Particle accelerators are everywhere!

# Particle accelerators are everywhere!

## Particle accelerators are everywhere!

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##### Presentation Transcript

1. Cobbled together from:i) “The quest for luminosity”, by Dr. Rob Applebyii) “An introduction to particle accelerators,” by Erik Adli

2. Particle accelerators are everywhere! • Daily applications • TV, computer monitor • Microwave oven, oscilloscopes • Industrial • Food sterilization • Electron microscopes • Radiation treatment of materials • Nuclear waste treatment

3. 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

4. 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)

5. 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 mainly in colliding beam applications

6. 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

7. The best accelerator in the universe…

8. 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

9. 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)

10. The development of accelerators • Accelerators have gone through a long development process, including • Electrostatic accelerators • The Van de Graaff accelerator • The Cyclotron • The Synchrotron

11. 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 AC voltage between “D”s timed so electric field always accelerates

12. 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." Lawrence and Livingston at Berkeley

13. Modern Particle Accelerators The particles gain energy by surfing on the electric fields of well-timed radio oscillations (in a cavity like a microwave oven)

14. Accelerating cavities • Modern machines use a time-dependent electric field in a cavity to accelerate the particles

15. 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

16. Lorentz equation • The two main tasks of an accelerator • Increase the particle energy • Change the particle direction (follow a given trajectory, focusing) • Lorentz equation: • FB v  FB does no work on the particle • Only FE can increase the particle energy • FE or FB for deflection? v  c  Magnetic field of 1 T (feasible) same bending power as en electric field of 3108 V/m (NOT feasible) • FB is by far the most effective in order to change the particle direction

17. Dipole F Quadrupole D Quadrupole Magnetic lattices • Magnets are combined to form a magnet lattice • The lattice steers and focuses the beam

18. 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!

19. 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!

20. L(arge)E(lectron)P(ositron)

21. The LEP tunnel (this is one of LEPs superconducting cavities)

22. Acceleration techniques: RF cavities • Electromagnetic power is stored in a resonant volume instead of being radiated • RF power feed into cavity, originating from RF power generators, like Klystrons • RF power oscillating (from magnetic to electric energy), at the desired frequency • RF cavities requires bunched beams (as opposed to coasting beams) • particles located in bunches separated in space

23. From pill-box to real cavities (from A. Chao) LHC cavity module ILC cavity

24. Why circular accelerators? • Technological limit on the electrical field in an RF cavity (breakdown) • Gives a limited E per distance •  Circular accelerators, in order to re-use the same RF cavity • This requires a bending field FB in order to follow a circular trajectory (later slide)

25. The synchrotron • Acceleration is performed by RF cavities • (Piecewise) circular motion is ensured by a guide field FB • FB : Bending magnets with a homogenous field • In the arc section: • RF frequency must stay locked to the revolution frequency of a particle (later slide) • Synchrotrons are used for most HEP experiments (LHC, Tevatron, HERA, LEP, SPS, PS) as well as, as the name tells, in Synchrotron Light Sources (e.g. ESRF)

26. Focusing field: quadrupoles • Quadrupole magnets gives linear field in x and y: Bx = -gy By = -gx • However, forces are focusing in one plane and defocusing in the orthogonal plane: Fx= -qvgx (focusing) Fy = qvgy (defocusing) • Opposite focusing/defocusing is achieved by rotating the quadrupole 90 • Analogy to dipole strength: normalized quadrupole strength: inevitable due to Maxwell

27. Optics analogy • Physical analogy: quadrupoles  optics • Focal length of a quadrupole: 1/f = kl • where l is the length of the quadrupole • Alternating focusing and defocusing lenses will together give total focusing effect in both planes (shown later) • “Alternating Gradient” focusing

28. The Lattice • An accelerator is composed of bending magnets, focusing magnets and non-linear magnets (later) • The ensemble of magnets in the accelerator constitutes the “accelerator lattice”

29. Example: lattice components

30. Conclusion: transverse dynamics • We have now studied the transverse optics of a circular accelerator and we have had a look at the optics elements, • the dipole for bending • the quadrupole for focusing • the sextupole for chromaticity correction • All optic elements (+ more) are needed in a high performance accelerator, like the LHC

31. But particles radiate energy! Synchrotron Radiation from an electron in a magnetic field: Energy loss per turn of a machine with an average bending radiusr: Energy loss must be replaced by RF systemcost scaling \$ Ecm2 ~3400 MeV for LEP200 (18 MW)

32. 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

33. bang! 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, \$totµE

34. 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!

35. The parts of a linear collider

36. 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

37. Event rate vs. Luminosity Rate = L*s e+e- annihilation cross-section approximately L=10E34/cm2s = 0.00001/fb/s luminosity results in rate 0.0015/s = 5.4/hr. Presumably interested in much more rare processes High luminosity is very important at high energy

38. 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) (We shall derive this next lecture)

39. The Livingstone plot

40. 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 2007no2009oops 2011 • There are a number of experiments

41. The LHC tunnel

42. LHC layout • circumference = 26658.9 m • 8 interaction points, 4 of which contains detectors where the beams intersect • 8 straight sections, containing the IPs, around 530 m long • 8 arcs with a regular lattice structure, containing 23 arc cells • Each arc cell has a FODO structure, 106.9 m long FODO = focus-drift-defocus-drift

43. LHC main parametersat collision energy 4000 in 2012 1400 in 2011-2

44. Colliding Proton/Antiproton Beams No problem with synchrotron radiation energy loss, but… Like throwing bags of marbles at each other at high velocity: Marble-marble collisions are interesting, not bag-bag collisions Fortunately, the number and arrangements of the “marbles” has been measured by other experiments

45. 1975 1980 1985 1990 1995 2000 2005 2010 2015 2020 Timeline of Proton Colliders Proton-proton Proton-antiproton Proton-proton Tevatron CDF/D0 Detectors LHC Collider CMS/Atlas Detectors SPS Collider UA1/UA2 Detectors ISR Top quark W/Z bosons Higgs, Supersymmetry etc

46. Proton-Antiproton Collisions at Fermilab (Chicago) • The Tevatron accelerator, 6 km circumference The CDF (Collider Detector at Fermilab) experiment

47. LHC Dipole Design

48. LHC Dipole Magnet (3D)