System Design Analysis of a 0.22-THz Sheet-Beam Traveling-Wave Tube Amplifier

The primary constituents of a 0.22-terahertz (THz) sheet-beam traveling-wave tube (TWT) amplifier, composed of a staggered double grating array waveguide, have been designed for broadband THz operation (~ 30%) using the fundamental passband (TE-mode). Currently, we are looking into the possibility of a pulsed low-duty test of this device as a proof of principle (POP) and have been making efforts to construct the system. The optimally designed input coupler has ≤ 1 dB insertion loss at 0.22 THz with ~ 75 GHz (34%) 1-dB matching bandwidths. A thin mica RF window provides a coupling bandwidth spanning multiple octaves. The collector is designed to have a jog for collecting the spent beam along the RF path coupled to the output RF window. Computer simulations show that the collector hybridized with a WR-4 window has ~ 60 GHz matching bandwidth with ~ - 0.5 dB insertion loss at 0.22 THz. The hybrid periodic permanent-magnet design combined with the quadrupole magnet (PPM-QM), intended for low-duty pulse operation in a proof-of-concept experiment, allows the elliptical sheet beam from an existing gun (25 : 1 aspect ratio) to unoptimized gun to have 73% beam transmission. The POP pulsed test is designed to be matched to our existing system, which will thereby tolerate beam transmission. However, a proper gun for the sheet-beam tunnel of the designed circuit will provide much better transmission. In our prior works, we successfully proved at W-band that the magnet design provided >; 99% beam transmission of a 10:1 aspect ratio sheet beam. Most of the TWT circuit components have been designed, and currently, a full simulation modeling effort is being conducted.