Preliminary Experimental Investigation of an -Band Low Magnetic Field Coaxial Relativistic Klystron Oscillator

An
$X$
-band coaxial relativistic klystron oscillator (RKO) is proposed to improve the beam–wave interaction efficiency in the low magnetic field and low impedance. The device adopts a four-gap modulation cavity to increase the fundamental current, and a three-gap extraction cavity is used to improve the microwave extraction capability. The simulation results show that when the guiding magnetic field and impedance are 0.55 T and 40
$\Omega $
, respectively, the output microwave power is 3.65 GW and the corresponding efficiency is 40%. Subsequently, a preliminary experimental investigation was carried out to verify the feasibility of this technical route. In the experiment, the output microwave with a power of 2.3 GW, a pulsewidth of 69 ns, and a center frequency of 9.39 GHz was generated when the magnetic field and impedance are 0.62 T and 41
$\Omega $
, respectively. Moreover, the explosive electron emission model of the extraction cavity is established, and the simulation results show that the explosive electron emission generated by the radio frequency (RF) breakdown at the extraction cavity is the main reason for the difference between the experimental and simulated microwave power.