Loss of transverse Landau damping by noise and wakefield driven diffusion

Furuseth, Sondre Vik; Buffat, Xavier

doi:10.1103/physrevaccelbeams.23.114401

Cited by 6 publications

(30 citation statements)

References 18 publications

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“…Feedbacks are working very well, but they cannot, at the moment, damp all types of instabilities: BNS or Landau damping still usually needs to be used (after optimisation of all the many machine and beam parameters available), and there is still a lot to be done on Landau damping and its possible loss, both in the transverse and longitudinal plane (see for instance Refs. [7][8][9]47]).…”

Section: Discussionmentioning

confidence: 99%

“…However, in some cases the transient behaviour can be important also in circular machines when, for instance, instabilities develop in a time much shorter than the synchrotron period, such as in [19], as discussed previously, or when transition is crossed or when some accelerators are designed close to the isochronous condition to reduce the required RF voltage or profit from the naturally shortest bunch length. In the case of the recently described loss of transverse Landau damping by noise and wake field-driven diffusion [8], the notion of latency was introduced and defined as the time from the start of the noise excitation, on an initially Gaussian distributed bunch, to the bunch instability. Depending on the conditions, this time can be very short or as long as few hours.…”

Section: Time: Latency and Instability Rise Timementioning

confidence: 99%

“…3 Loss of Landau damping due to noise drilling a hole in the stability diagram. This figure is courtesy of Furuseth [8] Fig. 4 Comparison between the TMCI instability without a resistive transverse damper (dotted blue line) and the ITSR instability in the presence of a resistive transverse damper (full red line) [6].…”

Section: Landau Dampingmentioning

confidence: 99%

“…It is hence expected that there is no loss of Landau damping in that case. The other effect which has been recently investigated in detail is the transverse noise that can locally significantly reduce the stability diagrams generated by magnetic octupoles and hence lead to a loss of Landau damping [8]. It is believed that this effect will not be present with RFQs or nonlinear chromaticity thanks to the separation of the longitudinal amplitude space and the transverse planes where the frequency spread is created.…”

Section: Advanced Landau Dampingmentioning

confidence: 99%

“…As the machines performance was pushed, new mechanisms were revealed and nowadays the challenge consists in studying the interplays between all these intricate phenomena, as it is very often not possible to treat the different effects separately. This led to several new instability mechanisms such as the destabilising effect of resistive transverse dampers [6] and the losses of transverse Landau damping due to linear coupling [7], noise [8], and beam-beam [9]. However, even some more basic mechanisms such as the transverse mode coupling instability (TMCI) for coasting beams were never discussed or predicted in the past [10][11][12][13], and therefore, there is still a lot to be done, despite the huge amount of work and results of the last decades.…”

Section: Introductionmentioning

confidence: 99%

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General mitigation techniques for coherent beam instabilities in particle accelerators

Métral

2021

Eur. Phys. J. Plus

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An important number of coherent beam instability mechanisms can be observed in a particle accelerator, depending if the latter is linear or circular, operated at low, medium or high energy, with a small or a huge amount of turns (for circular machines), close to transition energy or not (below or above), with only one bunch or many bunches, with counter-rotating beams (such as in colliders) or not, if the beam is positively or negatively charged, if one is interested in the longitudinal plane or in the transverse plane, in the presence of linear coupling between the transverse planes or not, in the presence of nonlinearities or not, in the presence of noise or not, etc. Building a realistic impedance model of a machine is a necessary step to be able to evaluate the machine performance limitations, identify the main contributors in case an impedance reduction is required, and study the interaction with other mechanisms such as optics (linear and nonlinear), RF gymnastics, transverse damper, noise, space charge, electron cloud, and beam–beam (in a collider). Better characterising an instability is the first step before trying to find appropriate mitigation measures and push the performance of a particle accelerator, as some mitigation methods are beneficial for some effects and detrimental for some others. For this, an excellent instrumentation is of paramount importance to be able to diagnose if the instability is longitudinal or transverse, single bunch, or coupled bunch, involving only one mode of oscillation or several, and the evolution of the intrabunch motion with intensity is a fundamental observable with high-intensity high-brightness beams. Finally, among the possible mitigation methods of coherent beam instabilities, the ones perturbing the least the single-particle motion (leading to the largest necessary dynamic aperture and beam lifetime) and easiest to implement for day-to-day operation in the machine control room should be preferred.

