[en] The DAPHINE Main Ring Vacuum System is designed for a mean operating pressure of 1 nTorr with a circulating current of about 5 A/beam. Finite element calculations have been carried out to check the maximum possible deformation for the Bending Quadrant vacuum chamber that will be made of Al 5083-H321. Water cooled copper absorbers are employed to cope with the Synchrotron Radiation, (SR), produced in the wigglers and dipoles. The total gas load due to SR is Q∼2.6x10^-5 Torr l/s per arc for CO, with a photodesorption rate η∼1x10^-6 molec/ph, (after ∼40Ahr of commissioning), as measured at NSLS-BNL. Nine sputter ion pumps and nine titanium sublimation pumps are located in each arc to provide, respectively, the 15% and the 85% of the required pumping speed

[en] Presently clearing electrodes are being considered as a possible cure of e-cloud driven problems in existing and future colliders. ''Invisible'' electrodes, made of a thin highly resistive layer pasted on a dielectric plate, have been proposed as one of design solutions for the e-cloud clearing. For the first time such electrodes were successfully used in the Electron-Positron Accumulator (EPA) of LEP. Similar electrodes had been used for a long time for ion clearing purposes in the DAΦNE electron ring. Theoretical considerations and experimental measurements at DAΦNE have revealed a substantial contribution of the Ion Clearing Electrodes (ICE) to the machine broad-band impedance giving rise to several harmful effects degrading the collider performance. In this paper we discuss the impact of the electrodes on DAΦNE beam dynamics, show the results of ICE wake field and impedance calculations and compare them with available experimental data. We also describe the procedure of ICE removal from the wiggler sections of the electron ring that has resulted in remarkable improvements in terms of beam dynamics and geometric luminosity

[en] The preliminary design for an all metal ultra high vacuum (UHV) system for DAΦNE machine is described. The machine is composed by 4 main items: linac, accumulator, transfer lines, and storage ring; each item has its own vacuum system designed accordingly with the operating requirements. The linac will be bought turn on key from an external firm, with its vacuum system, the accumulator and transfer lines vacuum systems will be made using standard technologies capable to reach a working pressure in the range of 10^-8 torr, the storage ring vacuum system will be made using special technologies in order to obtain a pressure of 1x10^-9 torr with 5 A of stored beam current. (author) 4 refs.; 4 figs.; 2 tabs

[en] Cu L₃ x-ray absorption near edge structure (XANES) and Cu L₃ x-ray photoelectron spectroscopy (XPS) of YBa₂Cu₃O_6.5+x are compared. The breakdown of one-electron picture of its electronic structure is reported. The data are interpreted by mixing of Cu 3d⁹ and of 3d⁹L-bar (where L-bar is a hole in the oxygen derived band, ligand hole) many body configuration in the initial state. The localization of Cu 3d⁹ configuration is indicated by the bare Coulomb interaction U_dd∼6 eV. The conductivity is assigned to the itinerant 3d⁹L-bar configuration. The experimental evidence that the additional oxygen x, giving higher T_c, increases the weight of the 3d⁹L-bar configuration is reported. The presence of holes on the oxygen atoms is confirmed by the 01s XPS spectra. The Cu³⁺ (Cu 3d⁸) configuration is not observed in L₃ XANES in agreement with valence band XPS giving the energy of the 3d⁸ excited state at about 12 eV above the ground state. An energy scheme of the many body configurations in YBa₂Cu₃O_∼7 is obtained. These experiments give experimental evidence that the high T_c superconductivity is due to pairing of holes in the oxygen valence band interacting with localized electrons at the Cu sites. (author). 36 refs, 8 figs

[en] The copper K-edge x-ray-absorption near-edge structure (XANES) of YBa₂Cu₃O₇ has been analyzed by using the full multiple-scattering approach. Using the atomic coordinates of the orthorhombic oxygen-deficient perovskite structure the absorption spectra of both the Cu(1) and CU(2) sites have been calculated. All features of the experimental Cu K-edge XANES spectrum can be simply interpreted as arising from one-electron transitions to final states mainly determined by the atomic distribution in the large clusters of 40 atoms surrounding the CU(1) and the Cu(2) central absorbing atoms. The XANES spectra in this strongly anisotropic system are strongly polarization dependent, therefore the prediction of the polarized Cu K-edge spectra for a single crystal is reported. The role of the mixing of different configurations of the passive valence electrons on the Cu K-edge XANES is discussed

