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[en] During the commissioning of the Frascati Φ-Factory DAΦNE, vertical and longitudinal multibunch coupled bunch oscillations have been observed. Modal analysis and measurement of the instability thresholds as a function of local orbit bumps have shown that, with high probability, the coupled bunch oscillations can be attributed to the beam interaction with parasitic resonant modes trapped in the injection kickers. By means of theoretical models and computer simulations (based on HFSS code by HP) an electromagnetic characterization of the kickers HOMs has been carried out and the obtained results have been compared with the impedance measurements made on a prototype. The study and design of a damping antenna coupled with the structure resonant modes is described. Measurements on a prototype equipped with two antennas confirm the effectiveness of the proposed solution to strongly reduce the kicker longitudinal and vertical coupling impedances, i.e. to eliminate the instability sources. (author)

[en] Multibunch operation in high current storage rings like DAΦNE can be seriously limited by coupled bunch oscillations driven by resonant e.m. fields trapped somewhere along the vacuum chamber. The design of each vacuum chamber component aims to keep the beam coupling impedance below the values for which multibunch instabilities can be controlled by feedback systems. The impedance of some of the most critical devices has been measured and a summary of the obtained results is presented. (author)

[en] The design of a tapered stripline fast Faraday cup (TSFFC) to perform the impedance matching between the fast cup itself and the signal line (connector, cable, and amplifier) is reported here. The frequency response of the TSFFC as a high-pass filter is analyzed from a theoretical point of view and some solutions to achieve a broadband response are given

[en] We describe the DAΦNE broad-band button electrodes used to measure the individual time and transverse bunch offset, on a bunch-by-bunch basis, i.e. without ''memory'' of the preceding bunches in the feedback systems and for general purpose diagnostics. We give analytical estimates of the transfer and coupling impedances. The numerical simulations and laboratory measurements are in good agreement with the analytical results. The button transfer impedance is reasonably high, flat and free of narrow-band resonances in the frequency range of utilization. The coupling impedance and parasitic losses are found to be within the acceptable values. (orig.)

[en] DAΦNE, the Frascati Φ-Factory presently under commissioning, is an e⁺/e^- collider whose injection system is composed by a = 60 m Linac and by a = 33 m long damping ring connected to each other and to the DAΦNE main rings by = 180 m of transfer line. Both the positron and the electron beams are alternately produced and accelerated by the Linac up to the operation energy of 510 MeV. Because of the high peak and integrated luminosity requested to DAΦNE, the requirements concerning some of the relevant Linac features, in particular the value of the positron macro bunch peak current are very demanding. During the Linac operation all the design values have been achieved and in most cases surpassed. A description of the relevant operational performances of the DAΦNE Linac is presented

[en] The multibunch operation of DAΦNE calls for a very efficient feedback system to damp the coupled-bunch longitudinal instabilities. A collaboration program among SLAC, LBL and LNF laboratories on this subject led to the development of a time domain, digital system based on digital signal processors that has been already successfully tested at ALS. The feedback chain ends with the longitudinal kicker, an electromagnetic structure capable of transferring the proper energy correction to each bunch. A cavity kicker for the DAΦNE bunch-by-bunch longitudinal feedback system based on a pill-box loaded by six waveguides has been designed and a full-scale aluminium prototype has been fabricated at LNF. Both simulations and measurements have shown a peak shunt impedance of about 750 ohm and a bandwidth of about 220 MHz. The large shunt impedance allows to economize on the costly feedback power. Moreover, the damping waveguides drastically reduce the device HOM longitudinal and transverse impedances. One cavity pre ring will be sufficient to operate the machine up to 30 bunches while a second device per ring together with a feedback power improvement will be necessary to reach the ultimate current. (G.T.)

[en] The DAΦNE beam position monitor (BPM) system consists of 150 monitors installed all along the machine. Design issues, calibration procedures, experimental results and performance of the system are described. The closed orbit in the main rings is extracted from the BPM signals through narrowband receivers (realized by Bergoz Precision Beam Instrumentation for DAΦNE), then acquired and processed by a real-time task based on four independent processors dealing with different machine areas. The data acquisition system is integrated in the DAΦNE control system and measures five complete orbits in a second. Implementation criteria, measurements and results are reported

[en] The development of very efficient longitudinal and transverse bunch-by-bunch feedback systems is one of the fundamental aspects for the operation of the high-current storage rings. The last part of the feedback chain is a kicker whose efficiency impacts directly on the system cost. The design and measurements of the DAΦNE longitudinal and transverse kickers are presented here. The longitudinal kicker design is based on a waveguide overloaded cavity, while a more conventional stripline structure has been chosen for the transverse kicker. The design of both devices has been optimised in order to increase the shunt impedance, i.e., their efficiency, and to lower the content of parasitic higher-order modes that could further excite coupled-bunch instabilities. copyright 1997 American Institute of Physics

[en] Multibunch instability is one of the main problems arising in the design of high current circular accelerators. Its analytical study can be integrated by using a dedicated simulation code describing the beam cavity high order mode interaction in the time domain. On the other hand, the high current storage rings require special techniques, such as fast RF feedback systems, to prevent the Robinson instability coming from the beam to cavity accelerating mode interaction. So far the realistic behavior of such systems has not been included in the existing codes. In this paper we describe the model adopted to implement the RF feedback proposed for the Frascati Φ-factory DAΦNE in the time domain code simulating the multibunch longitudinal dynamics. (orig.)