Cyclotron Accelerators

回旋加速器

The cyclotron principle involves using an electric field to accelerate charged particles across a gap between two "D-shaped" magnetic field regions. The magnetic field accelerates the particles in a semicircle, during which time the electric field is reversed in polarity to accelerate the charge particle again as it moves across the gap in the opposite direction. In this way a moderate electric field can accelerate charges to a high energy. This overcame the difficulty of electric discharge caused by the high DC voltages in the Cockroft-Walton and van de Graaf accelerators.

回旋加速器的原理是利用电场使带电粒子在两个‘D形’磁场区域之间的间隙中加速。磁场使粒子在半圆路径中加速，在此过程中电场的极性被反转，以再次加速粒子在相反方向穿过间隙。这样，一个中等强度的电场就可以将电荷加速到高能级。这克服了 Cockroft-Walton 和 van de Graaf 加速器中高直流电压引起的电弧问题。

In 1930, Earnest O. Lawrence operated the first successful cyclotron, accelerating protons with a radio frequency (RF) voltage applied across the gap between the two "Dee" magnetic field regions. The first model was only 10 cm in diameter. A larger unit built with the assistance of M. Stanley Livingston was about 25 cm in diameter and accelerated protons to about 1 MeV of energy.

1930年，Earnest O. Lawrence操作了第一个成功的回旋加速器，利用无线电频率（RF）电压在两个“Dee”磁场区域之间的间隙中加速质子。第一个型号的直径仅为10厘米。在M. Stanley Livingston协助下建造的更大型号直径约为25厘米，能够将质子加速到约1 MeV的能量。

The upper bound on energy obtainable from the cyclotron is set by relativistic effects. Since the cyclotron frequency of the RF accelerating voltage depends upon the particle mass, the effects of relativistic mass cause the particle to get progressively more out of step with the accelerating voltage as its speed increases. This problem is addressed in the synchrocyclotron by varying the frequency of the accelerating voltage to track the relativistic effects.

回旋加速器所能获得的能量上限由相对论效应决定。由于RF加速电压的回旋频率取决于粒子的质量，相对论质量效应会使粒子逐渐与加速电压失去同步。这个问题通过回旋加速器通过改变加速电压的频率来跟踪相对论效应而得到解决。

Synchrocyclotron

同步回旋加速器

Since the cyclotron frequency depends upon the relativistic energy of the particles being accelerated, the cyclotron with its fixed-frequency accelerating voltage gets progressivley out of synchronization with the motion of the particles as they reach relativistic speed. In 1945 the technology was developed to vary the frequency of the accelerating voltage to track the change in relativistic energy of the particles. This device is called a synchrocyclotron and has been used to accelerate particles to around 700 MeV of energy. That is about 100 times the energy obtainable from natural radioactivity.

由于回旋加速器的频率取决于被加速粒子的相对论能量，因此当粒子达到相对论速度时，回旋加速器的固定频率加速电压逐渐无法与粒子的运动保持同步。1945年，技术被开发出来以改变加速电压的频率，以跟踪粒子相对论能量的变化。这种装置称为回旋加速器，已被用来将粒子加速到约700 MeV的能量。这大约是通过自然放射性获得的能量的100倍。

Since the accelerating frequency is variable, it is no longer necessary to use the high accelerating voltages of the cylotrons which needed to get the largest possible energy in a few cycles. Accelerating voltages in the synchrocyclotron are typically about 10 kV, and the limitation on maximum particle energy is set by the size of the device (i.e., the radius of the magnetic field region).

由于加速频率是可变的，因此不再需要使用回旋加速器所需的高加速电压，因为这些电压需要在几个周期内获得尽可能大的能量。同步回旋加速器中的加速电压通常约为10 kV，而对最大粒子能量的限制则由设备的尺寸（即磁场区域的半径）决定。

Betatron

电子感应加速器

Invented in 1940 by D. W. Kerst, the betatron is a circular accelerator for electrons. It differs from the cyclotron in that the acceleration of the electrons is achieved by increasing the magnetic flux through the orbit of the electrons. The electrons travel in an orbit of fixed radius, and are accelerated by the magnetic field which also keeps them in the orbit.

由D. W. Kerst于1940年发明的贝他加速器是一种用于电子的环形加速器。它与回旋加速器的不同之处在于，电子的加速是通过增加电子轨道中的磁通量来实现的。电子在固定半径的轨道中运动，并由磁场加速，该磁场也保持电子在轨道内。

In the betatron, one must deal with the relativistic effects on the electron as well as the loss of energy from radiation. All accelerated charges radiate electromagnetic energy, and accelerated electrons radiate more energy in a given kinetic energy range than would protons. This radiative energy loss, called synchrotron radiation, limits the maximum energy from the betatron to a few hundred MeV. The acceleration program for the increasing of the magnetic flux to keep the electron accelerating in a fixed-radius orbit must account for the change in the relativistic particle energy γmc².

在电子感应加速器中，必须处理电子的相对论效应以及由于辐射造成的能量损失。所有被加速的电荷都会辐射电磁能量，而在给定的动能范围内，被加速的电子比质子辐射更多的能量。这种辐射能量损失被称为同步辐射，它限制了电子感应加速器的最大能量为几百兆电子伏。为了保持电子在固定半径轨道上持续加速，必须增加磁通量的加速程序，必须考虑相对论粒子能量γmc²的变化。