RU2777900C2 - Method for diagnosing plasma method and langmuir probe with a protective ring for implementation thereof - Google Patents

Abstract

FIELD: testing.

SUBSTANCE: invention relates to experimental technology for diagnosing plasma and can be used for a flat singular Langmuir probe. In the method for probe-based diagnostics of plasma, including installing a probe in the plasma and recording the current-voltage characteristic, used to determine the parameters of plasma, a protective ring is installed on the probe, the probe is put into the plasma with the protective ring, by means whereof two electrical layers appear on the probe and on the protective ring, overlapping with each other and thereby reducing the area of both electrical layers. In the apparatus for probe-based diagnostics of plasma, containing a power source, a probe, a voltage generator, and a measurement unit, connected to the probe, the probe comprises a protective ring made of a conductive material.

EFFECT: reduction in the error of measurement of the electron density and temperature of a non-stable plasma using a probe with a protective ring at 14 to 21%, as well as creation of an apparatus capable of reducing the effect of the thickness of a double electric layer on the result of probe measurements.

2 cl, 2 dwg

Description

The invention relates to an experimental technique for plasma diagnostics and can be used for a flat single Langmuir probe.

From the existing level of technology, a method for probe diagnostics of plasma using a single Langmuir probe is known (RF patent No. 2642493, class H05N 1/100, 03.11.2016). The essence of the method lies in the fact that a probe is placed in the plasma, in the form of a piece of a metal thread connected through a probe voltage source to the metal case of the gas discharge device or an additional reference electrode, taking measures to protect the probe circuit from electrical pickups and to clean the collecting surface of the probe, and register its volt-ampere characteristics.

The disadvantage of this method of devices is that due to the formation of a double electric layer on the surface of the probe, the area that "collects" electrons changes, which leads to errors in determining the current-voltage characteristics, and, consequently, in calculating the concentration and temperature of the plasma.

From the existing state of the art, a method for probe diagnostics of plasma using an electric Langmuir probe (RF patent No. 2503158, class H05N 1/100, December 27, 2012) is known, based on active probing of the investigated plasma with a low-intensity current. The essence of the method lies in the fact that a probe is placed in the plasma, discrete stepped voltage pulses are applied to it. Further, by recording the current-voltage characteristics, the potential of the plasma space is measured.

The disadvantage of this method is that due to the formation of a double electric layer on the surface of the probe, the area "collecting" electrons changes, which leads to errors in determining the current-voltage characteristics, and, consequently, in calculating the concentration and temperature of the plasma.

Closest to the claimed technical solution is the method of plasma probe diagnostics and a device for its implementation (Kozlov O.V. Electric probe in plasma. M .: Atomizdat, 1969, 292 p.), The essence of the method is that a metal conductor (hereinafter referred to as the probe) of various shapes - flat, cylindrical or spherical. Using an external voltage source, the potential of the probe of one of the electrodes initiating the discharge (most often at zero potential) is set. The dependence of the current to the probe on the potential applied to it is recorded, i.e. remove the probe current-voltage characteristic (CVC), which is used to judge the concentration of plasma electrons.

The disadvantage of this method is that due to the formation of a double electric layer on the surface of the probe, the area "collecting" electrons changes, which leads to errors in determining the current-voltage characteristics, and, consequently, in calculating the concentration and temperature of the plasma.

The task to be solved by the claimed invention is to improve the accuracy of determining the parameters of the plasma (electron density and temperature of non-stationary plasma), by reducing the measurement error.

The technical result is to reduce the measurement error of the electron density and temperature of non-stationary plasma by 14-21%.

The problem is solved, and the technical result is achieved by the fact that in the method of probe diagnostics of plasma, including installation of the probe into the plasma and registration of the current-voltage characteristic, according to which the plasma parameters are determined, according to the invention, a protective ring made of a conductive material is installed on the probe, then the probe is introduced into the plasma with a protective ring, by means of which it is ensured that electrical layers overlap each other on the probe and on the protective ring, and thereby reduce the area of both electrical layers.

