The method of excitation of glow discharge in the gas and device for its implementation

 

(57) Abstract:

The invention relates to the physics of gas discharge and can be used to improve investing electrical power in the ready plasma discharge. Essence: in the anode region of the discharge shall make additional external ionization of the gas through the inductor connected to the high-frequency generator. This leads to the disappearance of the anode oscillations and the formation of a homogeneous plasma column, which allows to increase the specific power invested in glow discharge. 2 S. p. f-crystals, 2 Il.

The invention relates to the physics of gas discharge and can be used to increase put electrical power into the plasma gas discharge.

A method of obtaining a glow discharge [1], which consists in passing a constant current through the gas at a pressure of 0.1-10 Torr. In order for the gas between the electrodes missed DC in Gaza must be supported ionized state, which is created by the electric field existing between the cathode and the anode. Plasma such discharge is heterogeneous and consists of a cathode region, a positive pole and the anode is utilised to create lasers, emitting at different wavelength ranges.

However, the known method has the following disadvantages. The homogeneity of the positive column is one of the conditions to obtain the maximum radiation power of the laser. Attempts to increase the output power of the electric discharge lasers by increasing the applied electric power inevitably come up against the limitations associated with the development of the instabilities of the discharge. The development of longitudinal instabilities leads to a positive pole of a powerful plasma oscillations, and stratificatory discharge, which significantly affects the parameters of the active medium gas lasers.

Known technical solutions closest to the technical nature of the claimed object, which serves as the base object is combined discharge, constant and high-frequency electric fields [2] . In the combined discharge is discharge constant current distance between the cathode and anode of a few centimetres. High-frequency capacitive discharge occurs between the anode and the outer electrode is located near the anode. As a result of applying the high-frequency emkosti is m and the anode.

The disadvantages of this method and device are [2]:

the implementation of the combined discharge is possible in discharge tubes, in which the distance between the main discharge electrodes is several centimeters, for long discharge tubes of the order of 1 m or more are required to install long along the tube electrodes connected to a source of RF field;

the imposition of high-frequency capacitive discharge in the main discharge plasma leads to the formation of inhomogeneities in the plasma column main discharge - plasma formation "coats" or delamination of the plasma column.

The technical result of the invention is to improve the uniformity of the discharge and the increase in the specific energy input by suppressing fluctuations in discharge.

Execution of the specified technical result is achieved by the use of additional ionization in the anode region of the discharge compensates for the flow of electrons to the anode and this contributes to the establishment in this area of the plasma parameters close to the parameters of the plasma of the positive column and the disappearance of the anode oscillations.

Experimental research suggests that you gas discharge showed on the development of instabilities in the positive column is affected by electrode surface discharge. Analysis of the properties of positive column indicates that the excitation of oscillations in the positive column cannot occur. These oscillations occur in the anode region, i.e., the processes occurring in the anode region, make the whole electric system is unstable.

Fluctuations in the plasma is directly related to the processes of formation and destruction of the electrons in the plasma volume. The equation of balance of the concentration of charged particles (electrons) is

< / BR>
where nethe electron density, Dais the coefficient of ambipolar diffusion,i- frequency ionization.

The second term in the left part of the equation DAnedetermines the rate of ambipolar care of particles from the plasma volume. Member in the right-hand side of the equation balanceinedetermines the formation of charged particles in the volume due to ionization. In the presence of small perturbations in the concentration of charged particles, harmonically independent of the longitudinal coordinate, the concentration of electrons can be written in the form

< / BR>
where

r is the radial variable, x is the longitudinal variable, t is time, n(e- defines a longitudinal scale disturbances or wavelength perturbationsk.

Considering small perturbations of the concentration of the charged particle balance equation takes the form

< / BR>
where

i*- the average frequency of ionization in the presence of perturbations,

i- in the absence of disturbance. Due to the smallness of the perturbation n(e1)n(e0)have

< / BR>
Finally, the balance equation takes the form

< / BR>
The solution of this equation is a function

n(e1)= n(1eo)exp(t)

where the odds

< / BR>
is called the increment of instability.

If > 0 is the exponential growth of perturbations.

As a criterion of the existence of the instability of the plasma can be put

< / BR>
The left part of the inequality describes the increase in the frequency of ionization, violate the ionization equilibrium in the presence of perturbations, and the right part determines the rate of diffusion diffusion perturbation

D~ DA/2k~ k2DA.

The existence of a positive increment > 0 in the plasma itself may not cause longitudinal vibrations.the concentration of electrons n(e0).

In [2] were measured electrokinetic parameters of plasma neon in the anode region at low values of current I 10-2And pressure P= 1 Torr. Under these conditions, the ionization instability of plasma positive column was absent due to the low speed of the ionization processes. In [2] it was also found that near the anode of the plasma parameters: electron density neand the distribution function of electron energy (FREE) f() change significantly. For example, the electron density decreases by orders of magnitude when approaching the anode due to diffusion and drift flow of electrons to the anode. Measurement of electrokinetic parameters in the anode region when the current I=10-2- 0.5 A and the pressure range p=10-2- 10 Torr, held probe method of Druyvesteyn using pulsed-periodic discharge of stroboscopic method of measuring the second derivative of the probe current, allowed us to conclude the following:

near the anode is formed of a two-dimensional potential well in which the minimum value of the potential e(x) is at a distance from the anode;

the profile of potential changes in plasma

e(x) = [grad ne
inside the potential well are locked slow electrons.

