linac 4 – control system and adaptive feedforward design
DESCRIPTION
LINAC 4 – Control System and Adaptive Feedforward Design. Anirban Krishna Bhattacharyya BE – RF – FB. Introduction. The Control Loops. Introduction. Total loop delay of 1100 ns. Start up strategy. - PowerPoint PPT PresentationTRANSCRIPT
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LINAC 4 – Control System and Adaptive Feedforward Design
Anirban Krishna BhattacharyyaBE – RF – FB
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Introduction
The Control Loops
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Introduction
Total loop delay of 1100 ns.
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Start up strategy
100 μsec are allowed for Low Level RF (LLRF) loops stabilization. The sequence leading to beam injection is as follows:
• Filling of cavity open-loop using feed forward set point (SPFF ) for 50 μsec. This set point can be computed from the saturation power of the klystron and is given by
For the first 10 μsec of the process the feed forward set point value is ramped from 0 to SPFF .•The feed back is then switched on and for 12 μsec the loop gains Kp and Ki are ramped to the desired values. The job of the controller is thus to follow the cavityvoltage set point by correcting for the error produced by the feed forward set point.•After 38 μsec the beam is injected.
PsatSPFF=
Vcav
1mW
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PIMS Cavity: ZTT = 26e6 MΩ/m L = 1.79 m Q0 = 17000 QL = 7100 Φ = -20° Z0 = 50 Ω Psat = 1.4 MW
Beam current: 40 mACavity voltage: 7.00542 MVPower loss: 5%
Parameters
Controller structure: , where, , and, 1+aτs
KP
1+τsΤ =
KP
KI
a = 10
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Smith-Predictor Design
Process model estimation:
1. Cavity is narrow band compared to all other loop components.
2. Cavity has only single resonance.3. Other loop components only contribute to gain.4. 10% error in knowledge of cavity parameters and delay.
Requirements:
1. Model for process/plant.2. Estimation of time-delay
What is this?
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Results: Single Resonance Cavity
KP = 30KI = 2.73e6
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Results: Single Resonance Cavity
0.5337°
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Results: Single Resonance Cavity
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PIMS Cavity Model (Experimental)
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Notch Filter for PIMS Cavity
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Effect of Notch
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Nyquist Plot
KP = 30KI = 2.73e6
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Comparison of Cavity models
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Results: PIMS Model
0.5926°
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Results: PIMS Model
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Conclusions
• Error for beam injection (40 mA) is 1.4% in Voltage and 0.5926° in phase. At steady state they reduce to 0.1913% in voltage and 0.1333° in phase.
• Parasitic resonance of PIMS can be compensated by notch filter.
• This is feedback alone, with Smith-Predictor. The Adaptive Feedforward should further improve on this, particularly in the case of Klystron ripple, which is reproducible from shot to shot.
• Klystron is operating very close to saturation with 40 mA beam current, 7.0054 MV cavity voltage and QL = 7100.
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Smith Predictor
Controller Plant
Delay
1+GCGe-sτd
GCGe-sτd
Transfer function =>