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Introduction to Accelerators Part 3

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  1. Introduction to AcceleratorsPart 3 M W Poole Director, ASTeC Cockcroft PG Education 2009 M W Poole

  2. Remaining Topics • Undulator sources • Periodic magnet technologies • 3rd Generation Light Sources (DIAMOND) • Free electron lasers • Energy recovery linac (ALICE) • 4th Generation Light Sources (NLS) • FFAG development (EMMA) Cockcroft PG Education 2009 M W Poole

  3. Multiple Source ID Concept Several successive wigglers Combined wiggles Multipole Wiggler = MPW Cockcroft PG Education 2009 M W Poole

  4. Trajectory in Multipole Wiggler Sinusoidal field with period lu and peak value B0: Electron also has a sinusoidal trajectory. Electron angle and displacement will be: Maximum angle is equal to K/g Cockcroft PG Education 2009 M W Poole

  5. Multipole Wiggler K >> 1 Trajectory in Multipole Wiggler The radiation opening angle is typically 1/g so there is little overlap between radiation from different poles K/g 2/g But what if K ~ 1 ? 2/g Interference effects can occur Cockcroft PG Education 2009 M W Poole

  6. Interference Condition for interference d q lu Electron Cockcroft PG Education 2009 M W Poole

  7. Undulator Equation Substituting in for the average longitudinal velocity of the electron, bs : For a 3 GeV electron passing through a 50 mm period undulator with K = 3, the wavelength of the first harmonic (n = 1) on axis (q = 0) is ~ 4 nm Cockcroft PG Education 2009 M W Poole

  8. Line Shape (q=0) Similar behaviour as diffraction grating with N slits Width ~ 1/nNl Angular spread of harmonic For l ~ 1nm and L ~ 5m, sr’ ~ 14 mrad Cockcroft PG Education 2009 M W Poole

  9. K < 1 Observer ‘sees’ the electron continuously as it oscillates by less than ~1/g. The electric field due to this electron is then a pure sinusoidal and so there is only one harmonic. Cockcroft PG Education 2009 M W Poole

  10. K > 1 (on axis) Observer ‘sees’ the electron briefly as it oscillates by more than ~1/g. The electric field due to this electron is then a series of spikes of alternating polarity. If the observer is on axis the spikes are equally spaced. The Fourier Transform of these spikes only contains odd harmonics (n = 1, 3, 5, …) Cockcroft PG Education 2009 M W Poole

  11. Different Kinds of SR Sources Cockcroft PG Education 2009 M W Poole

  12. Insertion Device Technologies Electromagnets Superconducting magnets Permanent magnets Typical periods required~ 20 - 500 mm Typical fields required~ 0.5 - 10 T Cockcroft PG Education 2009 M W Poole

  13. Electromagnets Separate coils wound around iron poles. Difficult to have small periods without excessive heat. Ophelie (France) - 250 mm period, 0.11 T in both planes Cockcroft PG Education 2009 M W Poole

  14. Permanent Magnets Most undulators and MPWs are built with permanent magnets High fields in short periods - no power supplies or cooling Combined with iron poles : ‘hybrid’configuration otherwise: ‘pure permanent magnet’ devices (PPMs) Modern permanent magnet materials are very powerful - SmCo or NdFeB (1 - 1.5 T remanence) Cockcroft PG Education 2009 M W Poole

  15. PPM Undulators or MPWs g = gap between the two arrays With 4 blocks per period the field is quite sinusoidal Cockcroft PG Education 2009 M W Poole

  16. Hybrid Undulators or MPWs Iron poles increase the magnetic field - but can make it less sinsoidal eg SRS 2.4 T MPW, 220 mm period Cockcroft PG Education 2009 M W Poole

  17. Periodic Magnet Engineering Daresbury Solutions Cockcroft PG Education 2009 M W Poole

  18. Magnet Gap The magnetic fields are very dependent upon themagnet gapso every effort is made tominimisethis number In a storage ring the minimum gap is typically10 - 20 mm It usually has to leave space for the electron beam vacuum chamber Cockcroft PG Education 2009 M W Poole

  19. In-Vacuum Undulators The latest generation of undulators put the complete magnet inside the vacuum chamber to save a few mm on the magnet gap Spring-8 (Japan) Cockcroft PG Education 2009 M W Poole

  20. Modern World of Synchrotron Light Sources Cockcroft PG Education 2009 M W Poole

  21. Storage Ring Brightness Scaling (Emittance is phase space area) SRS:2 GeV 16 cell 100 nm-rads ESRF:6 GeV 32 cell 4 nm-rads Cockcroft PG Education 2009 M W Poole

  22. Third Generation Light Source Brightness Diamond Main Parameters Circumference 561.6 m Energy 3 GeV Current 300 mA Lifetime 20 h Emittance - horizontal 2.7 nm - vertical 2.5–50 pm Min. ID gap 5-7 mm Cockcroft PG Education 2009 M W Poole

  23. Established Third Generation Light Sources ESRF 6 GeV Undulator Sources Grenoble Cockcroft PG Education 2009 M W Poole

