Almost at the same time, different ideas such as electrostatic accelerator (1928), cyclotron (1929) and voltage multiplier accelerator (1932) were put forward, and a number of acceleration devices were built one after another.
Tai Vatron
A device for artificially generating high-speed charged particles. It is an important tool to explore the essence, internal structure and interaction of nuclei and particles, and also has important and extensive practical applications in industrial and agricultural production, medical and health care, science and technology and other fields.
Since E Rutherford bombarded nitrogen atoms with A rays emitted by natural radioactive elements in 19 19, physicists have realized that in order to understand the nucleus, high-speed particles must be used to transform the nucleus. The particle energy provided by natural radioactivity is limited, only a few trillion electron volts (MeV). Although the particle energy in natural cosmic rays is high, the particle flow is extremely weak. For example, particles with energy of 10 14 electron volts (eV) only come to 1 square meter per hour on average, so it is difficult to carry out research work. Therefore, in order to carry out experimental research with expected goals, people have developed and built various particle accelerators for decades, and their performance is constantly improving. Most new transuranic elements and thousands of synthetic radionuclides have been discovered by particle accelerators. The basic structure of nuclear and its changing rules have been systematically and deeply studied, which has promoted the rapid development and maturity of nuclear physics. With the development of high-energy accelerators, people have discovered hundreds of kinds of particles, including baryons, mesons, leptons and various vibrating particles, and established particle physics. In recent 20 years, the application of accelerators has gone far beyond the fields of nuclear physics and particle physics, and has important applications in materials science, surface physics, molecular biology, photochemistry and other scientific and technological fields. In various fields of industry, agriculture and medicine, accelerators are widely used in isotope production, tumor diagnosis and treatment, radiation disinfection, nondestructive testing, radiation polymerization of polymers, radiation modification of materials, ion implantation, ion beam microanalysis, space radiation simulation, nuclear explosion simulation and so on. Up to now, thousands of particle accelerators have been built around the world, a small part of which are used for basic research of nuclear and particle physics, and continue to develop in the direction of improving energy and beam quality; Most of the rest belong to "small" accelerators that mainly use particle beam technology.
The structure of particle accelerator generally includes three main parts: ① particle source, which is used to provide accelerated particles, including electrons, positrons, protons, antiprotons and heavy ions. ② Vacuum acceleration system, in which there is a certain form of accelerating electric field. In order to accelerate particles without being scattered by air molecules, the whole system is placed in a vacuum chamber with extremely high vacuum degree. (3) Guiding and focusing system, which uses a certain form of electromagnetic field to guide and restrain the accelerated particle beam, so as to accelerate it along a predetermined trajectory under the action of the electric field. All these require the integration and cooperation of high-tech and high-tech technologies.
The efficiency index of accelerator is the energy that particles can reach and the intensity of particle flow (current intensity). According to particle energy, accelerators can be divided into low-energy accelerators (energy less than 108MeV), medium-energy accelerators (energy between 108 and 109mev) and high-energy accelerators (energy between10/kloc-0). At present, low and medium energy accelerators are mainly used in various practical applications.
Cockcroft
1932, American scientist J.D.Cockcroft and Irish scientist E.T.S.Walton built the world's first DC accelerator, named cockcroft-Walton DC High Voltage Accelerator. A proton beam with energy of 0.4MeV was used to bombard the lithium target, and the nuclear reaction experiment of α particles with helium was obtained. This is the first nuclear reaction realized by artificially accelerating particles in history, so it won the Nobel Prize in Physics in 195 1 year.
Irish scientist Walton
Van der Graf
1933, American scientist R.J.van de Graaff invented a high-voltage accelerator named van de Graaff electrostatic accelerator by using another method to generate high voltage. The above two kinds of particle accelerators belong to DC high voltage type, and the energy they can accelerate particles is limited by high voltage breakdown, which is about 10MeV.
Van der Graff experimental device
Lawrence and cyclotron
1924, G. Ising and E. Widlow respectively invented the linear accelerator based on the principle of drift tube and high frequency voltage. Due to the limitation of high frequency technology at that time, this accelerator can only accelerate potassium ions to 50keV, which is of little practical significance. However, inspired by this principle, American experimental physicist E.O. Lawrence built a cyclotron in 1932 and used it to produce artificial radioisotopes, for which he won the 1939 Nobel Prize in physics. This is the first person to win this honor in the history of accelerator development.
