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

 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

 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

 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, fm = m (Roughly the size of a proton)

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

 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

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

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”

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

 1930 (Berkeley)  Lawrence and Livingston  K=80KeV  ” 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

 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

 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 ( ) 12 Eric Prebys, "Particle Accelerators", QuarkNet Summer Institute at NIU June 7-17, 2010

 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

 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

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

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

 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 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

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

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

 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  1x 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

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

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

 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 = cm -2  1 fb-1 = 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

 “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

 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

 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

 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

As the trajectory of a charged particle is deflected, it emits “synchrotron radiation” An electron will radiate about 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

 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

 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

 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

 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

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

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

 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 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

ParameterTevatron“nominal” LHC Circumference6.28 km (2*PI)27 km Beam Energy980 GeV 7 TeV Number of bunches Protons/bunch275x x10 9 pBar/bunch80x Stored beam energy MJ MJ* Initial luminosity3.3x10 32 (cm -2 s -1 )1.0x10 34 (cm -2 s -1 ) Main Dipoles 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

 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 fb -1 /yr SHUTDOWN 1000 fb -1 /yr 200 fb -1 /yr fb -1 /yr ADD H(120GeV)   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

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

- 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

- 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

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

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

 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

 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.

 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

 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

 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

 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

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