The development of high-frequency RF linear accelerators (linacs) requires consideration of several technological challenges, such as electron bunch linearization. Presented in this paper is the design of the interaction circuit for a 48 GHz MW-level three-cavity gyroklystron amplifier, appropriate for application as a millimeter wave power source in a 4 th harmonic linearizing system for an X-band linac. The output cavity is operated at the cylindrical TE0,2,1 mode, while the input and buncher cavities are operated at the TE0,1,1 mode. The interaction circuit has been designed using a combination of analytical calculations and particle-in-cell (PIC) simulations. The optimized gyroklystron is shown, through simulation, to deliver an output power of up to 2.3 MW with gain of 36 dB and efficiency of 44% at 48 GHz, when driven by a 140 kV, 37 A electron beam.

A magnetron injection gun (MIG) can generate an annular electron beam with a high transverse-to-axial velocity ratio for gyrotron devices. This paper compares the different configurations of the MIGs and their suitable applications were analyzed from the theoretical study. Following that, a MIG for a 48 GHz, 2 MW output power gyroklystron was designed and optimized by parameterizing the MIG's geometry and the magnetic field. By using the standard triode-type configuration, a low alpha spread of 8.9% was achieved. The simulation results showed that the magnetic field profile also plays an important role in the MIG design. The angle of the magnetic field on the emitter surface affects the alpha value and the alpha spread, which was not able to be predicted by the synthesis method. It provides an extra degree of freedom for tuning the MIG's performance in the experiment where the geometry of the gun is fixed.

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