Engines of Discovery

Transcription

1 Engines of Discovery R.S. Orr Department of Physics University of Toronto Berkley MeV Geneva TeV

2 Birth of Particle Physics and Accelerators 1909 Geiger/Marsden MeV a backscattering - Manchester 1919 Rutherford disintegrates Nitrogen - Manchester 1927 Rutherford demands accelerator development Particle accelerator studies - Cavendish 1929 Cockcroft and Walton start high voltage experiments 1932 The goal achieved: Cockcroft + Walton split Li nucleus

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4 665 kv Cockcroft-Walton Generator

5 Ising 1924

6 Resonant Accelerator Concept Wideroe Alternating (radio frequency) fields allow higher voltages The acceleration occurs in the electric field between cylindrical drift tubes. The RF power must be synchronised with the motion of the electrons, so that acceleration occurs in every gap. Linear Accelerator = LINAC

7 Recirculation Concept - Cyclotron Radio frequency alternating voltage D-shaped RF cavities Hollow metal drift tubes time t =0 Lawrence: 4 80 kev MeV time t =½ RF period Orbit radius increases with momentum Orbital Frequency independent of momentum Particle motion and RF in phase

8 Equilibrium Orbit Constant revolution frequency f rev v 2 v eb 2 mv eb 2m Magnetic rigidity B mv e p e

9 Orbit Stability Slight Displacement from Equilibrium Orbit Particle Lost Vertical and Horizontal Focusing

10 Vertical Orbit Stability in Lawrence s Cyclotron Cross Section Thru Ds Electrostatic Focusing Lens

11 Orbital Stability in a Cyclotron SHIMS q F v B c

12 Horizontal B z n R Bz 2 0 r mv e vbz R c 0 0 Betatron Oscillations Field Index Equilibrium Orbit Centrifugal = Lorentz on equilibrium orbit m B x z 2 d y dt Vertical e vb c 2 x B z 0 x F x mv r 2 e vb c z Restoring Force 2 m d y n B z e v F 2 dt Rc z F x mv R 2 x R 1 n Simple Harmonic 2 2 d y v m nm dt R x v R 1 n Stable Oscillations around Equilibrium orbit n v z R 2 2 n 1 Weak Focusing n 0

13 This machine is just a model for a bigger one, of course This machine is just a model for a bigger one, of course Volts Volts Volts This machine is just a model for a bigger one, of course Volts

14 Invention of the Synchrotron Marcus Oliphant later to become Governor of South Australia

15 Synchrotron Ring Schematic Accelerating Bending magnets cavity Increase magnetic field during acceleration. Constant orbital radius Vacuum tube Focusing magnets

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17 L 1 L 1 f f f L 2 f L L 1 f 1 0 L 1 2 f L f Net Focusing FODO Lattice Strong Focusing

18 Strong Focusing Field Index set by Pole Face Shape Weak, n = 0.5 Strong, n = 3500 Strong Focusing = Alternating Gradient Combined Function Magnet

19 Enormous Cost Saving Weak Focusing Magnet Strong Focusing = Alternating Gradient Reduce amplitude of betatron oscillations Reduce diameter of vacuum pipe Reduce Aperture of Magnets Strong Focusing Magnet 35 GeV (CERN PS, AGS) costs same as 7 GeV (NIMROD)

20 TRAJECTORY 2 dy ds 2 K s Y 0 Y s A scos s Y s s cos s BEAM ENVELOPE 2 d ds K s s 2 s Amplitude of betatron oscillations

21 angle Single Particle Phase Space Beam Envelope position Real Accelerator Non-linear Shape of phase space changes along accelerator lattice Area constant -> Liouville

22 Successive turns around accelerator lattice A B C B is synchronous with RF phase A too energetic to be in phase B not energetic enough to be in phase E E ev s sin n1 s n s Closed Oscillations in Phase (non relativistic) Synchronous particle Change in transit time around lattice

23 E E ev sin s n1 s n s Synchronous Particle n1 n 2 n1 v Es n1 n 2 c E E E ev sin Non-Synchronous Particle sin s Symplectic Mapping Preserves Phase Space

24 Unconfined motion = lost particles Stable oscillations Trapped by RF Synchronous particle separatrix Transformed s into Φ position around lattice Particle orbits in energy-phase

25 d E E ev dn s n1 2 v E c s 2 s n E sin s de dn ev sin sin s Non-linear equations Describing deviation in phase and energy from synchronous orbit

26 H Initial condition cos sin s separatrix RF Bucket constant = Η d c = cos sin 2 2 s dn v E s

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28 CERN Seen from the Air Tunnels of CERN accelerator complex superimposed on a map of Geneva. Accelerator is 50 m underground 25 km in circumference

29 Superconducting Magnet 8 Tesla In order to accelerate protons to high energy, must bend them in circular accelerator 7 TeV momentum needs intense magnetic field

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31 LHC 2002

32 LHC 2003 Dipole Cold Masses

33 Ph. Lebrun ATLAS Plenary Meeting 18 February 2005

34 Infrastructure completed in 2003

35 Underground

36 Dipole-dipole interconnect

37 March 2006

38 Descent of the Last Magnet, 26 April m underground at 2 km/h!

39 RF Modules

40 Tunnel Cavern Shaft Surface Refrigeration Units at 1.8 K Point 8 Storage Air Liquide QSCC QSCA QSCB QSRA QSRB QSCC IHI Linde QURA QUIC QURC QURC Sector 7-8 Sector 8-1

41 Tunnel Cavern Shaft Surface Cryogenic Distribution Point 8 Storage QSCC QSCA QSCB QSCC QSRA QSRB QURA QUIC QURC QURC Sector 7-8 Sector 8-1

42 DFBA Electrical Feed Box Connection to magnets Shuffling module Vacuum equipment VAA Current lead chimneys 6kA leads 13kA leads x 16 2 per LHC Point SHM/HCM interconnect High current module 13kA & 6kA leads Jumper cryo connection to QRL Supporting beam 6kA leads Removable door 600A leads HCM/LCM interconnect Low current module 6kA & 600A leads 1.9K 4.5K

43 13 ka HTS Current Leads

44 6 ka current leads with water-cooled cables

45 Lyn Evans EDMS docment no

46 Beam 2 first beam D-Day 46

47 Beam on turns 1 and 2 Courtesy R. Bailey 47

48 No RF, debunching in ~ 25*10 turns, i.e. roughly 25 ms Courtesy E. Ciapala 48

49 First attempt at capture, at exactly the wrong injection phase Courtesy E. Ciapala 49

50 Capture with corrected injection phasing Courtesy E. Ciapala 50

51 Capture with optimum injection phasing, correct reference Courtesy E. Ciapala 51

52 LHC longitudinal bunch profile Beam 2 52

53 H wire scan Lyn Evans EDMS document no

54 54 Kick response compared with theoretical optics

55 Alors, c est fini! Et maintenant?

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58 Storage Ring Stable phase = 0 No acceleration

59 Synchrotron (phase) oscillations 2 2 d c ev cos s dn v E s 2 d t s s dn t s 0 ; ; cos 0 0 ; ; cos 0