Experimental investigation of miniaturized high frequency vacuum tube

Summary form only given. The concern with THz frequency located between the boundary of, electronic principle and photonic principle has been growing. There have been many efforts to generate THz radiation, from quantum cascade laser using tiny band gap of periodic solid state to free electron laser and gyrotron using the radiation by the periodic motion of electron beam in vacuum. However, the solid devices have fundamental limits such as low operation-temperature required and low output power, and the vacuum devices are restricted due to the bulk magnet. In order to overcome these problems, studies on miniature high frequency vacuum tube have been conducted. There are many challenges that should be characterized to realize a micro-fabricated high frequency vacuum tube with low-voltage electron beam. Among many problems in the miniature high frequency vacuum device, the Debye length of electron beam is the important part to characterize an interaction mechanism. If the Debye length is comparable to the bunching wavelength on the beams, electron bunches may be dissipated by the thermal motion of electrons. Therefore, a very considerate compromise is required to validate the circuit operation condition. However, there has been no experimental study to investigate the criterion for the collective behavior of an electron gas in the high frequency vacuum devices with a low-voltage electron beam. In order to establish the criterion, a scaled experiment using a single stage Ka-band folded-waveguide traveling-wave tube (FW-TWT) was performed. FW-TWT was adopted because they have compatibility with planar fabrication by MEMS technologies for high frequency circuit fabrication due to their simple structure. The hot test of Ka-band FW-TWT fabricated by LIGA process is underway in order to prove the validity of MEMS technology for high frequency micro-fabricated vacuum tube. All the experimental and computational results is presented in detail.