75 Years of Particle Accelerators Andrew M. Sessler Lawrence Berkeley National Laboratory Berkeley, CA 94720 Accelerators started with some theoretical work in the early 1920s, with the first accelerator producing nuclear reaction in 1931. Thus it is exactly 75 years of history we shall be reviewing.
Motivation The first motivation was from Ernest Rutherford who desired to produce nuclear reactions with accelerated nucleons. For many decades the motivation was to get to ever higher beam energies. At the same time, and especially when colliding beams became important, there was a desire to get to ever higher beam current. In the last three decades there has been motivation from the many applications of accelerators, such as producing X-ray beams, medical needs, ion implantation, spallation sources, and on and on.
Table of Contents I. Electrostatic Machines II. Cyclotrons III. Linacs IV. Betatrons Synchrotrons Colliders VII. Synchrotron Radiation Sources VIII. Cancer Therapy Machines IX. The Future X. Concluding Remarks
I. Electrostatic Accelerators • I.1 Voltage Multiplying Columns and Moving Belts • I.2 Tandems
I.1 Voltage Multiplying Columns The first accelerator that produced a nuclear reaction was the voltage multiplying column that Cockcroft and Walton built from 1930 to 1932. A small voltage was applied to condensers in parallel, and then by a spark gap, they were fired in series and produced a large voltage. At about the same time Van de Graaff developed moving belts that turned mechanical energy into electrostatic energy.
The original Cockcroft-Walton installation at the Cavendish Laboratory in Cambridge. Walton is sitting in the observation cubicle (experimental area) immediately below the acceleration tube.
The Cockcroft-Walton pre-accelerator, built in the late 1960s, at the National Accelerator Laboratory in Batavia, Illinois.
Van de Graaff's very large accelerator built at MIT's Round HillExperiment Station in the early 1930s.
Under normal operation, because the electrodes were very smooth and almost perfect spheres, Van de Graaff generators did not normally spark. However, the installation at Round Hill was in an open-air hanger, frequented by pigeons, and here we see the effect of pigeon droppings.
I.3 Tandems It was soon appreciate that a negative ion (say H-) could be accelerated by a positive electrostatic column, stripped of its electron (to say H+) and accelerated again so that one obtained twice the energy that previously had been obtained. These “swindletrons”, so-named by Luis Alvarez, later called tandems, are now in common use and, generally, are commercially made.
A tandem accelerator at ORNL, built by the National Electrostatics Corporation. The high-voltage generator, is located inside a 100-ft-high, 33-ft-diameter pressure vessel.
II. Cyclotrons • II.1 Lawrence and the Early Cyclotrons • II.2 Transverse Focusing and Phase Focusing • II.3 Calutrons • II.4 FFAG and Spiral Sector Cyclotrons
Major Nuclear Advances of the 1930s (My opinion) Accelerator produced nuclear reactions, Cockcroft and Walton, England, (1932), Nobel Prize 1951 2. Accelerator produced radioactivity, F. Joliot and Irene Joliot-Curie, France, Nobel Prize 1935 3. Slow neutron reactions, Fermi, Italy, Nobel Prize 1938 4. Nuclear fission, Otto Hahn, (1939), Germany, Nobel Prize 1944 (today Strassmann would be included; and a separate prize given to Lise Meitner and Otto Frisch) None of these advances were in Berkeley. Unfortunately, there was too much focus on machine development. However, for just that, Lawrence received the Nobel Prize in 1939 (today, Stan Livingston would be included).
The First Cyclotron Five inches in diameter.
The Original Rad Lab Located on the Campus near Le Conte Hall .
II.1 Lawrence and the Early Cyclotrons As we all know, Lawrence invented and made a succession of cyclotrons. Perhaps his greatest contribution was, however, the creation of a laboratory where physicists, engineers, biologist worked together to achieve far more that any one discipline could accomplish. Cyclotrons are still built for nuclear physics and medical purposes, but not for high-energy physics reasons.
A picture of the 11-inch cyclotron built by Lawrence and his graduate students, David Sloan and M. Stanley Livingston, during 1931.
The 60 Inch Cyclotron Donald Cooksey and E.O. Lawrence
II.2 Transverse Focusing and Phase Focusing The transverse focusing of particles was developed, by Stan Livingston and was crucial in making the very first cyclotron work. (He also realized how to remove the accelerating field foils and thus increase cyclotron intensity by orders of magnitude.) Longitudinal, or phase focusing was developed in 1944, independently by Ed McMillan and Vladimir Veksler. The concept made the 184-inch work, and has been used in essentially all accelerators since that time.
II.3 Calutrons The concept of electromagnetic separation of the isotopes of uranium, U238 and U235, only the later, which is only 1/2% of natural uranium, being fissionable, was developed by E.O.Lawrence. A first demonstration was made on the not-yet-completed 184’’, and soon Oak Ridge with 1000 calutrons was established. Although all the material for the Hiroshima bomb was electromagnetically separated, that method has not been used since WWII and, as we all know, centrifuges are now the method of choice.
