7.6 Linear accelerators

Question 1

Why may linear accelerators be used instead of cyclotrons

Answer 1

Usually cyclotrons can only be used for energies around 10MeV, but for energies above this we use linear accelerators. Also linear accelerators can be used to accelerate negatively charged particles as well as positively charged particles

Question 2

What is the basic setup of a linear accelerator

Answer 2

There are drift tubes which are connected to high frequency alternating voltage supply. The lengths of the tubes are calculated so that there is always a positive charge experienced by the electrons in the following tube.

Question 3

How does a linear accelerator work

Answer 3

A bunch of electrons are fired by an electron gun are attracted to the first positive tube. Due to the alternating voltage the following tube will also become positive, attracting the electrons in the previous tube.

Question 4

Why do the lengths of the tubes increase

Answer 4

as the speed of the bunch of the electrons increase the length of the tubes need to increase so the time the electrons stay in each tube will be the same

Question 5

At what speed do the electrons travel when they are in the tube

Answer 5

At a constant speed, (they drift), since there is no electric field inside of the tubes

Question 6

What is another name for linear accelerators and what are some real world uses

Answer 6

A linac; they are used in hospitals to produce beams of high energy electrons. When the beam hits a tungsten target this results in a beam of x rays

Question 7

How are the tubes structured for electrons moving close to the speed of light

Answer 7

The tubes in the linac do not get noticeably longer