1. Accelerators History-Why Particle sources Acceleration stage Space charge Diagnostics Application
• History-Why • Particle Sources • Acceleration stage • Space charge • Diagnostics • Application 1.Accelerators
Particle sources How particles are first produced? How to extract particles with the right properties? What are the limitations of the sources? The quality of the source is very important. if the particles emitted by the source do not have the right properties, it will be very difficult and/or expensive to rectify it later
12 Particle sources • How particles are first produced? • How to extract particles with the right properties? • What are the limitations of the sources? • The quality of the source is very important. If the particles emitted by the source do not have the right properties, it will be very difficult and/or expensive to rectify it later
Beams of nanoamperes to hundreds of amperes Very thin to very broad beams ( um to m2) Negative to highly charged state e to protein molecule
Beams of nanoamperes to hundreds of amperes Very thin to very broad beams (μm2 to m2 ) Negative to highly charged state e to protein molecule
Emission of electron Thermionic effect When a metal is heated more electrons can populate high energy levels Above a certain threshold they electrons can break their bound and be emitted This is thermionic emission (image source: wikipedia)
14 Emission of electron: Thermionic effect (image source: wikipedia) ⚫ When a metal is heated more electrons can populate high energy levels. ⚫ Above a certain threshold they electrons can break their bound and be emitted: This is thermionic emission
Work function To escape from the metal the electrons must reach an energy greater than the edge of the potential well The energy that must be gained above the fermi energy is called the work function "of the metal The work function is a propert specific to a given metal. It can vacuum vacuum × be affected by many parameters Itage-cnarg (eg: doping, crystaline state surface roughness . Example values F Fe:47eV. Cu: 5eV: Al: -41 eV Cs:2 ev zententiano (image source: wikipedia)
15 Work function • To escape from the metal the electrons must reach an energy greater than the edge of the potential well. • The energy that must be gained above the Fermi energy is called the “work function” of the metal. • The work function is a property specific to a given metal. It can be affected by many parameters (eg: doping, crystaline state, surface roughness,...) • Example values: (image source: wikipedia)