# 5.5: LHC Facility

Difficulty Level: At Grade Created by: CK-12

## Lesson Objectives

• Describe how the proton bunch gets up to speed.
• Describe some of the physics involved in the proton bunch’s motion.

## Overview

Several scientists have called the LHC “the largest scientific experiment in the world” (Cox, 2008). To successfully accelerate the particles to relativistic speeds, the particles must be energized in stages. The circular geometry of the LHC and the fact that it is built using previous machines makes this possible.

When launching a rocket to the moon, the rocket has multiple stages. Each stage pushes the rocket a little faster. The LHC does something similar to get the protons up to speed (www.YouTube.com What is CERN Large Hadron Collider LHC? End of the World? Search for God Particle and Micro Black Holes, 2008).

In the early stages, hydrogen gas is ejected into a chamber. Using electricity to generate a large electric field, the electrons are stripped from the atom. Protons are then sent into the linear accelerator. This is stage one of five for the process. This collection of charges contains protons. This collection is called a bunch. The device accelerating the bunch is called the “lineac 2.” By the time the proton bunch reaches the end of the tube it will be traveling at the speed of light. That is fast enough to go around the Earth’s equator two and a half times in one second. The charge injection process is repeated to create a collection bunches. This many bunches creates a beam of protons.

Upon leaving the lineac 2, the proton bunch enters stage 2. This booster stage consists of rings with a radius of meters. The packets are accelerated by electric fields. The electric fields are pulsed in such a way to speed up the packets and more tightly pack the protons together. Powerful magnets with a B-field perpendicular to the direction of motion steer the packets in the circular rings. The packet leaves this stage at % the speed of light.

Now in stage 3 of the acceleration, the packet is in the proton synchrotron. In this ring the bunch gets closer to the speed of light. Upon leaving this ring the protons will move as if they are 25 times heavier than when they were at rest. The proton will stay in this ring for seconds and reach a speed of % the speed of light before leaving the ring. Each proton will leave the ring with .

In stage 4 of the acceleration process the bunch enters a larger ring. This ring is called the super proton synchrotron. It has a radius of about . Energy added in this ring will increase the mass of the proton to 450 times its resting mass. At this point, each proton will leave the ring with an energy of . When the bunches leave this stage, half will enter the large ring traveling clockwise. The other half will leave the ring traveling counterclockwise (See Figure 6).

The packet enters the large ring. The large ring has a radius of . The protons will travel around 11,000 times per second. This large ring contains two tunnels. The beams will travel in opposite directions until they are directed to a location for a head-on collision. Each proton will reach an energy level of while traveling at % the speed of light. This head-on energy generates a temperature of (www.YouTube.com, What is CERN Large Hadron Collider LHC? End of the World? Search for God Particle and Micro Black Holes, 2008; CERN, LHC Beams, 2008).

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