Linear Accelerators Flashcards
what have scientists begun doing in order to study the infrastructure of subatomic particles
colliding them with each other at high speeds
why is it necessary to collide them at high speeds
- because they need to collide with very high energy levels
- to prevent them from just bouncing off each other
- but breaking down instead
what is the general purpose of an electric field in a particle accelerator
- to accelerate the charged particle in a straight line
- to very high speeds
what is the purpose of a magnetic field in a particle accelerator
- to change the direction of the charged particle along a curved path
- if it isnt in a linear accelerator
what is the simplest way to produce high energy collisions between charged particles
to accelerate a beam of the charged particles along a straight path
what is a limitation to this method
- the speed of the particles is limited by the maximum pd that can be achieved
- as the pd is what is exerting the force on the electrons, causing them to accelerate
what is the solution to the is pd limitation (still going in a straight line)
- the particles are accelerated in stages
- in each stage they are repeatedly accelerated through the maximum pd
- resulting in the particle gaining large amounts of KE
if a linear accelerator is to accelerate electrons, where would these electrons come from in the first place
- they would be generated by an electrostatic machine
- like a van de graaff generator
- then be fed into the accelerator
once inside the cylindrical accelerator, why does the electron only move in a straight line, not deviating from the centre of the cylinder
because the electrodes around the accelerator are equally attracting in all directions
what is the structure of a linear accelerator actually like
- it consists of a series of hollow cylinders all in a straight line
- the gap between the cylinders is equal throughout
- but the length of the cylinders increases as you go across
what kind of voltage supply is connected to the accelerator (specifically the cylinders)
an AC voltage
the first cylinder an electron is accelerated through is positively charged. what would be the charge on the second cylinder and why
- the second tube would be negatively charged
- because of the ac voltage giving it the opposite charge of the cylinders next to it
how would an electron be accelerated through the first positively charged cylinder
- the electron is attracted into the positively charged cylinder
- when it reaches the middle of it, the direction of the voltage is switched
- this causes the cylinder to become negative
- repelling the electron out of the tube (forwards)
how is the electron accelerated through the second cylinder
- because the direction of the voltage has switched
- the following cylinder would now be positively charged
- causing the electron to be attracted into that one
- the same thing with the first cylinder would happen again
therefore how is the electron accelerated through the accelerator throughout
- the cylinder the electron is repelled out of would be next to a cylinder that attracts the electron
- the process of the voltage switching when the electron is halfway through the cylinders repeats itself
- allowing for an acceleration in one direction
what is the rate of change of the pd like
- its fixed
- so the change in direction of pd happens at set intervals
why do the lengths of the cylinders increase across the accelerator
- the electron accelerating means its velocity is increasing
- in order for the electron to be in the middle of the cylinders when the ac voltage switches
- the length of the tube need to be increased to account for its increasing distance covered, over the set time intervals for the switch
if the rate of alternation of the pd supply is constant, what does that mean about the supplys frequency
- its uniform (constant)
- as frequency also indicates the rate of change of the supply
what is the average / usual frequency for a linear accelerator
- a couple gigahertz
- 3000 MHz (3 GHz)
what is a limit to this method of particle acceleration
- how long you can build the particle accelerator to be
- as the whole thing needs to be in a vacuum and be perfectly straight
why does the accelerator need to be in a vacuum
so the particle doesnt collide with air molecules
what kind of particles can linear accelerators only work with
charged particles
