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

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 Cavity dynamics - Beam current fluctuations - cavity filling - Pulsed beam transients - settling time of field - Multipacting and field emission - Excitation of HOMs o Cavity resonance frequency change - Excitation of other passband modes - thermal effects (power dependent) - Wake fields - Microphonics - Lorentz force detuning o Other o Cavity drive signal - Response of feedback system - HV- Pulse flatness - Interlock trips - HV PS ripple - Thermal drifts (electronics, power - Phase noise from master oscillator amplifiers, cables, power - Timing signal jitter transmission system) - Mismatch in power distribution S. Simrock & M. Grecki, 5 th LC School, Switzerland, 2010, LLRF & HPRF 3

Lorenz Force Detuning S. Simrock & M. Grecki, 5 th LC School, Switzerland, 2010, LLRF & HPRF 4

Cavity Deformation by Electromagnetic Field Pressure • Radiation pressure     2 2 µ − ε   H E   0 0 = P 4 • Resonance frequency shift ∆ = − ⋅ 2 f K E acc S. Simrock & M. Grecki, 5 th LC School, Switzerland, 2010, LLRF & HPRF 5

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 S. Simrock & M. Grecki, 5 th LC School, Switzerland, 2010, LLRF & HPRF 6

Measurement of Lorentz Force Detuning S. Simrock & M. Grecki, 5 th LC School, Switzerland, 2010, LLRF & HPRF 7

Microphonics S. Simrock & M. Grecki, 5 th LC School, Switzerland, 2010, LLRF & HPRF 8

Sources of Microphonics • Mechanical vibrations caused by the accelerator environment are always present and may be transferred to the cavity. S. Simrock & M. Grecki, 5 th LC School, Switzerland, 2010, LLRF & HPRF 9

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 S. Simrock & M. Grecki, 5 th LC School, Switzerland, 2010, LLRF & HPRF 10

Microphonics at JLAB S. Simrock & M. Grecki, 5 th LC School, Switzerland, 2010, LLRF & HPRF 11

Microphonics at FLASH S. Simrock & M. Grecki, 5 th LC School, Switzerland, 2010, LLRF & HPRF 12

Beam Current (Bunch Charge) Fluctuation S. Simrock & M. Grecki, 5 th LC School, Switzerland, 2010, LLRF & HPRF 13

Beam Loading Effect • Single bunch transient is not controllable • Bunch charge fluctuation will introduce energy spread S. Simrock & M. Grecki, 5 th LC School, Switzerland, 2010, LLRF & HPRF 14

Bunch Charge Pattern at FLASH S. Simrock & M. Grecki, 5 th LC School, Switzerland, 2010, LLRF & HPRF 15

Phase Noise of Master Oscillator S. Simrock & M. Grecki, 5 th LC School, Switzerland, 2010, LLRF & HPRF 16

Phase Noise of FLASH MO S. Simrock & M. Grecki, 5 th LC School, Switzerland, 2010, LLRF & HPRF 17

Thermal Drift S. Simrock & M. Grecki, 5 th LC School, Switzerland, 2010, LLRF & HPRF 18

Phase Drift of 80 m 7/8“ Reference Line at FLASH 12 hours 0.25 deg. One way S. Simrock & M. Grecki, 5 th LC School, Switzerland, 2010, LLRF & HPRF 19

Error Map S. Simrock & M. Grecki, 5 th LC School, Switzerland, 2010, LLRF & HPRF 20

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. S. Simrock & M. Grecki, 5 th LC School, Switzerland, 2010, LLRF & HPRF 21