Thermionic cathodes are commonly used electron sources, which are widely used in analytical instruments, electron beam processing equipment, microwave electronic devices, particle accelerators and so on. The magnetic field generated by the traditional cathode heater on the cathode surface will increase the initial equivalent emittance of the emitted beam, which will affect the improvement of the beam quality, especially for large-area thermionic cathodes. Heater magnetic field has a negative impact on beam propagation and focal spot of linear induction accelerators, which is directly related to the overall performance of accelerators. Adopting armored heater can reduce the residual magnetic field of heater and improve the beam quality of large-area thermionic cathodes. A new type of armored heater sample was developed. The heater was coiled in the shape of mosquito-repellent incense, with a diameter of about 10cm and a cold resistance of 3.5Ω. The experimental results of heater show that the heating power reaches 1.11 kW when the heating current is 9.80 A. The highest temperature on the heater is 1194.1 ℃, and the lowest temperature is about 1100 ℃. In view of the possible outgassing of armored heater, attention was paid to the change of vacuum in the heating process, and there was no obvious vacuum fluctuation caused by the outgassing of heater itself. The surface magnetic field of the heater is measured on the magnetic test platform. The residual magnetic field at the cathode surface is about (-0.833 ~ 0.6) gauss at 10A heating current. The experimental results preliminarily verify the feasibility of armored heater, which lays a foundation for further work.
 

thermionic cathode,heater,linear induction accelerator