Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 388.882 LHC PhysicsExperimental Methods and MeasurementsAccelerators[Lecture 2, February 9, 2009]C.Paus, 8.882 LHC Physics: Accelerators2Organizational Issues Please subscribe to mail list for discussion•at: http://mailman.mit.edu/mailman/listinfo/physics8.882•just follow the instructions•most of you are already subscribed Recitations•will be done by the lecturer•options are Tuesday/Thursday/Friday•1:00 pm seems to fit for most of you•this week: start with root tutorialC.Paus, 8.882 LHC Physics: Accelerators3Lecture Outline Accelerators●why do we accelerate particles?●basic physics of accelerators●various accelerator types●hadron versus lepton colliders●examples of recent accelerators●LEP, TeVatron, LHC●future of acceleratorsC.Paus, 8.882 LHC Physics: Accelerators4Why Do We Accelerate Particles? To take existing objects apart•1803 J.Dalton's indivisable atom•daring theory for the elements•ammonia: 1 azote + 1 hydrogen•ammonia nitrate: 1 nitric acid + 1 ammonia + 1 water•1896 M.&P. Curie find atoms decay•1897 J.J. Thomson discovers electron•1906 E.Rutherford: goldfoil experiment•1911 E.Rutherford: Physicist broke the nuclei shooting particles on itpictures from WikipediaC.Paus, 8.882 LHC Physics: Accelerators5Why Do We Accelerate Particles? To create new particles•1905 A. Einstein: energy is matter•1930 P. Dirac: math problem predicts antimatter•1932 C. Anderson: discovers positron in cloud chamber photos (electron curves other way)•1935 H. Yukawa: neutron-proton reaction requires pion•1936 V. Hess: discovers muon They used the big accelerator: The Universe Search for heavier antiproton and pion motivates particle acceleratorspictures from WikipediaC.Paus, 8.882 LHC Physics: Accelerators6Nobel Price 1936 The Nobel Prize in Physics 1936•Hess: “for his discovery of cosmic radiation”•Anderson: “for his discovery of the positron”Viktor F. HessCarl D. Anderson Interesting to read•http://nobelprize.org/nobel_prizes/physics/laureates/1936/hess-autobio.html•http://nobelprize.org/nobel_prizes/physics/laureates/1936/anderson-autobio.htmlC.Paus, 8.882 LHC Physics: Accelerators7Generating Particle Particle sources•cathod ray to generate electrons•heat cathod to produce electrons•apply electric field to collect electrons•cathode tube with hydrogen to generate protons Antimatter?•use pair production mechanism •very inefficientC.Paus, 8.882 LHC Physics: Accelerators8Basic Accelerator Physics Lorentz Force:electric forcemagnetic force Magnetic force perpendicular to velocity ==> no acceleration, changes direction Only electric force accelerates particles From the Maxwell equations: static:C.Paus, 8.882 LHC Physics: Accelerators9Accelerator TypesSimple battery•limited by discharge: 200 kV•electron gains energy of 1 eV per Volt•max. accelerations: 200 keV Cockroft-Walton (used at FNAL)•create cascade of high voltage gaps interrupted by diodes•open diodes to create short pulse•max. acceleration: 800 kV•at 700 kV:1932 first artificial nucleardesintegration in historyC.Paus, 8.882 LHC Physics: Accelerators10Accelerator Types Van de Graaff generator1) metallic sphere (pos.)2) electrode connected to sphere3) upper roller (plexiglass)4) belt with pos. charges5) belt with negative charges6) lower roller (metal)7) lower electrode (ground)8) spherical device with negative charges, used to discharge the main sphere9) spark from potential difference max. voltage 25 MVC.Paus, 8.882 LHC Physics: Accelerators11Accelerator Types Largest air insulated generator located at MIT•Van de Graaff was professor at MIT•Museum of Science exhibits the generatorLimit of electrostatic acceleratorsC.Paus, 8.882 LHC Physics: Accelerators12Accelerator TypesAlternating electric fields•beams are bunchedLinear acceleration•long accelerators•high powered RF cavitiesCircular accelerator•compact design with reasonable RF cavities•repeating sequence: resonance tuning etc.C.Paus, 8.882 LHC Physics: Accelerators13Surf's Up Charged particle ride the electromagnetic wave•create standing wave•use an RF cavity•high frequency•high amplitude•make particles arrive on time Self regulating•slow particle, larger push•fast particle, small push•oscillatory behaviourC.Paus, 8.882 LHC Physics: Accelerators14How to Create a Standing Wave? Use a Klystron (klys – electron) Compare to organ flute:•air flows into the flute•excites eigen modes of flute•create sound waves Correspondence with klystron•air flow = electron beam•flute = cavity•sound wave = electromagnetic wave•oscillation is induced by weak signalC.Paus, 8.882 LHC Physics: Accelerators15Radio Frequency Cavity Cavity is resonatorILC cavityLHC cavityC.Paus, 8.882 LHC Physics: Accelerators16Linear AcceleratorExample of Stanford Linear Accelerator (2 miles)C.Paus, 8.882 LHC Physics: Accelerators17Accelerator Types Cyclotron (1929 E.O. Lawrence) Physics idea•centripetal = magnetic•no dependence on r•alternating electric field = constant acceleration•Ebeam of up to 25 MeV•relativistic effects limiting•synchro-cyclotron•large dipole magnetspictures from WikipediaC.Paus, 8.882 LHC Physics: Accelerators18Accelerator Types Synchrotron (LEP, LHC)•constant radius, r•changing E and B Design advantage•use of beamline: vacuum•size is quite expandable•components can be designed freely•big magnet replaced with several small magnets•accommodates many acceleration sections Design limitations•synchrotron radiation for light particles (electrons)C.Paus, 8.882 LHC Physics: Accelerators19Summary on Accelerator Types Electrostatic accelerators•acceleration tube: breakdown at 200 keV•Cockroft-Walton: improves to 800 keV•van de Graaff: best electrostatic device at 25 MeV AC driven accelerators•linear: cavity design and length critical•circular accelerators:•cyclotron: big dipole magnet, non-relativistic, up to 25 MeV•synchrotron: vacuum beamline, expandable, small magnets and cavities, synchrotron radiation large for light particlesC.Paus, 8.882 LHC Physics: Accelerators20Hadron versus Electron CollidersFrom the physics point of view electron