This accelerator applies a high DC voltage to a pair or a series of accelerating electrodes connected in series. When charged particles pass through the gap between electrodes, they are accelerated by a high-voltage electric field and gain energy equivalent to this voltage. According to the different forms of DC high-voltage power supply, this accelerator can be divided into voltage doubling circuit accelerator and static accelerator.

There are two types of electron accelerators.

Voltage doubler circuit accelerator includes high voltage doubler (also called series voltage doubler rectifier or cockcroft-Wharton generator), Dina accelerator (also called parallel excitation high frequency high voltage generator), Max pulse voltage doubler, insulated core transformer, etc. These devices are suitable for generating high voltage of tens of kilovolts to several megavolts and can provide high beam power. The voltage of most high-voltage voltage doublers is between 100 ~ 600 kV, and they are mainly used as neutron generators for (d, d) or (d, t) reactions and ion implanters for developing semiconductor devices. "Dina Nano" and insulated core transformers with voltage of 1 ~ 4 MV are mainly used to accelerate high-power electron beams (tens of milliamps) for irradiation processing. Marx pulse voltage doubler is used to generate pulsed electron beam with intensity of tens of kiloamperes. Electrostatic accelerator particle accelerator

Van der Graf accelerator, also known as Van der Graf accelerator, continuously delivers charges to hollow metal electrodes through transmission belts or chains, charging them to a high voltage to accelerate particles. The whole accelerator is installed in a closed high-pressure container. The typical working voltage is 2 ~ 10 mV, and the accelerated particle flow can reach tens to hundreds of microamperes. Most ion electrostatic accelerators are used for neutron reaction cross section measurement, ion beam microscopic analysis and atomic and molecular physics research, while electron electrostatic accelerators are used for irradiation processing, disinfection and so on. In recent years, a number of small tandem accelerators with voltage of 1 ~ 2 mv have been produced, which are widely used in trace analysis of elements.

The common feature of DC high voltage accelerator is that it can accelerate any kind of charged particles, and the energy can be adjusted smoothly. However, the energy DC of this accelerator is limited by the breakdown voltage of the material and cannot be too high. In order to accelerate particles to higher energy, electromagnetic induction and resonance accelerators have been developed.

rheotron

Tai Vatron

The eddy current electric field induced by alternating magnetic field is used to accelerate the acceleration of charged particles, including common electron induction accelerators and ion linear induction accelerators under development. The former uses a specially distributed axisymmetric alternating magnetic field to guide electrons to rotate along a circular orbit with a constant radius. At the same time, the eddy electric field induced by this magnetic field accelerates electrons to high energy. The energy of a typical electron induction accelerator is about 25 MeV. In the process of acceleration, electrons have to rotate more than one million times.

The current intensity of the electron induction accelerator is relatively low, usually less than 0.5 μ a. The bremsstrahlung generated is about 1m 10 ~ 1gy/min from the target. It is mainly used for nondestructive testing of metal components and radiotherapy of tumors. An electron induction accelerator with an energy of 300 MeV was built in the University of Illinois. Because circular orbit induction accelerator is not suitable for accelerating ions, linear induction accelerator has been proposed in recent years, which is planned to accelerate the heavy ion current of 10 kA, and it is still in the development stage.

Linear resonance accelerator

An accelerator in which particles are accelerated along a linear orbit under the action of a high-frequency electric field. In order to accelerate the particles to the final energy in a short distance, the amplitude of the high-frequency electric field is usually1~10 mv/m. Therefore, it is necessary to use a high-power high-frequency microwave power supply to excite the acceleration cavity. This kind of power supply usually only works in pulse state. The main advantage of accelerator is that the beam intensity of accelerating particles is high, and its energy can be increased step by step without restriction. Disadvantages are high power consumption and large equipment investment during high frequency operation. In recent years, various low-temperature superconducting linear acceleration structures have been developed. Superconducting linear accelerator (see superconducting accelerator) can reduce the operating cost by 3 ~ 5 times, and in principle, it can provide particle clusters continuously.

