We’ve seen a number of examples of technology transfer in particle detector development from hep


Download 450 b.
Sana24.04.2017
Hajmi450 b.


Accelerators

  • We’ve seen a number of examples of technology transfer in particle detector development from HEP (basic science) to industry (medical, …)

  • Particle accelerators provide another such example

    • There are currently more than 30,000 particle accelerators in use throughout the world with only a small fraction being used in HEP/nuclear research

Accelerators

  • Circa 2000



Accelerators

  • A brief history



Accelerators

  • A brief history

    • Electrostatic (Cockcroft-Walton, van de Graaf)
    • Linac (linear accelerator)
    • Circular (cyclotron, betatron, synchrotron)
    • Development of strong focusing
    • Colliding beams (present day)
    • Plasma wakefield, ???


Accelerators

  • “Moore’s law” ~ e+t/C



Accelerators

  • “Moore’s law”



Linac

  • Linac = linear accelerator

  • Applications in both high energy physics and radiation therapy



Linac

  • Linacs are single pass accelerators for electrons, protons, or heavy ions

    • Thus the KE of the beam is limited by length of the accelerator
      • Medical (4-25 MeV) – 0.5-1.5 m
      • SLAC (50 GeV) – 3.2 km
      • ILC (250 GeV) - 11 km
  • Linac – static field, induction (time varying B field), RF

    • Operate in the microwave region
    • Typical RF for medical linacs ~ 2.8 GHz
    • Typical accelerating gradients are 1 MV/m – 100 MV/m


Linac

  • Brief history

    • Invented by Wideroe (Germany) in 1928
      • Accelerated potassium ions to 50 keV using 1 MHz AC
    • First realization of a linac by Sloan (USA) in 1931
    • No further progress until post-WWII when high power RF generators became available
    • Modern design of enclosing drift tubes in a cavity (resonator) developed by Alvarez (USA)
      • Accelerated 32 MeV protons in 1946 using 200 MHz 12 m long linac
    • Electron linac developed by Hansen and Ginzton (at Stanford) around the same period
      • Evolved into SLAC laboratory and led to the birth of medical linacs (Kaplan and Varian Medical Systems)


Linac

  • Wideroe’s linac



Linac

  • Alvarez drift tube linac

  • First stage of Fermilab linac



Linac

  • A linac uses an oscillating EM field in a resonant cavity or waveguide in order to accelerate particles

    • Why not just use EM field in free space to produce acceleration?
  • We need a metal cavity (boundary conditions) to produce a configuration of waves that is useful

    • Standing wave structures
    • Traveling wave structures


LINAC

  • Medical linacs can be either type



Waveguides



Waveguides

  • Cyclindrical wave guide



TM Modes



Waveguides



Waveguides



Waveguides

  • Phase and group velocity



Waveguides

  • The phase velocity can be slowed by fitting the guide with conducting irises or discs

  • The derivation is complicated but alternatively think of the waveguide as a transmission line

  • Conducting irises in a waveguide in TM0,1 mode act as discrete capacitors with separation d in parallel with C0



Waveguides

  • Disc loaded waveguide



Traveling Wave Linac

  • Notes

    • Injection energy of electrons at 50 kV (v=0.4c)
    • The electrons become relativistic in the first portion of the waveguide
    • The first section of the waveguide is described as the buncher section where electrons are accelerated/deaccelerated
    • The final energy is determined by the length of the waveguide
    • In a traveling wave system, the microwaves must enter the waveguide at the electron gun end and must either pass out at the high energy end or be absorbed without reflection


Traveling Wave Linac



Standing Wave Linac

  • Notes

    • In this case one terminates the waveguide with a conducting disc thus causing a /2 reflection
    • Standing waves form in the cavities (antinodes and nodes)
    • Particles will gain or receive zero energy in alternating cavities
    • Moreover, since the node cavities don’t contribute to the energy, these cavities can be moved off to the side (side coupling)
    • The RF power can be supplied to any cavity
    • Standing wave linacs are shorter than traveling wave linacs because of the side coupling and also because the electric field is not attenuated


Standing Wave Linac



Standing Wave Linac



Electron Source

  • Based on thermionic emission

  • Cathode must be insulated because waveguide is at ground

  • Dose rate can be regulated controlling the cathode temperature



RF Generation

  • Magnetron

    • As seen in your microwave oven!
    • Operation
      • Central cathode that also serves as filament
      • Magnetic field causes electrons to spiral outward
      • As the electrons pass the cavity they induce a resonant, RF field in the cavity through the oscillation of charges around the cavity
      • The RF field can then be extracted with a short antenna attached to one of the spokes


RF Generation

  • Magnetron



RF Generation

  • Magnetron



RF Generation

  • Klystron

    • Used in HEP and > 6 MeV medical linacs
    • Operation – effectively an RF amplifier
      • DC beam produced at high voltage
      • Low power RF excites input cavity
      • Electrons are accelerated or deaccelerated in the input cavity
      • Velocity modulation becomes time modulation during drift
      • Bunched beam excites output cavity
      • Spent beam is stopped


RF Generation

  • Klystron



Medical Linac

  • Block diagram



Medical Linac



Medical Linac



Cyclotron

  • The first circular accelerator was the cyclotron

    • Developed by Lawrence in 1931 (for $25)
    • About 4 inches in diameter


Cyclotron

  • Principle of operation

    • Particle acceleration is achieved using an RF field between “dees” with a constant magnetic field to guide the particles


Cyclotron

  • Principle of operation



Cyclotron

  • Why don’t the particles hit the pole pieces?



Cyclotron

  • TRIUMF in Canada has the world’s largest cyclotron



Cyclotron

  • TRIUMF



Cyclotron

  • NSCL cyclotron at Michigan State



Cyclotron



Betatron

  • Since electrons quickly become relativistic they could not be accelerated in cyclotrons

    • Kerst and Serber invented the betatron for this purpose (1940)
  • Principle of operation

    • Electrons are accelerated with induced electric fields produced by changing magnetic fields (Faraday’s law)
    • The magnetic field also served to guide the particles and its gradients provided focusing


Betatron

  • Principle of operation



Betatron

  • Principle of operation



TM Modes



TE Modes



Waveguides




Do'stlaringiz bilan baham:


Ma'lumotlar bazasi mualliflik huquqi bilan himoyalangan ©fayllar.org 2017
ma'muriyatiga murojaat qiling