  24. The DIAMOND Project Conceived 1994 ! 3rd Generation Light Source BOOSTER 3 GeV Transfer line Transfer line LINAC 100 MeV 300 mA STORAGE RING 3 GeV 24 cells Circumference = 560 m Instrument 5 m and 8 m straights Cockcroft PG Education 2009 M W Poole

  25. Schematic of DIAMOND Cell Insertion Device Dispersion (m) i Beta functions (m) Cockcroft PG Education 2009 M W Poole

  26. Linac and Booster Cockcroft PG Education 2009 M W Poole

  27. Storage Ring Installation Cockcroft PG Education 2009 M W Poole

  28. DIAMOND SRF Cavity (Cornell ring) Cockcroft PG Education 2009 M W Poole

  29. DIAMOND Experimental Hall (2005) Cockcroft PG Education 2009 M W Poole

  30. DIAMOND sited on Harwell Campus Cockcroft PG Education 2009 M W Poole

  31. Free Electron Laser (FEL) Principle Oscillator illustrated • relativistic electron beam passes through • periodic magnetic field - radiates • mirror feeds spontaneous emission back • onto the beam • spontaneous emission enhanced by stimulated emission Cockcroft PG Education 2009 M W Poole

  32. Classical Analysis of Free Electron Laser • Electron-wave energy exchange (Lorentz) • Transverse modulation • Magnet couples TEM field to particle (weakly) • Axial velocity modulation causes bunching • Relative phasing controls energy gain/loss Electron Decelerator Cockcroft PG Education 2009 M W Poole

  33. Gain Curve Cockcroft PG Education 2009 M W Poole

  34. FEL Oscillators • Infra-red FELs operated since 1977 • Tunable and high power • User facilities highly successful (eg FELIX in Nieuwegein) • Short wavelength limited by mirrors (EUFELE <200nm) • Mainly linacs but storage ring versions tried • 4th Generation Sources need to employ alternative FELs Cockcroft PG Education 2009 M W Poole

  35. High Gain FEL - Single Pass No Mirrors ! Need for very high peak currents ~ kA Cockcroft PG Education 2009 M W Poole

  36. High Peak Currents by Bunch Compression Compress (shorten) bunch to increase peak current (but at cost of energy spread from chirp) Cockcroft PG Education 2009 M W Poole

  37. Comparison 3rd and 4th Generation Sources Cockcroft PG Education 2009 M W Poole

  38. FLASH: Illustrating a High Gain FEL Light Source Previously called TESLA Test Facility (TTF) at DESY bunch compressor Early configuration before upgrades J. Rossbach/DESY Nov. 2001 Cockcroft PG Education 2009 M W Poole

  39. FLASH Undulator and Output Now achieved 6.5 nm at 1 GeV .J Rossbach/DESY Cockcroft PG Education 2009 M W Poole

  40. DESY X-FEL Parameters ~1 kA peak currents Cockcroft PG Education 2009 M W Poole

  41. XFEL Scale Construction started 2009 Cockcroft PG Education 2009 M W Poole

  42. New World Record - LCLS 2009 Recent Results! (25 of 33 undulators installed) gex,y = 0.4 mm (slice) Ipk = 3.0 kA sE/E = 0.01% (slice) 1.5 Å courtesy of P. Emma, SLAC Cockcroft PG Education 2009 M W Poole

  43. meanwhile in Japan … The Next X-Ray Project - Japan Start of User operation: end 2011 Cockcroft PG Education 2009 M W Poole

  44. Storage Ring Problems as Light Sources • Equilibrium beam dimensions set by radiation emission • Beam lifetime limits bunch density (1011 turns) • Demanding UHV environment • Undulators restricted by cell structure and apertures • Most issues worse at low energies (eg < 1 GeV) • FUNDAMENTAL 3GLS LIMITATIONS Cockcroft PG Education 2009 M W Poole

  45. Energy Recovery Linac Principle Converts linac to high current capability Courtesy G Neil Cockcroft PG Education 2009 M W Poole

  46. Testing Next Generation Ideas – ALICE at Daresbury Chirped beam compression ~100 fs FEL included ‘Green’ machine: energy recovery ALICE = Accelerators and Lasers in Combined Experiments Cockcroft PG Education 2009 M W Poole

  47. ALICE Photo-Gun Scheme Cathode ball Ceramic SF6 Vessel removed Cathode Electrons laser XHV Stem Anode Plate 350 keV Courtesy: David Holder Cockcroft PG Education 2009 M W Poole

  48. ALICE Accelerating Modules • 2 x Stanford/Rossendorf cryomodules • cryomodule = 2 x 9-cell (TESLA-type 1.3 GHz) • 0.35-8.35 MeV booster module • 4 MV/m gradient • ~50 kW RF power • 8.35-35.0 MeV linac module • 14 MV/m gradient • 16 kW RF power Delivered April/July 2006 Commissioned September 2007 Operating at reduced levels Cockcroft PG Education 2009 M W Poole

  49. ALICELayoutin Tower Building Cockcroft PG Education 2009 M W Poole

  50. ALICE at Daresbury Displaced linac now in line Cockcroft PG Education 2009 M W Poole