DOC PREVIEW
UT Arlington PHYS 3446 - Lecture Notes

This preview shows page 1-2-3-4 out of 11 pages.

Save
View full document
View full document
Premium Document
Do you want full access? Go Premium and unlock all 11 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 11 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 11 pages.
Access to all documents
Download any document
Ad free experience
View full document
Premium Document
Do you want full access? Go Premium and unlock all 11 pages.
Access to all documents
Download any document
Ad free experience
Premium Document
Do you want full access? Go Premium and unlock all 11 pages.
Access to all documents
Download any document
Ad free experience

Unformatted text preview:

PHYS 3446 – Lecture #18Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Wednesday, Nov. 10, 2010 PHYS 3446, Fall 2010 Andrew Brandt 1PHYS 3446 – Lecture #18Wednesday, Nov. 10, 2010Dr. Andrew BrandtParticle Detection•Accelerators•Particle PhysicsWednesday, Nov. 10, 2010 PHYS 3446, Fall 2010 Andrew Brandt 2•Cockcroft-Walton Accelerator–Pass ions through sets of aligned DC electrodes at successively increasing fixed potentials–Consists of ion source (hydrogen gas) and a target with the electrodes arranged in between–Acceleration Procedure•Electrons are either added or striped off of an atom•Ions of charge q then get accelerated through series of electrodes, gaining kinetic energy of T=qV through every set of electrodesElectrostatic Accelerators: Cockcroft-Walton•Limited to about 1MeV acceleration due to voltage breakdown and discharge•Available commercially and also used as the first step high current injector (to ~1mA).Wednesday, Nov. 10, 2010 PHYS 3446, Fall 2010 Andrew Brandt 3•Energies of particles through DC accelerators are proportional to the applied voltage•Robert Van de Graaff developed a clever mechanism to increase HV, based on the following known facts–The charge on any conductor resides on its outermost surface–If a conductor carrying additional charge touches another conductor that surrounds it, all of its charges will transfer to the outer conductor increasing the charge on the outer conductor, increasing HVElectrostatic Accelerators: Van de Graaff4•Basically high voltage ionizes gas, ions are collected, transferred to dome, thus increasing HV•“Sprayer” (S) adds positive charge to the conveyor belt (“electrons go to P”)•Charge is carried on a conveyor belt over motorized rollers (R)•The charges get transferred to the dome via the collector (C)•The ions in the source then get accelerated to about 12MeV•This acceleration normally occurs in high pressure gas that has very high breakdown voltage Electrostatic Accelerators: Van de GraaffWednesday, Nov. 10, 2010 PHYS 3446, Fall 2010 Andrew BrandtWednesday, Nov. 10, 2010 PHYS 3446, Fall 2010 Andrew Brandt 5•Fixed voltage machines have intrinsic limitations in their energy due to breakdown•Machines using resonance principles can accelerate particles to higher energies•Cyclotron developed by E. Lawrence is the simplest one•Accelerator consists of–Two hollow D shaped metal chambers connected to alternating HV source–The entire system is placed under a strong magnetic fieldResonance Accelerators: CyclotronWednesday, Nov. 10, 2010 PHYS 3446, Fall 2010 Andrew Brandt 6•Because of shielding of the metal D’s, there is no electric field inside them•Strong electric field exists only in the gap between the D’s•An ion source is placed in the gap•The path is circular due to the perpendicular magnetic field•Ion does not feel any acceleration inside a D but gets bent due to magnetic field•When the particle exits a D, the direction of voltage can be changed and the ion gets accelerated before entering into the D on the other side•If the frequency of the alternating voltage is just right, the charged particle gets accelerated continuously until it is extractedResonance Accelerators: CyclotronGap between D’s7•For non-relativistic motion, the frequency appropriate for alternating voltage can be calculated from the fact that the magnetic force provides centripetal acceleration for a circular orbit•For a constant angular speed, =v/r. The frequency of the motion is•Thus, to continue to accelerate, the particle the electric field should alternate at this frequency, the cyclotron resonance frequency (and the velocity and radius will increase at same rate) •The maximum kinetic energy achievable for an cyclotron with radius R is Resonance Accelerators: Cyclotron2vmr=v qBr mc=2fvp= =( )22 2 2max max21 12 2qBRT mv m Rmcv= = =vBqcw=2qBmcp=12q Bm cp� �� �� �Wednesday, Nov. 10, 2010 PHYS 3446, Fall 2010 Andrew Brandt 8•Accelerates particles along a linear path using resonance principle•A series of metal tubes are located in a vacuum vessel and connected successively to alternating terminals of radio frequency oscillator•The directions of the electric fields changes before the particles exits the given tube•The tube length needs to get longer as the particle gets accelerated to keep up with the phase•These accelerators are used for accelerating light particles to very high energiesResonance Accelerators: Linear AcceleratorWednesday, Nov. 10, 2010 PHYS 3446, Fall 2010 Andrew Brandt 9•For very energetic particles, relativistic effects must be taken into account•For relativistic energies, the equation of motion of a charge q under magnetic field B is •For v ~ c, the resonance frequency ( or f) becomes f=•Thus for high energies, either B or  should increase•Machines with constant B but variable  are called synchro-cyclotrons•Machines with variable B independent of the change of  are called synchrotronsSynchroton Acceleratorsdv v Bm m v qdt cg g v�= � =rr rr r2vnp= =1 12q Bm cp g� �� �� �Wednesday, Nov. 10, 2010 PHYS 3446, Fall 2010 Andrew Brandt 10•Electron synchrotrons, B varies while  is held constant•Proton synchrotrons, both B and  vary•For v ~ c, the frequency of motion can be expressed =•with p= mc and q=e•For magnetic field strength of 2 Tesla, one needs a radius of 50 m to accelerate an electron to 30 GeV/c.Synchroton Accelerators12 2v cfR Rp p= �( )( )/( )0.3 )p GeV cpcR mqB B Tesla= �1 12q Bm cp g� �� �� �Wednesday, Nov. 10, 2010 PHYS 3446, Fall 2010 Andrew Brandt 11•Synchrotons use magnets arranged in a ring-like fashion.•Multiple stages of accelerations are needed before reaching the GeV scale•RF power stations are located through the ring to pump electromagnetic energy into the particlesSynchroton


View Full Document

UT Arlington PHYS 3446 - Lecture Notes

Documents in this Course
Symmetry

Symmetry

18 pages

Load more
Download Lecture Notes
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Lecture Notes and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Lecture Notes 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?