Science & Technology

One of the most interesting topics in Physics. Which hasn’t yet specified by any other platform? Because it is definitely a difficult topic of physics. So let’s talk about ( LHC )”Long Hadron Collider” with its full depth.

LHC

1232 magnetic dipoles (14.3 m long and about 35 tons) placed along the tunnel will provide the protons, which travel inside vacuum tubes, the centripetal force necessary to keep them in the curved path of the accelerator to its passage through the eight arches of the LHC.

The mission of the magnetic field is to curve the path of the protons. This occurs because the magnetic force (Lorentz Force) is always perpendicular to the velocity of the protons.

Both vectors B acting in opposite directions on protons that travel in opposite directions generate a force with the same sense on all protons. That sense is always directed towards the center of the accelerator, being, as already said, the centripetal force that keeps all the protons in the correct path.

From previous calculations for the centripetal force we can now obtain the necessary value for B.

B ~8.33 T

(100,000 times the Earth’s magnetic field)

If the LHC

[/tooltip]carried traditional magnetic dipoles (not superconductors), it would take 120 km in length to reach the Same energy and electricity consumption would be huge.

To reach 8.33 T, we need 160 superconducting cables (80 on each side). The eighty cables are located in double layers around each tube, the current circulating in them in opposite directions to each side of the tube.

As each dipole covers a distance of about 15 m we can calculate a total superconducting length in the 1232 dipoles (2 tubes per dipole):

L =2 x 1232 x 160 x 36 x 6500 x 15? L =1.38•1012 m

This amount is more than 9 times the distance Sol-Terra (1.5•1011m).

We know that between parallel conductors attractive or repulsive forces appear depending on the senses of the electric currents that circulate through them. As in this case the currents on each tube go in the opposite direction, repulsive forces will appear between the two conductive layers that surround that tube.

The energy stored in each double dipole is:

Ed?7 MJ

Recital 1232 dipoles: ET?9 GJ

Given its length, the energy density in each main dipole is:

700014.3? 500 kJ / m

In addition to correctly curving the path of the protons, it is also necessary to focus them. Indeed, since protons repel each other, the proton beam tends to diverge and therefore collide with the inner walls of the tube. The consequent deposition of energy could cause the loss of the superconductivity conditions in the magnet.

This focusing is achieved with magnetic quadrupoles, which act on the beam of charged particles (protons in this case) in the same way that the lenses do on the light (that’s why we talk about “magnetic optics”).

There are a total of 858 magnetic quadrupoles.

In addition, another series of multiples helps in targeting and ensures the necessary corrections due to other interactions such as gravitational on protons, electromagnetic between packets, those created by clouds of electrons that are associated from the walls of the tubes, etc.

Sixth, they have the function of correcting the chromaticity, that is, correcting the particles with different energies than the nominal.

The dipoles and quadrupoles keep the protons in stable orbits with the correct energy, while the sextuples correct the trajectories of the protons that have slightly different energies than desired. The other multiples compensate for imperfections in the magnetic field.

The Lorentz Force plays another very important role in the LHC. It is responsible for curving the trajectory of the new particles created after the collision of the protons.

Depending on the electrical charge, mass and energy, the particles will be separated by the magnetic force in different ways, and can thus be analyzed separately.

In the image we see the simulation of the creation of a Higgs particle with the final appearance of two photons that are obviously not affected by the magnetic field of the detector.

Each detector has its own design for that magnetic field, and we will then take a look at two of them.

The CMS (Compact Muon Solenoid) detector is a 12,500 ton instrument (the iron core – in red in the picture – of the magnetic system contains more iron than the Eiffel Tower).

The magnet consists of three parts: the superconducting coil, the vacuum tank and the iron core. The coil produces the axial field while the core is responsible for the return of the magnetic flux on the outside of the solenoid. This return of the flow is the one that forms the set of lines of force that fill the detector in all its volume parallel to the axis, and that will bend the trajectories of the particles that are produced due to the collisions in the center of the detector.

