Measurement of the longitudinal microwave instability in the APS storage ring

Chae, Yong-Chul; Emery, L.; Lumpkin, A.H.; Song, J.J.; Yang, B.

doi:10.1109/pac.2001.987193

Cited by 6 publications

(6 citation statements)

References 5 publications

(5 reference statements)

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“…But the energy spread (red curve) shows a threshold behavior at a current of 6 mA or 7 mA. This is consistent with the threshold observed experimentally [4]. The rms values depicted as error bars in Fig.…”

Section: Applicationsupporting

confidence: 90%

“…The total inductive impedance at the low frequency expressed as Z/n is 0.22 Ω without ad hoc inclusion of HOM contribution, which is 80% lower than the estimated value based on the bunch-length measurement [4].…”

Section: Discussionmentioning

confidence: 56%

“…The bottom two traces below threshold show the coherent signal at the synchrotron frequencies f s and 2*f s , representing m=1 and m=2 mode, respectively. However, above the threshold the coherent signal near 4*f s is excited; it was also observed experimentally [4].…”

Section: Applicationmentioning

confidence: 52%

“…The longitudinal microwave instability in the APS storage ring had been measured and reported [4]. As an application of the impedance database we used the total impedance in Fig.…”

Section: Applicationmentioning

confidence: 99%

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Longitudinal coupling impedance of the APS storage ring

Chae

Harkay

Sun

Proceedings of the 2003 Bipolar/BiCMOS Circuits and Technology Meeting (IEEE Cat. No.03CH37440)

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The three-dimensional wake potentials of the APS storage ring have been reconstructed according to the impedance database concept. Every wakefield-generating component in the ring was considered including small-gap insertion device (ID) chambers, rf cavities, shielded bellows, beam position monitors, synchrotron radiation absorbers, scrapers, flags, various chamber transitions, septum chambers, and pulsed kickers. In this paper the result for the longitudinal wake potentials and its impedance are presented. The total impedance is not model-based but the direct sum of numerical functions. The fit parameters for the broadband resonator model are also included as a convenient representation. We used this impedance model to investigate the observed microwave instability, namely bunch lengthening, anomalous energy spread, and coherent excitation at high synchrotron sideband. IMPEDANCE DATABASEThe concept of impedance database is described in the companion paper [1]. We report highlights of building the database for the longitudinal impedance.The horizontal and vertical impedance are reported separately [2,3]. The rf cavities at the APS storage ring provide energy to the beam with 9.5 MV of gap voltage distributed in sixteen cavities in four sectors. One of the rf sectors is shown in Fig. 1. Rf-Sector (rf-cavities and transition)An rf sector consists of four cavities and the transition of vacuum chamber at both ends. The complexity is simplified in the simulation to axially symmetric geometry. We used the program ABCI in order to calculate wake potential The wake potential of one rf sector for a 5 mm bunch is shown in Fig. 2; the cavityonly wake potential is also included for comparison. We note that there exists significant interference effect between the transition and cavities. The impedance, the Fourier transform of the wake potential divided by the bunch spectrum, is shown in Fig. 3. The graph on the left shows the impedance of shortranged wake over 30 cm, which shows the characteristic cavity-type impedance in the form of. This short-ranged wake potential is included in the total wake potential. Note the imaginary part of the impedance is negative.The impedance of long-ranged wake over 10 m is also shown in Fig. 3 on the right. Higher-order modes (HOMs) as well as the fundamental mode resonating at 352 MHz are clearly shown. The total HOM contribution to Z/n is 0.2 Ω, which was estimated by using the formula ( ) ( )where R s is the shunt impedance, Q is the quality factor, and n is the harmonic number. This (Z/n) HOM is included in the impedance breakdown for Z/n.

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Section: Applicationsupporting

confidence: 90%

Section: Discussionmentioning

confidence: 56%

Section: Applicationmentioning

confidence: 52%

“…The longitudinal microwave instability in the APS storage ring had been measured and reported [4]. As an application of the impedance database we used the total impedance in Fig.…”

Section: Applicationmentioning

confidence: 99%

See 2 more Smart Citations

Longitudinal coupling impedance of the APS storage ring

Chae

Harkay

Sun

Proceedings of the 2003 Bipolar/BiCMOS Circuits and Technology Meeting (IEEE Cat. No.03CH37440)

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“…3), the beam reverts to steady state at half the peak amplitude before the limit is reached. The intensity limit is almost proportional to the bunch length when V rf is varied (47 ps at 9.5 MV and 68 ps at 7.1 MV [5]), implying an invariant peak intensity limit (see also Section 3.2). …”

Section: Intensity and V Rf Dependencementioning

confidence: 92%

Transverse sawtooth instability at the Advanced Photon Source

Harkay

Huang²,

Lessner³

et al.

PACS2001. Proceedings of the 2001 Particle Accelerator Conference (Cat. No.01CH37268)

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A detailed investigation has been made of the transverse sawtooth instability observed at the Advanced Photon Source. This horizontal single-bunch instability exhibits two modes: steady-state, with continuous centroid oscillations at fixed amplitude, and bursting, with an amplitude that varies quasi-periodically with a peak-topeak excursion of up to 2 mm. The transition between modes is sharp and, depending on machine conditions, multiple transitions are observed with increasing bunch intensity. The threshold and character of the instability also vary with chromaticity and rf voltage. The horizontal instability shows striking similarities to the longitudinal sawtooth instability observed in the Stanford Linear Collider damping ring, as well as clear and obvious differences. This paper presents experimental results and a possible mechanism for the sawtooth instability that is suggested by simulations.

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