LLRF model-based commissioning tools and operational insights C. Rivetta, D. Van Winkle, T. Mastorides, J.D. Fox 1 . Baudrenghien, A. Butterworth, J. Molendijk 2 P 1 AARD-LLRF Group, SLAC 2 AB-RF Group, CERN C. Rivetta () LARP CM 14, April 26th 2010 1 / 25
Outline Introduction 1 LLRF Configuration Tools 2 General Description Features and Operation Results and future work 3 C. Rivetta () LARP CM 14, April 26th 2010 2 / 25
Introduction Outline Introduction 1 LLRF Configuration Tools 2 General Description Features and Operation Results and future work 3 C. Rivetta () LARP CM 14, April 26th 2010 3 / 25
Introduction RF Station / Beam Dynamics Interaction Klystron Klystron RF Driver Polar Loop cav. + − Σ Digital RF Σ Feedback + + RF + Analog RF Σ reference Feedback + Beam 1−Turn(comb) LLRF Board Feedback The longitudinal beam dynamics is mainly defined by the impedance and associated circuitry of RF stations. The stable operation requires the control of higher-order mode impedances as well as the precise control of the accelerating fundamental impedance. Impedance controlled LLRF architectures modify the impedance seen by the beam with feedback techniques. This system has multiple dynamic loops. Stability of the operation point of the complete system is a necessary condition. C. Rivetta () LARP CM 14, April 26th 2010 4 / 25
Introduction LHC LLRF Effort RF station / Longitudinal beam dynamics effort is combined in two related activities Optimal Configuration Tools Model/Simulations Development Remote Measurement LLRF−beam interaction of RF System in Simulation Closed Loop Fit Model to Data to Extract LLRF configuration/RF Station parameters Determine Beam emittance dependence on RF noise Optimize Controller using Open Loop Model Determine current and Adjust Feedback stability limits, system Loops in real system sensitivities to noise and perturbations etc. Configuration Tools: Identifies the RF station model and defines the LLRF adjustable parameters to minimize the overall RF station impedance. Model/Simulation Development: Detailed model of both the RF station and the longitudinal beam dynamics. Impact of RF station operation configuration on the longitudinal beam dynamics. Common Area: RF station model and model-based design of the LLRF . C. Rivetta () LARP CM 14, April 26th 2010 5 / 25
Introduction Motivation Over the last two years with LARP support, SLAC personnel have established a strong collaboration with CERN AB-RF group, and have successfully developed a suite of tools to configure the LHC RF stations in operation, to help in setting up the stations after a down time, and to determine deviations between the nominal and measured system behavior (drift). These tools operate remotely and allow identifying the RF station transfer function and designing the feedback loops using model-based techniques. Remote operation was crucial under the new stricter CERN polices preventing tunnel access when the magnets are energized. C. Rivetta () LARP CM 14, April 26th 2010 6 / 25
LLRF Configuration Tools Outline Introduction 1 LLRF Configuration Tools 2 General Description Features and Operation Results and future work 3 C. Rivetta () LARP CM 14, April 26th 2010 7 / 25
LLRF Configuration Tools General Description Outline Introduction 1 LLRF Configuration Tools 2 General Description Features and Operation Results and future work 3 C. Rivetta () LARP CM 14, April 26th 2010 8 / 25
LLRF Configuration Tools General Description Main Features of the Tool Adjust off-set voltages in the analog LLRF and modulator circuitry Adjust phase rotation between digital and analog parallel paths in the LLRF boards. Set parameters of circuitry compesating the effects of klystron spurious resonance in the RF loop. Measurement of the open loop transfer function of the RF station. Measurement of the closed loop transfer function of the RF station. Measurement and Configuration of the klystron polar loop. Based on the identified open loop model of the RF station, the closed loop system is designed by defining the adjustable parameters of the LLRF to minimize the impedance of the RF station. C. Rivetta () LARP CM 14, April 26th 2010 9 / 25
