1 / 35

Focusing and Bending Or How to Build Your Own Storage Ring

Mike Forster 11 December 2006. Focusing and Bending Or How to Build Your Own Storage Ring. Lorentz Force Equation. Wikipedia.org. Make a Ring. Electrostatic plates or Dipoles?. B. E. Magnet Choices. Permanent Magnets Fixed field Ferrites typically up to .05-.10 T

Download Presentation

Focusing and Bending Or How to Build Your Own Storage Ring

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.


Presentation Transcript

  1. Mike Forster 11 December 2006 Focusing and Bending Or How to Build Your Own Storage Ring

  2. Lorentz Force Equation Wikipedia.org

  3. Make a Ring Electrostatic plates or Dipoles? B E

  4. Magnet Choices • Permanent Magnets • Fixed field • Ferrites typically up to .05-.10 T • Rare earth alloys typically up to 1.2 T or more • Iron-Copper Electromagnets • Copper coils around iron laminations • Superconducting Magnets • Cryogenically cooled • Conventional or Superferric

  5. Beam Coordinates y Actual Particle Trajectory r Reference Particle Trajectory x s

  6. Describing the Motion

  7. Multipole Expansion The field around the beam can be seen as a sum of multipoles. Dipole Sextupole Octupole Quadrupole

  8. Focusing Methods • Dipole Beam Loss • Horizontally stable • Vertical unstable • Weak Focusing • n = - (dB/B)/(dr/r) • Stability in both planes requires 0<n<1 • Gains vertical focusing at the expense of horizontal • Combined Function Magnets • More than one multipole term • Focusing to Bending Ratio is fixed B

  9. Focusing Methods • Strong or Alternate Gradient Focusing (Christofilos 1950, Courant et al. 1952) • First used operationally at Cornell in 1954 • Alternating combined function magnets "If you can't do two things together, you just do one after the other - that's all there is to it!" Ernest Courant, Brookhaven

  10. Quadrupoles • Hyperbolic shaped poles • Focusing in one transverse plane, defocusing in the other From J. Crittenden

  11. From circe.lnl.gov Good field region

  12. Trajectory Equations First assume on energy particles: Dp/p = 0. Look at horizontal motion in a horizontally defocusing quad (k > 0). Solutions are: Use x0 and x’0 as initial conditions for the constants of integration.

  13. Particle Trajectories and Transfer Matrices Which can be put into matrix notation as: M M is the transfer matrix for a defocusing quadrupole. Build up a toolbox of transfer matrices for various elements!

  14. Trajectory Tracking • Through a section of elements: • X1 = Mdrift·MQF·Mdrift·MQD·X0 • Or build up to a complete revolution of the ring • Combine transverse planes

  15. Dispersion • Realistically p/p  0. • Only significant when 1/R  0, i.e. in a bend. • Solve for a special trajectory, (s) and ’(s) , when p/p = 1. • A particle with momentum offset p/p will have a horizontal position of x(s) + (s) (p/p) • Likewise, the angle will be: x’(s) + ’(s) (p/p)

  16. Beta Functions and Betatron Oscillations Need to describe a beam of particles. Defines motion of transverse oscillation about the orbit called the betatron oscillation. Trial solution: x(s) = A u(s) cos( (s) +  ) After constants of integration are worked out:

  17. Beta Functions and Betatron Oscillations (s) is the beta function or amplitude function.  is the emittance. (s) is the phase. The square root of (s) defines transverse size of beam at any point s.

  18. Courant-Snyder Parameters or Twiss Functions These functions combine to describe an ellipse in x-x’ phase space:

  19. x’ x Beam Phase Space • Particles can be characterized by their position, x, and angle, x’ about the reference orbit. • The area of the ellipse remains constant and equals the emittance. (Satisfies Liouville’s Theorem.)

  20. From D. Robin USPAS lecture

  21. Beam cross section • Electrons and positrons are well approximated by a Gaussian charge distribution: • The standard is to use the phase ellipse of the particle at 1 to define the beam emittance. • Generally look for 10 clearance for good beam lifetime.

  22. Phase Space Propagation • Twiss parameters can also be propagated through optics elements with matrices. • Magnet focusing strengths are set to achieve the desired twiss properties at arbitrary points in the ring. • Typically done in “cells” like FODO cells: • Focusing Quad, drift or bend, Defocusing Quad, drift or bend • Designed so Twiss functions at the end of the cell match the beginning From J.Rossbach CERN Accelerator School lecture

  23. Periodicity • FODO Cells • Many large accelerators combine magnet power supplies • Independent magnet control at CESR • Flexibility has contributed to long term viability

  24. Tunes • The amount of phase advance through one complete revolution is call the Tune. • Integer tunes are trouble. • In fact, a lot of other tunes are trouble: m Qx + n Qy = p Where m, n, p are integers. • These are optical resonances • |m| + |n| is the order of the resonance

  25. Resonances • Linear Resonances (Integer and half integer) • Non-linear resonances • Coupling Resonance • Synchro-Betatron Resonance • Tune Plane From A. Temnykh talk at Frascati 2005

  26. Chromatic Errors • Focusing errors due to energy differences From D. Robin USPAS lecture

  27. Chromatic Errors • Correct with sextupoles From D. Robin USPAS lecture

  28. Insertion Regions Match twiss conditions at ends and insert: • RF Cavities • Wigglers • Separators • Transfer Lines • Detector

  29. Interaction Point Focusing • SCIR quads • Permanent magnet quads

  30. One beam will not make luminosity • Horizontal Separators • Horizontal tune of 10 • Pretzel Orbit • Lab ingenuity J. Crittenden 2004

  31. Detector Solenoid and Compensation • Solenoid coupling • Compensation with: tilted SCIR quads • Fixed 4.5 degree rotation • SCIR and normal conducting skew quads • Superconducting Anti-solenoids • Work to reduce any coupling between horizontal and vertical motion

  32. Cesr Optics

  33. Measurement and Correction

  34. See the real stuff! http://www.lns.cornell.edu/~hoff/LECTURES/07S_488/index.html

More Related