Reduction of the Apparent Impedance of Wide Band Accelerating Cavities by RF Feedback

Boussard, D.; Lambert, G.

doi:10.1109/tns.1983.4332774

Cited by 26 publications

(21 citation statements)

References 4 publications

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“…In particle accelerators the historic solution was to clock the hardware with a multiple of the revolution frequency [4], [5]. The treatment therefore inherits beam synchronism by design.…”

Section: State Of the Art In Signal Synchronous Processingmentioning

confidence: 99%

“…The digital processing, for instance filtering, needs to adjust its frequency response in real time to the changing signal spectrum during the acceleration ramp. When digital electronics was first introduced in particle accelerators in the mid-eighties, the obvious solution was to use a sampling clock which was a multiple of the revolution frequency [4]. The processing algorithm then needs not to be changed during the acceleration.…”

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confidence: 99%

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An Architecture for Real-Time Arbitrary and Variable Sampling Rate Conversion With Application to the Processing of Harmonic Signals

Guarch

Baudrenghien

Aróstegui

2020

IEEE Trans. Circuits Syst. I

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The paper presents a new solution for sampling rate conversion and processing of harmonic signals with known but possibly varying fundamental frequency. This problem is commonly found in particle accelerators, for tracking the beam signals whose revolution frequency varies during the acceleration ramp. It is also common among many other fields such as speech and music processing, removal of mechanical noises, filtering of biomedical recordings, active crack imaging, etc. The key element in the proposed solution is a new architecture for a Farrow-based resampler, in which the resampling ratio can take any value and can be modified continuously to follow the signal fundamental frequency. The combination of two complementary resamplers creates a processing region where signal synchronous processing is performed. The resampler architecture is optimized for modern FPGA features. It decouples the processing and sampling clocks, and uses a single processing (hardware) clock whose frequency remains fixed. The functional model was migrated to Xilinx System Generator and the overall performance is evaluated with an application that filters a periodic signal whose frequency follows a known linear ramp in the presence of additive white noise.

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“…In particle accelerators the historic solution was to clock the hardware with a multiple of the revolution frequency [4], [5]. The treatment therefore inherits beam synchronism by design.…”

Section: State Of the Art In Signal Synchronous Processingmentioning

confidence: 99%

mentioning

confidence: 99%

An Architecture for Real-Time Arbitrary and Variable Sampling Rate Conversion With Application to the Processing of Harmonic Signals

Guarch

Baudrenghien

Aróstegui

2020

IEEE Trans. Circuits Syst. I

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“…(iii) The oneturn feedback (OTFB) increases the gain by 10 (linear) in a narrow band (100 Hz) on the revolution frequency sidebands [13]. It was first proposed for CERN's Super Proton Synchrotron (SPS), where the distance between generator and cavities did not allow for the use of a fast rf feedback [14]. More recently it was used in PEP-II, in tandem with a fast rf feedback [15] as in the LHC.…”

Section: Llrf Loopsmentioning

confidence: 99%

Fundamental cavity impedance and longitudinal coupled-bunch instabilities at the High Luminosity Large Hadron Collider

Baudrenghien

Mastoridis

2017

Phys. Rev. Accel. Beams

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The interaction between beam dynamics and the radio frequency (rf) station in circular colliders is complex and can lead to longitudinal coupled-bunch instabilities at high beam currents. The excitation of the cavity higher order modes is traditionally damped using passive devices. But the wakefield developed at the cavity fundamental frequency falls in the frequency range of the rf power system and can, in theory, be compensated by modulating the generator drive. Such a regulation is the responsibility of the low-level rf (llrf) system that measures the cavity field (or beam current) and generates the rf power drive. The Large Hadron Collider (LHC) rf was designed for the nominal LHC parameter of 0.55 A DC beam current. At 7 TeV the synchrotron radiation damping time is 13 hours. Damping of the instability growth rates due to the cavity fundamental (400.789 MHz) can only come from the synchrotron tune spread (Landau damping) and will be very small (time constant in the order of 0.1 s). In this work, the ability of the present llrf compensation to prevent coupled-bunch instabilities with the planned high luminosity LHC (HiLumi LHC) doubling of the beam current to 1.1 A DC is investigated. The paper conclusions are based on the measured performances of the present llrf system. Models of the rf and llrf systems were developed at the LHC startup. Following comparisons with measurements, the system was parametrized using these models. The parametric model then provides a more realistic estimation of the instability growth rates than an ideal model of the rf blocks. With this modeling approach, the key rf settings can be varied around their set value allowing for a sensitivity analysis (growth rate sensitivity to rf and llrf parameters). Finally, preliminary measurements from the LHC at 0.44 A DC are presented to support the conclusions of this work.

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“…Then the EFEM N − 1 is driven by the full shunt impedance of the accelerating cavity. To operate in this regime the RF system must be equipped with feedback loops aimed at reducing the impedance presented to the beam [12,13].…”

Section: Fundamental Mode Impedancesmentioning

confidence: 99%

Architectures and Algorithms for Control and Diagnostics of Coupled-Bunch Instabilities in Circular Accelerators

Teytelman¹

2003

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Modern light sources and circular colliders employ large numbers of high-intensity particle bunches in order to achieve high luminosity. The electromagnetic coupling of bunches via resonant structures causes coherent instabilities at high beam currents. Achieving high luminosity requires the control of such unstable motion. Feedback control is challenging None of the experimental measurements presented in this work would be possible without the longitudinal feedback system designed by SLAC/LBL/LNF-INFN collaboration. And this system would not exist without engineering wizardry of Jack Hoeflich, Jeff Olsen, Gerard Oxoby, Bill Ross, Leonid Sapozhnikov, and Andrew Young. I have been lucky to help Ric Claus with system software development, learning a lot in the process. Success of our hardware projects was guaranteed by our technicians Dave Anderson and Boni F.

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Reduction of the Apparent Impedance of Wide Band Accelerating Cavities by RF Feedback

Cited by 26 publications

References 4 publications

An Architecture for Real-Time Arbitrary and Variable Sampling Rate Conversion With Application to the Processing of Harmonic Signals

An Architecture for Real-Time Arbitrary and Variable Sampling Rate Conversion With Application to the Processing of Harmonic Signals

Fundamental cavity impedance and longitudinal coupled-bunch instabilities at the High Luminosity Large Hadron Collider

Architectures and Algorithms for Control and Diagnostics of Coupled-Bunch Instabilities in Circular Accelerators

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