Design of an overmoded W-band TWT

Abstract

We report on the design and cold test validation of an overmoded TWT capable of producing power in excess of 100 Watts in the W-band and above. The TWT operates in the TM 31 mode of a rectangular cavity and has transverse dimensions three times larger than a conventional ladder TWT. Dielectric loading of a resonant cavity was utilized to suppress lower order modes and prevent parasitic oscillations. HFSS and MAGIC3D codes were used to predict performance. An X-Ku band scaled down version of the interaction structure was built and cold tests performed on it showed excellent agreement with HFSS simulations.

A Feasibility Study of Beam-Wave Interaction in 670 GHz Gyrotron for Radioactive Material Detection Application

“…PIC code has been used successfully in the interaction cavity design and power growth estimation for gyro-amplifiers and fusion gyrotrons such as 140 GHz gyrotron, 170 GHz gyrotron, etc. [29][30][31] Simple cylindrical interaction cavity consisting an input taper section, a straight middle section, and an output taper section is made with very fine meshing in the PIC code (Ár ¼ 0:05 mm, Á ¼ 10 , Áz ¼ 0:05 mm in cylindrical coordinate system). The gyrating electron beam (perpendicular to axial velocity ratio of electrons, ¼ 1:3) is launched at the co-rotating electric field of first radial maxima (1.88 mm) of the selected operating mode.…”

Overmoded W-Band Traveling Wave Tube Amplifier

“…Over-moded W-band TWTs have been proposed which would allow the possibility of larger beam tunnels and the need for less magnetic field overall [9], [8], [21]. An over-moded design, meaning a design which operates in a cavity mode which is at a higher frequency than the fundamental cavity mode, is oversized for its intended frequency of operation.…”

“…Over-moded TWTs were first explored at MIT by [8]. The design presented is for a 94 GHz TM 31 cavity mode with lower-order modes suppressed by selective dielectric loading.…”

“…The Aluminum Nitride (AlN) composite from Sienna Technologies that will be used in experiment has a loss tangent of tan δ = 0.26 and a relative permittivity of ε r = 34 at 12 GHz [59]. Previously, this material was used to show the supression of 10 GHz modes in a proof-of-concept TM 31 coupled-cavity design on which this work is based [8] These values were used in HFSS simulations, though they may be lower at higher frequencies. Cold tests, as reported in Chapter 4, show that the AlN composite properties are sufficient for the overmoded TWT performance.…”

Particle-in-Cell Analysis of 1 MW/110GHz Gyrotron Interaction Cavity

“…In our design for the 110 GHz, 1 MW gyrotron interaction cavity, the in-house developed code GCOMS and the particle-in-cell (PIC) code MAGIC ( [18]) have been used. The MAGIC code has already been used for the simulation of the low power, low frequency gyrotrons ( [19,20]) and the gyro amplifiers ( [21]) but the code has not been explored yet for the design of high power and high frequency gyrotrons. In this paper efforts have been made to design and simulate the interaction cavity for the high power, high frequency gyrotron by using the commercially available code MAGIC.…”