LLRF model-based commissioning tools and operational insights C. - - PowerPoint PPT Presentation

LLRF model-based commissioning tools and

• perational insights
• C. Rivetta, D. Van Winkle, T. Mastorides, J.D. Fox1

P . Baudrenghien, A. Butterworth, J. Molendijk2

1AARD-LLRF Group, SLAC 2AB-RF Group, CERN

• C. Rivetta ()

LARP CM 14, April 26th 2010 1 / 25

Outline

1

Introduction

2

LLRF Configuration Tools General Description Features and Operation

3

Results and future work

• C. Rivetta ()

LARP CM 14, April 26th 2010 2 / 25

Introduction

Outline

1

Introduction

2

LLRF Configuration Tools General Description Features and Operation

3

Results and future work

• C. Rivetta ()

LARP CM 14, April 26th 2010 3 / 25

Introduction

RF Station / Beam Dynamics Interaction

Σ reference RF + + + + +

−

Klystron Polar Loop Driver RF cav. 1−Turn(comb) Feedback Analog RF Feedback Digital RF Feedback LLRF Board Beam Klystron Σ Σ

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

Station parameters configuration/RF Extract LLRF Fit Model to Data to

Model/Simulations Development

dependence on RF noise emittance Determine Beam stability limits, system and perturbations etc. sensitivities to noise Remote Measurement Determine current and

• f RF System in

Closed Loop LLRF−beam interaction Simulation Adjust Feedback Loops in real system Optimize Controller using Open Loop Model

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

1

Introduction

2

LLRF Configuration Tools General Description Features and Operation

3

Results and future work

• C. Rivetta ()

LARP CM 14, April 26th 2010 7 / 25

LLRF Configuration Tools General Description

Outline

1

Introduction

2

LLRF Configuration Tools General Description Features and Operation

3

Results and future work

• 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

1

Introduction

2

LLRF Configuration Tools General Description Features and Operation

3

Results and future work

• 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 between LLRF digital and analog paths.

Klystron + + +

−

Polar Loop RF cav. 1−Turn(comb) Feedback Analog RF Feedback Digital RF Feedback LLRF Board Beam Klystron Noise In Noise Out + + + Driver Σ Σ Σ reference RF Σ

−60 −40 −20 20 40 60 10 20 30 Frequency (kHz) Gain (dB) Fit Data −60 −40 −20 20 40 60 −200 −150 −100 −50 Frequency (kHz) Phase (degrees)

Transfer function LLRF board St. 5, beam 1

• 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).

−8 −6 −4 −2 2 4 6 8 −30 −20 −10 10 Frequency (MHz) Gain (dB) Fit Data −8 −6 −4 −2 2 4 6 8 −200 −150 −100 −50 Frequency (MHz) Phase (degrees)

Transfer function LLRF board St. 5, beam 1

5 10 15 20 25 30 35 3.9 4 4.1 4.2 4.3 4.4 4.5 4.6 4.7 x 10

6

Notch steps Notch Frequency [MHz.] Notch Frequency vs. steps

• 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

−8 −6 −4 −2 2 4 6 8 −60 −40 −20 20 Frequency (MHz) Gain (dB) Fit Data −8 −6 −4 −2 2 4 6 8 −2000 −1000 1000 Frequency (MHz) Phase (degrees)

Transfer function Klystron St. 1, beam 1

5 10 15 20 25 30 3.9 4 4.1 4.2 4.3 4.4 4.5 4.6 4.7 x 10

6

Notch step Notch Frequency [MHz.] Selected Notch step for klystron bump compensation DAT = 0, fn = 4.69MHz. 3 3.5 4 4.5 5 5.5 6 −25 −20 −15 −10 −5 5 Frequency (MHz.) Gain (dB) Notch Klystron

• 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

Σ reference RF Σ + + +

−

Polar Loop Driver RF cav. 1−Turn(comb) Feedback Analog RF Feedback Digital RF Feedback LLRF Board Beam Klystron Noise In Noise Out + + + Klystron Σ Σ

−250 −200 −150 −100 −50 50 100 150 200 250 −40 −20 20 40 Frequency (kHz) Gain (dB) Fit Data −250 −200 −150 −100 −50 50 100 150 200 250 −400 −200 200 400 Frequency (kHz) Phase (degrees)

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

Σ reference RF Σ + + +

−

Polar Loop Driver RF cav. 1−Turn(comb) Feedback Analog RF Feedback Digital RF Feedback LLRF Board Beam Klystron Noise In Noise Out + + + + Klystron Σ Σ

−2 −1.5 −1 −0.5 0.5 1 1.5 2 −60 −40 −20 20 Frequency (MHz) Gain (dB) Fit Data −2 −1.5 −1 −0.5 0.5 1 1.5 2 −1000 −500 500 Frequency (MHz) Phase (degrees)

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)