Due to the limitation between the mass and energy of the accelerated particles, the cyclotron can only accelerate protons to about 25MeV. The reason is that Newton's law of motion is no longer applicable to the relationship between acceleration and external force, that is, the frequency of high-frequency acceleration electric field and cyclotron frequency no longer match; If the intensity of the accelerator magnetic field is designed to increase synchronously with the particle energy along the radial direction, protons can be accelerated to hundreds of mev, which is called an isochronous cyclotron.
Former Soviet scientist Veksler
In order to further explore the structure of the nucleus and produce new elementary particles, it is necessary to study the principle of building a particle accelerator with higher energy. 1945, Veksler, a scientist from the former Soviet Union, and E.M. McMillan, an American scientist, independently discovered the principle of automatic phase stabilization, and M.L. Oliphant, a British scientist, also suggested to build an accelerator based on this principle.
American scientist Macmillan
The discovery of the principle of automatic phase stabilization is an important revolution in the history of accelerator development, which has produced a series of new accelerators that can break through the energy limitation of cyclotron: synchrocyclotron (the frequency of high-frequency accelerating electric field decreases with the increase of the energy of double accelerating particles, keeping the cyclotron frequency synchronized with the accelerating electric field), modern proton linear accelerator, synchrotron (using a ring magnet whose magnetic field strength increases with the increase of particle energy to maintain the circular trajectory of particle motion, but maintaining the high-frequency frequency of accelerating field unchanged), etc.
Since then, the construction of accelerator has solved the principle limitation, but the improvement of energy has been limited economically. With the increase of energy, the weight and cost of magnets used in cyclotron and synchrocyclotron rise sharply, and the increase of energy is actually limited below 1GeV. Although the cost of the ring magnet of the synchrotron is greatly reduced, the size of the vacuum box must be very large due to the poor transverse focusing force, which leads to a large gap between the poles of the magnet and still requires a heavy magnet. It is still unrealistic to use it to accelerate protons above 10GeV.
1952, American scientists E.D.Courant, M.S.Livingston and H.S.Schneider published papers on the principle of strong focusing. According to this principle, the size of the vacuum box and the cost of the magnet can be greatly reduced, making it possible for the accelerator to develop to higher energy. This is another revolution in the history of accelerator development, with great influence. Since then, the principle of strong focusing has been widely used in ring or linear accelerators.
1954 A weakly focused proton synchrotron with an energy of 6.2GeV was built in Lawrence National Laboratory. The total weight of the magnet is 10000 tons. However, the total weight of the magnet of the 33GeV intense focused proton synchrotron at Brookhaven National Laboratory is only 4,000 tons. This shows the great practical significance of the strong focusing principle.
American scientist Lee Winston
American scientist Koster
The proton ring accelerator is mainly introduced above, but the situation is different for the electron accelerator. 1940, American scientist D.W.Kerst developed the world's first electron induction accelerator. However, due to the energy loss caused by the electromagnetic radiation emitted in the tangential direction when the electron moves along the curve, the energy improvement of the electron induction accelerator is limited, and the limit is about 100MeV. Electron synchrotron uses electromagnetic field to provide acceleration energy, which can allow greater radiation loss, and the limit is about 10GeV. There is no radiation loss when electrons move in a straight line. An electron linac accelerated by electromagnetic field can accelerate electrons to 50GeV, which is not a theoretical limit, but a high-cost limit.
The energy of the accelerator has developed to such a level that new problems have been exposed from the experimental point of view. When using accelerator to carry out high-energy physics experiments, it is generally to bombard the nucleus in a stationary target with accelerated particles, and then study the momentum, direction, charge and quantity of the generated secondary particles, which limits the practical useful energy that the accelerated particles can participate in high-energy reactions. If two accelerated particles collide, the energy of the accelerated particles can be fully used for high-energy reactions or the generation of new particles.
Italian scientist Tousek
1960, Italian scientist B.Touschek proposed this principle for the first time, and built the AdA collider with a diameter of about 1 m in Frascati National Laboratory, Italy, which verified this principle and opened up a new era of accelerator development.
Modern high-energy accelerators are basically in the form of colliders, which have been able to increase the equivalent energy of high-energy reactions from 1TeV to 10 ~ 1000 TEV, which is another fundamental leap in the history of accelerator energy development.