The cure of multibunch instabilities in ELETTRA

Svandrlik, M.; Bocchetta, C.J.; Fabris, A.; Iazzourene, F.; Karantzoulis, E.; Nagaoka, R.; Pasotti, C.; Tosi, L.; Walker, R.P.; Wrulich, A.

doi:10.1109/pac.1995.505683

Cited by 14 publications

(16 citation statements)

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“…However, interaction of a beam with narrowband impedance causes excitation of the long lived wake fields, which while affecting the subsequent bunches can induce instability of a beam motion in a multibunch mode. The longitudinal multibunch instability was observed and studied at a great number of facilities, namely, PEP (United States) [30], ELETTRA (Italy) [31], CESR (United States) [32], ESRF (France) [33], ALS, SPEAR (United States), DAFNE (Italy) [34], BESSY II (Germany) [35], VEPP 4M (Russia) [36], PEP II (United States) [38], and KEK PF (Japan) [39]. At present, a technique for suppression of this instability has been elaborated, including the feedback systems.…”

Section: Longitudinal Multibunch Instabilitymentioning

confidence: 99%

“…In fact, certain temper ature ranges can be found which correspond to separa tion of the frequencies of higher order modes from resonances. Using modern systems of automatic con trol makes it possible to stabilize temperature of cavi ties to an accuracy of 0.05°C, thus keeping the beam stability during the experiment [31,49].…”

Section: Longitudinal Multibunch Instabilitymentioning

confidence: 99%

“…The threshold current can be estimated with respect to the measured shift (30) of the betatron frequency for low currents. In the case of the beam with Gaussian den sity distribution, multiplier is commonly used, which follows from the definition of the peak value of the beam current (16): (31) where 〈ImZ ⊥BB β〉 is the resultant broadband reactive impedance, weighted over beta function. Figure 3 shows an example of the turn by turn measurements of current (top left panel) and a vertical coordinate (bottom left panel), as well as the oscilla…”

Section: Transverse Head Tail Instabilitymentioning

confidence: 99%

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Review of collective beam instabilities in electron-positron storage rings

Smaluk

2012

Phys. Part. Nuclei

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The review of studies of collective beam instabilities in electron positron storage rings is pre sented. The processes of excitation and suppression of the longitudinal microwave instability, transverse mode coupling instability, longitudinal and transverse multi bunch instabilities, and instabilities induced by an interaction of a beam with ions or electron clouds are discussed. Important equations for estimation of the threshold beam currents and the rise time of instabilities, as well as the references to the major original works are given. The methods for diagnostics and suppression of instabilities are considered using specific examples.

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Section: Longitudinal Multibunch Instabilitymentioning

confidence: 99%

Section: Longitudinal Multibunch Instabilitymentioning

confidence: 99%

Section: Transverse Head Tail Instabilitymentioning

confidence: 99%

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Review of collective beam instabilities in electron-positron storage rings

Smaluk

2012

Phys. Part. Nuclei

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“…At ELETTRA the distribution of the Coupled Bunch Modes (CBM) and their growth rates have been calculated as a function of cavity temperature [1], [2]. This allows a quite flexible operation of the storage ring, with the possibility of a lifetime increase by controlled use of CBI which lengthen the bunch [3].…”

Section: Curing Cbi By Hom Shiftingmentioning

confidence: 99%

Improvements in curing coupled bunch instabilities at ELETTRA by mode shifting after the installation of the adjustable higher order mode frequency shifter (HOMFS)

Svandrlik

Fabris²,

Pasotti³

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

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Mode shifting is the technique used at the third generation synchrotron light source ELETTRA to cure Coupled Bunch Instabilities (CBI). Temperature tuning of the RF cavities, based on an analytical prediction algorithm, allows longitudinal stable operating conditions to be obtained. However, once longitudinal stability has been achieved transverse instabilities can be observed, particularly during the energy ramp from 1.0 to 2.0 GeV. There has therefore been the need to extend the flexibility of the mode shifting technique. This has been achieved by the installation of adjustable HOMFS on the storage ring RF cavities. The HOMFS is effective on those longitudinal and transverse cavity Higher Order Modes which are unstable over a wide temperature range, by shifting them out of the operating temperature interval of the cavity. The installation of the HOMFS has improved the reliability and reproducibility of machine operation, also in view of the beam current upgrade. CURING CBI BY HOM SHIFTINGThe technique of curing CBI by shifting the frequency of the Higher Order Modes (HOM) of the RF cavities can be an interesting solution, particularly for high energy and compact storage rings. At ELETTRA the distribution of the Coupled Bunch Modes (CBM) and their growth rates have been calculated as a function of cavity temperature [1], [2]. This allows a quite flexible operation of the storage ring, with the possibility of a lifetime increase by controlled use of CBI which lengthen the bunch [3]. Characterisation of the excitation of Low Frequency Oscillations for different levels of CBI has also been possible [4]. Secondary effects on the RF cavities like cross-talk between cavities, cavity temperature oscillation and spurious vacuum interlocks could be observed and understood [5]. Mode shifting by temperature tuningCavity temperature intervals where the growth rates of all CBM are below the radiation damping level, which is a conservative condition to achieve stability, are more easily available if :• the radiation damping time is short; • the width of the temperature interval where a cavity HOM doesn't drive any unstable CBM is large; • the number of HOMs one has to deal with is small; • the temperature tuning range of the cavity is wide The first two conditions are more easily met by small, high energy rings. The RF cavities should not be provided with any HOM damping system, so that the HOM resonances are still sharp, high Q resonances. The experience at ELETTRA shows that the number of modes one has to deal with does not exceed about ten for the longitudinal case and ten for the transverse case (considering the double polarisation for the dipole modes). A cavity temperature tuning range of about 30 °C, as used in ELETTRA, is usually large enough to provide stable temperature windows. However, even a small bandwidth HOM can be unstable over a wide temperature range, if its temperature coefficient τ is low. Then the temperature tuning method can fail. This was the case for the first longitudinal mode, L1, of the E...

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“…Modes driven by the four rf cavities in ELETTRA are controlled by setting the temperatures of the cavities [4]. Most of the measurements were made in the presence of horizontal coupled bunch modes (HCBM), in that it was found quite difficult to excite vertical cavity driven modes in the range of temperatures at which the rf cavities routinely operate.…”

Section: Measurementsmentioning

confidence: 99%