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accelerators - University of Manchester - HEP

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					 Research masterclass:
The quest for luminosity
       Dr Rob Appleby
        Outline of the three lectures
   The three lectures will look at particle
    accelerator, and how they achieve the goal of
    luminosity (defined later)
       Lecture 1 – a overview of particle accelerators, what
        they do and big facilities around the world
            Directed reading : “The quantum universe”
       Lecture 2 – what is luminosity?
            Directed reading : “Parameters for a linear collider”
       Lecture 3 – how we achieve luminosity
            Directed reading : The LC/Snowmass05 web sites
   Lecture 1:
Introduction to
  accelerators
          What I shall talk about
   What a particle accelerator is
   How they work (very roughly!)
   A look at some large accelerators around the
    world, both past and future
   Your directed reading tells you WHY we
    perform particle colliding experiments

   I shall not talk for 50mins…please spend the
    time reading “The quantum universe”
Particle accelerators are everywhere!
   Daily applications
     TV, computer monitor
     Microwave oven, oscilloscopes

   Industrial
     Food sterilization
     Electron microscopes

     Radiation treatment of materials

     Nuclear waste treatment
Particle accelerators are everywhere!
   Medical applications
     Cancer therapy, Radiology
     Instrument sterilization
     Isotope production

   Research tools for many scientific fields
     High energy physics experiments
     Light sources for chemistry, biology etc
     Optics, neutron sources
     Inertial fusion
          The technologies used
   Large scale vacuum
   High power microwaves
   Superconducting technology
   Very strong and precise magnets
   Computer control
   Large scale project management
   Accelerator physics (beam dynamics)
          What is an accelerator?
   Put simply, an accelerator takes a stationary
    particle, with energy E0, and accelerates it to
    some final energy E.
   This is achieved using electric fields for
    acceleration and magnetic field for beam control
   The uses are many…we are interested in
     Light sources
     But mainly in colliding beam applications
            Why do we need them?
   We want to study the building blocks of nature
       Very small structure, 10-10m to 10-15m
   Our probe is electromagnetic radiation
       To probe 10-15m, we need =10-15m

                             hc
                  E   h      2 1010 J
                             
                 Ee  eU
                               Ee
                 Ee  E  U      1.2  109 V
                               e
The best accelerator in the universe…
     A basic 9eV accelerator
                (The simplest in the universe!)




The single electron passes through a potential difference
of 1.5 volts, thus gaining 1.5 electron-volts of energy
        An aside on electron volts
   Make sure you understand the units of particle
    and accelerator physics!
           1 eV = 1.602 x 10-19 joules

   So we speak of GeV (Giga-electron-volts) and
    TeV (Tera-electron volts)
   What about momentum [GeV/c] and mass
    [GeV/c2]?
The development of accelerators
   Accelerators have gone through a long
    development process, including
     Electrostatic accelerators
     The Van de Graaff accelerator

     The Cyclotron

     The Synchrotron
The Cyclotron
        A vertical B-field provides the
         force to maintain the
         electron’s circular orbit
        The particles pass repeatedly
         from cavity to cavity, gaining
         energy.
        As the energy of the particles
         increases, the radius of the
         orbit increases until the
         particle is ejected
The first million volt cyclotron




                                                                08/01/32

“we were concerned about how many of the protons would succeed in
spiralling around a great many times without getting lost on the way."
          Accelerating cavities
   Modern machines use a time-dependent electric
    field in a cavity to accelerate the particles
    How we manipulate the beam
   The charged particle beam is then manipulated
    by the use of powerful magnets
   In analogy with light optics, we call this process
    magnetic beam optics
   The beam is bent using dipole magnets and
    focusing using quadrupole magnets
   The magnets are very strong, often several Tesla,
    and use normal conducting, superconducting or
    permanent magnet technology
              Magnetic lattices
   Magnets are combined to
    form a magnet lattice
   The lattice steers and
    focuses the beam

