Electron Beam Transport System for 263-GHz Sheet Beam TWT

The efficient transport of high current density electron beams is essential for the success of millimeter wave and terahertz vacuum devices. To achieve high current density sheet electron beam transmission, an advanced periodic cusped magnet-tunable quadrupolar magnet (PCM-TQM) is proposed to improve the transmission factor of the sheet beam. Through numerical a nalysis, the TQM is shown to provide the ability to be compatible with a larger initial transverse velocity spread and match the current density increasing caused by beam bunching. This new PCM-TQM focusing system is employed to transport a 19 kV, 0.15 A, ~8.5:1 aspect ratio sheet beam with an elliptical cross section of 0.60 mm (width) × 0.07 mm (height), whose current density exceeds 400 A/cm
²
, through a 45-mm long circuit, whose beam tunnel is 0.7 mm × 0.12 mm. CST PARTICLE STUDIO is used to model the beam transport system and verify the analytical results. With the tunable feature of the QM poles, the “no RF” and “with RF” beam transmission factors under the focusing magnetic field of the advanced PCM-TQM are predicted to achieve 99.3% and 97.6%, respectively.