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发表于 2005-8-25 15:06:04
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Accelerators
粒子加速器
Why do physicists need accelerators? 物理学家们为什么需要粒子加速器？
Scientists have found that everything in the Universe is made from a small number of basic building blocks called elementary particles, governed by a few fundamental forces. 科学家们已经发现所宇宙中所有的东西最初是源自于一些被称为元素粒子的“混沌”演变而来的。这些物质被一些规则的力量所支配。
Some of these particles, such as the electron, are stable and form normal matter. Others, such as the muon, have a fleeting existence before decaying to the stable ones. Still others, such as the Higgs boson, are believed to have existed for a few instants after the Big Bang, but they are absent in today's universe. 一些粒子（如电子）对于正常的物质来说是稳定的。另外一方面，一些粒子（如μ介子）在衰退，变成相对稳定的粒子之前只存在很短的时间。还有一些粒子（如 Higgs 玻色子）被认为在巨大的碰撞以后会瞬间消亡。但我们仍未有在宇宙中找到此类粒子。
The enormous concentration of energy that can be reached in collisions between particles such as electrons or protons in an accelerator can recreate the conditions of the early universe, and generate particles like the Higgs boson for a fraction of a second, before such particles decay into more ordinary ones. It is the tell-tale traces left by these more ordinary particles that the physicists capture in huge detectors, placed around collision points on the accelerator. By a process of computational detective work, they can then deduce the proprieties on the new particles they created. 巨大的能量在粒子碰撞的一瞬间喷发。粒子加速器可以模拟早期的宇宙，在粒子都衰退成相对稳定的一类之前，用极短的时间放入 Higgs 玻色子。碰撞后，相对稳定的粒子留下的tell-tale痕迹会由由粒子加速器碰撞区周围的检电器检测到。通过计算处理，科学家们可能得出发现新粒子的结论。
Therefore, studying particle collisions is like "looking back in time", recreating the environment present at the origin of our Universe. 那样，研究粒子碰撞就像“检阅过去”，模拟早期的宇宙环境。
Accelerators: the ultimate microscope 粒子加速器——精细的显微镜
Humans use the information of bounced-around light waves to perceive the world (other animals, like dolphins and bats, emit and detect sound waves). In fact, any kind of reflected wave can be used to get information about the surroundings. The problem with using waves to detect the physical world is that the quality of the image is limited by the wavelength you use. 人类通过光的反射认清世界（其它动物，像海豚和蝙蝠利用声波探测周围的环境）。实际上，从所有可以发出波的东西都可以得出有关环境的信息。使用波来探测物理世界的问题在于图像的质量被我们所可以看见的波长所限制了。
Our eyes are adjusted to visible light, which has a wavelength between 0.4 and 0.8 micrometers (0.000001 metres, or 10-6m). This means that it can't be used to investigate details smaller then that, which usually is not warring since we don't need to look at things that are less then 0.000001 meters wide! 我们的眼睛探测到的光，波长一般在0.4—0.8微米（1微米等于0.000001米或10^－6米）。这意味着我们的眼睛不能检测到波长超出这个范围的光波，也就是比这更小的东西，我们就很难发现了。自从我们不需要看到比1微米还小的东西时，比这个范围还要小的东西就不再被我们所察觉。
But CERN physicists need to investigate the constituents of matter at the subatomic level, where the typical distances are of the order of the femtometre (0.000000000000001 m , or 10-15m) or smaller! 但是CERN的科学家们需要研究次原子级的问题，这需要发现波长为0.000000000000001 米（即10^-15 米）或更短的光波！
Early in the XXth century, it was discovered that moving particles of matter can also be considered as waves, whose wavelength would be smaller as their energy would be higher. Therefore, details smaller than a micron could, for instance, be examined using electrons, provided their energy is large enough. This is the principle of the electron microscope, which is used, among other things, in biology and metallography to look at details of cells or alloys. However, even the best scanning electron microscope can only show a fuzzy picture of an atom. 早在第几世纪之前，人们曾经探究过移动波的粒子，这些波的波长会更短，蕴藏的能量会更高。这样，我们就能看到比微米还小的细节。若电子有足够大的能量，我们利用它来观测。这就是电子显微镜的原理。电子显微镜用在生物学和金属组织学的用途，用来观测细胞或金属的细节。然而，连最好的电子显微镜也不能照出一张清晰的原子照片。
Since ALL particles have wave properties, physicists can use particles with the shortest possible wavelengths as their probes. To be able to investigate details a billion times smaller, we need to use particles that have energies a billion times higher. This means that the smaller the details you want to look at, the larger the machine you will have to build! 自从科学家可以利用工具检测波以后，他们能利用这些工具来研究比ALL粒子的波长短十亿倍的波。我们需要粒子释放出十亿倍更强的能量。想要得到更细的信息，就需要建造更大的机器！
