Cavity resonance control Feng QIU 10 th International

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

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

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

Detuning 0 Lorentz detuning Ø Lorentz detuning: usually effects the PS mode machine. Ø Microphonics: effects both of pulse mode and CW mode. Ø It is difficult to apply the FB control for Lorentz detuning (in PS mode), feedforward is recommended (think about Microphonics why? ). 4

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, 10 th International Accelerator School for Linear Colliders, Japan, 2016 5

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

Lorentz detuning Ø 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. 7

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

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

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

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

Results @ ACC 6 of FLASH Detuning ≈0 @ flat-time Problems Feng QIU, 10 th International Accelerator School for Linear Colliders, Japan, 2016 12

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

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

DOB for resonance control Ø 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, 10 th International Accelerator School for Linear Colliders, Japan, 2016 15

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

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

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

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

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

Reference [1] S. Simrock, Z. Geng. The 8 th 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 lowlevel radio-frequency system in a compact energy recovery linac at KEK, ” PRSTAB 18, 092801(2015). [4] A. Neumann, Compensation Microphonics in SRF Cavities to Ensure Beam Stability for Future Free-Electron-Lasers, Ph. D thesis, 2008 [5] F. QIU et al. , Progress in the work on the Tuner Control System of the c. ERL at KEK, Proceedings of IPAC 2016, Busan, Korea. Feng QIU, 10 th International Accelerator School for Linear Colliders, Japan, 2016 21