Design of the ILC Crab Cavity System

Adolphsen, C.; Beard, C.; Bellantoni, L.; Carter, R.; Chase, Brian; Church, M.; Edwards, H.; Goudket, P.; Jenkins, Richard O.; Jones, R. M.; Kalinin, A.; Khabiboulline, T.; Ko, K.; Li, Z.; Ma, Lili; McIntosh, Peter; Ng, C.; Seryi, Andrei; Schulte, Daniel; Solyak, N.; Tahir, I.; Xiao, Liling

doi:10.2172/915387

Cited by 10 publications

(6 citation statements)

References 4 publications

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“…The modes at 8.02 GHz are the π and 8π/9 modes of the 5 th dipole passband. Numerical simulations using the finite difference code, MAFIA [6], have previously shown that these modes are expected to have high loss factors [2]. The largest of these peaks was calculated to have an R/Q of 11.6 Ω/cm 2 which is in excellent agreement with the mean R/Q measured at a wire offset of 1mm for this mode.…”

Section: Discussionsupporting

confidence: 65%

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Impedance measurements on a test bench model of the ILC crab cavity

Goudket

Beard

McIntosh

et al. 2007

2007 IEEE Particle Accelerator Conference (PAC)

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In order to verify detailed impedance simulations, the resonant modes in an aluminium model of the ILC crab cavity were investigated using a bead-pulling technique as well as a stretched-wire frequency domain measurement. The combination of these techniques allow for a comprehensive study of the modes of interest. For the wire measurement, a transverse alignment system was fabricated and RF components were carefully designed to minimize any potential impedance mismatches. The measurements are compared with direct simulations of the stretched-wire experiments using numerical electromagnetic field codes. High impedance modes of particular relevance to the ILC crab cavity are identified and characterized. EXPERIMENTAL APPARATUSThe baseline ILC design calls for two superconducting nine-cell 3.9GHz dipole mode cavities [1] in order to rotate the bunches at the interaction point and preserve luminosity. A numerical study carried out on the cavity identified a number of modes that have significant loss factors [2] and therefore would require significant damping. In order to verify the impedances calculated by the numerical simulations, a modular aluminium model of the cavity was constructed.The model is composed of modular pairs of half-cells, connected at the equator. These can be arranged to form a cavity having anything from one to thirteen cells. The cell profiles are based on the C15 shape of the CKM 3.9GHz cavity [3]. Figure 1: Picture of the experimental model.The stretched-wire measurements were taken using matching sections at both ends of the cavity beam-pipe in order to minimise reflections and mode conversion. The matching sections were comprised of a tapered cone, and a quarter-wave transformer which allowed a reasonably good pass-band. It was possible to use different quarterwave transformers to study different frequency ranges.The wire position was controllable in the X and Y directions on both ends of the cone, which allowed measurements at various offsets and allowed control of the skew. The translation plates as well as tensioning mechanisms are shown in Figure 2. Figure 2: Schematic of the stretched-wire apparatus. STRETCHED-WIRE THEORYThe field pattern generated by a current passing through a wire in a coaxial structure is a TM mode that can be equated to the wake-fields left by a bunch passing through a structure.From simple transmission line theory, it is possible to derive a relationship between the coupling impedance of the device under test (DUT) and the ratio of transmission parameters, S 21 , of the DUT and a reference vessel [4]. The ratio can be expressed as follows:where θ is the TEM modes wavenumber multiplied by the length of the DUT and || 0 1 iZ Z ζ = − θHence if we can measure S 21 of a DUT and a reference vessel of known characteristic impedance Z 0 we can solve equation (1) to obtain the longitudinal coupling impedance Z || .

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Section: Discussionsupporting

confidence: 65%

“…A numerical study carried out on the cavity identified a number of modes that have significant loss factors [2] and therefore would require significant damping. In order to verify the impedances calculated by the numerical simulations, a modular aluminium model of the cavity was constructed.…”

Section: Experimental Apparatusmentioning

confidence: 99%

Impedance measurements on a test bench model of the ILC crab cavity

Goudket

Beard

McIntosh

et al. 2007

2007 IEEE Particle Accelerator Conference (PAC)

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“…The crab cavity needs ∼ 3 kW per cavity for about 10 msec, with a Q ext of ∼ 10 6 [196][197][198]201]. The crab cavity is placed in a cryostat with tuner,…”

Section: Crab Cavity Systemmentioning

confidence: 99%

The International Linear Collider Technical Design Report - Volume 3.II: Accelerator Baseline Design

Adolphsen

2013

106

135

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“…The ILC design foresees a horizontal crossing angle of 14 mrad between the e − and the e + beamlines at the IP. In order to maximise the luminosity, the bunches are correspondingly rotated by 7 mrad using crab cavities [15]. The collider experiments at the IP contain two types of magnets which also influence the beams.…”

Section: Beam Parameters and Interaction Regionmentioning

confidence: 99%

Spin transport and polarimetry in the beam delivery system of the international linear collider

et al. 2014

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Polarised electron and positron beams are key ingredients to the physics programme of future linear colliders. Due to the chiral nature of weak interactions in the Standard Model -and possibly beyond -the knowledge of the luminosity-weighted average beam polarisation at the e + e − interaction point is of similar importance as the knowledge of the luminosity and has to be controlled to permille-level precision in order to fully exploit the physics potential. The current concept to reach this challenging goal combines measurements from Laser-Compton polarimeters before and after the interaction point with measurements at the interaction point. A key element for this enterprise is the understanding of spin-transport effects between the polarimeters and the interaction point as well as collision effects. We show that without collisions, the polarimeters can be cross-calibrated to 0.1 %, and we discuss in detail the impact of collision effects and beam parameters on the polarisation value relevant for the interpretation of the e + e − collision data.

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Design of the ILC Crab Cavity System

Abstract: The International Linear Collider (ILC)

Cited by 10 publications

References 4 publications

Impedance measurements on a test bench model of the ILC crab cavity

Impedance measurements on a test bench model of the ILC crab cavity

The International Linear Collider Technical Design Report - Volume 3.II: Accelerator Baseline Design

Spin transport and polarimetry in the beam delivery system of the international linear collider

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