Particle Accelerators The particle accelerator plays the same role that the telescope plays for astronomy or the microscope plays for biology Wave nature of matter: Higher energy means smaller wavelength and the ability to resolve smaller structure For example, visible light with l~10-5m cannot resolve an individual nucleus 1/2/2019 Physics 590B - Fall 2014

Crooke’s Tube A Crooke’s Tube is a partially evacuated glass cylinder with metal electrodes at either end An applied high voltage causes electrons (cathode rays) to travel from the cathode to the anode Electrons are produced by ionization of the residual air in the tube “Maltese Cross” tube 1/2/2019 Physics 590B - Fall 2014

Cockroft-Walton Accelerator The Cockroft-Walton accelerator was the first transmutation of an element by artificially accelerated particles (1932): Achieved ~800kV Limited by spark discharge to surroundings Still in use today as injectors or neutron sources C-W from the BNL AGS (AC ripple on accelerating voltage) Cockroft, Rutherford and Walton 1/2/2019 Physics 590B - Fall 2014

Van de Graaf Accelerator The Van De Graaf is the most common electrostatic accelerator in use today Main idea is to enclose the high potential in an inert atmosphere to prevent discharge Tandem Van De Graff using the same accelerating voltage twice by stripping electrons from a negatively charged beam 10-12 MeV range Robert Van de Graaf 1/2/2019 Physics 590B - Fall 2014

Large Potentials All of the accelerators we have discussed so far require large potentials Widerӧe (1929) suggested a series of potentials: Zero net effect! ab is cancelled by bc However, if we reverse the field at just the right time… a b c d E + - + - a b c d a b c d + - - + - + + - (metal beam tube prevents the particle seeing changing field) 1/2/2019 Physics 590B - Fall 2014

Cyclotrons A cyclotron uses magnetic fields to confine the particles to an orbit Relativity comes into play: Synchrocyclotron (w varies) Isochronous cyclotron (B varies) cyclotron frequency constant! Limited to ~25MeV for protons 1/2/2019 Physics 590B - Fall 2014

Synchrotrons Essentially a linear accelerator bent back on itself Replace the large magnet in a cyclotron with a string of magnets The particle is accelerated in the ring, and the magnetic field is adjusted to keep the orbit at the same radius Particles are injected every 1-3s (from another accelerator) Lots of energy required to ramp the magnets up and down Very high energies possible LHC – “last dipole” installation FNAL – BOONE beamline 1/2/2019 Physics 590B - Fall 2014

Phase Stability (I) One of the advantages of this approach is that it will provide automatic regulation of the accelerated beam Particles from the source, having just the right velocity and phase, will be captured and accelerated An accelerator of this type will provide “bunches” of beam (not continuous) One of the advantages of this approach is that it will provide automatic regulation of the accelerated beam Particles from the source, having just the right velocity and phase, will be captured and accelerated An accelerator of this type will provide “bunches” of beam (not continuous) One of the advantages of this approach is that it will provide automatic regulation of the accelerated beam Particles from the source, having just the right velocity and phase, will be captured and accelerated An accelerator of this type will provide “bunches” of beam (not continuous) V V V V STABLE STABLE STABLE STABLE slow slow slow slow fast fast fast fast UNSTABLE UNSTABLE UNSTABLE UNSTABLE t t t t 1/2/2019 Physics 590B - Fall 2014

Phase Stability (II) Relativistic effects change the phase of the accelerating voltage for which the beam is stable. Consider a high energy beam where the energy is many times the mass of the particles The speed of particles is essentially v=c (constant) A “fast” particle arrives late because its orbit is larger A “slow” particle arrives early because its orbit is smaller The accelerator must “jump” from one phase to the next at transition. The CERN SPS was the first accelerator to demonstrate this. RHIC was the first superconducting machine to go through transition. fast - unstable fast - stable 1/2/2019 Physics 590B - Fall 2014

Weak and Strong Focusing To perform experiments we want narrow, well-defined beams We’ve discussed longitudinal stability, what about lateral? “Weak focusing” synchrotrons required very large, strong magnets to keep the beam focused Practical limit on the size a machine could be made By introducing a gradient in the magnetic fields, the beam could be alternately focused in horizontal and vertical directions Smaller magnets required Gradient field can be broken into dipole + quadrupole + sextupole +… Very small beampipes and apertures No theoretical limit to beam energies 1/2/2019 Physics 590B - Fall 2014

The “B” Factories High luminosity colliders designed to produce high statistics samples of “b” quarks for study Run continuously for long periods of time in a “factory” mode. Electron+ Positron machines Operate at the Upsilon(4s) resonance (b-bbar) SLAC/PEP-II (US) BaBar KEK-B (Japan) Belle 1/2/2019 Physics 590B - Fall 2014

Relativistic Heavy Ion Collider RHIC pC “CNI” polarimeters absolute pH polarimeter BRAHMS & PP2PP PHOBOS RHIC Siberian Snakes PHENIX STAR Siberian Snakes Spin Rotators 5% Snake LINAC BOOSTER AGS pC “CNI” polarimeter Pol. Proton Source AGS 200 MeV polarimeter Rf Dipoles 20% Snake 1/2/2019 Physics 590B - Fall 2014

Large Hadron Collider The highest energy particle accelerator in the world – the Large Hadron Collider – is operating now in Geneva, Switzerland . Currently operating at 7TeV, plan is to ultimately go to 14TeV. SPS LHC PS 1/2/2019 Physics 590B - Fall 2014

The Future - Next Linear Collider? Precision tests of the Standard Model best done in a very clean environment – electron/positron collisions. However, very difficult to accelerate e+/e- in a synchrotron Energy lost due to synchrotron radiation (Bremmstrahlung) Must be replaced Goes into the superconducting magnets! Lots of ongoing development and design 1/2/2019 Physics 590B - Fall 2014

BACKUP 1/2/2019 Physics 590B - Fall 2014

Alternating Gaps The time between the gaps must be ½ the period of the AC voltage Assume a fixed frequency and potential: Example: protons with Ln = 0.1m, neV0= 10MeV, f = 2.5MHz Very high frequencies (for the time) required! WWII development of klystrons made this practical n = gap number V0 = accelerating potential Length of nth gap grows like n1/2 1/2/2019 Physics 590B - Fall 2014

The Future - Muon Collider? What if we use muons instead of electrons? Won’t have Bremmstrahlung problems, but No “source” of muons Have to generate them from secondary beams from pion decays Currently being developed as a possiblity for FNAL. Must generate high intensity muon beams, capture, cool and collide them with high luminosity. 1/2/2019 Physics 590B - Fall 2014

HERA @ DESY The HERA collider interacted beams of electrons/positrons at 30GeV with proton beams at 820GeV. Measured much of what we know about parton distributions at low-x Asymmetric collisions Center of mass moving in the lab frame Much easier for certain experimental observables 1/2/2019 Physics 590B - Fall 2014