Travelling-wave Tube

At Birmingham, Kompfner was assigned to work with researchers P.B. Moon and R.R. Nimmo. "I owe a lot to them," he wrote. They taught him physics and electronics, how to experiment and how to set up theoretical models. He learned well.

His task was to further develop the klystron amplifier and improve its noise figure. He followed the received wisdom of how to do this and "spent two years building klystrons along these lines and getting very discouraged with it in the process". "There is nothing like a goodly amount of dissatisfaction and unhappiness to bring on invention," he has remarked.

Outside work, he began to follow a quite different idea to that of the klystron: he would move the field with the electrons. His notebook for the 6th September 1940 records the idea of making the field move at the same velocity as the electrons. He needed to reduce this velocity and, after discussions with colleagues, the idea of using a helix as a transmission line was born. Kompfner then went to see the acknowledged expert on transmission lines at Birmingham. The expert thought it a poor idea but, when Kompfner tried it, he found that it did work. "I was tactful enough not to go back and tell the expert, but I did not consult him again," said Kompfner. "I might remark that there is no harm in getting expert advice. But don't take it."

The story of the invention of the travelling-wave tube is too complex to describe fully here, and Kompfner himself has given a detailed account elsewhere. Ideas changed, blind alleys7 were followed (six months were wasted down one), the helix was abandoned and then returned to and colleagues pointed out mistakes in his theories.

In August, 1943, the group at Birmingham broke up and half the staff were moved to Los Alamos to work on the atom bomb. With others, Kompfner decided to stay in England where he would now be allowed to work officially on his, now well known, homework. Despite setbacks, progress was made. Then in 1944 the group at Birmingham was dispersed and he was moved to the Clarendon Laboratory at Oxford University.

At Oxford, he was visited by Dr John Pierce from Bell Laboratories who had read some of the secret wartime memoranda which described his work. (Incidentally, the first British publication describing the TWT appeared in Wireless World in 1946.) Back in America, Pierce was able to develop the theory of the tube, but it was Kompfner who, virtually single handedly8, conceived the idea and built working travelling-wave tubes. They were the first of a family of devices which came to be used in radar and space communications.

After the war ended, Kompfner became a British subject9 (1947) and in 1951 he received a D.Phil 10, in physics from Oxford. Meanwhile, Pierce had persuaded him to move to Bell Laboratories in the USA. After a long wait for a visa he joined Bell on the 27th December 1951 and continued his research on microwave tubes. In 1955 he became Director of Electronics Research.. By 1962 he was Associate Executive Director of Research and Communication Sciences Division and his influence was felt on research programmes as varied as masers, lasers, superconducting magnets and optical communications. Also, he had taken out American citizenship.

Satellites

In 1958 Kompfner and Pierce became interested in the idea of communication satellites. They wrote a paper exploring the possibilities for such satellites and Rudi's team designed the first one: Echo I. It was launched on the 12th August 1960. Pierce says the work was carried out under Kompfner's "inspiration and direction". Kompfner was also deeply involved with Telstar (1962), the first communications satellite to carry live television across the Atlantic.

Kompfner retired from Bell Labs in July 1973 and thereafter split his time between Stanford University (where he spent the winters) and All Souls College, Oxford (where he enjoyed the summers). At Oxford, his work centred on the use of fine lasers in scanning optical microscopes, whereas at Stanford he turned his attention to acoustical as well as optical microscopes. He left behind him a reputation as a generous and warm-hearted man who readily gave time and sound advice to his students. "No-one ever found him too busy to listen," wrote Pierce. No matter how many projects he had in hand, he always found time to discuss a new one.

Pierce has recounted many anecdotes about Kompfner. At one time Rudi used to conduct seminars for freshmen at his home and in his garage. He and the students suggested projects and one was chosen by vote. One year, he was very disappointed that his own favourite lost by one vote. It was to build a very small swimming pool in which one could swim long distances against a current without moving with respect to the pool. It still sounds like a great idea.

Another of his little inventions was a cat door which would prevent the entry of raccoons11 but still alow the cat in. An abandoned baby raccoon became a pet and he built it a house with an aerial tramway to take it food in winter. There seems to have been a large number of such diversions, including four-legged tables and chairs which would sit evenly on an uneven floor. Another, which Pierce describes as "unqualified success" was a mat or coaster to allow the port and madeira to slide easily along the table.

His short book describing the invention of the travelling-wave tube reveals a good-humoured modesty and the ability to joke and laugh at oneself. In his closing remarks, he stated that if he could live through it all again "I would try not to be so stupid". His mathematics was inadequate, he did not know enough physics, his soldering and glass-blowing were sloppy, he says. “I wanted to get jobs done quickly and therefore did them badly and often had to do them all over again. I found that it pays to take pains12. ”

A professional lesson he learned was not to get side-tracked13; doing so cost him far too much time. Yet on one occasion he resisted being side-tracked and missed discovering ferromagnetic resonance; a colleague followed up the lead14 and made the discovery instead. On two occasions he took expert advice only to be misled into not following through his own convictions. Finally, he remarked, a research worker must have imagination. His travelling-wave tube worked over the entire range of his signal source (60MHz). "That was fine with me," he says. "I should have had more imagination here," he added. "I little realised that I had a device that had a potential of several octaves. Pierce did."

Kompfner's life was not all work, however. As we have seen, he loved swimming and music and he was also a good skier. He met his future wife at a swimming club where he not only swam but played water polo as well. After he suffered a severe heart attack in December 1967, swimming and long walks were part of his recuperation process15. His love of music extended to playing as well as listening. Though he never mastered reading music he could play the piano well enough to accompany orchestral music from a record or the radio.

He was also something of a romantic, loving the ceremonial side of life at Oxford and delighting in having crossed the Atlantic in Concorde. Presumably he also enjoyed the collection of scientific medals and awards and honorary degrees he received. The latter came from both Oxford and Vienna, and the medals flowed from both sides of the Atlantic.

Late in 1977, Rudi suffered another heart attack. He was rushed from his home to Stanford hospital in California. Although he started to make a sustained recovery, it was not to be16 and he died on the 3rd December, 1977. He left a legacy of engineering achievements - and research scientists he had trained to listen to expert advice, but not necessarily take it.

Task I

Explain the words:”The secret of starting is to start. Starting means at least doing something”.

Task II

Tell what made Kompfner write the following “I might remark that there is no harm in getting expert advice. But don’t take it”.

Task III

Prove that Kompfner was really a generous and warm-hearted man.

Task IV

Speak on Kompfner’s scientific interests, researches and his most important invention.

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