The CR storage ring is part of the FAIR project at GSI. It serves as a first stage of stochastic cooling for secondary rare isotopes at v/c=0.83 as well as for antiprotons at v/c=0.97. To avoid the installation of dedicated structures for each kind of beam, electrodes have been developed which are usable for both beams. They are based on slotline structures mounted perpendicular to the beam. They are shorted at the ends, and their signal is extracted by two striplines on the rear side, placed a quarter wavelength away from the open ends. The width of the structures can be adjusted to the initial betatron oscillation amplitudes. Their length is 25 mm, and the signal from many of these structures mounted in a row can be combined. The signal combination can be matched to the different beam velocities. The paper shows results from field calculations, prototype tests, and estimates of the signal combination efficiency. The beam impedance of the novel structures is compared with the superelectrodes applied in the former CERN AC and with the slow-wave structures currently installed in the FNAL Debuncher.The CR storage ring is part of the FAIR project at GSI (see [1], [2] and references therein). Its main purpose is stochastic precooling of antiproton (pbar) beams at 3 GeV (β = 0.97) and of secondary rare isotope (RI) beams at 740 MeV/u (β = 0.83). In order to accomplish these tasks without having to exchange stochastic cooling hardware components, it is desirable to dispose of a type of electrodes with the following properties:• sufficiently high coupling impedance per installation length at both beam velocities (see below for definitions) • high bandwidth • usability as pick-up and kicker (with minor modifications) • applicability in a high vacuum environment (10 −9 mbar) • ease of manufacturing In this article we describe the layout of a structure which is suitable as a vertical kicker for a beam chamber with a full vertical size of ±53mm. s 0 s 1 ∆ E(x,y,s,t) Z L x y s V(t) Figure 1: Basic Description of Pick-up or Kicker
SENSITIVITY AND BEAM IMPEDANCEThe electrical properties of pick-ups or kickers with respect to a single particle with charge Qe are usually parametrized either by a sensitivity S or by an impedance Z. both descriptions are equivalent. If the device is operated at frequencies below the cut-off frequency of the beam chamber such that no waves can propagate, then it is reasonable to assume that the the reciprocity theorem holds. If the geometrical and electrical layout of pick-ups and kickers is the same, then both kinds of device can be described by the same impedance or sensitivity. In the following, we shall shortly characterize these properties quantitatively.A kicker can be visualized (Fig.1) as a device which is fed through a (coaxial) input port where an input voltage U in and a line impedance Z L are well-defined. In the vacuum chamber, this voltage gives rise to an electric field, of which we are only interested in the longitudinal component. If the kicker is a linear device, then the voltage ...
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