Design of electron gun and novel PPM focusing system for W-band sheet beam TWT

An 20 kV, 210 mA electron gun for a sheet beam traveling wave tube have been designed. BFE and anode dimensions are optimized using CST code to converge the beam coming from planar cathode of rectangular size 1.2 mm×1 mm. The beam waist is formed at 11.2 mm from the cathode with the beam size of 1.1 mm× 0.22 mm. Novel PPM focusing system is designed for stable transport of the beam. In this case no side magnets are used and pole-pieces are extended after beam edge. Absence of side magnets will reduce the cost of magnetic material, weight of the tube and make easier to insert couplers. The horizontal position of extended pole-piece is after 5 mm from the side wall of the drift tube tunnel in order to make mechanically possible to extend the pole-pieces. NdFeB magnates with Br value 1.4 T are considered. The shielding pole piece is extended towards cathode region to get Brillouin flow. Beam transmission is achieved more than 95% up to 40 mm and 90% up to 70 mm in a tunnel suitable for W-band sheet beam TWT.