Coaxial wire measurements of the longitudinal coupling impedance

Hahn, H.; Pedersen, F.

doi:10.2172/6591101

Cited by 29 publications

(22 citation statements)

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“…After the parameter measurement with this setup, the kicker is replaced by a reference, and the same procedure is repeated to obtain the beam coupling impedances. In this way, we can cancel out imperfect matchings in two transitions [33].…”

Section: Measurementsmentioning

confidence: 99%

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Longitudinal feedback system kicker for the PLS storage ring

Kim

Kwon

Huang

et al. 2000

IEEE Trans. Nucl. Sci.

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The higher order modes (HOM's) of RF cavities at the Pohang Light Source (PLS) storage ring cause longitudinal coupled bunch mode instabilities. A longitudinal feedback system (LFS) is introduced to cure these instabilities. As a key component of the LFS, there is a single-ridged waveguide-overloaded cavity for a longitudinal bunch-by-bunch LFS kicker. Since the RF frequency is 500 MHz, the bandwidth of this kicker should be wider than 250 MHz to damp any coupled bunch mode. Also, a higher shunt impedance of the kicker is selected to use a lower power amplifier. One aluminum kicker is fabricated, and the bandwidth, HOM's, and the shunt impedance of the kicker are measured with a network analyzer. This kicker has several different features from the LFS kicker for DA8NE. First of all, there are four input/output ports to obtain a wider bandwidth. Second, there is a nose cone to obtain a higher shunt impedance. Third, the symmetric frequency response of the shunt impedance around the central frequency is provided. Finally, low beam coupling power (4 W per port at 400 mA) is obtained. According to the simulation result by the high frequency structure simulator (HFSS) code, we obtained the high shunt impedance of 621.3 (transit time factor considered value) and the wide bandwidth of 255 MHz. These are compared with the measured result.Index Terms-Coupled bunch mode instability, HOM, longitudinal feedback system kicker, wake fields.

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Section: Measurementsmentioning

confidence: 99%

“…multiple reflections in the time domain accurately. The shunt impedance can be obtained by using the longitudinal beam coupling impedance which is given by[33] …”

mentioning

confidence: 99%

Longitudinal feedback system kicker for the PLS storage ring

Kim

Kwon

Huang

et al. 2000

IEEE Trans. Nucl. Sci.

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“…The normalized ratio, here simply taken as S 21 , has been interpreted via standard transmission line circuit theory. The result for a lumped device, i.e., short compared to the beam tube radius, was given by Hahn and Pedersen (HP) as [7] …”

Section: Introductionmentioning

confidence: 99%

Validity of coupling impedance bench measurements

Hahn

2000

Phys. Rev. ST Accel. Beams

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In this paper the validity of coupling impedance bench measurements is theoretically demonstrated for the standard model of a uniformly distributed wall impedance. Integral equations expressing the magnetic field at the wall are found for the two cases where the device is excited either by a beam or a central wire. The integral equations are solved by a perturbation method with the coupling impedance as the expansion parameter, leading to expressions for the coupling impedance of the beam and the forward scattering coefficient in the bench measurement. Conditions for the validity of bench measurements are indicated, and the interpretation of wire measurements via the scattering coefficient by the conventional formulas is discussed.

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“…. This is also consistent with the fact that the Sands-Rees formula can be derived from the Hahn-Pedersen one as the latter approximation for small values of the impedance [8].…”

Section: Real Impedancesupporting

confidence: 88%

“…The longitudinal impedance of a small (with respect to the wavelength) aperture on a coaxial beam pipe as shown in Fig.1 can be calculated from the measured S 21 parameter using the Hahn-Pedersen formula [8]:…”

Section: Measured Impedancementioning

confidence: 99%

Analysis of coupling impedance bench measurements using Bethe's diffraction theory

Santis

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

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In this paper we study the validity of coupling impedance bench measurements, comparing two of the most commonly used formulas to the result obtained applying a modified version of Bethe's theory of diffraction to a lumped impedance in a coaxial beam pipe. The equations found provide a quantitative expression for the influence of the wire thickness used in the measurement of the real and imaginary part of the longitudinal impedance. The precision achievable in an actual measurement is therefore discussed. The method presented can also be applied in the presence of distributed impedances as well as to the analysis of transverse impedance measurements.

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Coaxial wire measurements of the longitudinal coupling impedance

Cited by 29 publications

References 0 publications

Longitudinal feedback system kicker for the PLS storage ring

Longitudinal feedback system kicker for the PLS storage ring

Validity of coupling impedance bench measurements

Analysis of coupling impedance bench measurements using Bethe's diffraction theory

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