Cmw Isis Synch Talk

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  • Cmw Isis Synch Talk

    1. 1. An Introduction to the ISIS Synchrotron Chris Warsop
    2. 2. Outline <ul><li>Introduction </li></ul><ul><li>Acceleration and Trapping </li></ul><ul><li>Transverse Focusing and Injection </li></ul><ul><li>Extraction </li></ul><ul><li>The Challenges of a High Intensity Machine </li></ul>
    3. 4. What does the Synchrotron do for ISIS? <ul><li>On Target Require (with 10 Hz Variations for Target 2) </li></ul><ul><li>2.5x10 13 , 800 MeV Protons, in < 1 μ s pulse @ 50 Hz </li></ul><ul><li>3.7x10 13 , 800 MeV Protons, in < 1 μ s pulse @ 50 Hz </li></ul><ul><li>Linac Provides </li></ul><ul><li>2.8x10 13 , 70 MeV H - , in 250 μ s pulse @ 50 Hz </li></ul><ul><li>4.0x10 13 , 70 MeV H - , in 250 μ s pulse @ 50 Hz </li></ul><ul><li>Synchrotron </li></ul><ul><li>Compresses Pulse Length: 250 -> 1 μ s </li></ul><ul><li>Accelerates Beam: 70 -> 800 MeV </li></ul>
    4. 5. 52 m
    5. 6. Basic Principles <ul><li>Acceleration </li></ul><ul><li>Circular Machine </li></ul><ul><li>Repeated Use of Relatively Low RF Acceleration Voltage </li></ul><ul><li>ISIS Ring: Max ~140 kV per turn, (163 m), but over 10 4 turns </li></ul><ul><li>ISIS Linac: ~ 70 MV in a single pass (50 m) </li></ul><ul><li>Synchrotron Principle </li></ul><ul><li>Keep Beam on Constant Bend Radius </li></ul><ul><li>Vary Confining Field and Particle Momentum in Synchronism </li></ul><ul><li>Compression </li></ul><ul><li>Multi-Turn Charge-Exchange Injection, Bunching and Acceleration </li></ul>
    6. 7. Motion in a Dipole Magnet - Uniform Field <ul><li>For particle momentum P, charge e, in uniform field B </li></ul><ul><li>Trajectory is Circular Arc, Radius  </li></ul>
    7. 8. The Synchrotron <ul><li>Many Parameters Determined by </li></ul><ul><li>Main Dipole Magnet Field Variation with Time: B [ t ] </li></ul> 
    8. 9. Magnetic Field on ISIS …. f mag = 50 Hz B inj = 0.176 T B ext = 0.697 T  = 7.002 m <ul><li>Main Magnet Field is a Biased 50 Hz Sinusoid </li></ul><ul><li>Allows Energy Recovery in Magnet Power Supply </li></ul><ul><li>Main Dipoles and Quads all in series (White Circuit) </li></ul>Acceleration
    9. 10. RF Acceleration <ul><li>Pass particles through sinusoidally excited RF cavity </li></ul><ul><li>Gain energy ε from field across accelerating gap </li></ul>Needs to match energy gain requirements
    10. 11. Acceleration in a Ring <ul><li>Lock RF frequency to a harmonic of revolution frequency </li></ul><ul><li>Define ideal “Synchronous” particle, which follows </li></ul><ul><li>This particle sees the same phase of RF on every turn </li></ul><ul><ul><li>- surfs on wave propagating around machine </li></ul></ul><ul><li>Only two points on the wave where particle may receive correct energy </li></ul><ul><ul><li>- Synchronous Phase </li></ul></ul>
    11. 12. Acceleration Parameters on ISIS <ul><li>Two bunches on ISIS </li></ul><ul><li>Using relations above with ISIS B [ t ], get </li></ul>
