1. Eric Prebys FNAL Accelerator Physics Center June 7-17, 2010

2.  History and movitation for accelerators  Basic accelerator physics concepts  Overview of major accelerators  emphasis on LHC  Other uses for accelerators  The future  Crazy ideas 2 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU June 7-17, 2010

3.  The first “particle physics experiment” told Ernest Rutherford the structure of the atom (1911)  In this case, the “accelerator” was a naturally decaying 235 U nucleus  The first artificial acceleration of particles was done using “Crookes tubes”, in the latter half of the 19 th century  These were used to produce the first X-rays (1875) Study the way radioactive particles “scatter” off of atoms 3 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU June 7-17, 2010

4.  To probe smaller scales, we must go to higher energy  To discover new particles, we need enough energy available to create them  The rarer a process is, the more collisions (luminosity) we need to observe it. 4 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU June 7-17, 2010 1 fm = 10 -15 m (Roughly the size of a proton)

5. Accelerators allow us to probe down to a few picoseconds after the Big Bang! 5 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU June 7-17, 2010

6.  Radioactive sources produce maximum energies of a few million electron volts (MeV)  Cosmic rays reach energies of ~1,000,000,000 x LHC but the rates are too low to be useful as a study tool  Remember what I said about luminosity!  On the other hand, low energy cosmic rays are extremely useful  But that’s another talk Max LHC energy 6 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU June 7-17, 2010

7. The simplest accelerators accelerate charged particles through a static electric field. Example: vacuum tubes (or CRT TV’s) Cathode Anode Limited by magnitude of static field: - TV Picture tube ~keV - X-ray tube ~10’s of keV - Van de Graaf ~MeV’s Solutions: -Alternate fields to keep particles in accelerating fields -> RF acceleration -Bend particles so they see the same accelerating field over and over -> cyclotrons, synchrotrons 7 FNAL Cockroft- Walton = 750 kV

8. Nominal Energy Particles with lower E arrive later and see greater V. Nominal Energy Particles with lower E arrive earlier and see greater V. Particles are typically accelerated by radiofrequency (“RF”) electric fields. Stability depends on particle arrival time relative to RF phase  “bunched” beams If velocity dominates If momentum (path length) dominates 8 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU June 7-17, 2010 “bunch”

9. Fermilab Drift Tube Linac (200MHz): oscillating field uniform along length ILC prototype elipical cell “  -cavity” (1.3 GHz): field alternates with each cell JLab compact “toaster cavity” (400MHz): low frequency in a limited space 9 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU June 7-17, 2010

10.  1930 (Berkeley)  Lawrence and Livingston  K=80KeV  1935 - 60” Cyclotron  Lawrence, et al. (LBL)  ~19 MeV (D 2 )  Prototype for many 10 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU June 7-17, 2010

11.  60” cyclotron (1935)  Berkeley and elsewhere  Fermilab  Radius = 1km  Built ~1970  Upgraded ~1985, ~1997  Until recently, the most powerful accelerator in the world. 11 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU June 7-17, 2010

12.  Tunnel originally dug for LEP  Built in 1980’s as an electron positron collider  Max 100 GeV/beam, but 27 km in circumference!!  Now we’ll talk a little about how these things work… /LHC My House (1990-1992) 12 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU June 7-17, 2010

13.  The next few slides contain a lot of mathematical detail.  They’re not meant to be fully absorbed real time by everyone.  I’ll follow them with a “glossary”, which will qualitatively summarize the key concepts. June 7-17, 2010 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU 13

14.  A charged particle in a uniform magnetic field will follow a circular path or radius  Typical Magnet Strength  Conventional: ~1 T  Latest superconducting: ~8T  Next generation superconducting (Nb 3 Sn): ~15T side view top view “Thin lens” approximation: If the extent of the magnetic field is short compared to , then the particle experience and angular “kick” 14

15. Vertical Plane: Horizontal Plane: Luckily… …pairs give net focusing in both planes! -> “FODO cell” 15 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU June 7-17, 2010

16. For a particular particle, the deviation from an idea orbit will undergo “pseudo-harmonic” oscillation as a function of the path along the orbit: The “betatron function”  s  is effectively the local wavenumber and also defines the beam envelope. Phase advance Lateral deviation in one plane Closely spaced strong quads -> small  -> small aperture, lots of wiggles Sparsely spaced weak quads -> large  -> large aperture, few wiggles s x 16 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU June 7-17, 2010

