LLRF ILC GDE Meeting Feb.6,2007 Shin Michizono LLRF - Stability requirements and proposed llrf system - Typical rf perturbations - Achieved stability at FLASH - R&D items - Schedule - Other comments

LLRF 2 Stability Requirements for Main Linac phase tolerance limiting luminosity loss (deg) phase tol. limiting incr. in energy spread (deg) amplitude tolerance limiting luminosity loss (%) amplitude tolerance limiting increase in energy spread (%) Related fluctuations correlated BC phase errors.24.35HV uncorrelated BC phase errors.48.59Microphonics correlated BC amplitude errors0.51.8HV, Ibeam uncorrelated BC amplitude errors1.62.8Microphonics correlated linac phase errorslarge.36HV uncorrelated linac phase errorslarge5.6Microphonics correlated linac amplitude errorslarge.07HV, Ibeam Uncorr. linac amplitude errorslarge1.05Microphonics Summary of tolerances for phase and amplitude control. These tolerances limit the average luminosity loss to <2% and limit the increase in RMS center-of-mass energy spread to <10% of the nominal energy spread. Ref. Mike Church

LLRF 3 LLRF system configuration at ILC All electronics are located at service tunnel Vector-sum control of 26 cavities Total 26x3+6=84ch RF monitors

LLRF 4 LLRF Rack Detail

LLRF 5 FB algorithm 26x In the case of proportional control Output = Gain*Error+FF -> Sufficient dynamic overhead is necessary at high gain operation (>50)

LLRF Klystron operation point and MV/m operation, llrf overhead is <16.5% in power (8.25% in MV/m operation, overhead becomes 11% in power -> It is used for fluctuation compensation, detuning compensation and so on. 76.5% for cavity input 7% rf distribution loss 16.5% for llrf control* *neglect all other factors such as HV ripple Extra rf drive (Gx(error)) is necessary at FB. Proportional FB gain is limited around 80 (when we can pick-up 0.1% error). And the error can be suppressed 1/G=1/80

LLRF ILC GDE Meeting Feb.6,2007 Shin Michizono LLRF - Stability requirements and proposed llrf system - Typical rf perturbations - Achieved stability at FLASH - R&D items - Schedule - Other comments

LLRF 8 Sources of Perturbations o Beam loadingo Cavity dynamics - Beam current fluctuations- cavity filling - Pulsed beam transients- settling time of field - Multipacting and field emission - Excitation of HOMso Cavity resonance frequency change - Excitation of other passband modes - thermal effects (power dependent) - Wake fields- Microphonics - Lorentz force detuning o Cavity drive signal - HV- Pulse flatnesso Other - HV PS ripple- Response of feedback system - Phase noise from master oscillator- Interlock trips - Timing signal jitter- Thermal drifts (electronics, power - Mismatch in power distributionamplifiers, cables, power transmission system)

LLRF 9 Typical Parameters in a Pulsed RF System

LLRF 10 Lorentz Force detuning compensation Detuning of 30 Hz require additional 2% rf power.

LLRF 11 Microphonics From Thesis of Thomas Schilcher

LLRF 12 Suppression of fluctuations by FB *When the system can detect 0.1% error. **only FF Larger dynamic overhead is desired for the larger FB gain.

LLRF ILC GDE Meeting Feb.6,2007 Shin Michizono LLRF - Stability requirements and proposed llrf system - Typical rf perturbations - Achieved stability at FLASH - R&D items - Schedule - Other comments

LLRF 14 Field Regulation at FLASH By T. Schilcher

LLRF ILC GDE Meeting Feb.6,2007 Shin Michizono LLRF - Stability requirements and proposed llrf system - Typical rf perturbations - Achieved stability at FLASH - R&D items - Schedule - Other comments

LLRF 16 R&D items FPGA board development having >26 ADCs RF field stabilities <0.5% in amplitude and <0.24 deg. in phase Crate evaluation (VXI, ATCA, ….) –Redundancy, board size Software development –Feedback algorithm –Klystron linearization –Exception detection and handling –Warnings and alarms High IF study

LLRF 17 DESY SIMCON3.1 Controller

LLRF 18 FPGA & DSP 10 16bit-ADCs FPGA 2DACs Quench etc. Output max RF off (by diagnostics in DSP) Real time intelligent diagnostics by DSP board Custom FPGA board : Mezzanine card of the commercial DSP board 10 16bit-ADCs and 2DACs + 2Rocket IO 40 MHz clock Commercial DSP board (Barcelona) (same to J-PARC system) :4x TI C6701 DSPs Can access to FPGA like an external memory of DSP

LLRF 19 Now, the number of ADCs in a FPGA board is limited due to the substrate. (maybe ~15 with 16 layers in substrate) The idea is based on the ‘digital radio’ and obtaining cavity signals with a ADC. Mixture of two signals decrease the resolution of analog signals but averaging increases the resolution. R&D: Proposal of IF mixture Over-sampling: IF 8 MHz & 12 MHz with 48 MHz sampling -> include averaging effect ->increase resolution Cavity signals do not change during averaging (due to high Q values) → Enough IF separation

LLRF ILC GDE Meeting Feb.6,2007 Shin Michizono LLRF - Stability requirements and proposed llrf system - Typical rf perturbations - Achieved stability at FLASH - R&D items - Schedule - Other comments

LLRF 21 Schedule Support for (test) facilities (XFEL,SMTF,STF) Crate evaluation FPGA board development having >26 ADCs. Software development High IF study

LLRF ILC GDE Meeting Feb.6,2007 Shin Michizono LLRF - Stability requirements and proposed llrf system - Typical rf perturbations - Achieved stability at FLASH - R&D items - Schedule - Other comments

LLRF 23

LLRF 24

LLRF Rf distribution error v.s. max. cavity gradient in case of the 2 cavities Only rf distribution variation 10% error in rf distribution induces 8.5% higher cavity field 10% error in loaded Q induces 4% higher cavity field Examples: 5%pk-pk Ql variation + 0.2dB (2.3%)pk-pk distribution variation -> 2%+2%=4% cavity field overshoot 31.5*1.04=32.8 MV/m 10%pk-pk (1.7%rms)+0.07dBrms (4.6%pk-pk) -> 8% overshoot 34 MV/m Although Ql and RF distribution ratio control can helpful for flattening each cavity field, This does not work without beam condition. And some residual errors exist due to the imperfect setting.

LLRF 26 Limitation of coupling adjustment method By Julien Branlard Coupling adjustment method does not work at no-beam condition. In order to satisfy both beam/no-beam condition, complex technique (including detuning control) will be necessary. Vector sum Lower cavity