An Early History

Invention of the Klystron

by E. L. Ginzton

I first met Russell Varian in 1939 on a stairway landing in the Stanford University Physics Building. I had just been hired as a part-time research associate on the new Klystron Project at a then munificent $90 per month, and was going upstairs to meet the Varians and their small staff. I had heard of the invention of this new electron tube that could generate centimeter waves, but I did not know how it worked, and indeed I had never even seen one. Thus, when I stopped and introduced myself to Russ, he thought the first order of business ought to be an explanation of the principle of the klystron. I remember his saying something like this:

"Just picture a steady stream of cars from San Francisco to Palo Alto; if the cars left San Francisco at equal increments and at the same velocity, then even at Palo Alto they would be evenly spaced and you could call this a direct flow of cars. But suppose somshared/ehow the speed of some cars as they left San Francisco could be increased a bit, and others could be retarded. Then, with time, the fast cars would tend to catch up with the slow ones and they would bunch into groups. Thus, if the velocity of cars was sufficiently different or the time long enough, the steady stream of cars would be broken and under ideal circumstances would arrive in Palo Alto in clearly defined groups. In the same way, an electron tube can be built in which the control of the electron beam is produced by this principle - bunching - rather than by the direct control of the grid of triode."

This direct and simple explanation was an inspiring introduction to Russ and to the Klystron Project; it was destined to lead me to a lifetime profession, illuminated by close friendships with Russ, Sig Varian, Bill Hansen, and others at Stanford and, later, at Varian Associates, the company we started.

The Klystron Project was not only an important milestone in electronics, but with the benefit of hindsight, it can be seen as practically a textbook demonstration of the validity of some of today's best know axioms about invention and the "management of technology." It demonstrates, for instance, the wisdom of being "coupled to the marketplace," and of identifying societal or market needs rather than merely advancing technology for its own sake. It also illustrates the benefits of working in a creative research community rather than in small groups or in isolation.

The klystron was invented during the summer of 1937 and announced formally to the world on the brink of war by the Varians in the February 1939 issue of the The Journal of Applied Physics.Surrounding the first klystron are: (background, l to r) Sig Varian, Prof. David Webster, Prof. William Hansen, (foreground) Russ Varian, and John Woodyard.

Surrounding the first klystron are: (background, l to r) Sig Varian, Prof. David Webster, Prof. William Hansen, (foreground) Russ Varian, and John Woodyard.

The somewhat diffident announcement was apparently overlooked in Germany -- but not in England. Already deeply involved in the development of radar, scientists at Bristol University recognized that this ingenious new development would help make airborne radar possible by providing a lightweight source of microwaves for radar receivers. By late 1940 - just as the Luftwaffe was switching to deadly night bombing - the RAF succeeded in equipping its night fighters with the klystron radar receivers that would help them win the Battle of Britain.

Surrounding an early klystron are: (l to r) Al Miller, Bob Dunckel, Don Hunceker, Leo Hofmeister, Sam Federico, and Dick Walters.

The klystron turned out to be more than an important wartime development, however. It was destined to play an important part

in developing the new industry that is now generally referred to as microwave. It helped make commercial air navigation safe, it opened the possibility of world-wide communications for satellites, and it led to a variety of high-energy particle accelerators useful in medicine and in nuclear physics. It thus helped spawn a new technology and then a whole new industry. Surrounding an early klystron are: (l to r) Al Miller, Bob Dunckel, Don Hunceker, Leo Hofmeister, Sam Federico, and Dick Walters.

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