Historical notes on the cavity magnetron

Abstract

number.of exciting names; but it was to be a nuclear physics laboratory wi t‘h a 60-in cyclotron and not a microwave laboratory. In fsct there was really no interest in microwaves until the SUI:EImer of 1939. Such new words as klystron, rhumbatron, and velocity modulation arose in papers by Hansen and the Varian Brothers, and these intriguing new concepts wcre discussed at colloquia in the department. This interest would almost certainly have been juw a passing phase had it not also been painfully obvious t‘k at what is now called the second world war was about to br1ea.k out and that all thought of building the cyclotron wol..Id have to be put aside. The most closely guarded secret in England at that tjiine was the fact that a chain of radar stations had been br: ilt along the country’s east and south coasts for the detection of approaching aircraft, and those of us who had Brit. Eih nationality were told of its existence by Oliphant, who Itlad visited one of these secret stations with Cockroft, of .Ihe Cavendish, and with Appleton and Tizard and Wats“~Watt. Moreover, we were invited to spend six weeks of Ihe summer vacation at one of these stations but “would. vve please not tell anyone about it!” Such was security th!m. War did start within a month of joining our radar sttit.ion but during this time we had complete access to all d-~e circuit diagrams and were even allowed to switch off to make minor modifications, which of course always m.de its performance worse. But now we were all interested in the possibility of producing microwaves. We had seen how very large pon c:rs at 10-m wavelength could be produced by pulsed operation of relatively small tubes, and the prospect of doing thii3 at microwave frequencies for airborne and shipborne use was most exciting, but apparently impossible. So we all returned to Birmingham to try.