Radio frequency noise effects on the CERN Large Hadron Collider beam diffusion

Mastoridis, T.; Baudrenghien, P.; Butterworth, A.; Molendijk, John; Rivetta, C.; Fox, J.

doi:10.1103/physrevstab.14.092802

Cited by 9 publications

(13 citation statements)

References 3 publications

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“…Therefore, the required power is minimum when the generator current and the cavity voltage have identical phase modulation. This result deviates from previous works that aimed at keeping the generator current fixed in both amplitude and phase [1][2][3][4][5][6].…”

Section: Theoretical Model and Optimal Algorithmcontrasting

confidence: 55%

“…An LHC test was performed with nominal LHC conditions at 450 GeV followed by an acceleration ramp to 6.5 TeV [13]. After the initial 12 bunches, batches of 96 bunches were injected up to 1164 bunches for LHC's beam 2.…”

Section: Lhc Test a Experimental Conditionsmentioning

confidence: 99%

“…This method maintains the strong rf feedback and one-turn delay feedback (OTFB) though, with the corresponding positive effects for longitudinal stability. This algorithm was implemented in simulations [3,4] and during the first LHC run [5,6] with promising results. Figures 3 and 4 show the resulting cavity and klystron signals.…”

Section: Introductionmentioning

confidence: 99%

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Cavity voltage phase modulation to reduce the high-luminosity Large Hadron Collider rf power requirements

Mastoridis

Baudrenghien

Molendijk

2017

Phys. Rev. Accel. Beams

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The Large Hadron Collider (LHC) radio frequency (rf) and low-level rf (LLRF) systems are currently configured for constant rf voltage to minimize transient beam loading effects. The present scheme cannot be extended beyond nominal LHC beam current (0.55 A dc) and cannot be sustained for the highluminosity (HL-LHC) beam current (1.1 A dc), since the demanded power would exceed the peak klystron power. A new scheme has therefore been proposed: for beam currents above nominal (and possibly earlier), the voltage reference will reproduce the modulation driven by the beam (transient beam loading), but the strong rf feedback and one-turn delay feedback will still be active for loop and beam stability. To achieve this, the voltage reference will be adapted for each bunch. This paper includes a theoretical derivation of the optimal cavity modulation, introduces the implemented algorithm, summarizes simulation runs that tested the algorithm performance, and presents results from a short LHC physics fill with the proposed implementation.

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Section: Theoretical Model and Optimal Algorithmcontrasting

confidence: 55%

Section: Lhc Test a Experimental Conditionsmentioning

confidence: 99%

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Cavity voltage phase modulation to reduce the high-luminosity Large Hadron Collider rf power requirements

Mastoridis

Baudrenghien

Molendijk

2017

Phys. Rev. Accel. Beams

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“…The spectrum shows a side lobe extending from 1.3 GHz to 2.6 GHz. After a few hours into physics (2 to 3), the ion beam spectrum returns to a Gaussian shape, as consequence of intrabeam scattering 4 (Figs. 15 and 16).…”

Section: Beam and Cavity Spectra With Blowup Through The Beam Phase Loopmentioning

confidence: 97%

“…Using this treatment, a comparison of the estimated and measured longitudinal emittance growth rates was presented in Ref. [4].…”

Section: Introductionmentioning

confidence: 99%

Longitudinal emittance blowup in the large hadron collider

Baudrenghien

Mastoridis

2013

Nuclear Instruments and Methods in Physics Research Section A:

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a b s t r a c tThe Large Hadron Collider (LHC) relies on Landau damping for longitudinal stability. To avoid decreasing the stability margin at high energy, the longitudinal emittance must be continuously increased during the acceleration ramp. Longitudinal blowup provides the required emittance growth. The method was implemented through the summer of 2010. Band-limited RF phase-noise is injected in the main accelerating cavities during the whole ramp of about 11 min. Synchrotron frequencies change along the energy ramp, but the digitally created noise tracks the frequency change. The position of the noiseband, relative to the nominal synchrotron frequency, and the bandwidth of the spectrum are set by predefined constants, making the diffusion stop at the edges of the demanded distribution. The noise amplitude is controlled by feedback using the measurement of the average bunch length. This algorithm reproducibly achieves the programmed bunch length of about 1.2 ns 2 , at flat top with low bunch-tobunch scatter and provides a stable beam for physics coast. The noise can be injected either in the beam phase loop or directly in the cavity voltage set point. These two different technical implementations are presented and their respective advantages analyzed. The performance of the algorithm and its further applications are also presented in this paper.

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Simulation of beam–beam interaction with crab cavities for LHC upgrade

Qiang

Paret

Ratti

et al. 2018

Nuclear Instruments and Methods in Physics Research Section A:

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The crab cavities are a critical component in the high luminosity LHC upgrade project to compensate the luminosity loss from large crossing angle collision. However, these crab cavities will not be perfect in the real accelerator. In this paper, we studied the effects of crab cavity imperfections on colliding beam luminosity lifetime degradation for the LHC upgrade through detailed numerical simulations. Our simulation results suggest that the white noise jitter in the crab cavity RF phase and voltage rms amplitudes should be kept below a few 10 −5 for a good luminosity lifetime, while with frequency-dependent jitter, the amplitudes should be kept below a few 10 −4 for a good lifetime. The RF multipole errors in the current crab cavity designs are small enough and would not cause extra luminosity degradation.

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Radio frequency noise effects on the CERN Large Hadron Collider beam diffusion

Cited by 9 publications

References 3 publications

Cavity voltage phase modulation to reduce the high-luminosity Large Hadron Collider rf power requirements

Cavity voltage phase modulation to reduce the high-luminosity Large Hadron Collider rf power requirements

Longitudinal emittance blowup in the large hadron collider

Simulation of beam–beam interaction with crab cavities for LHC upgrade

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