17.  Generally, we don’t want the tune in either plane or their combination to be a low order rational number  As particles go around a ring, they will oscillate around the ideal orbit a fixed number of times. This number is called the “tune” (usually  or Q) Ideal orbit Particle trajectory 6.76.7 Integer : magnet/aperture optimization Fraction: Beam Stability “small” integers fract. part of X tunefract. part of Y tune 17 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU June 7-17, 2010

18. As a particle returns to the same point on subsequent revolutions, it will map out an ellipse in phase space, defined by Area =  Twiss Parameters An ensemble of particles will have a “bounding” . This is referred to as the “emmitance” of the ensemble. Various definitions: Electron machines: Contains 39% of Gaussian particles Proton machines: Contains 95% of Gaussian particles Usually leave  as a unit, e.g. E=12  -mm- mrad (FNAL) 18 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU June 7-17, 2010

19. As the beam accelerates “adiabatic damping” will reduce the emittance as: so we define the “normalized emittance” as: The usual relativistic  and   We can calculate the size of the beam at any time and position as: Example: Fermilab Booster 19 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU June 7-17, 2010

20.  When a particle hits another particle, the probability that a particular reaction will occur has units of area  Think about the probability of hitting a window while randomly throwing balls at a wall.  This is referred to as “cross-section” The higher the cross-section, the more probable an interaction  For historical reasons, we often use the unit of “barn”, where 1 barn  1x10 -24 cm 2  total nuclear cross-section  The processes we are interested in today are generally measured in small fractions of a “barn” picobarn (pb), femtobarn (fb), etc. June 7-17, 2010 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU 20

21. The relationship of the beam to the rate of observed physics processes is given by the “Luminosity” Rate Cross-section (“physics”) “Luminosity ” Standard unit for Luminosity is cm -2 s -1 For fixed (thin) target: Incident rate Target number density Target thickness Example: MiniBooNe primary target: 21

22. Circulating beams typically “bunched” (number of interactions) Cross-sectional area of beam Total Luminosity: Circumference of machine Number of bunches Record e+e- Luminosity (KEK-B): 1.71E34 cm -2 s -1 Record Hadronic Luminosity (Tevatron): 4.03E32 cm -2 s -1 LHC Design Luminosity: 1.71E34 cm -2 s -1 22 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU June 7-17, 2010

23.  The total number of interactions is given by the cross-section times the integral of the luminosity over time:  The integrated luminosity has units of cm -2, but for historical reasons it is almost always quoted in “inverse barns” (or more often “inverse picobarns” (pb -1 ), “inverse femtobarns” (fb -1 ), etc)  1 b -1 = 10 24 cm -2  1 fb-1 = 10 39 cm -2  The integrated luminosity is the ultimate measure of “what an accelerator has delivered”.  Example: the Fermilab Tevatron has delivered roughly 7 fb -1 of proton-antiproton collisions per experiment, so something with a 10 fb cross-section would have produced 7x10=70 events by now. June 7-17, 2010 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU 23

24.  “RF cavity”: resonant electromagnetic structure, used to accelerate or deflect the beam.  “Bunch”: a cluster of particles which is stable with respect to the accelerating RF  “Dipole”: magnet with a uniform magnetic field, used to bend particles  “Quadrupole”: magnet with a field that is ~linear near the center, used to focus particles  “Lattice”: the magnetic configuration of a ring or beam line  “Beta function (  )”: a function of the beam lattice used to characterize the beam size.  “Emittance (  )”: a measure of the spacial and angular spread of the beam  “Tune”: number of times the beam “wiggles” when it goes around a ring. Fractional part related to beam stability.  “Cross-section”: a measure of how likely a reaction is to occur.  “Luminosity”: a measure of the rate at which “particles hit each other”. You need a high luminosity to observe a rare process.  “Integrated Luminosity”: luminosity x time, the “bottom line” as to what an accelerator has delivered. 24 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU June 7-17, 2010

25.  How were the choices made?  Colliding beams vs. fixed target  Protons vs. electrons  Proton-proton vs. proton anti-proton  Superconducting magnets  Energy and Luminosity 25 June 7-17, 2010 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU

26.  For a relativistic beam hitting a fixed target, the center of mass energy is:  On the other hand, for colliding beams (of equal mass and energy):  To get the 14 TeV CM design energy of the LHC with a single beam on a fixed target would require that beam to have an energy of 100,000 TeV!  Would require a ring 10 times the diameter of the Earth!! 26

