Analysis of RF modes in the ANL APS vacuum chamber using computer simulation, electron beam excitation, and perturbation techniques

Kustom, R.L.; Bridges, J.F.; Chou, W.; Cook, J.M.; Mavrogenes, G.; Nicolls, G.

doi:10.1109/pac.1989.72915

Cited by 5 publications

(3 citation statements)

References 3 publications

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“…Several research groups have investigated the trapped resonant modes in insertion devices and verified that vacuum chambers with mode resonance, for example, a resonant waveguide-or cavitylike chamber could give disturbance to nearby accelerator devices like a beam position monitor (BPM) [21]- [23]. It has been also reported that the resonant modes in a vacuum chamber could be caused by a charged particle beam [22,24] and moreover, by a large resonance peak in transverse impedance of a chamber gap [25]. Such previous investigations allowed us to consider the mode resonance-assisted MP in vacuum chambers.…”

Section: Jinst 16 P11001mentioning

confidence: 99%

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Beam-induced electron multipacting with mode resonance in a vacuum chamber

Cha¹,

Jauregui²,

Grau³

et al. 2021

J. Inst.

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Some vacuum chambers in particle accelerators perform a waveguide- or resonator-like behavior due to their unique geometries. Electron multipacting caused by such a structural property might be able to overwhelm the classical beam-induced multipacting. This article shows that the wakefields of particle beams could stimulate the resonant modes of a vacuum chamber with a near-rectangular waveguide shape and accordingly induce much stronger electron avalanche in the chamber. Especially, it has been believed that the multipacting is responsible for pressure rise in a vacuum chamber, where energetic secondary electrons with growing numbers collide with gas particles at the chamber wall. Based on numerical simulations, the electron multipacting mechanism with the mode resonance is proposed, which can explain the significant pressure variation measured in our cryogenic vacuum chamber.

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Section: Jinst 16 P11001mentioning

confidence: 99%

“…The amplified E-field can be calibrated by direct measurements in the resonant chamber. It has been reported that beam WFs could give rise to mode resonance of a vacuum chamber, where the peak E-fields were more than MV/m level [23,24].…”

Section: Multipacting Simulationsmentioning

confidence: 99%

Beam-induced electron multipacting with mode resonance in a vacuum chamber

Cha¹,

Jauregui²,

Grau³

et al. 2021

J. Inst.

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show abstract

“…The cutoff of TE,o is low (about 0.33 GHz [2]). When the bunch enters the beampipe, T M waves are generated and propagate.…”

mentioning

confidence: 98%

3-D computer simulations of EM field sin the APS vacuum chamber. Part 2: Time-domain analysis

Chou¹

1989

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3-D Computer Simulations of EM Fields in the APS Vacuum ChamberPart 2: Time-Domain AnalysisIn Ref.[l], we analyze the RF modes of the 1-meter-long sector of the APS vacuum chamber in the frequency-domain. This note is a parallel analysis in the time-domain.There are quite a few measurements completed on this 1-meter-long sector.[2] In order to understand these experimental results, in particular, the cause of the strong peak around 4 GHz observed in the narrow gap, the 3-D real-the computer simulations are carried out using MAFIA. [3] In these simulations, the vacuum chamber is approximated by the geometry shown in Fig. 1. The 1-inch-diameter beampipes, which are attached at both ends of the beam chamber, are infinitely long (so-called the open boundary condition). A Gaussian-distributed rigid bunch traverses this structure along (or slightly above) the a x i s of the beampipes and generates wakefields, which are computed by the time-domain solver T3. Five probes are placed inside the top of the vacuum chamber along the horizontal direction. One is in the beam chamber, three in the narrow gap and one in the antechamber, see Fig. l(b). These probes record the E and H fields at each location as a function of the wall clock time t. The E(t) and H(t) are then Fouriertransformed and the spectra are compared with that obtained from measurements.The resolution of our Fourier transform is about 0.17 GHz. This means that there are about 60 points in the region from 0 to 10 GHz, within which the real and imaginary parts of the Fourier transform of E(t) and H(t) are plotted. The power spectra, which are the sum of the squares of the two parts, is not plotted; but its peaks should be easily located in the figures below.Several types of simulations have been performed, each using the upper half of the geometry but with different configurations and boundary conditions. 4. Same as 3, but the beam holes are displaced horizontally by 1 cm.

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