Cyclotron resonance accelerator

Tai Vatron

An arc orbit accelerator using high frequency electric field to accelerate particles. The particles in this accelerator whirl under the control of the guided magnetic field, and are repeatedly accelerated through the accelerating electric field region until they reach the rated energy. Cyclotron resonance accelerators can be divided into two categories. In the first category, the magnetic field does not change with time, and the radius of curvature of accelerated particles increases with the increase of energy. Classical cyclotron, fan-shaped focusing cyclotron, synchrocyclotron and electron cyclotron all belong to this category. In another type, the intensity of the guiding magnetic field increases synchronously with the momentum of the particles, but the radius of curvature of the particles remains unchanged. Such as electron synchrotron and proton synchrotron belong to this category. All the accelerators mentioned above, except the fan-shaped focusing cyclotron, have the phenomenon of automatic phase stabilization.

Cyclotron particle accelerator

The classic cyclotron has a magnet that generates a uniform magnetic field and a pair of hollow D-shaped high-frequency electrodes. A high-frequency accelerating electric field with a fixed frequency is applied between the electrodes. When the particle energy is low, its cyclotron frequency resonates with the high-frequency electric field, and they accelerate every half turn. When the energy is high, the rotation frequency of particles will be lower and lower than the frequency of electric field with the increase of energy, which will eventually lead to the inability of electric field to accelerate. Therefore, the highest energy of protons in the classical cyclotron is only about 20 mev. In order to overcome this difficulty, the magnetic field can be gradually increased along the radius direction to keep the rotation period of particles unchanged. However, the magnetic field that simply increases along the radius will cause the particle beam to defocus in the axial direction, so it cannot be applied.

synchrocyclotron

A cyclotron in which the magnetic field is accelerating and the frequency of the electric field decreases synchronously with the particle rotation frequency is also called a frequency-modulated cyclotron or a phase-stabilized accelerator. According to the principle of automatic phase stabilization, protons can be accelerated to infinitely high energy in principle by using this acceleration method. However, the largest synchrocyclotron energy in history only reaches 700MeV. This is because its magnet weighs 7000 tons, which exceeds the weight of ordinary high-energy accelerator magnets. Economically and technically, it is not suitable to build a FM accelerator with higher energy. Because the frequency of electric field must change with time, synchrocyclotron can only work in pulse state. The pulse repetition frequency is about 30 ~ 100 Hz. The average current intensity is a few microamperes, which is one or two orders of magnitude smaller than the fan-shaped focusing cyclotron with the same energy. For this reason, a considerable number of synchrocyclotron were closed and some were converted into synchrocyclotron.

Electron cyclotron

Also known as microwave cyclotron, it is specially used to accelerate electrons. Like the classical cyclotron, the magnetic field of the accelerator is uniform and the frequency of the accelerating electric field is constant. The difference is that the acceleration gap is located at one end of the magnetic pole, and the orbit of the electron is a series of circles tangent to the center line of the acceleration gap. After each acceleration, the rotation period of electrons increases to an integer multiple before acceleration, so whenever these electrons turn back to the acceleration gap, the electric field just accelerates them again. The energy of most electron accelerators is between 10 ~ 30 MeV, and the current intensity is between 30 ~120 μ a. Most of them are used for medical treatment and dose standards.

Synchrotron particle accelerator

A cyclotron that accelerates high-energy particles. It has a big ring magnet. Under the guidance and control of the annular magnetic field, charged particles gyrate along a circular or nearly circular orbit with a fixed radius, and gain energy through some high-frequency accelerating cavities arranged along the way. In the process of acceleration, the magnetic field increases with time, keeping the orbital radius of particles unchanged. The frequency of the high-frequency electric field changes synchronously with the magnetic field to maintain resonance with the cyclotron motion of particles. Because the electric field and magnetic field change with the time period, the accelerator works in the pulse state. In order to accelerate the particle beam confined in a narrow vacuum chamber, sufficient focusing force is needed. In the early stage, the constant gradient magnetic field with small gradient value is used for focusing. Because of the weak focusing force, the acceleration chamber and the whole accelerator have to be made quite large, which limits the energy development of synchrotron above 10GeV economically and technically. Later, the strong focusing mode of alternating gradient was invented, and the effective focusing force greatly exceeded the former, which greatly reduced the volume of the acceleration chamber. For example, the weight of a strongly focused 30GeV proton synchrotron magnet is about 4000 tons, but if constant gradient focusing is adopted, the weight is 100000 tons.

