John Paul Blewett, a key figure in the development of particle accelerators, died of acute pancreatitis in Chapel Hill, North Carolina, on 7 April 2000.
Blewett was born in Toronto on 12 April 1910. He earned his bachelor’s (1932) and master’s (1933) degrees in physics at the University of Toronto and his PhD in physics from Princeton University in 1936. After receiving his doctorate, he spent a year at the Cavendish Laboratory in Cambridge, England, working under Ernest Rutherford, Mark Oliphant, and others on range–energy relations for alpha particles, among other projects.
From 1937 to 1946, Blewett worked in the research laboratory of the General Electric Co in Schenectady, New York. During that period, Donald Kerst built a 20-MeV betatron at GE in 1941, and, in 1945, Ernest Charlton and William Westendorp built a record-breaking 100-MeV betatron at GE, achieving by far the highest particle energy in the world. About the same time, Blewett came across a paper by Russian physicists Dimitri Iwanenko and Isaak Ya. Pomeranchuk, in which they pointed out that high-energy electron beams circulating in a betatron would lose some energy by radiation. After performing some calculations, Blewett concluded that the radiation would indeed be significant and would make it difficult to build machines for higher energy. He predicted that the radiation would cause the orbit of the new betatron to shrink—and indeed it was found to shrink by precisely the amount Blewett had calculated. This was the first observation of what is now known as synchrotron radiation.
Next, following a visit by Edwin McMillan from the Radiation Laboratory at the University of California, Berkeley, in 1945, Blewett and colleagues decided to use McMillan’s new synchrotron idea to build what they hoped would be the first operating synchrotron—a 70-MeV machine—before McMillan himself could finish his 300-MeV synchrotron. Blewett and colleagues’ synchrotron was finished by 1947; however, the honor of being the first to demonstrate the principle had gone to Frank Goward and D. E. Barnes in England, who had converted a small betatron to synchrotron operation. The new machine, unlike the 100-MeV betatron, had a transparent vacuum chamber, and the radiation turned out to be visible.
Blewett missed the first visual observation of the synchrotron in 1947 because he had left GE. He and Hildred Blewett, an accelerator physicist who was his wife at the time, joined the new Brookhaven National Laboratory on Long Island. Unfortunately, when they arrived at BNL, the security authorities of the US Atomic Energy Commission barred them from going to work. Apparently, a friend of Blewett’s from earlier days had been arrested in Canada and charged with transmitting secret information to the USSR (a charge that was later dismissed). That association made Blewett and Hildred “security risks,” and they had to cool their heels for six months before obtaining the necessary clearance to join the BNL staff.
Blewett’s first major project at BNL was to participate in the design and construction of a new particle accelerator that aimed to extend the energy of available accelerated particles not just incrementally, but by a leap of an order of magnitude to 3 GeV (three billion electron volts). This proton synchrotron was called the Cosmotron because it got into the energy range of cosmic rays. Blewett took charge of the design and construction of the magnet and the radio-frequency accelerating system. He devised the structure of the Cosmotron’s relatively compact C-section magnet. A major problem with the acceleration system was that, with a reasonable injection energy, the frequency would have to increase by a factor of 10 during the acceleration cycle, a range much larger than could be easily handled by devices such as mechanically-varying capacitors. Blewett decided to use ferrite—then a new material—in the accelerating cavities; this was a far more elegant and efficient solution to the modulation problem.
In 1952, the Cosmotron came into operation as the world’s first billion-volt machine. A group of BNL physicists, with Blewett at the forefront, then came up with the alternating-gradient or “strong-focusing” method, which promised to make it possible for accelerators to go up at least into the 30-GeV range. Blewett saw that this technique would also solve a serious dilemma in the design of proton linear accelerators, in which the acceleration process was inherently defocusing, and focusing had previously been achieved only by the inelegant method of having grids intrude into the aperture, inevitably killing a large part of the beam while it was being accelerated. Replacing the grids with quadrupoles was a huge improvement.
When the new European high-energy physics laboratory, CERN, was proposed in 1952, a group of physicists from several European countries visited BNL and inquired about the possibility of building a machine like the Cosmotron, only a bit bigger. Learning of the ideas that had just come up at BNL, the European physicists decided to build a strong-focusing synchrotron of 25–30 GeV in Europe. This group invited Blewett and Hildred to join them to help with the new laboratory. Because CERN was split among working groups in several European locations, pending a move to Geneva where the lab was to be established, Blewett and Hildred went to Bergen, Norway, to join in the effort to create CERN’s centerpiece: the proton synchrotron. They contributed to the initial design and pushed to have everything moved to Geneva, where construction for the lab began at the end of 1953.
At BNL in early 1954, the Alternating Gradient Synchrotron was approved for construction. Ken Green was in charge and Blewett was the deputy. In 1960, a 33-GeV proton beam was attained, setting yet another world record for energy. This achievement was the impetus for a study on how far one could go toward even higher energies. Blewett and Luke Yuan joined in an intensive study of the possibilities of proton synchrotrons up to 1000 GeV. That study led to the proposal for ISABELLE, a proton collider of 200–400 GeV at BNL, which was started, then abandoned, and finally reincarnated in the form of the Relativistic Heavy Ion Collider.
In 1962, Blewett, together with Stanley Livingston of MIT, published Particle Accelerators (McGraw-Hill, 1962), which summarized the development in the field up to that time. In 1970, Blewett founded the journal Particle Accelerators , for which he was the first editor.
Blewett continued as deputy chairman of the accelerator department until 1973. He then worked as a special assistant to the director until 1978, when he retired. During his “retirement,” he returned to an early interest—synchrotron radiation. He took part in initiating the proposal to build the National Synchrotron Light Source at BNL, the first machine built explicitly for the purpose of producing synchrotron radiation as a tool for studies in condensed matter physics, chemistry, biology, and engineering. He also was a consultant to the Synchrotron Radiation Research Center in Taiwan. In 1993, Blewett was awarded the Robert R. Wilson Prize by the American Physical Society.
Blewett enjoyed sailing and gardening with his second wife of 17 years, Joan Warnow-Blewett, who recently retired as the associate director of the History Center at the American Institute of Physics.
