In traveling wave tube (TWT) amplifiers, an axial focusing magnetic field is required to keep electrons traveling in a narrow, pencil-like beam over the considerable length of the circuit. Conventionally, this focusing has been accomplished by using a periodic permanent magnet system housing axially polarized ring magnets. Making the structure to this point has been a complicated process consisting of brazing multiple metals together and honing the piece to the desired specifications. We present a new method of fabricating this housing structure monolithically using iron, developing magnetically oversaturated housing regions, and saving processing time and effort.
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8. Zhang, H., W. Liu, S. Bai, and K. Chen, "Periodic permanent magnet focusing system with high peak field," J. Magn. Magn. Mater., Vol. 320, 1675-1679, 2008.
doi:10.1016/j.jmmm.2008.01.017
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