УДК 612.382

Chen Xin, О.M. Nikitenko, ScD, P.M. Yevseev

Kharkiv national university of radioelectronics, Kharkiv

THE EXPERIMENTAL RESEARCH OF MAGNETRON OUTPUT SPECTRUM COMPONENTS

Output spectral components radiated from magnetrons were experimentally measu 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.

Introduction. 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 5(10-5 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.
        Out
        Outside spectral components when pressures are 2,1*10-4 до 3,2(10-4 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 5(10-5 torr



Figure 4 – Output specfor 3(10-4 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

,
where b 
,
where b – constant defined by kind of gas;
x – gas ionization energy;
w – electron energy;
ωH – cyclotron frequency;
p – residual gases pressure;
k – Boltzmann constant;
T – gas tempe
;
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;
ε0 – dielectric coefined  as

,
where
n0 – electron density;
e – electron charge;
mi – electron mass;
ε0 – dielectric constant.
The ion-hybrid oscillations had excited due to presenceefined 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 , 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. Gdańsk : 14th International Conference on Microwaves, Radar and Wireless Communications, Volume 1,  20-22 May 2002. – pp. 93 - 94 

Надійшла до редакції 10.5.2013

Рецензент: д.ф.–м.н., проф. Грицунов О.В. Харківський національний університет економіки, Харків