27.  Electrons are point-like  Well-defined initial state  Full energy available to interaction  Can calculate from first principles  Can use energy/momentum conservation to find “invisible” particles.  Protons are made of quarks and gluons  Interaction take place between these consituents.  At high energies, virtual “sea” particles dominate  Only a small fraction of energy available, not well-defined.  Rest of particle fragments -> big mess! So why don’t we stick to electrons?? 27 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU June 7-17, 2010

28. As the trajectory of a charged particle is deflected, it emits “synchrotron radiation” An electron will radiate about 10 13 times more power than a proton of the same energy!!!! Protons: Synchrotron radiation does not affect kinematics very much Electrons: Beyond a few MeV, synchrotron radiation becomes very important, and by a few GeV, it dominates kinematics - Good Effects: - Naturally “cools” beam in all dimensions - Basis for light sources, FEL’s, etc. - Bad Effects: - Beam pipe heating - Exacerbates beam-beam effects - Energy loss ultimately limits circular accelerators Radius of curvature 28 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU June 7-17, 2010

29.  Proton accelerators  Synchrotron radiation not an issue to first order  Energy limited by the maximum feasible size and magnetic field.  Electron accelerators  Recall  To keep power loss constant, radius must go up as the square of the energy (weak magnets, BIG rings): The LHC tunnel was built for LEP, and e + e - collider which used the 27 km tunnel to contain 100 GeV beams (1/70 th of the LHC energy!!) Beyond LEP energy, circular synchrotrons have no advantage for e + e - -> International Linear Collider (but that’s another talk) 29 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU June 7-17, 2010

30.  Beyond a few hundred GeV, most interactions take place between gluons and/or virtual “sea” quarks.  No real difference between proton-antiproton and proton-proton  Because of the symmetry properties of the magnetic field, a particle going in one direction will behave exactly the same as an antiparticle going in the other direction  Can put protons and antiprotons in the same ring This is how the SppS (CERN) and the Tevatron (Fermilab) have done it.  The problem is that antiprotons are hard to make  Can get ~2 positrons for every electron on a production target  Can only get about 1 antiproton for every 50,000 protons on target!  Takes a day to make enough antiprotons for a “store” in the Fermilab Tevatron  Ultimately, the luminosity is limited by the antiproton current.  Thus, the LHC was designed as a proton-proton collider. 30 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU June 7-17, 2010

31.  For a proton accelerator, we want the most powerful magnets we can get  Conventional electromagnets are limited by the resistivity of the conductor (usually copper)  The field of high duty factor conventional magnets is limited to about 1 Tesla  An LHC made out of such magnets would be 40 miles in diameter – approximately the size of Rhode Island.  The highest energy accelerators are only possible because of superconducting magnet technology. Power lost Square of the field 31 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU June 7-17, 2010

32.  Conventional magnets operate at room temperature. The cooling required to dissipate heat is usually provided by fairly simple low conductivity water (LCW) heat exchange systems.  Superconducting magnets must be immersed in liquid (or superfluid) He, which requires complex infrastructure and cryostats  Any magnet represents stored energy  In a conventional magnet, this is dissipated during operation.  In a superconducting magnet, you have to worry about where it goes, particularly when something goes wrong. 32 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU June 7-17, 2010

33. TcTc  Superconductor can change phase back to normal conductor by crossing the “critical surface”  When this happens, the conductor heats quickly, causing the surrounding conductor to go normal and dumping lots of heat into the liquid Helium  This is known as a “quench”. Can push the B field (current) too high Can increase the temp, through heat leaks, deposited energy or mechanical deformation 33 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU June 7-17, 2010

34. *pulled off the web. We recover our Helium. 34 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU June 7-17, 2010

35.  W (M W =80 GeV)  Z (M Z =91 GeV)  The rate of physical processes depends strongly on energy  For some of the most interesting searches, the rate at the LHC will be 10- 100 times the rate at the Tevatron.  Nevertheless, still need about 30 times the luminosity of the Tevatron to study the most important physics June 7-17, 2010 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU 35

