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Introduction to Accelerators Part 1

Introduction to Accelerators Part 1. M W Poole Director, ASTeC. Daresbury Campus. Cockcroft Institute. Basic Acceleration Principle. A voltage drop accelerates charged particles. Electrostatic acceleration in cathode ray tubes: televisions computer monitors oscilloscopes.

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Introduction to Accelerators Part 1

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  1. Introduction to AcceleratorsPart 1 M W Poole Director, ASTeC Cockcroft Education Lectures2007 M W Poole

  2. Daresbury Campus Cockcroft Institute Cockcroft Education Lectures2007 M W Poole

  3. Basic Acceleration Principle A voltage drop accelerates charged particles • Electrostatic acceleration in cathode ray tubes: • televisions • computer monitors • oscilloscopes Cockcroft Education Lectures2007 M W Poole

  4. Practical Electrostatic Accelerators Guns VDUs CROs Vacuum tubes • Corona limit (MV ?) 1932Cockroft-Walton cascade350 kV Split atom NOBEL PRIZE Actually measured at 250 keV (and later lower) !!! • Van de Graaf belt driven terminal: 1.5 MV Cyclotron 1MV Cockcroft Education Lectures2007 M W Poole

  5. Birth of Particle Physics and Accelerators • 1909 Geiger/Marsden MeVa backscattering - Manchester • 1919Rutherford disintegrates Nitrogen - Manchester • 1927Rutherford demands accelerator development Particle accelerator studies start - Cavendish • 1929Cockcroft and Walton start high voltage experiments • 1932 The prize achieved: Cockcroft + Walton split Li !!!! ‘High’ voltage generation is UK achievement at this stage – brute force UK grid initiated (132 kV) and industrial base started Cockcroft Education Lectures2007 M W Poole

  6. Walton, Rutherford, Cockcroft - 1932 Start of the modern era – particle accelerators Cockcroft Education Lectures2007 M W Poole

  7. Cockcroft-WaltonGenerator ISIS 665 kV Removed 2005 Greinacher 1921 Cockcroft Education Lectures2007 M W Poole

  8. Electrostatic Monster: the NSF • 1936 van der Graaff pioneers electrostatic solution (2.5 MeV) • 19616 MeV machine at Liverpool (Manchester collaboration) • 1972 Design Study of 20-30 MV facility at Daresbury • 1974 Civil construction starts • 1983 NSF commissioned • 1992Closure World’s highest voltage machine No nuclear physics replacement Cockcroft Education Lectures2007 M W Poole

  9. Daresbury Nuclear Structure Facility (NSF) Van de Graaf 20+ MV Last of the line ! Cockcroft Education Lectures2007 M W Poole

  10. Seriously high voltages ! Cockcroft Education Lectures2007 M W Poole

  11. Resonant Accelerator Concept 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 cavity. This naturally produces bunches of electrons Wideroe - 1928 Linear Accelerator = LINAC Cockcroft Education Lectures2007 M W Poole

  12. Recirculation Concept - Cyclotron Radio frequency alternating voltage D-shaped RF cavities Lawrence: 4” – 80 keV 11” - 1.2 MeV time t =0 Hollow metal drift tubes time t =½ RF period q v B = mv2 / r r = mv / qB T = 2pm / qB Orbit radius increases with energy Expensive/impractical for high energies (1 GeV) Synchronisation Necessary Cockcroft Education Lectures2007 M W Poole

  13. Phase Synchronism Synchronous particle (A) crosses cavity after one turn at same phase relative to RF peak Particle B delayed behind A receives higher accelerating voltage and therefore after next turn returns nearer or even ahead of A Particles undergo harmonic synchrotron oscillations about A as they orbit the accelerator NOTE: This leads to BUNCHING about A Cockcroft Education Lectures2007 M W Poole

  14. Types of Accelerator • Linear Accelerators (Linacs) • Multi-cell concepts TW and SW • Cyclotrons • Low energy limit • Synchrocyclotrons • RF variation compensates mass change – extends energy reach • Betatrons • Beam is ‘secondary’ of a transformer - magnetic field limit • Synchrotrons and Storage Rings • Ramped magnetic field matches energy – annular design • Other variants • Microtron RFQ FFAG ??? Cockcroft Education Lectures2007 M W Poole

