The electron synchrotron accelerator was developed between 1944 and 1945 Β.И. Wexler and E M. The principle of particle automatic phase stabilization independently discovered by Macmillan (see synchronous cyclotron) was developed. In 1947, the United States built its first electron synchrotron accelerator, and subsequently various countries built electron synchrotron accelerators with energies ranging from tens to hundreds of megaelectron volts. The electron synchrotron accelerators initially built were all weakly focused. In 1952, the principle of strong focusing was highly valued, and since then, high-energy (energy higher than 1GeV) electron synchronous accelerators have generally adopted the principle of strong focusing.

The electron synchrotron uses C-shaped magnets to form a circular structure, which generates a magnetic field to control the trajectory of electrons. The annular vacuum box is placed in the gaps between each magnet, and is equipped with an accelerating electrode or resonant cavity. The high-frequency power supply generates a fixed frequency high-frequency electric field, which accelerates electrons through the accelerating electrode or resonant cavity. Due to the small static mass of electrons, their motion speed approaches the speed of light when the energy is greater than 2 megaelectron volts. As the energy increases, the speed changes very little. Electrons move in a circular motion within a magnetic field, and their orbital radius and period remain basically unchanged. Therefore, the frequency of the high-frequency power supply can remain unchanged. Usually, linear or high-pressure accelerators are used to accelerate electrons to a certain speed before injecting them into a synchronous accelerator. Large electron synchronous accelerators often use a combination of multiple circular orbits, with each ring connected by a straight track.

In an electron synchrotron, the curvature radius of the electron orbit is given by ε (t) It is the total energy of the electron, Bo (t) is the magnetic induction intensity on the electron orbit, and e is the charge of the electron. From this, it can be seen that in order to maintain a constant electron orbital radius ro, the electron energy ε (t) As time increases, the orbital magnetic induction intensity Bo (t) must increase synchronously. Due to the small static mass of electrons, their velocity approaches the speed of light when the energy is not very high (about 2MeV or above); When the energy increases again, its speed changes very little (the mass increases). Therefore, the period To for these electrons to rotate on a constant orbit remains basically unchanged; In the formula, v is the velocity of the electron, с It's the speed of light. So in an electron synchrotron, the frequency of the high-frequency acceleration electric field does not need to be adjusted, it can be a constant value; As long as the rotational frequency of the electron on the equilibrium orbit is the same or an integer multiple, resonance acceleration can be guaranteed.



In order to make the initial velocity of electrons entering a synchrotron close to the speed of light, induction accelerator start-up or injector mode is generally used. The first method is to set a special magnetic flux bar on the inner magnetic yoke of the track to start, and first work according to the principle of electron induction accelerator; When the electron speed approaches the speed of light, the acceleration method is changed and a high-frequency acceleration voltage is applied to transition it to a synchronous acceleration state. The latter method is to use a high-pressure electron accelerator or a low-energy electron linear accelerator to pre accelerate electrons to a certain energy and inject them into a synchrotron; This method is generally used in high-energy electron synchrotron accelerators.
The working state of an electron synchrotron is pulsed. When the magnetic induction intensity of the orbit reaches its maximum value, the energy of the accelerated electron also reaches its maximum value, and the acceleration process ends. In the future, the magnetic induction intensity of the orbit will decrease, return to the initial value, and then proceed to the next acceleration pulse. Therefore, the ray output is also pulse like, and the repetition rate is determined by the period of magnetic field changes, generally ranging from 10 to 60 pulses per second.

When electrons move in a circular motion, electromagnetic radiation is generated due to the continuous centripetal force acting on them. This electromagnetic radiation is one of the main obstacles to further increasing energy for high-energy synchronous accelerators. However, when the speed of electrons approaches the speed of light, due to relativistic effects, the angular distribution of their radiation is concentrated in the tangent direction of the electron orbit, and they have extremely superior light source characteristics. This phenomenon was discovered in the 1940s on electron synchrotron accelerators, commonly known as synchrotron radiation, abbreviated as synchrotron radiation or synchrotron light.