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
          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

                  E   h      2 1010 J
                 Ee  eU
                 Ee  E  U      1.2  109 V
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
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
        As the energy of the particles
         increases, the radius of the
         orbit increases until the
         particle is ejected
The first million volt cyclotron


“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


            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
   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!

                              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
                                   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
   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
The SRS at Daresbury
       “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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