The Solenoid consists of 5 modules 2.5 m long each.

Each module is formed by an aluminum cylinder with four internal winding layers,109 turns each.

Therefore:

B?4 T

Magnetic flux through the surface is

:?230 kWb

With,?= L • I? L =230000/19500? L?12 H

We are talking about an energy stored in the solenoid of:

E =½• L • I2? E?2.3 GJ

equivalent to half a ton of TNT.

The ATLAS detector (A Toroidal LHC Apparatus) offers a hybrid system of four superconducting magnets: a central solenoid surrounded by 2 extreme toroids (End-cap) and a “barrel”(BT) toroidal system. The dimensions of this magnetic system are 20 m in diameter and 26 m in length. With its nearly 2 GJ of stored energy, it is truly the world’s largest superconducting magnet.

The central solenoid, weighing 5.5 tons,2.5 m in diameter and 5.3 m long, provides a 2 T axial magnetic field in the center of the ATLAS tracking area. Since this solenoid precedes the argon-liquid electromagnetic calorimeter (LAr), its thickness should be the minimum possible to allow maximum calorimeter response. It contains 9 km of superconducting cables cooled by liquid helium and an electric current of 8000 A circulates through it.

With 7 km of superconducting cables do we have

B?2T

The energy stored by the solenoid is: E =½• L • I2? E?44.8 MJ

ATLAS also has a huge superconducting toroidal magnetic system (Barrel Toroid – BT) with dimensions of 25 m long and 22 m in diameter. This toroidal system provides the magnetic field for the areas of muonic detection. The toroid is composed of 8 structures of 25m x 5m where they circulate. superconducting currents of 20500 A.

Its total mass is 850 t.

Each of these structures has a length of (25+25+5+5)~60 m

## DETECTORS

The events (an event is a collision with all its resulting particles) are studied in giant detectors that are capable of reconstructing what happened during the collisions, and all this in a very high collision rate environment. They can be compared to huge three-dimensional digital cameras that can take 40 million “sequences”(digitized by tens of millions of sensors) per second. The detectors are built in layers, each layer having a certain functionality. The internal ones are the least dense, while the outer ones are the densest and most compact.

The very massive particles that scientists hope to create have a very short life, decaying into lighter and more familiar ones. After a collision due to hundreds of these light particles such as electrons, muons and photons, but also protons, neutrons and others, fly through the detector with speeds close to that of light. The detectors use these light particles to deduce the brief existence of the new and heavy ones produced.

The trajectories of the charged particles are curved by magnetic fields, and the radii of curvature are used to calculate their moments: the higher the energy, the more open is the curvature. Therefore, particles with a lot of kinetic energy have a sufficient trajectory through the detector to measure its radius of curvature and therefore its momentum. Other parts of the detector are calorimeters intended to measure the energy of the particles (both charged and unloaded). Calorimeters should also be large enough to absorb as much energy as possible. These two are the reasons that the LHC detectors are so great. The detectors surround the interaction point to collect all the energy of the particles and the balance of the moments of each event to reconstruct it in detail.

The particles – electrons, protons and muons – leave traces by ionization. Electrons are very light and therefore lose their energy very quickly, while protons penetrate deeper into the detector. The photons do not leave traces by themselves but in the calorimeter they become electron-positron pairs, whose energies can be measured. The energy of neutrons can be measured indirectly from their transfer to protons. Muons are the only particles that reach and are detected by the outermost layers of the detector.

Each part of the detector is connected to an electronic reading system through thousands of wires. At the moment when an impulse is produced, the system records the exact place and moment by sending the information to the computer. Hundreds of computers work together to combine that information. At the top of the computational hierarchy it is decided in a fraction of a second which event is interesting and which is not. There are several criteria for selecting potentially significant events, thus reducing the number of events from 600 million produced to a few hundred that will be investigated in detail.