In Fig.1 shows the change of the plasma parameters near the anode, where e(x) is the profile of the axial change of the potential in the plasma, ne(x) is the profile of the axial changes in the concentration of electrons (x) is the increment of instability, x0- the minimum value of the potential e , AB - width of the potential well, lcharacteristic length of decay of ne.

The dimensions of the anode potential drop is determined by the length of the energy relaxation of electrons in plasma

< / BR>
Studies have shown that the longitudinal electric field vanishes at a distance of one-fourth the length of the energy relaxation of electrons from the anode, i.e.

< / BR>
where

1the first potential excitation of the atoms of the gas, e is the electron charge, E is the intensity of the longitudinal electric field. Inside the potential well away from the anode is the increasing concentration of charged particles neand the concentration of metastable atoms nmin the state of2P2therefore, the total frequency of ionizationithat leads to an increase in increment of longitudinal instability.

Her positive, occurs because of the existence of slow trapped electrons, oscillating inside the potential well. Getting to the area of the potential well, in which > 0, the electrons become the excitation source and cause of ionization waves

n(e1)(t) = n(1eo)exp(t)

which extends along the axis of the tube from the anode to the cathode in the form of waves

ne(x,t) = Re[n(1ek)(t)exp(-ikx)].

Thus, a decisive role in the processes of the origin of oscillations in the plasma glow discharge is played by the change in electron density near the anode due to their flow to the anode. Compensation care of electrons with optional external ionization in the field of existence of the potential well leads to equalization of the values of nenear the anode and the electron density in the positive column. This eliminates the conditions for the occurrence of the anode oscillations, which propagate in the plasma of the positive column.

It is an additional external ionization of the gas in the region of existence of the potential well provides, according to the present method, the removal of the conditions of occurrence of the anode oscillations. A comparison of the proposed tehnichesknh technical solutions in this field of technology characteristics, distinguish the claimed invention, were not identified, and therefore they provide the claimed technical solution according to the criterion of "significant differences".

An example of the method

The suppression of the anode oscillations and strata according to the present method is the translation of classical glow discharge in the glow discharge with deformed anode region. Thus natural for classical glow discharge distribution parameters in the anode region is changed by artificial means. This change is due to additional ionization of the gas in the discharge region adjacent to the anode, i.e. the existence of the plasma potential well. With this purpose, in the anode region and a high frequency (HF) discharge, which is an additional source of charged particles near the anode. By changing the RF power discharge to achieve compensation of the decline in the concentration of electrons in the anode region. The result disappear conditions for the occurrence of the anode oscillations and, therefore, the discharge has no jitter and stratum.

To perform the described method, a device for excitation of glow retraceability the cathode 2 and the anode 3. The power of the discharge tube is made through the ballast resistance 4 from the constant current source 5. Near the anode is located, the inductor 6, which is connected to a RF generator 7.

The inductor 6 is 4 turns of copper wire. The diameter of the inductor 16 mm Inductor is positioned relative to the discharge tube so that the axis of the coil perpendicular to the axis of the discharge tube and, accordingly, the distance x0from the anode. Moreover, this distance x0corresponds to the location of the minimum value of the potential well e(xoin the plasma.

It was the introduction of an additional source of ionization of the gas, representing an inductor connected to the RF generator, and the location of the inductor relative to the discharge tube and the anode, provide, in accordance with the claimed device, the removal of the conditions of occurrence of the anode oscillations.

The device operates as follows. Using the power source 5 light inside of the discharge tube 1 between the oxide hot cathode 2 and a flat molybdenum anode 3 glow discharge. Through the inductor 6 transmit the RF current from the RF generator 7. RF generator 7 is assembled in the usual way of relaxation oscillator or multivibrator n is of the order of 50 MHz. At this frequency it is easy to get a glow discharge at low power electromagnetic waves. The inductor 6 were located at distances of about 10 mm from the anode 3. In these ranges of current I = 10-2- 0.5 a and pressure p = 10-2- 10 tor a distance x0to the minimum of the potential well was changed slightly and was about 10 mm. Fluctuations in the discharge plasma was determined using a probe located at a distance of 300 mm from the anode, and the photodiode PD 27, movable along the discharge tube connected to the oscilloscope S1-55. By changing the RF power generator achieved the disappearance of oscillations and strata in the plasma. Required for this electric HF power was 15% of the electric power invested in the main glow discharge.

Using the proposed method and device for initiating a glow discharge in a gas, in which additional external ionization of the gas in the region of existence of the potential well using an inductor connected to the RF generator, allow to suppress the anode oscillations and thereby to obtain a uniform plasma column. This in turn allows you to increase the specific power invested in glow discharge.

1. Sing the cell electrodes and the additional ionization of the gas in the area of the anode potential drop, characterized in that the additional ionization of the gas carried out at a distance x from the anode, which is determined by the ratio

< / BR>
where1the first potential excitation of the atom gas;

e - electron charge;

E - the tension of the longitudinal electric field in the region of the anode potential drop.

2. Device for initiating a discharge in a gas containing the discharge tube with two connected to the constant voltage source electrodes at the ends and RF generator, characterized in that the device introduced an additional external source of ionization, made in the form of an inductor connected to an RF generator and installed so that the axis of the coil perpendicular to the axis of the discharge tube in the area of the anode potential drop.

 

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