  15. Early (UK) History (Synchro)Cyclotrons Berkeley (Lawrence) 60” (1939) Liverpool 37” 20 MeV (1939) Harwell 110” 175 MeV (1949) Liverpool 156” 380 MeV (1954) (extraction) Linacs Harwell 3.5 MeV (1947) 15 (Mullard), 55 (Met Vickers), 136 MeV Synchrotrons Woolwich Arsenal - Goward & Barnes 8 MeV (1946) (Betatron 1943) Malvern 30 MeV (1950) Oxford 125 MeV (1952) Birmingham 1 GeVp (1953) Glasgow 350 MeV (1954) NIMROD RAL7 GeV p (1960) NINA DL5 GeV (1966) Clatterbridge Oncology Centre 65 MeV Cockcroft Education Lectures2007 M W Poole

  16. Synchrotron Ring Schematic Bending magnets Accelerating cavity Vacuum tube Focusing magnets Bending and focussing often combined Cockcroft Education Lectures2007 M W Poole

  17. Magnet Focusing Quadrupole magnets are used to focus the beam. FQUADs (shown above) focus the beam horizontally. DQUADs (as above, rotated 90º) focus the beam vertically. Cockcroft Education Lectures2007 M W Poole

  18. RF Accelerating Cavities Single cell example Cockcroft Education Lectures2007 M W Poole

  19. SRS Klystron Cockcroft Education Lectures2007 M W Poole

  20. Dipole D Quadrupole F Quadrupole Simple Accelerator Lattice FODO Cell Cockcroft Education Lectures2007 M W Poole

  21. Betatron Oscillations Transverse motion of particles in both planes is harmonic - as they deviate from the design orbit a restoring force increases with displacement The particles follow betatron oscillations as they orbit the accelerator The amplitude and wavelength of this motion is characterised by the beta functions of the accelerator Off-energy particles follow a dispersion function Cockcroft Education Lectures2007 M W Poole

  22. Phase Space Emittance measures phase space area Betafunction gives transverse envelope Cockcroft Education Lectures2007 M W Poole

  23. The Double Bend Achromat Cell Dispersive Path Quadrupoles Dipole Dipole Quadrupole Dipole Sextupoles Non - Dispersive Cockcroft Education Lectures2007 M W Poole

  24. Lattice Functions - DBA Example Cockcroft Education Lectures2007 M W Poole

  25. Sextupole Magnets Chromatic Correction (off energy particles) In finite dispersion region focussing matches energy Cockcroft Education Lectures2007 M W Poole

  26. Penalty: Collapse of Dynamic Stability No sextupoles Corrected to zero chromaticity Cockcroft Education Lectures2007 M W Poole

  27. Recovery of Stability - Sextupoles in Patterns Four families Six families Eight families Cockcroft Education Lectures2007 M W Poole

  28. Origins of Daresbury Laboratory • 1957 Wilkinson proposes HE electron synchrotron • 1960 Cockcroft + Cassels propose 4 GeV version • 1961 Cockcroft proposes Cheshire site !!!! • 1962NINA approved - £3.5M Many local sites considered • 1963 Daresbury selected HEI driving force: Liverpool/Manchester/Glasgow/Sheffield/ (Lancaster) Cockcroft Education Lectures2007 M W Poole

  29. Daresbury Laboratory - 1964 Cockcroft Education Lectures2007 M W Poole

  30. Constructionof NINA - 1964 Cockcroft Education Lectures2007 M W Poole

  31. A Bad Day at the Office ! Cockcroft Education Lectures2007 M W Poole

  32. Grand Opening of NINA - 1967 Cockcroft Education Lectures2007 M W Poole

  33. The NINA Synchrotron Cockcroft Education Lectures2007 M W Poole

  34. Chadwick’s 75th Birthday – Daresbury Event Cockcroft Education Lectures2007 M W Poole

  35. NINA Closure • UK joined SPS at CERN on condition domestic programme terminated (NINA AND NIMROD) • NINA switched off in 1977 • Alternative major facilities already sought - and found: • NSF (discussed) • ISIS and SRS (part 2 next week) Cockcroft Education Lectures2007 M W Poole

