THE EFFECT OF AIR EXPOSURE ON VARIOUS CATHODES FOR DEMOUNTABLE VACUUM SYSTEMS

摘要

Various nickel matrix and tungsten matrix cathodes have been investigated for applications in demountable vacuum systems. Results on emission measurements as the cathodes are repeatedly exposed to air indicate that both the Ni "molded" and Ni 'impregnated" matrix cathodes offer no ad¬vantages over the conventional oxide cathode since they do not exhibit diffusion properties but rather are subject to the same flaking phenomenon of the coating as observed in the oxide cathodes. Furthermore, they have the disadvantage of slightly longer activation times and more complicated fabrication. The two W matrix cathodes (Philips BP-1B and CP-2B) dis¬played true diffusion properties which allowed the emissionlevel to recover after each air exposure. However, both of these cathodes have the disadvantage of lengthy activation time and show a strong susceptibility to self-poisoning if the tube parts cannot be cleaned or baked after each air exposure. It appears that if the flaking problem can be controlled the standard oxide cathode would show most promise as an elec¬tron emitter for demountable vacuum systems and present effort is being placed in that direction.