Sources of Field Perturbations LLRF Lecture Part2 S. Simrock, M. - - PowerPoint PPT Presentation

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Sources of Field Perturbations LLRF Lecture Part2 S. Simrock, M. - - PowerPoint PPT Presentation

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Sources of Field Perturbations LLRF Lecture Part2 S. Simrock, M. Grecki ITER / DESY RF System Architecture S. Simrock & M. Grecki, 5 th LC School, Switzerland, 2010, LLRF & HPRF 2 Sources of Field Perturbations o Beam loading o

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Sources of Field Perturbations

LLRF Lecture Part2

  • S. Simrock, M. Grecki

ITER / DESY

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  • S. Simrock & M. Grecki, 5th LC School, Switzerland, 2010, LLRF & HPRF

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RF System Architecture

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  • S. Simrock & M. Grecki, 5th LC School, Switzerland, 2010, LLRF & HPRF

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Sources of Field Perturbations

  • Beam loading
  • Beam current fluctuations
  • Pulsed beam transients
  • Multipacting and field emission
  • Excitation of HOMs
  • Excitation of other passband modes
  • Wake fields
  • Cavity dynamics
  • cavity filling
  • settling time of field
  • Cavity resonance frequency change
  • thermal effects (power dependent)
  • Microphonics
  • Lorentz force detuning
  • Cavity drive signal
  • HV- Pulse flatness
  • HV PS ripple
  • Phase noise from master oscillator
  • Timing signal jitter
  • Mismatch in power distribution
  • Other
  • Response of feedback system
  • Interlock trips
  • Thermal drifts (electronics, power

amplifiers, cables, power transmission system)

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  • S. Simrock & M. Grecki, 5th LC School, Switzerland, 2010, LLRF & HPRF

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Lorenz Force Detuning

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  • S. Simrock & M. Grecki, 5th LC School, Switzerland, 2010, LLRF & HPRF

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Cavity Deformation by Electromagnetic Field Pressure

  • Radiation pressure
  • Resonance frequency shift

2 acc

E K f ⋅ − = ∆

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2 2

      − = E H P   ε µ

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  • S. Simrock & M. Grecki, 5th LC School, Switzerland, 2010, LLRF & HPRF

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Lorenz Force Detuning

  • Effects of Lorenz force detuning

– Change cavity voltage and phase during RF pulse – Generate more reflection power – Limit maximum repetition rate of RF pulses

  • Properties

– Gradient dependent – Predictable from pulse to pulse – Perturbations are correlated from cavity to cavity

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  • S. Simrock & M. Grecki, 5th LC School, Switzerland, 2010, LLRF & HPRF

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Measurement of Lorentz Force Detuning

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  • S. Simrock & M. Grecki, 5th LC School, Switzerland, 2010, LLRF & HPRF

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Microphonics

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  • S. Simrock & M. Grecki, 5th LC School, Switzerland, 2010, LLRF & HPRF

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Sources of Microphonics

  • Mechanical vibrations caused by the accelerator environment are

always present and may be transferred to the cavity.

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  • S. Simrock & M. Grecki, 5th LC School, Switzerland, 2010, LLRF & HPRF

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Microphonics

  • Effects of microphonics

– It mainly influences the resonance frequency of the cavity and therefore the RF phase with respect to the beam

  • Properties

– Slow perturbation – Not predictable – Uncorrelated along the Linac

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Microphonics at JLAB

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Microphonics at FLASH

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Beam Current (Bunch Charge) Fluctuation

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Beam Loading Effect

  • Single bunch transient is not controllable
  • Bunch charge fluctuation will introduce energy spread
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Bunch Charge Pattern at FLASH

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Phase Noise of Master Oscillator

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Phase Noise of FLASH MO

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Thermal Drift

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Phase Drift of 80 m 7/8“ Reference Line at FLASH

0.25 deg. One way 12 hours

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Error Map

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Reference

[1] T. Schilcher. Vector Sum Control of Pulsed Accelerating Fields in Lorentz Force Detuned Superconducting Cavities. Ph.D. Thesis of DESY, 1998 [2] V. Ayvazyan, S. Simrock. Dynamic Lorenz Force Detuning Studies in TESLA Cavities. EPAC 2004, July 2004.