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18.07.2017: Application of E14-x40 module for measuring the spatial distribution of electron beams' current density


Scientists from MPEI proposed a method for direct measurement of the current density distribution of technological electron beams using the E14-140-M ADC module [1]. This theme is relevant for the development of electron-beam welding technology, surfacing and perforation.

The experimental stand (Fig. 1) was created on the basis of the ELA-15I installation, equipped with an electron gun with an accelerating voltage of 60 kV, which forms beams up to 15 kW. Above the collector 1 there was installed a grounded copper shield with a hole 11 with a diameter of 1 mm, and the entire system was moved along the trajectory-meander at a speed of 25 mm/s using an electric drive of the coordinate table. The displacement amplitude was 20 mm, and the step between scan lines was 1 mm. A part of the beam electrons passing through the hole 11 hit the collector and, when passing a current, created a potential difference on the measuring resistor 5, recorded with the E14‑140‑M transducer.

 

Figure 1. Scheme for measuring the current density distribution of the electron beam: 1 - collector; 2 - electron beam; 3 - shielded cable; 4 - filter; 5 - measuring resistor; 6 - overvoltage protection circuit; 7 - measuring transducer; 8 - trajectory of the collector's movement; 9 - insulator (glass); 10 - screen; 11 - calibrated hole.

 

Figures 2 and 3 show the obtained linear distributions of the electron beam's current density at a current of 35 mA and an accelerating voltage of 60 kV (power is 2.1 kW). A series of experiments were carried out for beam currents from 20 to 100 mA.

 

Figure 2.

 

Figure 3.

 

The experimentally obtained current density distributions differ significantly from the normal distribution functions widely used in the modeling of technological processes and have deviations from axial symmetry. Deviations are due to aberrations of the electron-optical system of the electron gun, caused by misalignment of the electrodes, and, possibly, by the presence of a crater on the surface of the cathode due to ion bombardment. They can have a significant negative impact on the quality of the welding or surfacing process, as when moving along mutually perpendicular directions the shape and dimensions of the liquid bath will be different. Deviations of beam current density distributions from axial symmetry can not be eliminated directly during processing, to compensate them a mechanical or magnetic alignment of the cathode unit is required, and the beam parameters themselves can be controlled using the proposed method.

 

Source:
Shcherbakov A.V., Kozhechenko A.S., Rodyakina R.V., Gaponova D.A., Khomutsky V.A. Spatial distributions of the current density of technological electron beams. Proceedings of the International Scientific and Technical Conference "The State and Prospects of Electrotechnology Development " (XIX Benardos Readings). - Ivanovo. - 2017. - B. 1. - P. 6-9.

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