M. Zobov

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.

The SPARC/X SASE-FEL Projects

SPARC and SPARX are two different initiatives toward an Italian Free Electron Laser ~FEL! source operating in the Self Amplified Spontaneous Emission ~SASE! mode, in which several national research institutions are involved. SPARC is a high gain FEL project devoted to provide a source of visible and VUV radiation while exploiting the SASE mechanism. An advanced Photo-Injector system, emittance compensating RF-gun plus a 150 MeV Linac, will inject a high quality e-beam into the undulator to generate high brilliance FEL radiation in the visible region at the fundamental wavelength, ~;500 nm!. The production of flat top drive laser beams, high peak current bunches, and emittance compensation scheme will be investigated together with the generation of higher harmonic radiation in the VUV region. SPARX is the direct evolution of such a high gain SASE FEL toward the 13.5 and 1.5 nm operating wavelengths, at 2.5 GeV. To get the required value for the bunch peak current, Ipeak ’ 2.5 kA, the “hybrid” scheme, RF-compression stage plus magnetic chicane, is analyzed and compared with the more standard double stage of magnetic compression. The two options are reviewed considering the tolerance to the drive laser pulse phase jitter.

Status report on DA/spl Phi/NE

DA/spl Phi/NE, the Frascati LNF /spl Phi/-factory, is providing luminosity for the KLOE experiment since July 2000. A steady increase of daily integrated luminosity in KLOE has been obtained, due to interspersed machine physics studies. The main results are: increase of single bunch luminosity by reduction of the effects of nonlinear terms in the machine, background reduction, refill of the colliding beams while keeping the KLOE detector taking data and increase of stable stored current. A fraction of machine time has been used to tune luminosity and reduce background in the DEAR configuration. The luminosity delivered to DEAR was sufficient to conclude the first phase of the experiment.

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.

DAFNE Interaction Regions upgrade

DAΦNE, the Frascati Φ-factory, has recently completed experimental runs for the three main detectors, KLOE, FINUDA and DEAR achieving 1.6x10 32 cm -2 s -1 peak and 10 pb -1 daily integrated luminosities. Improving these results by a significant factor requires changing the collision scheme. For this reason, in view of the SIDDHARTA detector installation, relevant modifications of the machine have been realized, aimed at implementing a new collision scheme based on a large Piwinski angle and crab-waist, together with several other hardware modifications involving injection kickers, bellows and beam pipe sections.

DAΦNE shielded bellows

Abstract We describe the design of DAΦNE bellows having an RF screen without sliding contacts and present the results of numerical simulations and impedance measurements. The methods to eliminate and damp the residual High Order Modes (HOMs) in the bellows are discussed. The power loss due to both the HOMs and the screen strip resistivity as well as the thermal load of the screen are estimated.

Bunch length control in DAΦNE by a higher harmonic cavity

Abstract A higher harmonic RF cavity is considered to be an important tool to control the bunch length in storage rings. In this paper we compare the effects of the active and passive harmonic cavities on the bunch length for the DAΦNE machine. The enhancement of the Landau damping given by the cavity is estimated for the multibunch instability.

Simulation of Crab Waist Collisions in DAΦNE with KLOE-2 Interaction Region

After the successful completion of the SIDDHARTA experiment run with crab waist collisions, the electron-positron collider DAΦNE has started routine operations for the KLOE2 detector. Similarly to the SIDDHARTA configuration, the new interaction region exploits the crab waist collision scheme, but features certain complications including the experimental detector solenoid, compensating anti-solenoids, and tilted quadrupole magnets, that lead to significant coupling of the horizontal and vertical betatron motion. It is not immediately obvious if the crab waist scheme would be as efficient in the strongly coupled case as it was in the uncoupled configuration. We have performed simulations of beam-beam interactions in the collider taking into account the real machine nonlinear lattice. In particular, we have evaluated the effect of crab waist sextupoles and beam-beam interactions on the collider dynamical aperture and energy acceptance. A new betatron tune working point has been proposed for the DAΦNE electron ring, and its implementation resulted in more than 20% background reduction and injection efficiency improvement. Exploiting this working point has allowed reaching the best present luminosity of 2.0 × 1032 cm-2 s-1. The numerical simulations have shown that for the given bunch currents in collision, the powering of the crab waist sextupoles should decrease the beam core blow up by a factor of 2 indicating that even higher luminosity can be achieved in DAΦNE thus encouraging further collider optimization.

PRESENT STATUS OF THE DAΦNE UPGRADE AND PERSPECTIVES

The DAΦNE collider has been recently upgraded in order to implement a new collision scheme based on large Piwinski angle and cancellation of the synchro-betatron resonances by means of electromagnetic sextupoles (Crab-Waist compensation). The novel approach has proved to be effective in improving beam-beam interaction and collider luminosity. The results and the measurements taken during commissioning as well as the perspectives for the SIDDHARTA run are presented and discussed.

Beam-beam effects in crab crossing and crab waist schemes

To boost up the luminosity performance in B factories, crab crossing and crab waist schemes are proposed. The crab crossing scheme compensates crossing angle, while the crab waist scheme compensates nonlinear terms induced by crossing angle with sextupole magnets. We discuss which nonlinear terms in the beam-beam map are enhanced by the crossing angle and which terms are compensated by the crab waist sextupole.