[en] The installation of a passive 3rd harmonic cavity in both the e⁺ and e^- rings of the Frascati Φ-factory DAΦNE has been decided in order to improve the Touschek lifetime by increasing the bunch length. The implications of the RF harmonic system on the beam dynamics, in particular those related to the gap in the bunch filling pattern, have been carefully studied by means of analytical and numerical tools. A single-cell cavity incorporating a ferrite ring for the HOM damping has been designed through the extensive use of MAFIA and HFSS simulation codes. One cavity prototype has been built and extensively bench tested, while the fabrication of the two final cavities is almost completed. A description of the design and construction activities, and a set of experimental measurements are reported in this paper

[en] SPARC-X is a two branch project consisting in the SPARC test facility dedicated to the development and test of critical subsystems such as high brightness photoinjector and a modular expandable undulator for SASE-FEL experiments at 500 nm with seeding, and the SPARX facility aiming at generation of high brilliance coherent radiation in the 1.5-13 nm range, based on the achieved expertise. The projects are supported by MIUR (Research Department of Italian Government) and Regione Lazio. SPARC has completed the commissioning phase of the photoinjector in November 2006. The achieved experimental results are here summarized together with the status of the second phase commissioning plans. The SPARX project is based on the generation of ultra high peak brightness electron beams at the energy of 1 and 2 GeV generating radiation in the 1.5-13 nm range. The construction is at the moment planned in two steps starting with a 1 GeV Linac. The project layout including both RF-compression and magnetic chicane techniques has been studied

[en] DAΦNE is a double ring electron-positron collider, designed to provide very high luminosity at the energy of the Φ resonance (1.02 GeV c.m.). After storing the first beam in fall 1997, the collider was commissioned without solenoidal detectors until the end of 1998, reaching a single bunch luminosity of 1.6 x 10³⁰ cm^-2s^-1 with 20 mA in each beam, corresponding to a beam-beam tune shift of ∼ 0.03. A longitudinal bunch-to-bunch feedback has been implemented, allowing the storage of more than 0.5 A in 30 bunches for both electrons and positrons. The KLOE detector, embedded into a superconducting solenoid with strong longitudinal field integral (2.4 Tm, to be compared to a magnetic rigidity of 1.7 Tm) compensated by two other solenoids of opposite field, was installed in winter 1999 and commissioning resumed with a careful correction of the coupling effects. Particular effort has been dedicated to the reduction of background in the experiment, which led to the possibility of injecting the beams in interaction without switching off data taking. The total stored current has reached more than 1 A in each beam, while a transverse feedback system has been realized to counteract vertical instabilities occurring during injection. The collider is now running in the multibunch mode for KLOE data taking with peak luminosity up to 1.8 x 10³¹ cm^-2s^-1 and integrated luminosity larger than 0.8 pb^-1 per day

[en] The e⁺e^- collider DAΦNE, a 1.02 GeV c.m. Φ-factory, has reached a peak luminosity of about 1.4 x 10³² cm^-2 s^-1 and a peak integrated luminosity in one day of about 8.6 pb^-1. With the current rates the physics program of the three main experiments DEAR, FINUDA and KLOE will be completed by the end of 2007. In this paper we describe in detail the steps which have led to the luminosity improvement and the options for the upgrade of the collider towards higher energy and/or luminosity

[en] Obtaining very short bunches is an issue especially for colliders but also for CSR sources. The modulation of the bunch length in a strong rf focusing regime had been proposed, corresponding to a high value of the synchrotron tune. A ring structure where the function R56 along the ring oscillates between large positive and negative values will produce bunch length modulation. The synchrotron frequency can be tuned both by the rf power and by the integral of the function R56, up to the limit of zero value corresponding to the isochronicity condition. The proposal of a bunch length modulation along the ring in DAΦNE is here described. DAΦNE lattice can be tuned to positive or negative momentum compaction values, or to structures in which the two arcs are respectively set to positive/negative integrals of the R56 function. With the installation of an extra rf system at 1.3 GHz, experiments on bunch length modulation both in the regime of high and low synchrotron tune can be realized