0. Introduction
A magnetron is invented by Dr. Hull (USA) in 1921.
During the Second World War, the development of the pulse magnetron had
been accelerated for the use of a military radar.
After World War a large amount of works on the development and analysis
of a magnetron for other use than a radar or communication had been done.
Raytheon (USA) developed CW (Continuous Wave) magnetron and produced the
prototype of a microwave oven first in the world in 1949.
In 1955 Tappan (USA) started sales of a microwave oven for commercial and
domestic use, and contributed for wide use of a microwave oven.
In Japan Toshiba and Sharp started the production of a microwave oven in 1962.
Mass production of Toshiba magnetron started at Toshiba Horikawacho works.
Toshiba have the longest history for a magnetron production among existing
manufactures.
1. Development Period (1958-1965)
In 1958 Toshiba Research Center developed a microwave oven first in Japan
which supplied to the Defense Agency.
The magnetron 2M20 was developed for this first microwave oven, which refers
to Raytheon magnetron.
In 1960 Toshiba developed 2M21 which was used for a microwave oven installed
in the buffet of Japan Railway.
However still the first step of designing a magnetron was to analyze USA
magnetrons and measure those dimensions by vernier calipers, and production
quantity was several tens to hundreds per month.