                     Dipole


            F Quadrupole


                  D Quadrupole
                    A mini tour
   Now we’ll look at some of the world’s biggest
    circular accelerators
       Just LEP and the LHC
   Note that I only scratch the surface, miss many
    out and spend very little time on non-colliding
    machines
   There is much more life than I show!
               What was LEP?
   LEP was a circular electron-positron collider,
    built at Cern, Geneva.
   The ring design (c=27km) meant that the
    accelerating structures are seen many times by
    the circulating beams of particles
   The ring had 4 experimental sites - ALEPH,
    DELPHI, L3 and OPAL.
   Final collision energy was 209 GeV (2 x Ebeam)
   It almost discovered the Higgs boson!
L(arge)E(lectron)P(ositron)




                              LEP at CERN, CH
                              Ecm = 180 GeV
The LEP tunnel




 (this is one of LEPs superconducting cavities)
        The large hadron collider
   The large hadron collider (LHC) uses the same
    tunnel as LEP, at Cern in Geneva
   The machine is a 14 TeV proton-proton collider, so
    each stored beam will have an energy of 7 TeV
   It is being built now, and shall start operation
    sometime in 2007
   There are a number of experiments
The LHC tunnel
     But particles radiate energy!

Synchrotron Radiation from              e 2c 2
an electron in a magnetic field:   P         C E 2 B 2
                                         2
             B
                                   Energy loss per turn of a
                                   machine with an average
                                   bending radius :

                                                C E 4
                                   E / rev 
                                                  
         Energy loss must be replaced by RF system
                     cost scaling $ Ecm2
              End of the road?
   So, because of the low mass of an electron, LEP
    is the end of the road for circular electron
    machines!
   The higher proton mass means that we can build
    the LHC (what matters is =E/E0)
   So the next generation of electron colliders
    cannot use a ring…so we need to stretch out
    that ring into a straight line
            A linear machine

e+                                                e-

     ~15-20 km


              For a Ecm = 1 TeV machine:
        Effective gradient G = 500 GV / 14.5 km

                    = 35 MV/m
             Note: for LC, $tot  E
The International Linear Collider
   The International Linear Collider (ILC) is a
    proposed machine, to complement the LHC
   It shall collider electron and positrons together
    at a centre-of-mass energy of 1 TeV
   The anticipated cost is a cool $8,000,000,000!
   Currently, a detailed physics case and accelerator
    design is being formulated, in an attempt to get
    someone to pay for it!
The parts of a linear collider
            The key parameters
   The linear collider is driven by 2 key parameters
     The collision energy
     The luminosity

   The two beams collide head-on, so the collision
    energy is the sum of the beam energies E=2Ebeam

   The luminosity tells us the probability of the two
    beams interacting – essentially the overlap of the
    two colliding beams
                 How to get Luminosity
    To increase probability of direct e+e- collisions
     (luminosity) and birth of new particles, beam sizes at
     IP must be very small


Beam size: 250 * 3 * 110000 nanometers
(x y z)




                                             f rep nb N 2
                                          L              HD
                                             4  x y
                                         (We shall derive this next lecture)
The Livingstone plot
                 Light sources
   Remember the he photons emitted when we
    bend a particle beam? They can be useful!
   Light sources store a single beam of particles,
    for the purpose of shining this light at useful
    experiments…so-called light sources
   We can also “wiggle” the particle beam to
    produce radiation in specific parts of the EM
    spectrum
The SRS at Daresbury
DIAMOND
       “The Quantum Universe”
   This is the directed reading for this lecture
   Today, I’ve explained what particle accelerators
    are, and a little on how they work
   “The Quantum Universe” tells you why we
    bother to build colliding beam accelerators
   The reason is to probe fundamental physics, a
    little of which you will have met in other courses
                 Next lecture
   In the remaining two lectures, we’ll look at the
    key parameters needed to describe an accelerator
     The beam energy
     The luminosity

   We also will look at how we achieve these goals,
    with specific application to the International
    Linear Collider
   Next week shall be a double lecture…
   And shall be more detailed than this one

				
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posted:7/3/2011
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