II.4 FFAG In the early 1950’s, just after the development of strong focusing (described in the next section), it was realized by the Midwestern Research Group (MURA), that it was possible to have many configurations of an accelerator, and some of these configurations were advantageous for various purposes. In particular they developed the concept of fixed field (fixed in time) alternating gradient (FFAG) accelerators. Spiral ridge cyclotrons have been extensively employed for nuclear physics studies (88”) and, today, various other applications of FFAG are being considered.
The “Mark 2”. A spiral sector FFAG built by the MURA Group in Wisconsin from 1956 to 1959.
TRIUMF, the world's largest cyclotron at Canada's National Laboratory for Particle and Nuclear Physics. (520 MeV). The machine started in 1974 and is still in operation (now for rare isotope acceleration).
III. Linear Accelerators • III.1 Proton and Heavy Ion Linacs • III.2 Induction Linacs • III.3 Electron Linacs
III.1 Proton and Heavy Ion Linacs Luis Alvarez was the first one to maker a linear accelerator that only involved a single frequency. In the 60’s radio frequency RFQs were invented in the Soviet Union by V. A. Teplyakov, with actual construction pioneered by a group at Los Alamos
The Materials Testing Accelerator (MTA), built, in the early 1950s, at a site that would later become the Lawrence Livermore Laboratory. The purpose of the machine was to produce nuclear material, but it never produced any (due to uncontrollable sparking).
The inside of a Radio Frequency Quadrupole. The RFQ has replaced the very large Cockroft-Waltons as injectors in to synchrotrons.
III.2 Induction Linacs First invented, at Livermore, for magnetic confined fusion. Used for the Electron Ring Accelerator at LBL.Then used to study nuclear weapon implosions at LLNL and LANL. And, also, the basis of LBL work on heavy ion fusion (but that program has been terminated by the US Government).
The world’s first induction accelerator, Astron, built at the Lawrence LivermoreLaboratory in the late 1950s and early 1960s by Nick Christofilos.
The induction accelerator, FXR, built, at Lawrence Livermore, in order to study the behavior of the implosion process in nuclear weapons.The facility was completed in 1982.
The Dual Axis Radiological Hydrodynamic Test Facility (DARHT) at the Los Alamos National Laboratory, New Mexico. This device is devoted to examining nuclear weapons from two axes rather than just one. This reveals departures from cylindrical symmetry which is a sign of aging which can seriously affect performance.
III.3 Electron Linacs The high powered klysron was invented, during WWII, by The Varian Brothers and Ed Ginzton. Using it, Bill Hansen invented the electron linac. A succession of machines at Stanford culminated in the two-mile accelerator, SLAC, led by WKH Panofsky. That machine made many important high-energy physics discoveries and then became the injector for PEP and PEP II, and now has become the LCLS.
IV. Betatrons Very few betatrons are built these days, but at the time, around the 1940’s, they were very important for they provided the only way to accelerate electrons to higher energies than could be obtained with electrostatic machines. Many physicists had tried to make circular electrons accelerators, but they all failed until Don Kerst was able to make a betatron by careful attention to the details of particle orbit dynamics. One of his early machines was used at Los Alamos during WWII.
One of the first betatrons, built in the early 1940s. The so-called 20 inch machine at the University of Illinois.
A picture of the 100 MeV betatron (completed in the early 1940s) at the G.E. Research Laboratory in Schenectady after Kerst had returned to the University of Illinois.
A modern, very compact betatron, commercially produced. It is used to produce x-rays to look for defects in large forgings, steel beams, ship’s hulls, pressure vessels, engine blocks, bridges, etc.
V. Synchrotrons • V.1 First Synchrotrons • V.2 Strong Focusing Made possible by the synchrotron (RF) concept, the concept of strong focusing, and the concept of cascading synchrotrons. First proposed, even prior to the invention of strong focusing, by the Australian, Macus Oliphant. They were first built after WWII and all modern accelerators are based upon the synchrotron principle.
Late in World War II the Woolwich Arsenal Research Laboratory in the UK had bought a betatron to "X-ray" unexploded bombs in the streets of London. Frank Goward converted the betatron into the first “proof of principal” synchrotron.
This 300 MeV electron synchroton at the General Electric Co. at Schenectady, built in the late 1940s. The photograph shows a beam of synchrotron radiation emerging.
Although the first Proton Synchrotron to be planned, this 1 GeV machine at Birmingham University, achieved its design goal only in 1953.
The 3 GeV Cosmotron was the first proton synchrotron to be brought into operation.
Overview of the Berkeley Bevatron during its construction in the early 1950s. One can just see the man on the left.
V.2 Strong Focusing The invention of strong focusing, in the early 1950’s, by Ernie Courant, Hartland Snyder and Stan Livingston, revolutionized accelerator design in that it allowed small apertures (unlike the Bevatron whose aperture was large enough to contain a jeep, with its windshield down). The concept was independently discovered by Nick Christofilos.