  36. Accelerator Physics Challenges • Classical electrodynamics - Maxwell(mainly !) • Lorentz forces:Deflection and acceleration • Single particle dynamics • transport, stability, nonlinear dynamics - tracking & differential algebra • Multi-particle dynamics • collective effects, wake fields, space charge, coherent instabilities Production Transport Injection Acceleration Extraction Manipulation Delivery Analytic modelling + Computer simulation (Start-to-End) (Major code development) Experimental verification (Commissioning !) fs nm Cockcroft Education Lectures2007 M W Poole

  37. Accelerator Technologies • Sources - electron gunsphotoinjectors, ion sources, …….. • Magnets - EM / SCM / PM DC / AC / Pulsed • Harmonic / Periodic Power supplies • RF System - structures power sources • Vacuum - UHV modelling diagnostics pumping • Diagnostics - fast high precision non-interactive • Geodesics - alignment feedback • Radiation - losses shielding personnel safety • Dumps - spallation targets collimators • Engineering - mechanical electrical civil • Controls - advanced process control • NB Multi-disciplinary teams. Resource issues - construction/operation. Cockcroft Education Lectures2007 M W Poole

  38. Big Accelerators - CERN Cockcroft Education Lectures2007 M W Poole

  39. LEP Technical Challenges • 27km machine • 3% energy loss per turn • 20MW synchrotron radiation • Superconducting RF systems 288cavities 3 GV total Cockcroft Education Lectures2007 M W Poole

  40. LEP Superconducting RF Systems Superconducting cavity performance extremely sensitive to dust and particle contamination, as well as to surface treatments Specific cleaning procedures developed to improve the maximum accelerating voltage Manipulation is only allowed in clean room of Class 10 Cockcroft Education Lectures2007 M W Poole

  41. Superconducting RF Technology • Slower to be adopted than superconducting magnets • Serious technical challenges • Power saving is only one issue • Structure quality reduces (some) beam instabilities Cockcroft Education Lectures2007 M W Poole

  42. Choice of SRF Operating Temperature 9-cell TESLA cavity Rs = 3-4 nW Q0 = 1011 Tc = 9 K (Nb) Cockcroft Education Lectures2007 M W Poole

  43. Optimum Frequency Selection Cockcroft Education Lectures2007 M W Poole

  44. Example Module Jefferson Laboratory System (750MHz ) Cockcroft Education Lectures2007 M W Poole

  45. Coaxial Power Coupler - 75 kW Cockcroft Education Lectures2007 M W Poole

  46. LEP Tides and TGV !!!! • Influence on the beam energy • moon, sun and tides • level of lake Geneva • rainfall • AND the fast train......... Cockcroft Education Lectures2007 M W Poole

  47. LEP Localised Orbit Error QL10.L1 Cockcroft Education Lectures2007 M W Poole

  48. Zoom on Quadrupole beer bottle Cockcroft Education Lectures2007 M W Poole

  49. Circumference (km) 26.7 100-150m underground Number of Dipoles 1232 Cable Nb-Ti, cold mass 37million kg Length of Dipole (m) 14.3 Dipole Field Strength (Tesla) 8.4 Operating Temperature (K) 1.9 Super-fluid helium Current in dipole sc coils (A) 13000 1ppm resolution Beam Intensity (A) 0.5 2.2.10-6 loss causes quench Beam Stored Energy ( MJoules) 370 1MJ melts 2kg Cu Magnet Stored Energy (MJoules) 1220 Sector Powering Circuit 8 1612 different electrical circuits LHC: Some Technical Challenges Cockcroft Education Lectures2007 M W Poole

  50. First LHC Cryodipole (Mar 2005) Cockcroft Education Lectures2007 M W Poole

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