1. Cavity resonance control
Feng QIU, 10th International Accelerator School for Linear Colliders, Japan, 2016

2. Resonance control Stabilize the RF field (A&P) for beam acceleration
Minimize the cavity input power
Feng QIU, 10th International Accelerator School for Linear Colliders, Japan, 2016

3. Source of detuning
Feng QIU, 10th International Accelerator School for Linear Colliders, Japan, 2016

4. Detuning Lorentz detuning: usually effects the PS mode machine.
Microphonics: effects both of pulse mode and CW mode.
It is difficult to apply the FB control for Lorentz detuning (in PS mode), feedforward is recommended (think about why?).
Lorentz detuning
Microphonics

5. Sources of Microphonics
Scheme showing a technical drawing of a TESLA cavity welded in its cryounit. Possible detuning sources due to external vibrations or liquid helium level changes (microphonics) as well as the system response to external excitation are shown.
Feng QIU, 10th International Accelerator School for Linear Colliders, Japan, 2016

6. Microphonics FFT Microphonics will leads to a error in the RF field.
Phase
FFT
Detuning (Microphonic)
Feng QIU, 10th International Accelerator School for Linear Colliders, Japan, 2016

7. Lorentz detuning
A standing electromagnetic wave in a cavity exerts pressure on the surrounding resonator walls, This radiation pressure is
The quantities H and E denote the magnetic and electric field on the walls. The deformation of the cavity will result of detuning (think about why?).
Detuning
Acc. field
Const.

8. Resonance control
Feng QIU, 10th International Accelerator School for Linear Colliders, Japan, 2016

9. Tuner control Tuner system is used to compensate the cavity detuning.
Feng QIU, 10th International Accelerator School for Linear Colliders, Japan, 2016

10. Piezo & Tuner
Mechanic Tuner: usually for slow control or course control (slow and low precision)
Piezo: Fast and high precision (piezoelectric effects)
Cavity side
Feng QIU, 10th International Accelerator School for Linear Colliders, Japan, 2016

11. Lorentz detuning compensation
Mainly Lorentz detuning, can be compensated by piezo feedforward system.
Feng QIU, 10th International Accelerator School for Linear Colliders, Japan, 2016

12. Results @ ACC6 of FLASH Detuning ≈0 @ flat-time Problems
Feng QIU, 10th International Accelerator School for Linear Colliders, Japan, 2016

13. Resonance control for CW mode
In CW mode machine, cavity is operated in CW mode, thus the cavity field is almost constant (steady state).
The main detuning is Microphonics.
Tuner (μTCA)
Fine ctrl.
∆𝜃= 𝜃 𝑃 𝑓 − 𝜃 𝑝𝑖𝑐𝑘 𝑢𝑝
Coarse ctrl.
Phase difference
Sensor: same with LLRF control
Feng QIU, 10th International Accelerator School for Linear Colliders, Japan, 2016

14. Applications in Resonance control
Feng QIU, 10th International Accelerator School for Linear Colliders, Japan, 2016

15. DOB for resonance control
It is also okay to use the DOB technique for tuner control if you have enough information of the tuner’s transfer function.
Feng QIU, 10th International Accelerator School for Linear Colliders, Japan, 2016

16. DOB ctrl for resonance control @ KEK cERL
It works but the gain margin is limited by some resonance peaks
Feng QIU, 10th International Accelerator School for Linear Colliders, Japan, 2016
ERL(2015), F. QIU

17. TF of tuner system @ DESY XFEL
TF of tuner system is some how complicated compared with cavity system.
Feng QIU, 10th International Accelerator School for Linear Colliders, Japan, 2016

18. TF of tuner system
Some advanced adaptive FF control DESY.
Feng QIU, 10th International Accelerator School for Linear Colliders, Japan, 2016

19. TF of tuner system FF PI PI + adaptive FF PI PI + AFF
Feng QIU, 10th International Accelerator School for Linear Colliders, Japan, 2016

20. Summary
We have learnt
The main two disturbances related to resonance control.
Piezo tuner and mechanic tuner for resonance control.
Lorentz force detuning can be compensated by piezo tuner with FF control.
Microphonics can be compensated by FB and FF if we know the TF of the piezo system.
Feng QIU, 10th International Accelerator School for Linear Colliders, Japan, 2016

21. Reference
[1] S. Simrock, Z. Geng. The 8th International Linear Accelerator school.
[2] T. Schilcher. Vector Sum Control of Pulsed Accelerating Fields in Lorentz Force Detuned Superconducting Cavities. Ph. D. Thesis of DESY, 1998
[3] F. Qiu et al., “Application of disturbance observer based control in low-level radio-frequency system in a compact energy recovery linac at KEK,” PRSTAB 18, (2015).
[4] A. Neumann, Compensation Microphonics in SRF Cavities to Ensure Beam Stability for Future Free-Electron-Lasers, PhD thesis, 2008
[5] F. QIU et al., Progress in the work on the Tuner Control System of the cERL at KEK, Proceedings of IPAC2016, Busan, Korea.
Feng QIU, 10th International Accelerator School for Linear Colliders, Japan, 2016