Longitudinal Phenomena in the CERN SPS

Boussard, D.; Dome, G.; Linnecar, T.; Millich, A.

doi:10.1109/tns.1977.4328957

Cited by 11 publications

(8 citation statements)

References 3 publications

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“…It was conjectured as early as 1976 [1] that the large number of discontinuities in the machine vacuum chamber could be the cause of the microwave instability responsible for blow-up during the debunching and recapture process at 10 GeV in the SPS. The problem was solved at that time by installing a 200 MHz RF bunching system in the PS (the SPS injector) and injecting bunch into bucket.…”

Section: What Type Of Problems Do We Expect?mentioning

confidence: 99%

“…Here are a few examples. Already in the first two years of operation the impedance of two higher order modes, one transverse at 460 MHz and the other longitudinal at 628 MHz [1] in the main RF cavities, were identified as causing instability and intensity limitation and had to be passively damped. When preparing for SppS, bunch intensities were limited when crossing transition by both a longitudinal negative mass instability and a transverse head-tail instability to 2 × 10 10 protons [2].…”

Section: Introductionmentioning

confidence: 99%

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Impedance issues in the CERN SPS

Linnecar¹

1999

AIP Conference Proceedings

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The future use of the CERN SPS accelerator as injector for the Large Hadron Collider, LHC, and the possible use of the SPS as a neutrino source for the Gran Sasso experiment are pushing the maximum intensity requirements of the accelerator much higher than achieved up to now. At the same time the requirements on beam quality are becoming far more stringent. The SPS machine, built in the 70's, is not a "smooth" machine. It contains many discontinuities in vacuum chamber cross-section and many cavity-like objects, as well as the 5 separate RF systems at present installed. All these lead to a high impedance, seen by the beam, spread over a wide frequency range. As a result there is a constant fight against instabilities, both single and multi bunch, as the intensity increases. A programme of studies is under way in the SPS to identify, reduce, and remove where possible the sources of these impedances.

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Section: What Type Of Problems Do We Expect?mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Impedance issues in the CERN SPS

Linnecar¹

1999

AIP Conference Proceedings

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“…Note that the beam of 243 bunches, intensity 10 11 per bunch, filling 3/11 of the machine circumference, combines the high single bunch intensities obtained during collider operation in the past, where the microwave instability was a limitation [3], with the large total intensities achieved in fixed target operation, where coupled bunch instabilities are seen. The microwave instability, first observed in the SPS in 1976 [4], is not harmful for present operation, but it limits the single bunch intensity of the LHC beam. A new measurement technique [5], used last year and described below, has allowed us to determine the dominant sources of longitudinal impedance in the SPS responsible for this instability.…”

Section: Introductionmentioning

confidence: 99%

The fine structure of the longitudinal machine impedance observed with single bunches

Bohl

Linnecar²,

Shaposhnikova³

Proceedings of the 1997 Particle Accelerator Conference (Cat. No.97CH36167)

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Using a beam spectrum measurement the detailed structure of the CERN SPS longitudinal machine impedance has been observed over a wide frequency range. Single high intensity proton bunches were injected into the machine with RF off. The spectrum of the unstable bunch modes, produced by the different resonant impedances in the ring, was measured during slow debunching. The maximum mode amplitude as a function of frequency was recorded for many injected bunches. The central frequency of each bunch mode is close to the resonant frequency of the impedance and the width depends upon the bunch length. Using sufficiently long bunches allowed the machine impedance to be seen in detail in the frequency range 100MHz to 4GHz. The low frequency of this range is defined by the initial stable bunch spectrum, and the high frequency by the vacuum chamber cut-off frequency. The dominant peaks in the spectrum have been identified with different impedance sources in the machine -some previously unknown.

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“…At the SPS this method has already been applied in the past with the proton fixed target beam of 5 ns bunch spacing and 4 10 8 protons per bunch [10]. LHC type beams have 25 ns bunch spacing and intensities of 10 11 protons per bunch.…”

Section: Introductionmentioning

confidence: 99%

“…Every bunch is exposed to a different rf voltage and has therefore its own synchrotron frequency. In [10] the rf amplitude was modulated sinusoidal whereas we applied a linear rf amplitude change.…”

Section: Introductionmentioning

confidence: 99%

rf amplitude modulation to suppress longitudinal coupled bunch instabilities in the CERN Super Proton Synchrotron

Vogel

Bohl

Wehrle

2005

Phys. Rev. ST Accel. Beams

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Without specific counter measures, the LHC type beam in the SPS suffers from longitudinal coupled bunch instabilities. To prevent them, the SPS impedance has been decreased over the last few years and the operation of a high frequency Landau damping system has been established. In the absence of this Landau damping system one may alternatively introduce an rf amplitude modulation to stabilize the beam. We present results obtained by this method in the SPS and considerations for a potential increase of the longitudinal beam stability in the LHC.

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Longitudinal Phenomena in the CERN SPS

Cited by 11 publications

References 3 publications

Impedance issues in the CERN SPS

Impedance issues in the CERN SPS

The fine structure of the longitudinal machine impedance observed with single bunches

rf amplitude modulation to suppress longitudinal coupled bunch instabilities in the CERN Super Proton Synchrotron

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