Ribbon Electron Beam Transport And Focusing Method

A new urgent need for high-frequency, high-power millimeter device has been emerging for advanced radar and communications. Previous work has indicated that a sheet beam driven traveling wave tube can meet this need,but it require the beam which can carry higher current. Sheet electron beam is one of the most important one. Sheet beam has lots of attractive virtues. For example, when it was used in microwave tubes, can transmit high current with small horizontal size that means it can generate higher power than traditional tubes. Second, sheet electron beams could greatly decrease the space charge force that might reduce the focusing requirement. Converting form traditional cylinder beams to sheet beam may permit substantial reduce in space charge effects on the efficiency of tubes. The more higher frequency we need smaller of the structure. We can use sheet beam in millimeter devices. Finally, sheet beams could put close to slow wave structure which makes the tubes more efficiently than traditional tubes.Although sheet beam has so much merit, the research of sheet beam has interrupted in the past few decades for it is hard to be focused. Transmitting in solenoid magnetic fields, sheet beam comes into being Diocotron instability. Stability of sheet-beam has been recognized as one of the key technologies of this type of TWT.In this paper, we discussed the transmitting and focusing methods of the elliptical sheet beams. Elliptical sheet beam can carry higher current and greatly reduce the space charge force than rectangular sheet beam, but it requires new method for focusing.The formation theory of rectangular sheet beam's Diocotron mode is discussed and the space charge field of elliptical sheet beam is derived. Using 3D PIC software, the Diocotron mode of the rectangular and elliptical sheet beam is observed.Given the specificity of elliptical sheet beam, using 3D dimensional PIC simulation software, the parameters of the beam impact on the Diocotron instability is studied. The expression for the magnetic field of the Wiggler and PCM is derived in detail. The single-particle transverse equation of motion with nature focusing in Wiggler and PCM is discussed. We not only study the semi-infinite elliptical sheet beam stability condition in them, but also deduced the envelope equation of each direction of the beam, with both space-change and emittance efforts. The 3D PIC result and the theoretical conclusion coincide with each other very well.The Offset-PCM configuration is proposed in order to solve the edge focusing. The magnetic field of this structure is obtained. The stability condition for edge focusing is discussed. The 3D PIC code was used to study sheet-beam focusing in Offset pole fields. The result shows that Offset-PCM can restrain the Diocotron mode of elliptical sheet beam.