History of linacs - page 3

      In 1970 two Russian scientists, I.M. Kapchiski and V.A. Teplyakov, proposed an rf linear accelerator structure with a symmetry corresponding to that of an electric quadrupole. This rf structure, which has become known world-wide as the radio frequency quadrupole (RFQ) linac, is shown schematically in figure 3. The RFQ's electric fields are produced by the rf fields applied to four electrodes that are colinear with the beam axis. By modulation of this pure quadrupole focussing geometry an axial field component can be introduced in the regions between adjacent "hills and valleys" which then causes a dc beam injected into the structure along its axis to be focused, bunched and accelerated simultaneously by the rf fields. This unique rf accelerator structure has the property of the Wideröe linac that particles are only accelerated in every other gap. However, unlike the Wideröe structure, the beam does not get shielded from the field as it changes, but rather the particles drift through a region where the four vanes have the same geometry and where only a focusing field is present when the electric field changes polarity.



      The RFQ concept was experimentally verified by the Russians in 1974, although the results were not published until late 1975. The Western world did not become aware of the Russian invention until the summer of 1977 when, according to S.O. Schriber of the Accelerator Technology Division at Los Alamos, informal discussions were first held between Western scientists and Teplyakov at an accelerator conference in the USSR. A presentation at Los Alamos on October 1977 by J.J. Manca, a Czechoslovakian immigrant to the US, marked the beginning of the intense activity undertaken at the laboratory to understand and utilize the Russian concept. Word of this concept spread among accelerator physicists around the world and by the end of 1978 there were several other groups studying the RFQ structure, particularly in Germany and Japan. Several models of the structure were fabricated at Los Alamos and computer codes were written to study the effects of the perturbed quadrupole electric fields on the ions. These studies produced a concise theoretical description of the structure, which in turn led to the decision in 1979 to construct the proof-of-principle device that was successfully demonstrated at Los Alamos on February 14, 1980. (Valentine's Day—which prompted R. Hamm, who participated on the proof-of-principle work and would later become CEO of AccSys, to some years later quip that the RFQ was "from Russia with love".) Since that first demonstration of the concept in the Western world, the RFQ and the design codes developed at Los Alamos have proliferated, reaching many research laboratories, universities and private enterprises around the world.