Operation principle of relativistic ubitron is based on emission of electron beam, distributed in waveguide which is placed inside spatially periodic magnetic field. Waveguide could be of round and coaxial design.
By passing through spatially periodic magnetic field (undulator), electrons of relativistic beam (travelling at velocity of light) could emit electromagnetic oscillations much less than modulation period (strength alteration) of magnetic field.
If frequency of this emission matches with band of waveguide dispersion, this emission would result in-phase (coherent) emission of electrons distributed in this waveguide.
For coherent beam emission in the waveguide, placed into undulator, the following condition of synchronism between wave and electrons should be met:
This gives possibility to generate high power pulse emission in short-wave spectral region.
This also means that controlling electrons velocity, it is possible to alternate ubitron operating frequency.
Block diagram of ubitron is submitted below (Drg. 1)
1 – HV power supply source; 2 – cathode; 3 – anode; 4 – undulator (segment of spatially modulated magnetic field); 5 – electron beam; 6 – waveguide; 7 – horn antenna; 8 – solenoid.
This simple design ubitron utilizes round shape waveguide. However, despite simplicity of design, it does not allow to achieve required operation and dimensional features. Thus, it is proposed to apply coaxial waveguide system.
Geometry of undulator with opposite oriented magnetic systems is submitted below (Drg. 2).
1 – Ring type constant magnets
2 – Iron rings (pole piece)
Application of coaxial waveguides in ubitron allows to achieve several advantages compared to ring type waveguides. These advantages could be summarized as follows:
- stable transmission of relativistic beam in alternating magnetic field of undulator;
- field reduction of beam space charge in coaxial waveguide, where beam is drifting;
- higher efficiency of operation due to higher resistance of connection between electron beam and amplified wave.
Basic characteristics of coaxial ubitron, operating in wave band 3 – 10 cm: