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Diagnostics Part 4: High Level Measurements

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  1. Cockcroft Institute Postgraduate Lectures Autumn 2008 Diagnostics Part 4: High Level Measurements Guenther Rehm Diamond Light Source

  2. Outline • Measurement of Emittance • In a LINAC or Transfer Line • In a Storage Ring • Measurement of Betatron-Tune • Broadband Excitation and Fourier Transfor • Swept Excitation and Detection • Measurement of Chromaticity • Orbit /Trajectory Measurements • Synchronisation • Dispersion • Diagnostics Integration with Control System • Live Demostration

  3. Emittance measurement in LINAC or Transfer Line

  4. Derivation of Emittance and Twiss Parameters from Beam Sizes

  5. Alternative Method using Adjustable Focussing Element

  6. Emittance Measurement in Storage Ring • Measure sx,y at location of known bx,y • If then one measurement is enough • Else, measurements at two locations of different hx,y are required

  7. 12.7m Source points 4.5m Pinholes Screens Optics Cameras 9.6m 3.85m Two Pinhole Camera System

  8. Tune Measurement • Beam needs to execute betatron oscillations to be measured: • Kick beam, measure decaying oscillation • In hadron machines, damping time is often so long, that oscillations are almost permanent (‘beam has memory’) • Excite with broadband noise and record response • Sweep sinusoidal excitation across betatron frequency and record response • Excitation / detection can be either for all bunches or just for a single bunch • When exciting with kick or noise, beam motion needs to be Fourier transformed into frequency domain to retrieve betatron tune • When exciting with sinusoid, the tune can be directly inferred from a record of oscillation amplitude over excitation frequency. Additional information is available from the relative phase between excitation and oscillation.

  9. Kick and Fourier Transform

  10. Synchrotron Sidebands are Indication of Chromaticity fb fs fb-fs fb+fs Chromaticity not corrected Chromaticity corrected to 0

  11. Tune Tracking during Booster Ramp

  12. Swept Sine Excitation and Detection Exitation In phase cos Out of phase sin Beam Position Pickup

  13. 800 in phase signal 600 out of phase signal 400 200 0 -200 -400 0.2 0.205 0.21 0.215 0.22 0.225 0.23 tune 800 200 600 100 magnitude phase 400 0 200 -100 0 -200 0.2 0.2 0.205 0.205 0.21 0.21 0.215 0.215 0.22 0.22 0.225 0.225 0.23 0.23 tune Amplitude and Phase of Beam Response to Swept Sine Excitation

  14. Tune Measurement of Individual Bunches • Only one bunch is excited with swept sine wave • Tune depends on charge per bunch • Head-Tail mode leads to asymmetry of Synchrotron sidebands for larger charges

  15. Chromaticity Measurement • Change energy of stored beam, ie change main RF frequency • Measure tune • Repeat for several setting and fit parabola

  16. Orbit / Trajectory Measurement • An ensemble of beam position measurements is call a: • Orbit in a storage ring • Trajectory in a LINAC or transfer path • It is important to synchronise the acquisition across all BPMs to ensure real beam movements correlate between BPMs as predicted • Synchronisation is achieved by distributing clocks / triggers to all BPMs and collecting readings before the next trigger

  17. Measurement of Dispersion • Measure initial orbit • Change stored beam energy, ie change main RF frequency • Measure orbit including dispersion • Subtract initial orbit and normalise to momentum offset

  18. Diagnostics and Integration with Control System • Live Demonstration

  19. Cockcroft Institute Postgraduate Lectures Autumn 2008 Diagnostics Part 4: High Level Applications The End