Electron synchrotron particle accelerator

Electron cyclotron or linear accelerator is usually used as injector to pre-accelerate electrons to near the speed of light, and then inject synchrotron to further accelerate to the rated energy. Small electron synchrotron usually does not need an injector. It starts in the state of electron induction accelerator. When the electrons are pre-accelerated to near the speed of light, the high-frequency acceleration cavity is started to accelerate the particles synchronously. The cyclotron frequency of electrons rotating near the speed of light does not change with energy, so the electron synchrotron uses a constant-frequency accelerating electric field. A typical electron synchrotron has an energy of 0.3~8 GeV, a current intensity of 10pps (particles per second) and a beam pulse repetition frequency of 10 ~ 60 Hz.

Electromagnetic radiation emitted by high-speed electrons moving in circular orbit is an important factor limiting the energy increase of electron synchrotron. When the electron energy reaches 10 GeV, it radiates 10 MeV per revolution. However, this kind of synchrotron radiation has a series of special advantages: it emits a controllable continuous spectrum from infrared to X-ray, and the radiation is polarized, with high intensity and strong directivity, which has high practical value. It has been widely used in solid state physics, molecular biology, integrated circuit development and other fields.

Proton synchrotron particle accelerator

Usually, high voltage multiplier and proton linear accelerator are used as injectors to pre-accelerate protons to 20 ~ 200 MeV, and then inject them into the annular orbit of synchrotron for acceleration. Large synchrotron usually adds a smaller fast pulse synchrotron as an intermediate stage (also called "intensifier") after the injector to accelerate protons to about 10 GeV, thus increasing the current intensity of accelerated particles. In the process of acceleration, the velocity of protons changes in a considerable range, and the frequency of electric field must be modulated in a considerable range accordingly, and it needs to be accurately controlled to synchronize with the rise of magnetic field. Therefore, a pick-up plate is often set around the beam orbit to monitor the movement of protons and use this signal to automatically correct the frequency modulation process of high-frequency electric field. The main magnet of the old high-focus synchrotron adopts the scheme of "compound action", that is, each magnetic segment has two functions of deflection guidance and focusing. The orbital magnetic field of this magnet should not be too high, only about 1.4T, so the iron consumption is high. The new giant synchrotron adopts the "separation effect" scheme, that is, the steering and focusing are borne by two-pole magnets, such as quadrupole lenses. In this way, the field strength on the track can be increased to 2T, which greatly saves the iron consumption.

Up to now, there are more than a dozen proton synchrotrons built in the world, 9 of which were built in the 1960s, and the largest one is the 1000GeV accelerator of Fermi National Accelerator Laboratory in the United States.

Heavy ion synchrotron

Its structure is the same as that of proton synchrotron. However, the speed range of heavy ions in the acceleration process is much larger than that of protons, so the frequency of high-frequency electric field needs to be modulated in a larger range. On the other hand, due to the long acceleration distance of heavy ions and the large charge exchange cross section with the surrounding gas molecules, the air pressure in the acceleration chamber is required to be as low as10torr (1torr =133.322pa). The Beva Lake Accelerator of Lawrence Laboratory in Berkeley, USA, was the first to accelerate high-energy heavy ions by synchronous acceleration. At present, many heavy ions, such as N, Ne, Ar and Fe, can be accelerated to more than 2GeV per core. The flow intensity reaches 10 ~ 10 PPS.

Storage ring and collider particle accelerator

This is an ultra-high energy experimental device developed on the basis of synchrotron. In the past, people always used relativistic particles to bombard stationary targets for particle physics experiments. However, in this mode of action, only a small part of the energy in the centroid system can be used to produce new particles or various meaningful reactions. If the mode of action is changed, two high-energy particle beams moving in opposite directions collide with each other, and the effective action energy will be much higher than the former mode.

The advantage of the collider is that it can carry out ultra-high energy experiments with ordinary high energy accelerators, and the cost is low. However, it can only realize the collision between stable particles, and can't produce various secondary particle beams like ordinary accelerators. Therefore, it cannot replace the ultra-high energy accelerator. For this reason, at present, all high-energy physics centers tend to develop accelerator-collider complexes, which can not only collide with various particles, but also experiment with stationary targets.

Laser particle accelerator

American scientist TomasPlettner reported in the recently published Physical Review Letters that together with his colleagues from Stanford University and Stanford Linear Accelerator Center (SLAC), he used a commercial laser with a wavelength of 800 nm to adjust the energy of electrons running in vacuum, and obtained the same modulation effect as that of an electric field, with a decrease of 40 million volts per meter. This technology is expected to develop into a new type of laser particle accelerator, accelerating particles to the order of Tev (trillion electron volts).