    12. 13. ISIS Ring RF System Details <ul><li>Harmonic Number 2 -> 2 bunches </li></ul><ul><li>6 Tuned Resonant Cavities </li></ul><ul><ul><li>Sweep 1.3-3.1 MHz </li></ul></ul><ul><ul><li>0 - 26 kV per cavity </li></ul></ul><ul><ul><li>Supply ~150 kW of beam power </li></ul></ul><ul><li>Ferrite Loaded Coaxial Resonator </li></ul><ul><ul><li>Bias current 200-2000 A </li></ul></ul><ul><li>RF Driver </li></ul><ul><ul><li>Two 250 kW tetrodes per cavity </li></ul></ul><ul><li>Multiple Control Loops </li></ul><ul><ul><li>Frequency </li></ul></ul><ul><ul><li>Voltage </li></ul></ul><ul><ul><li>Beam position, current etc. </li></ul></ul><ul><li>4 additional cavities for DHRF </li></ul>
    13. 14. Finite Bunch Length, Oscillations in the Bunch <ul><li>What about particles not at correct phase? </li></ul><ul><ul><li>i.e. non synchronous particles? </li></ul></ul><ul><li>Depends on Revolution Time </li></ul><ul><ul><li>variation of velocity with P </li></ul></ul><ul><ul><li>variation of path length with P </li></ul></ul><ul><li>On ISIS obeys ‘common sense’ </li></ul><ul><ul><li>Higher energy particles take less time </li></ul></ul><ul><ul><li>Lower energy particles take more time </li></ul></ul>RF Phase -> RF Volts -> P Error ->
    14. 15. The ISIS Machine Cycle Extraction Acceleration Trapping Injection
    15. 16. Bunch Size : Stable Regions <ul><li>Injected beam is effectively unbunched </li></ul><ul><ul><li>Fills the machine circumference </li></ul></ul><ul><li>Phase Stable region shrinks as dB [ t ]/ dt increases </li></ul><ul><li>Most particles trapped in stable regions </li></ul><ul><ul><li>Not all  Trapping Loss! </li></ul></ul><ul><li>Have simplified processes </li></ul><ul><ul><li>Complicated Trajectories </li></ul></ul><ul><ul><li>Space Charge </li></ul></ul>RF Phase -> P Error ->
    16. 17. Dual Harmonic RF Upgrade <ul><li>Add More RF Cavities </li></ul><ul><ul><li>Run at 2 x frequency </li></ul></ul><ul><ul><li>Half the volts </li></ul></ul><ul><ul><li>Carefully Phased </li></ul></ul><ul><li>Enlarge Stable Region </li></ul><ul><ul><li>Optimise Trapping </li></ul></ul><ul><ul><li>Reduce Loss </li></ul></ul>P Error -> RF Phase -> Single Harmonic RF Phase -> Dual Harmonic
    17. 18. New DHRF Cavities 6 h=2 cavities 2 h=4 cavities 2 h=4 cavities
    18. 19. Some Measurements of Longitudinal Motion Injected Chopped Beam (100 ns, 1/15 of circumference) RF Off RF On
    19. 20. Transverse Motion <ul><li>Beam consists of many particles, not all aligned with reference orbit </li></ul><ul><ul><li>small angular spread about beam direction </li></ul></ul><ul><li>Need to focus beam to prevent it diverging </li></ul><ul><ul><li>hitting vacuum vessel </li></ul></ul><ul><li>Quadrupole Magnet provides the focusing required </li></ul>Beam with angular spread Focusing Elements Focused Beam Unfocused Beam
    20. 21. Motion in a Quadrupole – Linear Focusing Field <ul><li>Linear force with transverse displacement </li></ul><ul><ul><li>Focusing in one plane </li></ul></ul><ul><ul><li>Defocusing in the other </li></ul></ul><ul><li>Arrange Alternating Channel </li></ul><ul><ul><li>Overall Focusing in both planes </li></ul></ul>
    21. 22. Form a Stable Focusing Channel <ul><li>Design repeating pattern of magnets for optimal stability (lattice) </li></ul><ul><li>&quot;Modified&quot; Simple Harmonic Motion </li></ul><ul><ul><li>distorted sinusoidal oscillation about equilibrium orbit </li></ul></ul><ul><li>Beam larger in focusing elements -> overall focusing </li></ul><ul><li>ISIS Synchrotron Lattice </li></ul><ul><ul><li>Horizontal -> [QD QF QD BF] x 10 (plus trim quads) </li></ul></ul><ul><ul><li>Vertical -> [QF QD QF QD] x 10 </li></ul></ul>Beam Width -> Distance along beam axis -> Horizontal Vertical