The problem is solved, and the technical result is also achieved by the fact that in the device for probe diagnostics of plasma, containing a power source, a probe and a measurement unit connected to the probe, according to the invention, the probe contains a protective ring made of a conductive material. When a probe with a protective ring is introduced into the plasma, electrical layers appear on the protective ring and on the probe, overlapping each other, and thereby reducing the area of both electrical layers.

Due to the fact that a double electric layer appears on the surface of the probe, the area "collecting" electrons is constantly changing, which causes errors in measurements. When adding a protective ring of conductive material, an electric double layer will also appear on it. As a result, a region will appear between the protective ring and the probe, in which two electrical layers will cross each other. As a result of overlapping, the area of both electrical layers will decrease, due to which the error of the taken current-voltage characteristics will decrease, and, consequently, the measurements.

In addition, it is possible to change the diameter of the protective ring, due to which it will be possible to use a Langmuir probe with a protective ring at different pressures.

The essence of the invention is illustrated by drawings, Fig. 1 shows the design of the device, Fig. 2 shows a diagram of the implementation of the method.

The device contains a single Langmuir probe 1 (Fig. 1), a double electron layer 2, an insulating layer 3 and a protective ring 4. The method implementation scheme (Fig. 2) contains a single Langmuir probe 1 with a protective ring 4, a vacuum chamber 5, an anode electrode 6, power supply 7, measurement unit 8.

The device works as follows. A single flat Langmuir probe 1 with a protective ring 4 is placed in a vacuum chamber 5. Due to the fact that a double electric layer 2 appears on the surface of a single flat Langmuir probe 2, the area "collecting" electrons is constantly changing, which causes measurement errors . When the protective ring 4 is added, the electric double layer 2 will also appear on it. As a result, between the protective ring 4 and a single flat Langmuir probe 1 there will be an area in which two electrical layers will cross each other. As a result of overlapping, the area of both electrical layers will decrease, due to which the error of the taken current-voltage characteristics will decrease, and, consequently, the measurements. By changing the diameter of the protective ring 4, it is possible to use a single flat Langmuir probe 1 with a protective ring 4 at different pressures.

An example of a specific implementation of the method.

The method is carried out in the following way. A single flat Langmuir probe with a protective ring 4 is placed in the vacuum chamber. The vacuum chamber 6 is evacuated until the ultimate vacuum (200 Pa) is reached, the working gas 35% N2 + 15% H + 50% Ar is supplied to the vacuum chamber and power is supplied to the inductor. Plasma is created in the vacuum chamber. The voltage is set to 400-500 V using a power source 8. The current-voltage characteristics are determined for steady-state values of the current of charged particles to a single flat Langmuir probe with a protective ring 4. Further, according to known methods for processing probe current-voltage characteristics, the electron density and plasma temperature are determined.

The thickness of the electrical layer is constant for identical conditions and is found from formula (1):

where ε is the dielectric constant of the medium;

n is the concentration of charged particles;

kT is the thermal energy of the ion;

q - electron charge

The measurement error is caused by the difference between the area of the flat Langmuir probe and the area of the electrical layer. This error can be found from formula (2):

where d is the diameter of the flat Langmuir probe.

Calculating the approximate thickness of the electrical double layer for our parameters and taking the diameter of the flat Langmuir probe equal to 10-15 mm, we get that the error of the area that “collects” electrons is equal to:

Thus, it can be seen from the calculations that the error of the area that "collects" electrons is 14-21%.

The claimed method has the following advantage: improving the accuracy of determining plasma parameters (concentration and temperature).

Claims (2)

1. The method of probe diagnostics of plasma, including the installation of the probe into the plasma and registration of the current-voltage characteristic, according to which the plasma parameters are determined, characterized in that a protective ring of a conductive material is installed on the probe, then a probe with a protective ring is introduced into the plasma, through which the occurrence of probe and on the protective ring of electrical layers overlapping each other, and thereby reduce the area of both electrical layers. 2. A device for plasma probe diagnostics, containing a power source, a probe and a measurement unit connected to the probe, characterized in that the probe contains a protective ring made of a conductive material.

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