Chapter10-ParticleAccelerators.ppt

NUCLEAR ENERGY PROFESSIONAL(SPECIAL) ENGLISH COURSE Chapter 10 Particle Accelerators (粒子加速器) Chapter 10 Particle Accelerators (粒子加速器) A device that provides forces on charged particles by some combination of electric and magnetic fields and brings the ions to high speed and kinetic energy is called an accelerator. Many types have been developed for the study of nuclear reactions and basic nuclear structure, with an ever-increasing (持续增长) demand for higher particle energy. In this chapter we shall review the nature (性质) of the forces on charges and describe the arrangement (结构) and principle of operation of several important kinds of particle accelerators. 10.1 ELECTRIC AND MAGNETICFORCES (电磁力) Let us recall how charged particles are influenced (感应) by electric and magnetic fields. First, visualize (想象) a pair of parallel metal plates separated by a distance d as in the sample capacitor (电容器) shown in Fig. 10. 1. P139第二段第四行末 A potential difference (势差) V and electric field ε=V/d are provided to the region of low gas pressure by a direct-current (直流电) voltage supply such as a battery (电池). If an electron of mass m and charge e is released at the negative plate (阴极板), it will experience a force Fe, and its acceleration will be Fe /m. It will gain speed, and on reaching the positive plate (阳极板) it will have reached a kinetic energy mv2/2 = Ve. Next, let us introduce a charged particle of mass m, charge e, and speed v into a region with uniform magnetic field (均匀磁场) B, as in Fig.10.2. P139倒数第四行末 If the charge enters in the direction of the field lines (场力线), it will not be affected, but if it enters perpendicularly ([, p?:p?ndikjul?]垂直地) to the field, it will move at constant speed on a circle. Its radius, called the radius of gyration ([,d?ai?rei??n]回旋半径), is r = mv/eB, such that the stronger the field or the lower the speed, the smaller will be the radius of motion. Let the angular speed (角速度) be ? (omega), equal to v/r. Using the formula for r, we find ? =