36. ParameterTevatron“nominal” LHC Circumference6.28 km (2*PI)27 km Beam Energy980 GeV 7 TeV Number of bunches362808 Protons/bunch275x10 9 115x10 9 pBar/bunch80x10 9 - Stored beam energy1.6 +.5 MJ366+366 MJ* Initial luminosity3.3x10 32 (cm -2 s -1 )1.0x10 34 (cm -2 s -1 ) Main Dipoles7801232 Bend Field4.2 T8.3 T Main Quadrupoles~200~600 Operating temperature4.2 K (liquid He)1.9K (superfluid He) *2 MJ ~ “stick of dynamite” -> Very scary 36 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU June 7-17, 2010

37.  Even with the higher rates, still need a lot of interactions to reach the discovery potential of the LHC June 7-17, 2010 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU 37 100 fb -1 /yr SHUTDOWN 1000 fb -1 /yr 200 fb -1 /yr 3000 300 30 10-20 fb -1 /yr SUSY@3TeV Z’@6TeV SUSY@1TeV ADD X-dim@9TeV Compositeness@40TeV H(120GeV)   Higgs@200GeV 50 x Tevatron luminosity 500 x Tevatron luminosity (will probably never happen) Note: VERY outdated plot. Ignore horizontal scale. Would probably take until ~2030 to get 3000 fb -1

38. LEP (at CERN): - 27 km in circumference - e+e- - Primarily at 2E=M Z (90 GeV) - Pushed to E CM =200GeV - L = 2E31 - Highest energy circular e+e- collider that will ever be built. - Tunnel now houses LHC SLC (at SLAC): - 2 km long LINAC accelerated electrons AND positrons on opposite phases. - 2E=M Z (90 GeV) - polarized - L = 3E30 - Proof of principle for linear collider 38 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU June 7-17, 2010

39. - B-Factories collide e+e- at E CM = M(  (4S)). -Asymmetric beam energy (moving center of mass) allows for time- dependent measurement of B-decays to study CP violation. KEKB (Belle Experiment): - Located at KEK (Japan) - 8GeV e- x 3.5 GeV e+ - Peak luminosity 1E34 PEP-II (BaBar Experiment) - Located at SLAC (USA) - 9GeV e- x 3.1 GeV e+ - Peak luminosity 0.6E34 39 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU June 7-17, 2010

40. - Located at Brookhaven: - Can collide protons (at 28.1 GeV) and many types of ions up to Gold (at 11 GeV/amu). - Luminosity: 2E26 for Gold - Goal: heavy ion physics, quark-gluon plasma, ?? 40 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU June 7-17, 2010

41.  Locate at Jefferson Laboratory, Newport News, VA  6GeV e- at 200 uA continuous current  Nuclear physics, precision spectroscopy, etc 41 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU June 7-17, 2010

42. 42 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU June 7-17, 2010

43. A 1 GeV Linac will load 1.5E14 protons into a non- accelerating synchrotron ring. These are fast extracted onto a Mercury target This happens at 60 Hz -> 1.4 MW Neutrons are used for biophysics, materials science, industry, etc… 43 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU June 7-17, 2010

44.  Put circulating electron beam through an “undulator” to create synchrotron radiation (typically X-ray)  Many applications in biophysics, materials science, industry.  New proposed machines will use very short bunches to create coherent light. 44 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU June 7-17, 2010

45.  Radioisotope production  Medical treatment  Electron welding  Food sterilization  Catalyzed polymerization  Even art… June 7-17, 2010 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU 45 In a “Lichtenberg figure”, a low energy electron linac is used to implant a layer of charge in a sheet of lucite. This charge can remain for weeks until it is discharged by a mechanical disruption.

46.  LEP was the limit of circular e + e - colliders  Next step must be linear collider  Proposed ILC 30 km long, 250 x 250 GeV e + e -  BUT, we don’t yet know whether that’s high enough energy to be interesting  Need to wait for LHC results  What if we need more? June 7-17, 2010 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU 46

47.  Use low energy, high current electron beams to drive high energy accelerating structures  Up to 1.5 x 1.5 TeV, but VERY, VERY hard June 7-17, 2010 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU 47

48.  Muons are pointlike, like electrons, but because they’re heavier, synchrotron radiation is much less of a problem.  Unfortunately, muons are unstable, so you have to produce them, cool them, and collide them, before they decay. June 7-17, 2010 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU 48

49.  Many advances have been made in exploiting the huge fields that are produced in plasma oscillations.  Potential for accelerating gradients many orders of magnitude beyond RF cavities.  Still a long way to go for a practical accelerator. June 7-17, 2010 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU 49

50.  Lots has been done.  Lots more to do. June 7-17, 2010 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU 50