The experimental research of magnetron output spectrum components

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The experimental research of magnetron output spectrum components

Chen Xin

Output spectral components radiated from magnetrons were experimentally measured. It was found correlation with some oscillations which influence on electromagnetic surrounding. As quality factors were proposed number of outside components and their magnitudes.

Keywords: quality factor, magnetron, output spectrum, residual gas.

Експериментально досліджено складові спектру, що випромінюється з магнетрону. Виявлено кореляцію певних коливань, які впливають на електромагнітне оточення. Як показники якості запропоновано кількість складових спектру та їх величину.

Ключові слова: показник якості, магнетрон, вихідний спектр, залишкові гази.

Экспериментально исследованы составляющие спектра, излучаемые магнетроном. Выявлена корреляция колебаний, влияющих на электромагнитную обстановку. В качестве показателей качества предложены количество спектральных составляющих и их величина.

Ключевые слова: показатель качества, магнетрон, выходной спектр, остаточные газы.

The quality factors influencing on modes of magnetron output spectrum components were identified in earlier works [1, 2]. These devices are widely used in industry, communications, medicine and everyday life.

It is well known the manufacturing technology influences to magnetron's operation.

To determine the quality factors of crossed fields devices one of them are magnetrons it were considered each block and processes.

As a result [1], it was identified 29 quality factors for such devices. All mentioned factors can be considered as separate indicators of the magnetron quality.

Here we consider the influence of post manufacturing quality factors to output magnetron spectrum.

There are such quality factors of anode system:

- technological maps of some units designing for magnetron;

- technological maps of some units manufacturing for magnetron;

- technological maps of magnetron designing;

- technological maps of magnetron manufacturing;

- technological maps of manufacturing device training;

- emission current magnitude;

- output spectrum components.

We shall consider one of these factors: output spectrum components and their measurement.

Experimental plant. To measure spectrum components it was assembled experimental plant its schema was shown in fig.1.

The experimental plant consisted of:

magnetron which output spectrum components were measured;

microwave wide-band directional coupler;

waveguide system to measure any waveguide modes;

spectrum analyzer to fixed spectrum components, their frequencies and levels.

Figure 1 - Experimental plant

Total error of experimental plant was 10 - 15 dB.

Spectrum analyzer's using allowed to simplify the waveguide system of experimental plant as we had not necessity to measure every mode by selective receiver.

Initial output magnetron spectrum was shown in fig. 2

Figure 2 - Initial output spectrum

Anode system of vacuum devices including magnetrons was manufactured from copper or aluminium. In natural conditions these materials were absorbed gases' molecules both air (nitrogen, oxygen) and technological (argon, hydrogen, helium).

When such devices were operated above mentioned gases' molecules presented in interaction space. Gases' molecules interacting with electron beam were ionized. Positive charged ions made oscillated ion cloud.

The methodology of the experiment was:

measured pressures inside magnetron for one of gas's kind;

next repeated these measurement for other gas's kind.

When pressure was 510-5 torr it presented stable side components with frequencies f0 400 kHz (fig. 3). There magnitude is near -35 dB to level of fundamental mode.

Further pressure increasing was caused to enlarge number of spectral components in output magnetron spectrum.

Outside spectral components when pressures are 2,1*10-4 до 3,210-4 torr (fig. 4) stretched for frequency domain 1,3 MHz - 4,5 MHz, and there levels are -25 - -45 dB.

Figure 3 - Output spectrum for 510-5 torr

magnetron electromagnetic oscillation

Figure 4 - Output spectrum for 310-4 torr

Thus one of quality factors is a spectral lines. This factor can measured by megahetrzes or percent and characterized pressure of residual gases in crossed-field device is less or equal dozens millitorrs.

Research results. Main content of measured results was researched influence of residual gases' pressure via outside spectral components.

Pressure changing was caused to change number of spectral components and their broadening.

When magnetrons were operated residual gases' molecules presented in interaction space. Gases' molecules interacting with electron beam were ionized. Positive charged ions made oscillated ion cloud. These oscillations are low frequency oscillations and excite due to the relaxation mechanism. Such mechanism is responsible for periodic relaxation of the ions and potential decrease. These oscillations are ion-relaxation oscillations.

To calculate the frequencies the ion-relaxation oscillations we used a result of investigation that were carrier out in [2] and obtained the following expression

magnetron electromagnetic oscillation

,

where b - constant defined by kind of gas;

x - gas ionization energy;

w - electron energy;

щH - cyclotron frequency;

p - residual gases pressure;

k - Boltzmann constant;

T - gas temperature;

;

r - radius;

rc - cathode radius [3].

As results of theoretical investigation it is get the ion-relaxation oscillations exist when pressure of residual gases in crossed-field device is less or equal dozens microtorrs and frequency band stretches from some Hetrz to dozens kilohetrzes. Such oscillations made parasitic oscillations in super long wave band and widen spectral lines of fundamental and other oscillations. Typical ion-relaxation spectrum was shown in fig. 2.

Second oscillations mechanism is ion--plasma and ion-hybrid ones. It is well known the frequency of plasma oscillations was defined as

,

where

n0 - electron density;

e - electron charge;

mi - electron mass;

е0 - dielectric constant.

The ion-hybrid oscillations had excited due to presence of crossed electric and magnetic fields. The frequency of such oscillations defined as

,

where B - magnetic density [3].

As results of theoretical investigation it is get the ion-plasma and ion-hybrid oscillations exist when pressure of residual gases in crossed-field device is less or equal dozens millitorrs and frequency band stretches from some hundred kilohetrzes to hundred megahetrzes. Such oscillations made parasitic oscillations in radio and TV wave band and appear new spectral lines near fundamental and other oscillations. Typical ion-plasma spectrum was shown in fig. 3, and typical ion-hybrid was shown in fig.4.

During experiment as quality factors we defined number of outside components and their magnitudes. Processed data we obtained image depends (fig. 5 and 6).

Figure 5 - Outside components' magnitude

As results of experimental research of the magnetron output spectral components are next:

assembled the experimental plant allowed to measure outside radiation from microwave devices;

defined outside radiation levels both continuous and pulse magnetron operation;

investigated residual gases' influence on magnetron operation both continuous and pulse options.

Figure 6 - Number of outside components

Conclusions. Here we discussed quality factors of magnetron. To analyze such components as residual gases' pressure into vacuum devices we come to the conclusion the quality factors of post manufacturing can be

- kind of residual gas;

- widen spectral lines;

- number of outside components;

- outside components' magnitude.

References

1. Chen Xin, I.V. Ruzhentsev, O.M. Nikitenko Quality factors of crossed-field electron systems // Information processing system. - 2011. - No 6. - pp. 72 - 76. (in Ukrainian)

2. Chen Xin, О.M. Nikitenko, I.V. Ruzhentsev Anode system quality factors of crossed-field devices // Electrotechnic and computer systems. - 2012. - No 6(82). - pp. 154 - 157

3. Nikitenko O.M. Ion oscillations in crossed-field systems. Gdanмsk : 14th International Conference on Microwaves, Radar and Wireless Communications, Volume 1, 20-22 May 2002. -- pp. 93 - 94

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