−150 −100 −50 50 100 150 −20 20 40 60 Frequency (kHz) Gain (dB) Fit Data −150 −100 −50 50 100 150 −500 500 Frequency (kHz) Phase (degrees)

Transfer function RF station 1, beam 2

−150 −100 −50 50 100 150 −4 −2 2 Frequency (kHz) Gain (dB) Fit Data −150 −100 −50 50 100 150 −220 −200 −180 −160 −140 Frequency (kHz) Phase (degrees)

Transfer function RF station 2, beam 2

• C. Rivetta ()

LARP CM 14, April 26th 2010 17 / 25

LLRF Configuration Tools Features and Operation

LHC LLRF Tools

Model-Based design tools Based on the mathematic model estimated, the tool calculates the magnitude of the adjustable parameters in the LLRF control to configure the feedback loops of the RF station. The parameter adjusted are: gain and phase in the direct loop, gain, delay in the 1-turn delay filter and gain and phase polar loop.

Σ reference RF Σ + + +

−

Polar Loop Driver RF cav. 1−Turn(comb) Feedback Analog RF Feedback Digital RF Feedback LLRF Board Beam Klystron + + + Measure Out Step In Klystron Σ Σ

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 x 10

−3

4200 4300 4400 4500 4600 4700 4800 4900 5000 Time [sec.] ADC counts Polar Loop: Gain Step and Fit vToFit Vfitted

e.g. Adjustment of the gain in the polar loop using step function

• C. Rivetta ()

LARP CM 14, April 26th 2010 18 / 25

LLRF Configuration Tools Features and Operation

LHC LLRF Tools

Model-Based design tools Example of calculation and adjustment of the gain and phase in the direct loop Measurement of the RF station transfer function...

• C. Rivetta ()

LARP CM 14, April 26th 2010 19 / 25

LLRF Configuration Tools Features and Operation

LHC LLRF Tools

Model-Based design tools Calculation of the optimal closed-loop transfer function and LLRF parameters (gain and phase in direct loop)....

−2 −1.5 −1 −0.5 0.5 1 1.5 2 −20 −10 10 Closed−Loop Transfer Function Frequency (MHz) Gain (dB) Initial Final −2 −1.5 −1 −0.5 0.5 1 1.5 2 −600 −400 −200 200 Frequency (MHz) Phase (degrees) Initial Final

• C. Rivetta ()

LARP CM 14, April 26th 2010 20 / 25

LLRF Configuration Tools Features and Operation

LHC LLRF Tools

Model-Based design tools Set the suggested gain and phase parameters in the LLRF board ....

−2 −1.5 −1 −0.5 0.5 1 1.5 2 −60 −40 −20 20 Frequency (MHz) Gain (dB) Fit Data −2 −1.5 −1 −0.5 0.5 1 1.5 2 −1000 −500 500 Frequency (MHz) Phase (degrees)

• C. Rivetta ()

LARP CM 14, April 26th 2010 21 / 25

Results and future work

Outline

1

Introduction

2

LLRF Configuration Tools General Description Features and Operation

3

Results and future work

• C. Rivetta ()

LARP CM 14, April 26th 2010 22 / 25

Results and future work

Results and future work

LLRF configuration tools have been useful to the CERN AB-RF group to set up remotely the feedback loops of the RF stations during start up in November 09 / February 10. Crucial to reduce the impact in the RF system start-up and

• peration of the new CERN police restricting the access to the

underground caverns. The configuration tool allows setting the feedback loop in the RF station to obtain

ZRFstation = 45KΩ uniformly for all RF station (all QL’s). x10 extra reduction in ZRFstation at syncrotron sideband with the 1-turn delay filter. Reduction of low frequency spurious signals of klystron power supply (more than 30dB, f= 50 Hz-3KHz)

It takes a few minutes to set the complete feedback loop per station.

• C. Rivetta ()

LARP CM 14, April 26th 2010 23 / 25

Results and future work

Results and future work

From November 09 to February 10, the tools were crucial to design calibration curves to adapt the gain and phase of the direct loop to compensate the change in cavity’s QL during operation (coupler moves, QL = 20K injection, QL = 60K physics). Future Plans During FY2010, finish commisioning of 1-turn delay feedback configuration tool in all the LHC RF stations. Tested in RF station prototype and one LHC station. Follow with studies relating to longitudinal beam dynamics and RF station configuration and parameters More details in "LLRF studies at LHC - models, anticipated beam dynamics and emittance effects" Accelerator systems session.

• C. Rivetta ()

LARP CM 14, April 26th 2010 24 / 25

Results and future work

Acknowledgments

We would like to thank the CERN AB-RF group for their help, support, interest, and hospitality in all phases of this project. We have been grateful for their help and continuous participation during our visits and the development of these tools We would also like to thank the SLAC Accelerator Research Division for their support and help This work is supported by the US-LARP program and DOE contract #DE-AC02-76SF00515 Thanks to the audience.....Questions?,

• C. Rivetta ()

LARP CM 14, April 26th 2010 25 / 25