Design of uniform permanent magnet electronic optical system for 220 GHz sheet electron beam traveling wave tube

Abstract

The sheet electron beam (SEB), for which is the low current density and large current, is highly attractive in the region of millimeter wave and terahertz vacuum electronic devices (VEDs). A uniform permanent magnet (UPM) electronic optical system (EOS) driven by a SEB for 220 GHz traveling wave tube (TWT) is designed in present work, in which the voltage and current for SEB is 17 kV and 0.3 A, respectively. For obtaining the stable high transmission rate EOS, the characteristics of SEB in UPM EOS are studied, including the emittance, orbital angle, and beam trajectories, which are discussed through the CST simulation. The results show that the emittances in the x-direction are varied from 0.003 to 0.016 mm rad and in y-direction are various from 1 × 10 −4 to 3 × 10 −4 mm rad, respectively, keeping below than 2.5 × 10 −4 mm rad during transmission, which guarantees the stability of SEB in y-direction. For the design of complete EOS, the normal rectangular collector is used, in which the SEB is uniformed scattering. Recently, terahertz (THz, 1 THz = 10 12 Hz) bands have been attracted many attentions for its myriad application 1, such as biochemical sensing, imaging for medical and security, astrophysics and remote atmospheric monitoring, and high-bandwidth communications, etc. Therefore, THz sources are highly focused on 2-4 , for which they are the key components of extensive applications, especial those with characteristics of wide band, high power and room temperature operation. Traveling wave tube (TWT) is one of the devices which can work at high frequency, and it is one of the most highlighted THz vacuum amplifiers due to its outstanding combined performances in bandwidth and power capacity 4. In VED branch, the output power is scaled as the volume size, it will be sharply decreased with the increasing of operation frequency. On the other hand, the efficiency of beam-wave interaction is very low for the surface attenuation resulting by the light skin depth 5. As we know, the SEB is attracted and widely used to improve the output power in high frequency VED, such as the TWT, backward wave oscillator (BWO), and extended interaction klystron (EIK), etc. The SEB driving beam-wave interaction system of VED are widely appeared many literatures, Baig et al. 6 analyzed the beam-wave interaction of 0.22 THz TWT driven by SEB with a help of CST simulation, and the high frequency characteristics are studied with cold measurements. Mark Field et al. developed a stagger-grating amplifier driven sheet beam, which produced the output power 107 W and a power-bandwidth product of 642 W GHz at centered frequency of 200 GHz 7. The hybrid periodic permanent-magnet combined with the quadrupole magnet for a 220 GHz TWT is designed, the planar circuit is for interaction with a SEB with dimensions of 700 × 100 μm 2 (7:1 aspect ratio) 8. A SEB EOS for a G-band klystron is designed, the beam with a rectangular cross section of 2.5 mm × 0.15 mm is focused by uniform solenoidal magnetic field 9. The difficulties of the SEB in VED EOS ...

Design of planar distributed three beam electron gun with narrow beam separation for W band staggered double vane TWT

“…However, planar distributed multi-beam TWT, with independent of beam tunnels and convergent beamlets, can achieve high output power by sustaining the total high beam current with a small current for each beam, which may avoid the over-mode beam tunnels comparing with the sheet beam devices. Moreover, the planar interaction circuit suitable for the planar distributed multi-beam array is not only easier in fabrication than the circular structures in the millimeter wave and THz regime, but also it can meet the trend of planarity, miniaturization and integration for next generation of vacuum electron devices 7 , 8 .…”