Mario Serio

DAΦNE broad-band button electrodes

Abstract 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.

Status report of the IR FEL project on the superconducting linac LISA at LNF-Frascati

Abstract We report the progress of the superconducting linac LISA at LNF (Frascati National Laboratories) and the status of the FEL experiment. The design of the optical cavity is presented.

High current multibunch operation at DA/spl Phi/NE

At present the Frascati /spl Phi/-factory DA/spl Phi/NE is operating in multibunch regime with stored currents in the range of 0.5-1 A in both e/sup +/ and e/sup r/ings. A longitudinal bunch-by-bunch feedback system has been operating in each DA/spl Phi/NE main ring since the beginning of the machine commissioning. The transverse bunch-by-bunch feedback system working in the vertical plane has been implemented last year in both rings. This paper describes the performance of the feedback systems and reports the instability observations and the rise-time measurements. The present current limitations and the plans aimed at further current increase are also discussed.

A longitudinal multi-bunch feedback system using parallel digital signal processors

A programmable longitudinal feedback system based on four AT&T 1610 digital signal processors has been developed as a component of the PEP‐II R&D program. This longitudinal quick prototype is a proof of concept for the PEP‐II system and implements full‐speed bunch‐by‐bunch signal processing for storage rings with bunch spacings of 4 ns. The design incorporates a phase‐detector‐based front end that digitizes the oscillation phases of bunches at the 250 MHz crossing rate, four programmable signal processors that compute correction signals, and a 250‐MHz hold buffer/kicker driver stage that applies correction signals back on the beam. The design implements a general‐purpose, table‐driven downsampler that allows the system to be operated at several accelerator facilities. The hardware architecture of the signal processing is described, and the software algorithms used in the feedback signal computation are discussed. The system configuration used for tests at the LBL Advanced Light Source is presented.

Single Bremsstrahlung luminosity measurements at DAΦNE

Abstract At DAΦNE luminosity measurements are performed by detecting the photons from single Bremsstrahlung at the two interaction points. Set up and measurement method are presented with special emphasis on background subtraction schemes, error evaluation and machine related issues.

Design and implementation of IIR algorithms for control of longitudinal coupled-bunch instabilities

The recent installation of third-harmonic RF cavities at the Advanced Light Source has raised instability growth rates, and also caused tune shifts (coherent and incoherent) of more than an octave over the required range of beam currents and energies. The larger growth rates and tune shifts have rendered control by the original bandpass FIR feedback algorithms unreliable. In this paper we describe an implementation of an IIR feedback algorithm offering more flexible response tailoring. A cascade of up to 6 second-order IIR sections (12 poles and 12 zeros) was implemented in the DSPs of the longitudinal feedback system. Filter design has been formulated as an optimization problem and solved using constrained optimization methods. These IIR filters provided 2.4 times the control bandwidth as compared to the original FIR designs. Here we demonstrate the performance of the designed filters using transient diagnostic measurements from ALS and DAΦNE.

Experimental results with the SPARC emittance-meter

The SPARC project foresees the realization of a high brightness photo-injector to produce a 150-200 MeV electron beam to drive a SASE-FEL in the visible light. As a first stage of the commissioning a complete characterization of the photoinjector has been accomplished with a detailed study of the emittance compensation process downstream the gun-solenoid system with a novel beam diagnostic device, called emittance meter. In this paper we report the results obtained so far including the first experimental observation of the double emittance minimum effect on which is based the optimised matching with the SPARC linac.

Multibunch feedback—Strategy, technology, and implementation options

The proposed next generation accelerator and synchrotron light facilities will require active feedback systems to control multi‐bunch instabilities. These feedback systems must operate in machines with thousands of circulating bunches and with short (2–4 ns) interbunch intervals. The functional requirements for transferse (betatron) and longitudinal (synchrotron) feedback systems are presented. Several possible implementation options are discussed and system requirements developed. Results are presented from a digital signal processing based synchrotron oscillation damper operating at the SSRL/SLAC SPEAR storage ring.

Status of the LISA superconducting linac project

The installation of the 25-MeV superconducting electron linac LISA is in progress as Frascati INFN National Laboratory. The installation is scheduled to be completed in Summer 1991 and commissioning will follow immediately. The status of the project is reviewed, and the results of the first tests on various components are presented.<<ETX>>

A perturbation method for HOM tuning in a rf cavity

Abstract The cure of multibunch instabilities is of utmost importance for the next generation of very high current storage rings. The parasitic modes of the rf cavities are chiefly responsible of these instabilities. A perturbation method is proposed to decouple the cavity parasitic modes from the bunch relative oscillation sidebands, without affecting the fundamental mode. Signal level measurements on a test pillbox cavity give encouraging results.