The LHC detectors were designated, built and carried out by international collaborations from all over the world. There are four major experiments (ATLAS, CMS, LHCb and ALICE) and three small ones (TOTEM, LHCf and MoeDAL). Twenty years were necessary for the design and construction of the detectors and the duration of the experiments will be of the order of 15 years. This is equivalent to the total career of a physicist.

The construction of these detectors is the result of what could be called “group intelligence”: while all the scientists participating in a detector generally understand the functions of the device, none knows precisely the details and the precise function of all parts of the detector. In such collaboration, each scientist contributes with his knowledge in the experiment to total success.

## ATLAS

The ATLAS detector (A Toroidal LHC ApparatuS) is the largest detector in Particle Physics dedicated to general purposes (designated to “see” a wide range of particles and phenomena produced in collisions in the LHC). It measures 46 meters long,25 meters high and 25 meters wide; It weighs 7000 tons and consists of 100 million sensors to measure the particles that will emerge from proton-proton collisions in the LHC. The first piece of ATLAS was installed in 2003 and the last one was downloaded in March 2008, thus completing the gigantic puzzle.

ATLAS could respond to the mysterious “dark matter and energy”, and look for extra dimensions in space-time. It is designed to be able to discover new particles and new phenomena expected as extensions of the Standard Model: supersymmetry or the Higgs Boson.

If the Higgs field is not the answer sought to understand the mass of the particles, the ATLAS experiment is expected to guide physicists in the right direction.

ATLAS is a worldwide collaboration that involves some 2100 scientists and engineers from 167 institutions in 38 countries. They are: Argentina, Armenia, Australia, Austria, Azerbaijan, Belarus, Brazil, Canada, Chile, China, Colombia, Czech Republic, Denmark, France, Georgia, Germany, Greece, Hungary, Israel, Italy, Japan, Morocco, Holland, Norway , Poland, Portugal, Romania, Russia, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Taiwan, Turkey, United Kingdom and USA.

## CMS

CMS (Compact Muon Solenoid) is, together with ATLAS, a “general purpose” detector designed to explore physics on the scale of the TeV in a wide range of particles and phenomena produced in collisions in the LHC. It is expected to find answers to questions such as: Are there still fundamental principles undiscovered? Is the Higgs mechanism responsible for the visible mass of the universe? How can we solve the mystery of dark energy? Are there extra dimensions in space? How was the universe created? Is the Higgs Boson behind the mass of the particles?

The main body of the CMS detector is a multilayer cylinder about 21 m long and 16 m in diameter, with a total weight of more than 13000 tons. The innermost layer is the silicon-based particle tracker (trace detector made of silicon) surrounded by scintillating crystal electromagnetic calorimeter, which in turn is covered by sampling calorimeter for hadrons ( sample calorimeter for hadrons) measuring the energy of the particles. All these subdetectors are located inside the central superconductor solenoid (3.8 Tesla),13 m long and 6 m in diameter, which will allow the momentum of the charged particles to be measured. Outside the solenoid are the large muon detectors,

https://en.wikipedia.org/wiki/Compact_Muon_Solenoid

The CMS collaboration comprises 2300 scientists from 159 institutions in 37 countries.

88 Spanish researchers participate in CMS. CIEMAT) has participated in the development and manufacture of superconducting magnets for the accelerator, as well as in the design and construction of 70 muon chambers (25% of the total) of CMS and in the manufacturing of the reading electronics of these chambers. CIEMAT and the Institute of Physics of Cantabria (IFCA), a mixed center of the CSIC and the University of Cantabria, are responsible for the alignment system and the associated electronics of CMS muon chambers. The University of Oviedo and the Autonomous University of Madrid also collaborate in this system, also involved in the development of the data selection system or “Trigger”. The Spanish participation in the LHC is promoted through the Consolider-Ingenio 2010 CPAN project (National Center for Particle Physics,

https://widelyexplore.com/history-of-cern-lhc-lep-and-particle-accelerator/

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• ### CERN LHC Experiments and Detectors: Atlas, CMS, Alice, LHCf and TOTEM

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