Parameters to Define the Electron Beam Trajectory of a Double-Tapered Disc-Loaded Wideband Gyro-TWT in Profiled Magnetic Field Vishal Kesari & P. K. Jain & B. N. Basu Received: 8 March 2007 / Accepted: 30 March 2007 / Published online: 18 April 2007 # Springer Science + Business Media, LLC 2007 Abstract In the method of tapering the cross section of the interaction structure for broadbanding a gyro-TWT, the different portions of the interaction length of the tapered- cross-section waveguide become effective for different frequency ranges if the magnetic field and beam parameters are profiled to maintain the condition of electron cyclotron resonance throughout the interaction length. In the present paper, the study of profiling the magnetic field and beam parameters in steps of the stepped analytical model of a double-tapered disc- loaded circular waveguide was made throughout the steps of the model. In the observed profile, the magnetic flux density in a typical step relative to its value in first-step decreases from first-step (gun-end) to end-step (collector-end) of the model considering the up-tapering schemes, in which structure parameters increase from gun-end to collector-end. Also, the transverse beam velocity in a typical step relative to its value in first-step decreases from gun- end to collector-end. However, the Larmor radius in a typical step relative to its value in first- step as well as the hollow-beam radius in a typical step relative to its value in first-step, both increase from gun-end to collector-end in the model considering the up-tapering schemes. Keywords Disc-loaded waveguide . Magnetic field profile . Gyrotron . Wideband gyro-traveling-wave tube (gyro-TWT) . Millimeter-wave amplifier 1 Introduction The developments of the gyrotrons, the gyro-klystrons and the gyro-TWTs have received the maximum attention in the development of gyro-devices [1–4]. The gyrotrons find application as high-power millimeter-wave sources, for instance, in plasma heating for controlled Int J Infrared Milli Waves (2007) 28:443–449 DOI 10.1007/s10762-007-9223-y V. Kesari (*) Department of Electronics and Communication Engineering, Birla Institute of Technology, Mesra, Ranchi 835 215, India e-mail: vishal_kesari@rediffmail.com P. K. Jain : B. N. Basu Centre of Research in Microwave Tubes, Department of Electronics Engineering, Institute of Technology, Banaras Hindu University, Varanasi 221 005, India