带你了解CERN 之 管道与圈圈 CERN · The Tubes and Rings

上次，我们了解了CERN, LHC和ATLAS的一些基本信息，接下来我们继续探索为实验们带来生命的重要部件们。

Last time, we learnt about the basic facts of CERN, LHC and ATLAS, next to we continue to explore the critical components that bring life to the experiments.

超强质子生产线

The Production Line

LHC是一个同步加速器(一种循环粒子加速器)，也是世界上最大、动力最强的机器之一。自2008年开始使用，主要用于质子-质子碰撞，现在仍然是最新CERN组合系统的一员。
The LHC is a synchrotron (a type of cyclic particle accelerator) and one of the world’s largest and most power machine. Started using since 2008, it was set up to perform proton-proton collision and still remains in the latest addition of the CERN complex.

在质子准备好进入LHC之前，它们必须经历一系列的过程，从普通的核子转变为超高能量的“Bing Bang”粒子。

Before the protons are ready to enter the LHC, they have to go through a series of process to transform from ordinary nucleons to ultra-high energy ‘Bing Bang’ particles.

加速器组合的主要组成部分包括直线加速器(Linac) 2(4)、质子同步推动加速器(PSB)、质子同步加速器(PS)、低功率超导质子直线加速器(LPSPL)、质子源2(PS2)、超级质子同步加速器(SPS) 和大型强子对撞机(LHC)。*

The main parts of the accelerator complex consisting of the Linac 2(4), the Proton Synchrotron Booster (PSB), the Proton Synchrotron (PS), the Low Power Superconducting Proton Linac (LPSPL), the Proton Source 2(PS2), the Super Proton Synchrotron (SPS) and the LHC. *

图为CERN加速器组合的整个结构，图中最大的圈为LHC，四个黄色标记为四个最主要的实验位置

The CERN accelerator complex, the largest ring is the LHC and the yellow points being the 4 main experiments. 

流水线第一步 – 材料采集

Stage 1 - Collection

质子的来源是一大瓶氢气。以一个恒定的速率注入第一个加速器- Linac 2 (4) 后，那里会首先利用电场剥离氢原子中的电子以产生质子，然后将它们加速到大约1/3光速，能量为50 MeV的状态。*
The source of protons is a bottle of hydrogen gas and is feed at a constant rate into the first accelerator of the chain – Linac 2 (4), which is a linear accelerator. There, an electric field is first used to strip off the electrons from the hydrogen atoms to yield protons and then accelerates them to around 1/3 the speed of light with the energy of 50 MeV. *

注意，能量单位电子伏特(eV)会在以下描述中经常用到。1eV是电子处电势增加一伏特时，电子获得的能量，等于1.602×10-19焦。缩写MeV表示100万eV; GeV, 10亿eV; TeV, 1万亿eV。

Note, the energy unit electron volt (eV) will be used frequently below, 1eV is the energy gained by an electron when the electrical potential at the electron increases by one volt, it is equal to 1.602 × 10^-19 joule. The abbreviation MeV indicates 1 million eV; GeV, 1 billion eV; and TeV, 1 trillion eV.

一般来说，一个LED灯泡每秒消耗2-17焦，也就是每秒1000万TeV。但是，在一根电线中，每个电子只有约1eV，以每秒1cm的速度移动。因此，用Linac 2中的50MeV电子与“正常”电子相比后，可以看出它们在加速器中它们会变得多么能量十足。

Generally, a LED light bulb uses 2-17 joules per second, which is about 10 million TeV per second. However, the electrons in the wire each only have ~1eV and travel at the speed 1cm per second. So, comparing the 50MeV electrons in Linac 2 to ‘normal’ electrons, it shows how powerful they become in the accelerators.

图为Linca 2加速器的一部分。在CERN开始为期一年的保养维修前，在工作40年后于2018年11月13日正式退休。现在由Linac 4 接替它的工作。

Part of the Linca 2 accelerator. Before CERN's Long Shutdown 2 between 2019-2020, it officially retired on 13 November 2018, after 40 years of work. Now Linac 4 will take over.

流水线第二步 – 初步加工

Stage 2 - Preliminary Processing

回到加速器组合，PSB由四个环组成，是质子流水线的第二道工序地点。为了使质子束的强度最大化，它被分成四等份，每一份进入各自的环性加速器。

Back to the accelerator complex, the PSB is made up of four rings and is the site of the second stage of the process. In order to maximise the intensity of the beam, it is divided into four equal shares, each entering their own ring.

由于加速质子所需的距离很长，线性加速器不再实用，因此这里使用了周长为157m的圆环性加速器。偶极磁铁垂直放置于质子的路径，这样质子束的轨迹就是可以弯曲成圆形；当质子反复绕环运动时，也会有脉冲电场帮助质子速度的提升，在离开助推器质子时速将达到91.3% 的光速 (1.4GeV)。*

Due to the long distance needed to accelerate the protons, linear accretors are no longer practical, therefore rings with 157m in circumference are used. Dipole magnets are placed perpendicular to the path of protons so the beam can be bent into a circular trajectory; and an electric filed is pulsed around the protons while they repeatedly travel around the rings to reach 91.3% speed of light (1.4GeV) by the time they leave the booster. *

大型强子对撞机粒子加速深入解释 (1:05时为粒子束进入PBS之前与之后的状态模拟。在被分为四等分后，进入PBS的粒子会被电场加速，被磁铁控制方向）

LHC Particle Acceleration In-depth Explanation (At 1:05: an animation of the particle beam before and after entering the PBS. After the beam being split up into four equal parts, they are accelerated by the electric field and their trajectories controlled by the dipole magnets.)

