Design and experimental studies of foilless diode for high power terahertz wave generation

A high beam quality foilless diode for high power 0.14 Terahertz backward wave oscillator (BWO) is presented in this paper. Limited by the wavelength in terahertz region, the diode is so small that its cathode radius is only 2.5 mm, and its anode radius is 9 mm. Based on an empirical formula for foilless diode, the initial structural parameters are estimated. Then the static electric field simulations with Superfish code and particle simulations using a 2.5 dimensional UNIPIC code are performed to optimize these parameters. The simulation results show that the beam parameters satisfy our design requirements. Finally, the experiments of the diode are carried out. The copper targets by beam bombardment are measured to prove that the electron beam is azimuthally uniform with an inner radius of 2.0 mm and outer radius of 2.54 mm. From the experimental results, the diode can provide a high quality beam over a wide range of diode voltage (160 kV<U<220 kV) and current (600 A<I<1.5 kA). Meanwhile, the diode resistance versus the distance between the cathode and anode is compared with numerical simulations. This foilless diode is being used in the experiment of high power terahertz wave generation.