    22. 23. Lattice and Main Magnets <ul><li>10 super-periods </li></ul><ul><ul><li>16.3 m long </li></ul></ul><ul><li>Main Dipole </li></ul><ul><ul><li>4.4 m long </li></ul></ul><ul><ul><li>0.16 – 0.69 T </li></ul></ul><ul><li>Main Quads </li></ul><ul><ul><li>Doublet & Singlet </li></ul></ul><ul><ul><li>0.7 m long </li></ul></ul><ul><ul><li>0.8 – 3.0 T/m </li></ul></ul><ul><li>Half Apertures </li></ul><ul><ul><li>~ 60 mm x 80 mm </li></ul></ul><ul><li>I AC = 400 A, I DC = 660 A </li></ul><ul><li>Power 1.8 MW </li></ul><ul><li>Also 20 Trim Quads </li></ul><ul><ul><li>Programmable </li></ul></ul>
    23. 24. Particle Motion and Formation of a Beam <ul><li>Single Particle Trajectory </li></ul><ul><li>Oscillation about equilibrium orbit </li></ul><ul><li>Number of Oscillations per turn </li></ul><ul><ul><li>Q Value </li></ul></ul><ul><ul><li>On ISIS Q H =4.31, Q V =3.83 </li></ul></ul><ul><li>Avoid Integer Q </li></ul><ul><ul><li>Stability </li></ul></ul><ul><li>Beam formed by </li></ul><ul><ul><li>many particles (~10 13 ) </li></ul></ul><ul><ul><li>incoherent oscillations </li></ul></ul><ul><li>Maximum Extent of beam </li></ul><ul><ul><li>Beam Envelope </li></ul></ul><ul><li>Oscillation in (x,x') space </li></ul>Transverse Angle Transverse Position
    24. 25. Beam Self-Field for Uniform Charge Distribution <ul><li>High Intensity Beam </li></ul><ul><ul><li>must allow for beam's own field </li></ul></ul><ul><li>Simplest case </li></ul><ul><ul><li>long uniform cylinder of charge </li></ul></ul><ul><ul><li>moving at velocity β c </li></ul></ul> c <ul><li>Gauss/Ampere Law </li></ul><ul><li>Defocusing Radial Force </li></ul><ul><ul><li>Strong energy dependence </li></ul></ul><ul><li>At low energy affects stability </li></ul><ul><ul><li>Charge distribution is important </li></ul></ul><ul><ul><li>Take great care to control it </li></ul></ul>
    25. 26. Relationship Between Transverse Particle Motion and Charge Distribution <ul><li>Transverse Motion </li></ul><ul><ul><li>Modified SHM </li></ul></ul><ul><li>Average Charge Density </li></ul><ul><ul><li>Depends on amplitude distribution </li></ul></ul><ul><ul><li>Avoid small amplitudes </li></ul></ul><ul><li>Optimise Amplitude Distribution </li></ul><ul><ul><li>Approach Uniform </li></ul></ul><ul><li>Injection Process Crucial </li></ul><ul><ul><li>Determines initial distribution </li></ul></ul>particles with large amplitudes particles with small amplitudes Transverse Profile Particle Density -> Transverse Axis Transverse Axis Transverse Axis Transverse Axis Beam Axis -> Corresponding Trajectory
    26. 27. Injection – Simplest Model Injection Septum Magnet Injected Particles Machine Circumference Transverse Displacement
    27. 28. Simple Injection with a Bump ~ a few turns Injection Septum Magnet Injection Bump Magnets <ul><li>Use Magnet Bump </li></ul><ul><ul><li>Equilibrium Orbit near Septum during Injection (reasonable amplitudes) </li></ul></ul><ul><ul><li>Remove bump after Injection so particles miss Septum </li></ul></ul><ul><li>OK for injecting a few turns </li></ul><ul><li>Not for the 100's required on ISIS </li></ul>
