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Beam based measurements

Beam based measurements. 3 rd September 2015 BND school Dieter Prasuhn. Outline: What can be measured. Lattice properties Closed orbit Betatron tunes Chromaticity g transition Properties of the beam Beam intensity Beam profile Momentum spread Time structure.

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Beam based measurements

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  1. Beam based measurements • 3rd September 2015 BND school Dieter Prasuhn

  2. Outline: What can be measured • Lattice properties • Closed orbit • Betatron tunes • Chromaticity • gtransition • Properties of the beam • Beam intensity • Beam profile • Momentum spread • Time structure Dieter Prasuhn

  3. Lattice properties

  4. Closed Orbit measurements • What is the origin of closed orbit deviations? • How to measure closed orbit? • Why to measure and correct CO deviations? Dieter Prasuhn

  5. The origin of closed orbit deviations • Beampipe • defocussing • focussing • Quadrupoles Dieter Prasuhn

  6. The center of mass of the beam • Beampipe • defocussing • focussing • Quadrupoles Dieter Prasuhn

  7. One quadrupole is misaligned • Beampipe • defocussing • focussing • Quadrupoles Dieter Prasuhn

  8. How to measure the closed orbit • Make use of the image current of the beam induced in the outer vacuum pipe Dieter Prasuhn

  9. Beam Position Monitors (Button type): • mainly used in electron synchrotrons, electron storage rings and light sources etc. Dieter Prasuhn

  10. Beam Position Monitors (capacitive pick-ups): • mainly used in hadron synchrotrons and storage rings • D • S Dieter Prasuhn

  11. Why do we measure (and correct)the closed orbit? • The centered beam has more space in the vacuum chamber • Quadrupole changes will not change the beam position • The beam - target overlap can be optimized Dieter Prasuhn

  12. Optimizing the Luminosity • Counting rate of the experiment • Closed orbit bump • Beam Intensity Dieter Prasuhn

  13. Betatron tunes • We follow 1 particle through the accelerator Dieter Prasuhn

  14. Betatron tunes • We follow many particles through the accelerator Dieter Prasuhn

  15. The motion of each particle seen at one position follows the phase space ellipse: • The betatron tune is the number of oscillations on the phase ellipse during one revolution in the storage ring Dieter Prasuhn

  16. Magnet errors generate angle kicks • x` • x Dieter Prasuhn

  17. Betatron resonances • x` • q = integer • shows the effect of emittance growth and beam loss • x Dieter Prasuhn

  18. Resonances occur, if • q = integer 1storderresonance • 2*q = integer 2ndorderresonance • 3*q = integer 3rdorderresonance • qx + qy = integer 2ndordersumresonance • qx - qy = integer 2ndorderdifferenceresonance • In general: • l*qx+ m*qy = n Dieter Prasuhn

  19. The resonance plot • l*qx+ m*qy = n Dieter Prasuhn

  20. How to measure a tune • BPM • Stripline unit • x` • D signal of BPM • RF-output • Spectrum analyzer • Beam path • x Dieter Prasuhn

  21. Frequency spectrum of the PU signal • Deuterons • pc = 970 MeV • f0 = 570.6 kHz • = 0.459 Qx = 3.65 Qy = 3.56 • Since fractional tune q > 0.5: • f+ = (2+q)f0 • f- = (2-q)f0 • f+ = (1+q)f0 • f0 • 2f0 • 3f0 • 4f0 • 5f0 • horizontal • Result with f- = (2-q)f0 • and f+ = (1+q)f0: • revolution frequency f- + f+ = 3f0 • fractional tune q = f+/f0 - 1 • vertical • Measured with BPM09 • Green and red curves: stored spectra when cavity is ON to make revolution frequency visible • Courtesy: Hans Stockhorst Dieter Prasuhn

  22. Chromaticity x =

  23. For Correction: Sextupoles Dieter Prasuhn

  24. How to measure the chromaticity • The widthofthebetatronsidebandsdepend on xanddp/p • q = q0 + x dp/p Dieter Prasuhn

  25. or with electron cooled beam • Change the voltage of the electron beam • The energy of the proton beam follows • Measure the new tune Dieter Prasuhn

  26. g transition (momentum compaction factor) • Beam particles have different momenta • Different momenta result in different velocities • and different paths and path lengths • Momentum spread leads to frequency spread =h Dieter Prasuhn

  27. How to measure gtransition • Switch off the RF to measure the free revolution frequency • Now introduce a change in B-field (corresponding to a momentum change) • Measure the new revolution frequency due to the new orbit length • The change of frequency due to magnetic field is proportional to the g2transition Dieter Prasuhn

  28. Dieter Prasuhn

  29. with electron cooler • Have de-bunched beam • Change theelectron cooler voltage • Measuretheshift in the longitudinal Schottkyspectrum Dieter Prasuhn

  30. Why do we measure gtransition • If g=gtransition bunched beams become unstable • Stochastic cooling needs „mixing“ (Hans Stockhorst). Mixing is defined by the difference of g and gtransition. Dieter Prasuhn

  31. And for experiments: to measure the target thickness • Mean energy loss leads to a frequency shift Dieter Prasuhn

  32. Result Dieter Prasuhn

  33. Beam properties

  34. Beam Intensity • Beam currenttransformer • Chargedparticlescirculatingwith a frequency f0 in storage ring areseenas a windingof a tranformer. • The currentImeasured in a 2ndwindingis proportional tothenumberofcirculatingparticlesNcirc I = Ncirc * f0 * Z*e Dieter Prasuhn

  35. One example of BCT • Beam Dieter Prasuhn

  36. One picture of the BCT signal • Experiment counting rate • BCT signal Dieter Prasuhn

  37. Beam Profile Monitors • Thin fibers are moved quickly through the beam • Seconary electrons emitted from the target are measured as function of the fiber position • Disadvantage: destructive measurement Dieter Prasuhn

  38. Ionisation Beam Profile Monitor • Advantage: non-destructive measurement Dieter Prasuhn

  39. The IPM at COSY Dieter Prasuhn

  40. Beam profile measured with the IPM • Beam profile before and after cooling Dieter Prasuhn

  41. Momentum spread • For experiments often the momentum resolution is of big interest • = h Dieter Prasuhn

  42. Measure gtransition or h • Measure the width of the longitudinal Schottky spectrum Dieter Prasuhn

  43. Time structure of the beam • Makroscopic time structure Defined by the cycle of the accelerator Dieter Prasuhn

  44. Microscopic structuredue to bunching • A de-bunched beam delivers a quasi DC-beam • In LINACS, Colliders, electron accelerators and in hadron machines with internal target bunching is mandatory. • Experiments will directly show the time structure of the beam Dieter Prasuhn

  45. Different Bunch signals • Pure sinusoidal voltage on an integer harmonic of the revolution frequency • Colliders and synchrotron light sources work on high harmonics • Medium energy hadron accelerators work at low harmonics • At COSY usually h=1 is used for acceleration Dieter Prasuhn

  46. Bunch signals during electron cooling Dieter Prasuhn

  47. Barrier bucket • Advantage: homogenious beam intensity in the bucket, short time without beam Dieter Prasuhn

  48. Summary • Introduction to some measurements of lattice parameters and beam parameters • Exercises are planned during the afternoon excursion Dieter Prasuhn

  49. Outlook: The afternoon excursion • We prepared three demonstration objects: • COSY control room • Magnetic field measurements • RF-cavity measurements • Walk around COSY Dieter Prasuhn

  50. Map of Forschungszentrum Jülich • Institute for Nuclear Research • COSY • COSY test hall • Main gate • „face control“ Dieter Prasuhn

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