ABSTRACT In this paper, the design of an interaction structure for a 10-kW, W-band gyrotron is presented. The beam voltage and beam current are chosen as 30 kV and 1 A, respectively. The mode of interaction was chosen as TE6,2. A parametric design code and a gyro large-signal analysis (LSA) code were developed. The computational steps are discussed in brief. The LSA was done using the in-house developed code and the Gyro-K code. The results of these two codes were found to be in good agreement. The design of the nonlinear taper (NLT) was also carried out. Based on Ohmic loss, the power dissipated in the cavity was estimated. A novel cooling arrangement was proposed with two concentric cylindrical jackets around the cavity. The computational fluid dynamics (CFD) analysis was done using the software FloEFD. Steady-state analysis for the CW mode of operation and the transient analysis for the pulsed mode of operation were carried out for various flow-rates of the coolant.