated cathode, with a time delay relative to voltage pulses at the output of its independent channel, which is connected to the input of a complex voltage pulse generator to control the drift tube, not more than the sum of the time of flight of the ion component of the plasma flow through the drift tube and the time of deionization of the residual charge ions in the ionization chamber, and at the output of an independent channel that is connected to the input of a complex voltage pulse generator to control the ionization chamber d, - with a time delay with respect to voltage pulses at the output of its independent channel, which is connected to the input of a voltage pulse generator of complex shape to control a heated cathode equal to the ionization time of the neutral component of the plasma stream by electrons.

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