    28. 29. H - Charge Exchange Injection ~ many turns <ul><li>Inject an H - Beam </li></ul><ul><li>Bring together H - with circulating beam in dipole </li></ul><ul><li>Strip to H + with foil (~2% loss H - , H 0 ) </li></ul><ul><li>Circulating beam Passes through foil (20 times) </li></ul><ul><li>Inject on top of circulating beam over 100's of turns </li></ul><ul><li>Allows HI Beam! </li></ul>Injection Bump Magnets Stripping Foil    2 e - + H    H  H    Re-circulating H 
    29. 30. Injection Painting <ul><li>To introduce a range of oscillation amplitudes during injection: </li></ul><ul><ul><li>Vary Injection Point </li></ul></ul><ul><ul><li>Vary Equilibrium Orbit </li></ul></ul><ul><li>On ISIS do both </li></ul><ul><ul><li>Vertical Plane </li></ul></ul><ul><ul><li>Horizontal Plane </li></ul></ul><ul><li>Inject current at constant rate </li></ul><ul><ul><li>Vary amplitude non linearly with time </li></ul></ul><ul><ul><li>1. Vary Injection Point </li></ul></ul><ul><ul><li>2. Vary Equilibrium Orbit </li></ul></ul>
    30. 31. Injection on the Falling Magnet Field <ul><li>Inject before field minimum </li></ul><ul><li>Field is 'too high' </li></ul><ul><ul><li>Beam circulates on smaller orbit </li></ul></ul><ul><li>As field drops, orbit moves out </li></ul><ul><ul><li>At 0.0 ms is on design orbit </li></ul></ul><ul><li>Inject at one point on inside radius </li></ul><ul><ul><li>Movement of orbit gives painting </li></ul></ul><ul><li>Best configuration: </li></ul><ul><ul><li>Painting process exploits B [ t ] </li></ul></ul><ul><ul><li>Gives more time for trapping </li></ul></ul>Inject Eq m Orbit Moves Out Extraction Acceleration Trapping Injection
    31. 32. Injection Details <ul><li>Accumulate 2.8x10 13 protons over 150 turns </li></ul><ul><li>Stripped with alumina foil </li></ul><ul><ul><li>0.3 μ m thick </li></ul></ul><ul><ul><li>120 mm x 40 mm </li></ul></ul><ul><ul><li>98% efficient (2% H 0 , H - ) </li></ul></ul><ul><ul><li>Protons pass through foil ~20 times </li></ul></ul><ul><li>Injection Bump Magnets </li></ul><ul><ul><li>Single turn, 14 000 A </li></ul></ul><ul><ul><li>Pulsed (45 mr) </li></ul></ul><ul><li>Septum </li></ul><ul><ul><li>6 turn, 4000 A </li></ul></ul><ul><ul><li>DC (285 mr) </li></ul></ul>
    32. 33. Extraction of Beam <ul><li>At Extraction </li></ul><ul><ul><li>Protons Circulating at 800 MeV (  =0.84) </li></ul></ul><ul><ul><li>3.2 kJ per pulse </li></ul></ul><ul><ul><li>Two bunches with 200 ns gap </li></ul></ul><ul><li>Extraction System </li></ul><ul><ul><li>3 fast kicker magnets </li></ul></ul><ul><ul><ul><li>deflect the beam into … </li></ul></ul></ul><ul><ul><li>a septum magnet </li></ul></ul><ul><ul><ul><li>which lifts it into the EPB </li></ul></ul></ul><ul><li>Kickers need to be fast to avoid beam loss </li></ul><ul><ul><li>Go from zero to full field between passage of bunches </li></ul></ul>
    33. 34. Extraction Details <ul><li>Kickers </li></ul><ul><ul><li>3 units give 15 mr kick </li></ul></ul><ul><ul><li>0 to 0.04 T in < 210 ns </li></ul></ul><ul><ul><li>Single turn, 5000 A </li></ul></ul><ul><ul><li>0.5 m long </li></ul></ul><ul><li>Septum </li></ul><ul><ul><li>~ 8 m downstream </li></ul></ul><ul><ul><li>8 Turn, 8900 A </li></ul></ul><ul><ul><li>DC </li></ul></ul><ul><ul><li>1.8 m long (21 degrees) </li></ul></ul><ul><ul><li>Lifts beam out of machine </li></ul></ul>
