SU911266A1 - Method of plasma parameter determination - Google Patents

Description

The invention relates to plasma physics, and specifically to the diagnosis of equilibrium, low-temperature plasma formations by their own microwave radiation, and can be used to determine the characteristics of plasma produced in various devices, laboratory installations.

Methods are known for determining plasma by its own microwave radiation. According to the methods, the plasma parameters are determined from the measurement of the radiation intensity at various frequencies.

However, in order to increase accuracy, measurements are required in a wide frequency band, which is possible either using radiometric receivers with a wide tuning range, or receivers of different frequency channels. All this complicates the apparatus, the calibration and the measurement procedure.

The closest to the proposed technical essence is a method for determining plasma parameters, based on measuring the scattering matrix of modes in a multimode waveguide, contacting a plasma.

According to this method, the scattering matrix is determined by exciting the modes in the waveguide with a generator and measuring the amplitude and phase of the modes reflected from the plasma and propagating in the opposite direction. This method is simpler as the measurements are carried out at the same frequency. For diagnostics, use is made of the difference in the field structures of various waveguide modes f2.

However, this method does not allow direct determination of the temperature of the plasma, which is an important parameter characterizing the plasma. In addition, it requires two end devices: a receiver and a generator. The active diagnostic method has

20 the disadvantage that it introduces disturbances in the plasma. This impairs the accuracy of measurement of true plasma parameters.

The purpose of the invention is to simplify

25 measurement procedures and determination of an additional parameter: plasma temperatures.

This goal is achieved by the fact that, according to the method of determining 30 plasma parameters, comprising -.

The measurements at one frequency of the characteristics of the modes of an electromagnetic field in a multimode system measure the cropping of the amplitudes of the modes of the natural microwave radiation of the plasma and determine the plasma parameters from them.

For covariance of the amplitudes of modes excited by the plasma's own radiation, the generalized Kirchhoff's law is valid, which can be written in the following form:

%, m: I Zi WS wa p u, v) dqv, w, (.z),

-oh

where S is the covariance of pth and mth

Maud;

ayi (t) — fluctuating amplitudes of C – t) modes;

T (X; Y, 2) is the temperature of the elementary volume: dv at the point (x, y, z);

dQ (x, y, z) - mixed loss of fields

p-6th and t-th modes in the volume dv;

C. is a normalizing constant. This means that the contribution of individual sections of the plasma to the covariance of two modes is proportional to the temperature of this section and the mixed losses of the fields of these modes, which are equal to:

WL, Y | wE, (Xjy, z) E (x, y, z) E, U, y, g)

where E (x, y, z) is the fraction of the dielectric constant of the plasma;

E „(x y, z),

, (x, y, 2) are the electric directions at the point () of the fields of the nth and gh modes, respectively, appearing in the plasma, if it is probed on these modes at the frequency w.

The modes differ in the structure of the field, i.e., the distribution of the electric and magnetic strength of the electromagnetic field in the space where the measurements are made. Therefore, these distributions will also be different in plasma if probed on these modes. Thus, the covariances of the amplitudes of the modes of the intrinsic microwave radiation of the plasma for different ndp modes depend differently on the electrical parameters of the plasma, i.e. different profiles of plasma parameters change; the covariance values will be different. By calculating these values for the expected possible profiles and comparing with the measured values, you can determine the true profile of the parameter changes. When using a computer, such a choice is made according to a program according to a given criterion, with a given accuracy.

FIG. Figure 1 shows the distribution of the values of the diagonal elements of the mode covariance matrix in a plane waveguide for various profiles of temperature variation in plasma; in fig. 2 - mutual arrangement of the waveguide and plasma; in fig. 3 shows the device by which the proposed method is implemented.

The covariance values in FIG. 1 are given depending on the parameter Y) X / 2C1 / where D. is the microwave wavelength

radiation;

2a is the width of the waveguide; p - the number of fashion.

Curves 1-3 correspond to the temperature profile

T 300 + BZ, curves 4-6 profile

T 300 + BZ + B sin {- | - BZ)

The dependences are plotted for various gradients B t 10, 5.10 10 / s. It was considered that the plasma parameters were only in the direction perpendicular to the waveguide flange. The coefficients were calculated using the following formula:

".T (x) g.g. (z) exp (ikHU Ve. (2 :)) V)

.-WITH,

Vetz) - (MM2c ()

where T (-z-) is thermodynamic

plasma temperature in section 2;

E (2.} Is the complex dielectric penetrability of the plasma, E (Z) is the imaginary part of the complex

dielectric constant, cementability, K - wave number;

C 2 is the normalizing constant, the mod numbers, and the numbers n, are integers. For a waveguide of finite width, the total number of modes is equal and on the axis shown the coefficient value will be located discretely. As a result, the measurements receive the values of the diagonal elements. The vertical lines in FIG. Figure 1 shows such covariance values for a waveguide 2A 10 X with a temperature profile T 300 + 5-loV 5-10 siri (-iCz / o, 47, i.e., coinciding with curve 5.

Claims (2)

The investigated plasma 7 is located close to the flange of the waveguide 8. The device contains a multimode waveguide 8, a single mode waveguide 9, directional couplers 10 individual modes, matched load 11, a circuit 12 of devices for multiplying mode amplitudes, at the 1st output of which the signal amplitude is U ;, (t) a, (t)), where a (t) and aj (t) fluctuating amplitudes of the modes p and m ,, respectively, a switch of 13 channels, receiver 14. Connecting the receiver to the outputs of the device and installing it. Your large receiver integration time gives you N N values of mode amplitudes covariances in many. "i mode waveguide, where N 2. After that, the obtained values are compared with those calculated for different profiles (Fig. 1) and a coma temperature profile is found. According to the method, only one End Device is used for measurements - a radiometric receiver, operations at a fixed frequency, no calibrations at several frequencies and knowledge of the frequency dependence of plasma parameters, which increases the accuracy of measurements, are not required. Claims The method of determining plasma parameters, which consists in measuring at one frequency the characteristics of an electromagnetized field in a multimode system, characterized in that, in order to simplify the measurement procedure and determine the plasma temperature, the covariances in time of the amplitudes of the natural microwave radiation are measured. Sources of information taken into account during the examination 1.Vashirinov A.E. and others. Microwave radiation of low-temperature plasma. Under. ed. Bashirinova A.E. Soviet Radio, 1974, p. 97 - 108. 2. USSR author's certificate number 527097, cl. G 01 N 21700,16.11.73 (prototype). 3 ... 3 | Ci С // R about with ob 6 o