Focusing of an Electron Beam from a Low-noise Gun with Different Magnet Systemsâ€
Titel:
Focusing of an Electron Beam from a Low-noise Gun with Different Magnet Systemsâ€
Auteur:
Chen, Tsung-Shan
Verschenen in:
International journal of electronics
Paginering:
Jaargang 20 (1996) nr. 1 pagina's 1-20
Jaar:
1996
Inhoud:
This article is the first part of a series of papers devoted to the computer solutions on the trajectories of the outermost electron in a beam focused by means of different magnet systems. The electron beam is produced by a low-noise gun which is immersed in a constant magnetic field. The beam voltage and beam current have the values usually found in X-band, medium-power, low-noise travelling-wave tubes. In the present paper, the boundary of an initially ' ideal' beam which is confined by a uniform magnetic field throughout the drift space is determined (L) by linearizing and solving the paraxial-ray differential equation, and (2) by solving the exact equation with use of a computer. Emphasis is laid upon the determination of the size of beam ripples, the wavelength of rippling or the scalloping wavelength, and the lowest constraining magnetic flux density below which the linearization process does not hold valid. Part II of this series deals with the trajectories traced by the outer-edge electron in an initially perturbed beam which is focused by a constant magnetic field. Part III treats the profile of the beam when it is focused by a long-period reversed-field magnet system. The conventional short-period periodic permanent magnet can produce a well-behaved beam or a running-away beam, depending on the amplitude and period of the alternating magnetic flux density and on the type of flux compensation between the gun and drift regions. Such beam contours ore discussed in Part IV. The beam boundaries in the electron-gun region are solved for four sets of electrode potentials and spacings, and also for several values of magnetic field; the beam profiles, and the beam radii and boundary slopes at the end of the gun region are to be discussed in Part V. The mathematical analysis will be relegated for treatment in a subsequent article.
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