Vii. Tube Research and Development

The ceramic-insulated cathode leads have been subjected to cyclic heating to a maximum temperature in excess of 7000C. Two such tests have been made, the metal-ceramic seal failing on the first lead, while a coppermolybdenum soldered joint failed on the second lead after six cycles. The design of the cathode lead has been changed to eliminAte this joint. Some experiments have been performed with butt-type metal-ceramic seals with inconsistent results. On the unsuccessful seals, the ceramic broke apart about 1/16 in. above the metal-ceramic soldered joint. Most of these seals either were broken when removed from the vacuum furnace or broke shortly afterwards even under gentle treatment. The successful seals of the same type and made by the same process were vacuum-tight and withstood much rougher treatment than they would undergo in normal use. Calculations of the stresses in the ceramic have been made and the deductions based on this information are being used in future metal-ceramic seals. The fact that the power output of our successful high-power magnetrons has apparently been limited by arcing in the pressurized testing tank has led to an investigation of its possible causes. An examination of the ceramic window on MF-6, our last operating tube, showed considerable evidence of arcing across the face of the ceramic. As a result the question of the design of ceramic windows is being investigated more closely. The design criteria and method of assembly of a more satisfactory window have been determined. The new type window will be made in the near future and then subjected to hydraulic pressure in a destruction test.