March 29, 2024

Design of Double-Magnetic Cutting Electron Gun with Large Cyclonic Electron Beam

Starting from the conservation of regular angular momentum, the angular velocity vi of the electrons after passing through the first and second cross-cut magnetic fields, the guide center radius rg and the Larmor radius rL can be obtained in order. The radial position at the cathode and the first magnetic meeting point.

It can be seen from equation (4) that to obtain a large cyclotron orbit electron beam, it is only necessary to make / 1 = one / 2.

The electrons pass through the adiabatic compression zone, and the adiabatic compression magnetic field slowly changes from Bo to / mB (/ m is the adiabatic compression magnetic field scale factor). According to the adiabatic compression theory, it is known that the electronic magnetic moment remains unchanged and the electron beam surrounds the magnetic flux remains unchanged. The final angular velocity of the electron beam and the radius of the guide center are the electron beam velocity ratio. From this, it can be seen that the electron beam velocity ratio is determined by the scaling factor of the magnetic field / 1 and / 2, the adiabatic compression magnetic field scaling factor / m and the electron The radial position r1 during the first magnetic resection is jointly determined, which provides a great degree of freedom for the adjustment of the transverse speed ratio of the dual-magnetic resection electron gun.

2 Numerical simulation and analysis of the dual-magnetic cutting electron gun According to the above theoretical model of the dual-magnetic cutting electron gun, the electronic trajectory simulation program EGUN is used to numerically calculate the dual-magnetic cutting electron gun. At the same time, some parameters that affect the performance of the large cyclotron electron beam are analyzed and discussed according to the simulation results.

2.1 The numerical simulation of the dual magnetic reciprocating electron gun gives the theoretical calculation result of the relationship between the speed ratio and the cathode magnetic field at the radial position r = lcm under different interaction magnetic fields. The anode voltage is 70kV. From equation (7), It can be seen that under a certain interaction magnetic field, as the cathode magnetic field increases, the numerator term of this formula increases, and the denominator decreases accordingly, so that the electron beam speed ratio also increases / deniers when the cathode magnetic field increases to a certain value, The centripetal force of the electron motion and the Lorentz force are out of balance, and the electron beam eventually reflects. Generally, the speed ratio is required to be above 1, and the cathode magnetic field can be set at 0. The relationship between the speed ratio and the radius of the cathode under different interaction magnetic fields, the anode voltage is still 70kV, and the cathode magnetic field is 0. It can be seen that when the cathode radius exceeds a certain Range, the electric field around the cathode changes, and the electron beam speed ratio increases sharply. The cathode radius should be selected in the linear growth of the electron beam. Here, the cathode radius should be 10mm. The electron gun parameters calculated according to the design requirements and theoretical calculation of the electron gun are shown in Table 1.

Table 1 Performance requirements and calculation parameters of the electron beam The above electron gun parameters and working magnetic field are added to the EGUN software for simulation, and are continuously adjusted and optimized to obtain the shape and electron trajectory of the dual-magnetic cutting electron gun after considering the space charge effect, as shown.

Table 2 is the specific parameters of the electron beam obtained when the electron trajectory converges. It can be seen that the electron beam generated by the dual-magnetic-cut electron gun has basically met the requirements of the entire tube on the quality of the electron beam.

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