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Section: Discussionmentioning

confidence: 99%

Section: Time: Latency and Instability Rise Timementioning

confidence: 99%

Section: Landau Dampingmentioning

confidence: 99%

Section: Advanced Landau Dampingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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General mitigation techniques for coherent beam instabilities in particle accelerators

Métral

2021

Eur. Phys. J. Plus

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New generation of very low noise beam position measurement system for the LHC transverse feedback

Valuch

Stopjakova²

2023

J. Phys.: Conf. Ser.

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Recent studies showed that the transverse feedback system noise floor in the Large Hadron Collider (LHC) must be reduced by at least factor of two in order to operate the machine with large beam-beam tune shift as foreseen in the High Luminosity (HL) LHC. Also, the future feedback system foreseen to suppress the LHC Crab Cavity noise relies on improved noise performance of the beam position measurement system. An upgrade program was launched to lower the LHC transverse feedback system noise floor during the LHC Long Shutdown II. A new generation, very low noise beam position measurement module was developed and tested with beam. Innovative methods in the RF receiver, digital signal processing, thorough optimization of every element in the signal chain from pickup to the kickers allowed to achieve a significant reduction of the system noise floor. This unprecedented noise performance opens also new possibilities for auxiliary instruments, using the position data from the transverse feedback. The paper presents the new system, notable implementation details and measured performance.

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Wake field, impedance and collective instability

Métral¹

2021

J. Inst.

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The first mention of the impedance concept appeared on November 1966 in the CERN internal report Longitudinal instability of a coasting beam above transition, due to the action of lumped discontinuities by V.G. Vaccaro. Then, a more general treatment of it appeared in February 1967 in the CERN yellow report Longitudinal instabilities of azimuthally uniform beams in circular vacuum chambers of arbitrary electrical properties by A.M. Sessler and V.G. Vaccaro. The concept of wake field came two years later, in 1969, in the paper The wake field of an oscillating particle in the presence of conducting plates with resistive terminations at both ends by A.G. Ruggiero and V.G. Vaccaro. This was the beginning of many studies, which took place over the last five decades, and today, impedances and wake fields continue to be an important field of activity, as concerns theory, simulation, bench and beam-based measurements. Building a reliable impedance or wake field model of a machine is the first necessary step to be able to evaluate the machine performance limitations, identify the main contributors in case an impedance reduction is required, and study the interaction with other mechanisms such as optics nonlinearities, transverse damper, noise, space charge, electron cloud, beam-beam (in a collider), etc. Beam collective instabilities, and their mitigation, cover a wide range of effects in particle accelerators and they have been the subjects of intense research. As the machines performance was pushed new mechanisms were revealed and nowadays the challenge consists in studying the interplays between all these intricate phenomena, as it is very often not possible to treat the different effects separately. With the increasing power of our computers this becomes easier but the need to continue and develop theories remains, to have a better understanding of the interplays between all these effects: the subject of impedance and beam instabilities in particle accelerators is far from being exhausted, as testified by the many new instability and stabilizing mechanisms which have been recently explained or discovered. Furthermore, in the context of the studies for possible future accelerators, some uncharted territories remain such as, for instance, the collective instabilities during the necessary ionization cooling for a muon collider.

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Loss of transverse Landau damping by noise and wakefield driven diffusion

Cited by 6 publications

References 18 publications

General mitigation techniques for coherent beam instabilities in particle accelerators

General mitigation techniques for coherent beam instabilities in particle accelerators

New generation of very low noise beam position measurement system for the LHC transverse feedback

Wake field, impedance and collective instability

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