LLRF Configuration Tools General Description LHC LLRF Tools Built-in Network Analyzer The buit-in Network Analyzed operates by injecting a base-band complex noise sequence and measuring the complex signal response of the circuit to that excitation. The transfer function between the injection and measurement points is estimated as the quotient between the cross power spectral density of both signals and the power spectral density of the input signal. To obtain a mathematical model of the system, the measured transfer function measured is parameterized by fitting the transfer function of a lineal model representative of the system. C. Rivetta () LARP CM 14, April 26th 2010 10 / 25
LLRF Configuration Tools Features and Operation Outline Introduction 1 LLRF Configuration Tools 2 General Description Features and Operation Results and future work 3 C. Rivetta () LARP CM 14, April 26th 2010 11 / 25
LLRF Configuration Tools Features and Operation LHC LLRF Tools LLRF circuitry adjustments Adjust off-set voltages Adjust phase rotation 30 Fit Data between LLRF digital and 20 Gain (dB) analog paths. 10 0 − 60 − 40 − 20 0 20 40 60 Frequency (kHz) Klystron 0 Klystron RF Driver Σ Noise In Polar Loop cav. Phase (degrees) + − 50 − 100 − + Digital RF Σ Σ Noise Out Feedback − 150 + + RF + − 200 Analog RF Σ reference − 60 − 40 − 20 0 20 40 60 Feedback Frequency (kHz) + 1−Turn(comb) Beam LLRF Board Transfer function LLRF board St. 5, beam 1 Feedback C. Rivetta () LARP CM 14, April 26th 2010 12 / 25
LLRF Configuration Tools Features and Operation LHC LLRF Tools LLRF circuitry adjustments Calibration of klystron spurious resonace compensator (Notch circuit). 10 6 Notch Frequency vs. steps x 10 4.7 0 Gain (dB) 4.6 − 10 4.5 Fit − 20 Notch Frequency [MHz.] Data 4.4 − 30 − 8 − 6 − 4 − 2 0 2 4 6 8 4.3 Frequency (MHz) 0 4.2 Phase (degrees) − 50 4.1 − 100 4 − 150 3.9 0 5 10 15 20 25 30 35 Notch steps − 200 − 8 − 6 − 4 − 2 0 2 4 6 8 Frequency (MHz) Transfer function LLRF board St. 5, beam 1 C. Rivetta () LARP CM 14, April 26th 2010 13 / 25
LLRF Configuration Tools Features and Operation LHC LLRF Tools Compesation the effects of klystron spurious resonance in the RF loop 20 Fit 0 Data Selected Notch step for klystron bump compensation 5 Gain (dB) 6 4.7 x 10 − 20 0 4.6 − 40 4.5 − 60 − 5 − 8 − 6 − 4 − 2 0 2 4 6 8 Notch Frequency [MHz.] Frequency (MHz) 4.4 Gain (dB) 1000 − 10 4.3 Phase (degrees) 4.2 0 − 15 4.1 − 1000 − 20 4 Notch DAT = 0, fn = 4.69MHz. − 2000 Klystron − 8 − 6 − 4 − 2 0 2 4 6 8 3.9 − 25 0 5 10 15 20 25 30 3 3.5 4 4.5 5 5.5 6 Frequency (MHz) Notch step Frequency (MHz.) Transfer function Klystron St. 1, beam 1 C. Rivetta () LARP CM 14, April 26th 2010 14 / 25
LLRF Configuration Tools Features and Operation LHC LLRF Tools Measurement of the Open Loop Transfer Function 40 Fit 20 Data Gain (dB) 0 − 20 Klystron Klystron RF Driver − 40 Σ Noise In Polar Loop cav. − 250 − 200 − 150 − 100 − 50 0 50 100 150 200 250 + Frequency (kHz) 400 − + Digital RF Σ Σ Noise Out Feedback Phase (degrees) + + 200 RF + 0 Analog RF Σ reference Feedback + − 200 Beam − 400 1−Turn(comb) LLRF Board − 250 − 200 − 150 − 100 − 50 0 50 100 150 200 250 Feedback Frequency (kHz) Transfer function RF station 2, beam 2 C. Rivetta () LARP CM 14, April 26th 2010 15 / 25
LLRF Configuration Tools Features and Operation LHC LLRF Tools Measurement of the Closed Loop Transfer Function 20 Fit 0 Data Gain (dB) − 20 − 40 Klystron − 60 Klystron RF Driver Σ − 2 − 1.5 − 1 − 0.5 0 0.5 1 1.5 2 Noise In Polar Loop cav. + Frequency (MHz) + 500 − + Digital RF Σ Σ Noise Out Phase (degrees) Feedback + + 0 RF + Analog RF Σ reference − 500 Feedback + − 1000 1−Turn(comb) Beam LLRF Board − 2 − 1.5 − 1 − 0.5 0 0.5 1 1.5 2 Feedback Frequency (MHz) Transfer function RF station 1, beam 1 C. Rivetta () LARP CM 14, April 26th 2010 16 / 25
LLRF Configuration Tools Features and Operation LHC LLRF Tools Measurement of the Open Loop / Closed Loop Transfer Functions including the 1-turn delay filter (Comb) 2 60 Fit Fit Data 40 Data Gain (dB) 0 Gain (dB) 20 − 2 0 − 4 − 20 − 150 − 100 − 50 0 50 100 150 − 150 − 100 − 50 0 50 100 150 Frequency (kHz) Frequency (kHz) 500 − 140 Phase (degrees) Phase (degrees) − 160 0 − 180 − 200 − 500 − 220 − 150 − 100 − 50 0 50 100 150 − 150 − 100 − 50 0 50 100 150 Frequency (kHz) Frequency (kHz) Transfer function RF station 2, beam 2 Transfer function RF station 1, beam 2 C. Rivetta () LARP CM 14, April 26th 2010 17 / 25
Recommend
More recommend
