Increased periodic magnetic fields for traveling wave tubes

The power output of a traveling-wave tube depends strongly on the strength of the axial magnetic field that guides its electron beam. Such fields are usually less than 5.0 kOe. With conventional permanent-magnet stacks, such fields are attainable only with periodic structures with periods of the order of the working bore diameters. The axial fields resulting from such structures have root-mean-square fields of about 3.5 kOe. The authors describe two novel stacks employing magic spheres that offer root-mean-square fields that are from two to three times as great, and that afford order-of-magnitude power increases over those of the conventional structures