How an accelerator works 一台粒子加速器是怎样工作的？
An accelerator usually consists of a vacuum chamber surrounded by a long sequence of vacuum pumps, magnets, radio-frequency cavities, high voltage instruments and electronic circuits. Each of these pieces has its specific function. 一台粒子加速器通常由一个真空管、真空泵、磁铁、射频放电器、高电压的器械和线圈组成。每一个组成部分都有它准确的职能。
The vacuum chamber is a metal pipe where air is permanently pumped out (by the vacuum pumps) to avoid that the accelerated particles collide with normal matter (like air molecules) and annihilate or get deflected off course. 真空管 由金属管组成，里面将会被真空泵抽空。这是为了消除空气以及空气中其他粒子对粒子加速实验的影响。
Inside the pipe, particles are accelerated by electric fields. These are provided by Radio-Frequency (RF) cavities. Each time charged particles traverse an RF cavity, the electric field inside the cavity gives them a "kick", i.e. some of the energy of the radio wave is transferred to them and they are accelerated. To make a more effective use of a limited number of RF cavities, accelerator designers can force the particle beam to go through them many times, by curving the beam trajectory into a closed loop. That is why most accelerators are roughly circular. 射频放电器 在真空管内，粒子被电磁场加速，这是由射频放电器 （RFC）发生的。每当粒子穿过射频放电器发生的磁场是，它们就会被加速，像被磁场提了一脚一样。粒子加速器把粒子束的加速轨道成为一个封闭的圈，使粒子束可以多次穿过磁场，这使 RFC发挥更强效能。这就是为什么很多粒子加速器都是圆环形的原因。
The curving of the beam's path, to make sure the particles stay within their circular track, is usually achieved by the magnetic field of dipole magnets (which have a North and a South pole, like the well-known horseshoe magnet). They are also called "bending magnets". This is because the magnetic force exerted on moving charged particles is always perpendicular to their velocity - perfect for curving the trajectory! The higher the energy of a particle, the stronger the field that is needed to bend the particle's path. This means that, as the maximum magnetic field is limited (to some 2 Tesla for conventional magnets, some 10 Tesla for superconducting ones), the more powerful a machine is, the larger it needs to be. 磁铁 通常粒子束都可以通过弯曲轨道，到达磁铁的磁场。这些磁铁又被称作挠度磁铁。这是因为磁力使活跃的粒子总是保持匀速，这对于弯曲的轨道来说是完美的。粒子的能量越强，使粒子轨道弯曲的磁场就要越强。这就意味着磁场的强度是限制了的（常规的用 2 Tesla 超导电的甚至用10 Tesla）。机器更强，磁场要更大。
In addition to just curving the beam, it is also necessary to focus it. Just like a shot from a shotgun, a particle beam spreads out as it travels. Focusing the beam allows its width and height to be constrained so that it stays inside the vacuum chamber. This is achieved by quadrupole magnets (which have four poles), which act on the beam of charged particles exactly the same way a lens would act on a beam of light. They are also called "focusing magnets". 四极磁铁 在加速之余，我们也需要对粒子束进行调焦。就像霰弹枪发射子弹一样，粒子束会自由地分散开来。调焦使粒子束不至于跑出了真空管。这需要四极磁铁的帮助。此磁铁对活跃的粒子束起作用。同样，一个镜头对光速起作用。他们起调焦作用，也被称作调焦磁铁。
A view of the LEP accelerator
These are some of the basic ingredients needed to make an accelerator. If you look around CERN's existing accelerators, like the PS or the SPS, you will see that there are many more objects such as:
- other magnets (to perform "fine tuning" on the trajectory or of the focusing)
- injection/ejection elements( to put the beam into the accelerator or to take it out)
- measurement devices (to give the operators information on the behaviour of the beam
- safety elements (to ensure smooth operation of the accelerator). 这些建造粒子加速器的是一些基本的因素。如果您对CERN现有的粒子加速器加以观察（像PS或 SPS）您将会看到更多的部件，比如：
其它的磁铁（调谐粒子束的轨道）
出入口（粒子束的进出口）
测量设备（把信息反馈给操作员）
安全设备（确保粒子加速过程和粒子加速器的安全）
All of these elements are controlled from a control centre, which is very much like the control centres used for space missions! 所有的这些设备都由控制中心控制。这个控制中心就像太空任务的控制室一样！
图片和源文件url：http://www.equn.com/forum/viewth ... id=zjylub#pid156148
[ Last edited by Grё@thΙll on 2005-8-25 at 16:13 ] |
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