8-Fold Helically Corrugated Interaction Region for High Power Gyroresonant THz Sources

Abstract

A manufacturing study of a 0.372 THz 8-fold (8F) helically corrugated interaction region (HCIR) and measurement of its wave dispersion characteristics are reported. This demonstrates the structure's suitability as the electron beam / electromagnetic wave interaction region in a high power frequency tunable Gyroresonant THz source. The 8F HCIR has an eigenmode, which is ideal for broadband tuning, created by the coupling of the TE 61 and TE 23 modes. Maximum power handling of 14 times larger than a 3-fold HCIR at the same frequency is calculated. A TE 11 to TE 61 7-fold (7F) helically corrugated waveguide (HCW) mode converter, needed to measure the wave dispersion of the 8F HCIR, was designed and constructed. Negative aluminium mandrels of the 7F HCW mode converter and 8F HCIR were manufactured. Copper structures were constructed through electroforming. The measured wave dispersion of the 0.372 THz 8F HCIR agreed well with simulated dispersion characteristics.

Fivefold Helically Corrugated Waveguide for High-Power W-Band Gyro-Devices and Pulse Compression

“…During the machining process, the aluminium rod is first turned on a lathe to the required cylindrical profile. It is then transferred to the milling machine and physically supported along its length as a ball nosed cutter removes the unwanted material via a repeat series of small axial cuts [13], [14]. This delivers the required profile to an accuracy of ± a few µm with a very high quality surface finish: photographs of the completed mandrel are shown in Fig.…”

“…A 3F HCW has been fabricated and measured at frequencies up to 372 GHz [13]. An eight-fold (8F) HCW in the same 372 GHz frequency range [14] increased the possible power handling while reducing the sensitivity to electron beam optics but has a higher level of mode competition and narrower band components. The 8F HCW allows the opportunity to explore the operation at a higher order mode.…”

Dispersion Curve of the Helically Corrugated Waveguide Based on Helicoidal Coordinate Transform

“…By varying the geometric parameters, different dispersion curves can be generated to satisfy the requirements of different applications. For example, a dispersion curve with a constant group velocity at small axial wavenumbers over a large frequency band is desired for broadband amplification in gyrotron traveling wave amplifiers (gyro-TWAs) [9][10][11]. While in microwave pulse compressors, dispersion curves with large differences in the group velocities and low Ohmic loss at a wide Introducing the helicoidal coordinate transform in equ.…”