流水线第三步 – 拼装

Stage 3 – Assemble

从四环出来重新组合后，质子束会飞进下一阶段 - PS，并在这一阶段停留1.2秒，达到光速的99.9%。PS是CERN建造的第一个同步加速器，周长628米，有277个常规(室温)电磁铁，其中100个是用来弯曲粒子束的偶极子。

Recombing from the four rings, the beam is flown into the PS for the next stage for 1.2 second reaching the speed of 0.999c. The PS was CERN’s first synchrotron and is 628m in circumference, it has 277 conventional (room-temperature) electromagnets, 100 of which are dipoles for bending the beams. 

在这一阶段，质子们到了关键性的一步 - 现在质子速度已经到了最大限，脉冲电场无法再给质子束增加速度，因此，质子在光速运动的基础上质量开始增加，能量达到了25GeV。*

Here the point of transition is reached, where pulsating electric field cannot add velocity to the beams anymore, as they are already reaching the maximum limit. So, the protons gain mass instead, reaching energy of 25GeV. *

图为628米长的质子同步加速器 (PS) 的一部分

Part of the 628m long Proton Synchrotron (PS)

流水线第三步 – 发货

Stage 4 – Dispatch

第四阶段是在7公里长的SPS中进行的。专门为高能粒子设计的它，运行能量高达450 GeV。它的任务就是将这些粒子送入LHC和其他实验的加速器。作为CERN的第二大对撞机，它拥有1317个常规电磁铁，包括744个偶极子。*

Stage four is done in the 7km long SPS. It is designed specifically for particles with high energy and operates at up to 450 GeV, which are then feed into the LHC and other experiments. Being the second largest collider at CERN, it has 1317conventional electromagnets, including 744 dipoles. *

图为7公里长的超级质子同步加速器 (SPS) 的一部分

Part of the 7km long Super Proton Synchrotron (SPS)

最后，质子束进入LHC进行碰撞。作为CERN加速器组合最庞大的部分，

每次填满它需要4分20秒，达到6.5 TeV的最大能量需要20分钟。

Finally, the beam of protons enters the LHC, which is the largest part of the CERN complex, for the collisions. It takes 4 minutes and 20 seconds to fill each of the rings and 20 minutes for them to reach their maximum energy of 6.5 TeV.

一般，一束质子在进入LHC循环后会在系统中持续循环10个小时以上。这里仍然会使用电场让质子在转每一圈的时候提高能量，使它们以每秒11000次的速度绕管道运动。为了让两个质子束可以向相反的方向运动，在27公里长的环形系统里其实有两个平行的超高压真空管，在四个探测器位置进行交叉并碰撞。*

On average, a beam stays in the circulation for more than 10 hours. Here the electric field is still being used to boost the protons’ energy at each revolution, making them travel around the pipes over 11 thousand times per second. The 27km long ring has two ultrahigh vacuum pipes for the proton beams to travel in opposite directions, though they are crossed over at each of the four detectors allowing for collisions. *

图为CERN 2013年第一次大型维护，在LHC的工作场景

General activity at the LHC tunnel during the Long Shutdown 1 in 2013

为了控制粒子束的轨迹，必须使用超导磁体才能让这些飞速运动的粒子及时转弯。

超导磁体功能的最大化需要用超流氦把它冷却到1.9K（-271.45 c）的温度，因为只有冷却到这样的低温将确保在超导状态下运行的特殊电缆线圈的能量损失最小。

With their trajectories controlled by superconducting magnets cooled with superfluid helium at 1.9K (-271.45 c). Cooling to such low temperature will ensure the minimum energy loss of the special electric cable coils operating at the superconducting state.    

在附属文章将更多的关于超导磁铁以及冷却系统的介绍。如果没有这些技术的支持，粒子束的弯曲会变得非常困难，也就会需要更大的加速器来进行实验，升高实验的成本和难度。

In the attached articles will be more on the magnets as well as the cooling systems. Without those technology in support, the bending of beams would have been very much more difficult and therefore in need of a much larger accelerator for the experiments to operate.

下期我们将进入

ATLAS探测仪和LHC中的碰撞，

深入了解奇幻粒子们的神奇邂逅。

尽情期待！

Next time we'll look at 

the collisions in the LHC as well as the inside of ATLAS and 

learn more about the magical encounters of the fantastic particles. 

Look forward to it!

图为CERN 2013年第一次大型维护，LHC 偶极磁铁替换的场景

The replacing of a dipole magnet in the LHC during CERN's Long Shutdown 1 in 2013

图片和视频来自 CERN 官网

文中除*部分英文信息应用于CERN官网，

其余中英文内容为原创

Pictures and video from official website of CERN.

The * parts of English information was cited from official websites of CERN,

the rest of the Chinese and English content is original