High Precision Welding for Magnetic Shielding Assembly of Electron-Gun of Space Traveling Wave Tube

A novel technique was developed to weld the magnetic shielding assembly, comprising a 4 J33 mu-metal “flat-lid” and a monel-metal input end-cover rod, for electron gun of space traveling wave tube (TWT) .The original work included the laser welding, high precision laser positioning and mold control.First, the cold flat-lid and rod were aligned by means of laser and lab-made mold so accurately that the concentricity was below 0.2 mm;second, the temporary lid-rod alignment was firmly fixed with four symmetric spots welded by laser welding at the circular interface;and finally, the point-contacted lid-rod assembly was brazed at 960 oC in hydrogen furnace.The welded seam was evaluated with scanning electron microscopy.The preliminary results show that the newly-developed welding technique outperforms the conventional one because of smaller thermal deformation, better concentricity, shorter assembling period, lower fabrication cost, easier welding and higher rate of finished product.