This paper presents the research progress of a pulsed G-band 50 W traveling wave tube (TWT) with pencil beam focused by periodic permanent magnet (PPM). Three approaches have been combined to improve the tube’s operation performances including setting the operating point near the cutoff frequency, using the folded waveguide (FWG) slow wave structure (SWS) with modified circular bends (MCBs), and adopting phase velocity tapering (PVT) technique. The measured output power can be over 50 W at 5% duty cycle with a bandwidth of 3.6 GHz when the beam voltage is 24.25 kV and the beam current is 59 mA. Corresponding electronic efficiency and gain are higher than 3.5% and 35 dB, respectively. The results provide a demonstration of a compact terahertz amplifier with high power, high electronic efficiency and significant bandwidth.

The development of a G-band traveling wave tube for wireless communications and airborne radars is described. The maximum output power of this device is over 20 W. This device provides a saturation output power over 15 W and a saturation gain over 32 dB with a bandwidth of 7.6 GHz. A folded waveguide circuit with modified circular bends is utilized to eliminate the band-edge instability caused by the high beam voltage of 20 kV. A pencil beam of 50 mA with a transmission ratio over 95 % is realized, making the device capable of operating in continuous wave mode. Periodic permanent magnets are employed for compactness. Chemical vapor deposition diamond disc is used in the input and output RF windows to minimize the loss and voltage standing wave ratios of the traveling wave tube. The weight and the size of the device are 2 kg and 300 mm × 70 mm × 70 mm, respectively. The efficiency of the device is over 5 %.

Nuclear fusion energy is perhaps one of the most demanding challenges that the scientific community is facing. Unfortunately, the plasma is affected by microturbulence, which is still not fully understood, but which can degrade plasma confinement. The 0.346-THz backward-wave oscillator (BWO) is the enabling device for a high-k plasma collective scattering diagnostic that will provide unprecedented insight on turbulence thereby contributing to the realization of fully operational fusion reactors. This paper describes the final fabrication phase of the 0.346-THz BWO for the collective scattering diagnostic jointly performed in an international project, involving three leading institutions in vacuum electronics. The advancements in technology will open the route to new families of terahertz vacuum electron devices to enable new terahertz applications and provide industry with new advanced processes.

A terahertz power module (TPM) based on 0.34 THz traveling wave tube (TWT) is described. A novel modified staggered double vane (SDV) slow wave structure (SWS) is employed in the TWT to realize broad bandwidth. This device provides an output power over 1 W and a gain over 18 dB from 0.33 THz to 0.355 THz. Although the available solid-state signal source is unable to drive the TPM to saturation, a maximum 1.6 W output power and 22 dB gain have been measured. The power dissipation of the TPM is 100 W and is cooled by conduction. It is a promising solution of power amplifiers for terahertz wireless communication.

A sheet beam traveling-wave tube (TWT) amplifier focused by periodically cusped-magnetic (PCM) fields has been successfully developed. The amplifier produces ~115 W of peak power at 212.4 GHz with a voltage of 25.8 kV. The output power is more than 100 W from 210.2 to 213.6 GHz. The measured transport current is about 106 mA accounting for 81.5% of the total current. The high-efficiency circuit design, along with the novel coupling structure, makes it possible to greatly reduce the required current, enabling the use of the PCM focusing. As a result, large power and a wide band have been achieved in a compact volume with an overall weight of less than 1.8 kg. The results demonstrate a significant breakthrough in developing the sheet-beam amplifier at terahertz frequencies. Although a single-section circuit without the attenuator is used at this stage, we have verified all the key technologies. The measured results are in good agreement with the design.