核专业英语.pptx
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1、PROFESSIONAL(SPECIAL)PROFESSIONAL(SPECIAL)ENGLISH COURSEENGLISH COURSENUCLEAR ENERGYNUCLEAR ENERGYChapter 8 Particle Accelerators(粒子加速器粒子加速器)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
2、called an accelerator.Many types have been developed for the study of nuclear reactions and basic nuclear structure,with an ever-increasing(持续增长持续增长)demand for higher particle energy.In this chapter we shall review the nature(性质性质)of the forces on charges and describe the arrangement(结构结构)and princi
3、ple of operation of several important kinds of particle accelerators.8.1 ELECTRIC AND MAGNETICFORCES (电磁力电磁力)Let us recall how charged particles are influenced(感应感应)by electric and magnetic fields.First,visualize(想象想象)a pair of parallel metal plates separated by a distance d as in the sample capacit
4、or(电容器电容器)shown in Fig.8.l.P73第二段第三行中A potential difference(势差势差)V and electric field E=V/d are provided to the region of low gas pressure by a direct-current(直流电直流电)voltage supply such as a battery(电池电池).If an electron of mass m and charge e is released at the negative plate(阴极板阴极板),it will experie
5、nce a force Ee,and its acceleration will be Ee/m.It will gain speed,and on reaching the positive plate(阳极板阳极板)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(均匀磁场均匀磁场)B,as in Fig.8.2.P73末
6、行尾If the charge enters in the direction of the field lines(场力线场力线),it will not be affected,but if it enters perpendicularly(垂直地垂直地)to the field,it will move at constant speed on a circle.Its radius,called the radius of gyration(旋转旋转),is r=mv/eB,such that the stronger the field or the lower the speed
7、,the smaller will be the radius of motion.Let the angular speed(角速度角速度)be (omega),equal to v/r.Using the formula for r,we find =eB/m.If the charge enters at some other angle,it will move in a path called a helix(螺旋状螺旋状),like a wire door spring(金属丝制的门弹簧金属丝制的门弹簧).P75首段Finally,let us release a charge i
8、n a region where the magnetic field B is changing with time.If the electron were inside the metal of a circular loop(圆环圆环)of wire of area A as in Fig.8.3,it would experience an electric force induced by the change in magnetic flux(磁通量磁通量)BA.The same effect would take place without the presence of th
9、e wire,of course.8.2 HIGH-VOLTAGE MACHINES(高压设备高压设备)One way to accelerate ions to high speed is to provide a large potential difference between a source of charges and a target.In effect,the phenomenon of lightning(闪电闪电),in which a discharge(放电放电)from charged clouds to the earth takes place,is produ
10、ced in the laboratory.Two devices of this type are commonly used.The first is the voltage multiplier(电压倍增器电压倍增器)or Cockroft-Walton machine.The second is the electrostatic generator(静电发生器静电发生器)or Van de Graaff accelerator(Fig.8.5).An insulated(绝缘的绝缘的)metal shell is raised to high potential by bringin
11、g it charge on a moving belt(传动带传动带),permitting the acceleration of positive charges such as protons or deuterons.Particle energies of the order of 5MeV are possible,with a very small spread in energy.8.3 LINEAR ACCELERATOR(直线加速器直线加速器)Rather than(胜于胜于)giving a charge one large acceleration with a hi
12、gh voltage,it can be brought to high speed by a succession of(一连串一连串)accelerations through relatively small potential differences,as in the linear accelerator,sketched in Fig-8.6.P73第三行末It consists of a series of(一连串的一连串的)accelerating electrodes(电极电极)in the form of tubes with alternating electric po
13、tentials applied as shown.An electron or ion gains energy in the gaps between tubes and“drifts(漂流漂流)”without change of energy while inside the tube,where the field is nearly zero.By the time the charge reaches the next gap,the voltage is again correct for(做做的校正的校正)acceleration.8.4 CYCLOTRON AND BETA
14、TRON(一一)CYCLOTRON (回旋加速器回旋加速器)Successive electrical acceleration by electrodes(电极电极)and circular motion(圆周运动圆周运动)within a magnetic field are combined in the cyclotron.(Fig.8.7)P77第四行末Two hollow(空的空的)metal boxes called“dees(D字盒字盒)”(in the shape of the letter D)are supplied with alternating voltages(交
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