    34. 35. Measurements of Transverse Motion Transverse oscillation observed at one point in ring over 30 turns
    35. 36. Measurements of Transverse Motion Development of Horizontal and Vertical Profiles -0.5 – 1.5 ms
    36. 37. Why is a High Intensity Machine Difficult to Run? <ul><li>Must Have Tight Loss Control on a High Power Beam </li></ul><ul><ul><li>Mean Power: Injection 16 kW -> Extraction 160 kW </li></ul></ul><ul><ul><li>Fractional losses must be low </li></ul></ul><ul><ul><li>Minimal Activation for Maintenance </li></ul></ul><ul><ul><li>Prevent damage </li></ul></ul><ul><li>Losses on a High Intensity Beam are not easy to control! </li></ul><ul><ul><li>Complicated loss mechanisms which are very sensitive to many parameters </li></ul></ul><ul><ul><li>E.G. Beam Distributions, Correction Dipoles, Quadrupoles, RF, Linac, etc. </li></ul></ul><ul><li>Some important aspects of beam physics are not yet fully understood </li></ul>
    37. 38. Ring Tuning and Loss Control <ul><li>Loss control </li></ul><ul><ul><li>Absolute levels </li></ul></ul><ul><ul><li>Location </li></ul></ul><ul><ul><li>Time ~ i.e. Particle Energy </li></ul></ul><ul><li>Monitoring </li></ul><ul><ul><li>40 Beam Loss Monitors </li></ul></ul><ul><ul><li>Beam Toroids </li></ul></ul><ul><ul><li>5 Profile Monitors </li></ul></ul><ul><ul><li>30 Position Monitors </li></ul></ul><ul><ul><li>Wire scanners, scintillators … </li></ul></ul><ul><li>Optimising Handles </li></ul><ul><ul><li>Correction Dipoles (14) </li></ul></ul><ul><ul><li>Correction Quadrupoles (20) </li></ul></ul><ul><ul><li>Injection System </li></ul></ul><ul><ul><li>RF System </li></ul></ul><ul><ul><li>Extraction System </li></ul></ul><ul><ul><li>Linac </li></ul></ul><ul><li>Many 100's of parameters </li></ul>
    38. 39. Diagnostics ~ Some Machine Details
    39. 40. So What’s New on a 20 year old Machine? <ul><li>Plenty of R&D Underway </li></ul><ul><ul><li>Important for ISIS ~ to achieve optimal running with major upgrade </li></ul></ul><ul><ul><li>Important for New Machines </li></ul></ul><ul><li>Main Topics </li></ul><ul><ul><li>Longitudinal Trapping i.e. DHRF upgrade and optimisation </li></ul></ul><ul><ul><li>Transverse Space Charge and Related Losses </li></ul></ul><ul><ul><li>Instabilities </li></ul></ul><ul><ul><li>Loss Control </li></ul></ul><ul><li>Involves </li></ul><ul><ul><li>New Diagnostics & Measurements </li></ul></ul><ul><ul><li>Computer Simulation/Theory </li></ul></ul><ul><ul><li>Improved Beam Control and Manipulation (Software/Hardware) </li></ul></ul><ul><li>Paves the way for MW ISIS Upgrades </li></ul>
    40. 41. Closing Comment … <ul><li>First injected beam into the ring in 1984 </li></ul><ul><ul><li>20 years on ISIS is still a world leader </li></ul></ul><ul><li>Enormous credit to those who designed, built, commissioned machine </li></ul><ul><ul><li>Few things stay ahead for so long … </li></ul></ul><ul><li>Still upgrading, improving … to get to 0.24 MW </li></ul><ul><li>Next steps 1 MW, 4 MW … </li></ul>~ Twenty Years ~

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