File:The Bell System technical journal (1922) (14570073469).jpg

Identifier: bellsystemtechni25amerrich (find matches)
Title: The Bell System technical journal
Year: 1922 (1920s)
Authors: American Telephone and Telegraph Company
Subjects: Telecommunication Electric engineering Communication Electronics Science Technology
Publisher: (Short Hills, N.J., etc., American Telephone and Telegraph Co.)
Contributing Library: Prelinger Library
Digitizing Sponsor: Internet Archive

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ed (approximately 30 amps./cm.-) the activecoating was rapidly lost as a result of arcs, and frequently the nickel supportitself was fused and vaporized. The problem of arcing to the cathode surface in small magnetrons wassoon recognized as the most important cathode problem. It preventedsteady operation and hastened destruction of the cathode surface and theend of useful magnetron life. All of these cathodes were found to requirean initial break-in period during which the arcing is particularly violent.As the input voltage and current are gradually increased, the violentarcing gradually subsides. The tendency to arc at any time subsequent tothis initial period depends on the nature of the cathode surface, but beyondthat, it depends also on the operating conditions to which the magnetronis subjected. Increase in power input, either as increased voltage or current,or both, rapidly increases the frequency of arcs. Similarly, increased pulse MAGNETRON AS GENERATOR OF CENTIMETER WAVES 343
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344 BELL SYSTEM TECHNICAL JOURNAL length makes the arcing much worse; in the 725A for example, changingthe pulse length from 1 /xs to 2 /zs may increase the arcing rate by a factorof 10 to 20. A decrease in recurrence rates with some types of cathodesalso causes a noticeable increase in the rate of arcing. In the great majority of cases, magnetron cathodes have employed coat-ings of the ordinar)^ strontium and barium carbonates as the source ofprimary and secondary electrons. All-metal, secondary emitting cathodeswith primary emitting, starter cathodes have been tried in some labora-tories with some success but have not yet come into general use. The effortsat the Bell Laboratories have been directed toward developing and im-proving the oxide coated cathode along lines making it more nearly possibleto satisfy requirements (3), (4), (5), and (6) listed in Section 10.7 Magne-tron Cathodes of PART I without impairing the ability to meet require-ments (1) and (2). Most of the cathode deve

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