arXiv subjects
Publications and source records attributed to A. Stella.
The DA{\Phi}NE operations during the last year have been devoted to deliver a statistically significant data sample to perform the first-ever measurement of kaonic deuterium X-ray transitions to the fundamental level. Operations for the SIDDHARTA-2 detector using a deuterium gas target started officially on the second half of May 2023, and have been organized in several runs here described.
In this article, we share our experience related to the new photo-injector commissioning at the SPARC\_LAB test facility. The new photo-injector was installed into an existing machine and our goal was not only to improve the final beam parameters themselves but to improve the machine handling in day-to-day operations as well. Thus, besides the pure beam characterization, this article contains information about the improvements, that were introduced into the new photo-injector design from the machine maintenance point of view, and the benefits, that we gained by using the new technique to assemble the gun itself.
This Document contains a complete technical description of the system devoted to the upgrade of the STAR Linear Accelerator (STAR Linac). According to the Contract signed between Universita della Calabria (UniCal) and Istituto Nazionale di Fisica Nucleare (INFN) on May 7th, 2021, INFN is committed to install, test and commission the upgrade of the STAR Linac denominated STAR-HE-Linac (STAR High Energy Linac), hereafter STAR-HEL. The technical components as well as the installation / test procedures and the ancillary equipment involved in such an upgrade are the object of this Document, named Complete Detailed Design Report. A technical offer was submitted by INFN in the frame of its participation to the tender issued by UniCal, describing a possible energy upgrade of the STAR Linac, with an electron beam energy boosted from 65 MeV up to 150 MeV by means of Radiofrequency (RF) accelerating sections and power stations based on S-band technology (ie, 2856 MHz RF frequency). Following the Contract signature, INFN conceived and conceptually designed a technology change that offers several advantages both on performances and on operational reliability of STAR-HEL, based on adopting C-band technology (ie, 5712 MHz RF frequency) for accelerating sections and RF power stations. Such a technology change was illustrated in a dedicated document named "improvement option for STAR-2 HE-Linac", addressed to UniCal STAR Management Board and tender R.U.P. for approval on June 9th, 2021. INFN received a formal letter of approval on June 16th, 2021.
A design study of the diagnostics of a high brightness linac, based on X-band structures, and a plasma accelerator stage, has been delivered in the framework of the EuPRAXIA@SPARC_LAB project. In this paper, we present a conceptual design of the proposed diagnostics, using state of the art systems and new and under development devices. Single shot measurements are preferable for plasma accelerated beams, including emittance, while $μ$m level and fs scale beam size and bunch length respectively are requested. The needed to separate the driver pulse (both laser or beam) from the witness accelerated bunch imposes additional constrains for the diagnostics. We plan to use betatron radiation for the emittance measurement just at the end of the plasma booster, while other single-shot methods must be proven before to be implemented. Longitudinal measurements, being in any case not trivial for the fs level bunch length, seem to have already a wider range of possibilities.
Advanced linear accelerator design may use Optical Transition Radiation (OTR) screens to measure beam spot size; for instance, such screens are foreseen in plasma based accelerators (EuPRAXIA@SPARC_LAB) or Compton machines (Gamma Beam Source@ELI-NP). Optical Transition Radiation angular distribution strongly depends on beam energy. Since OTR screens are typically placed in several positions along the Linac to monitor the beam envelope, one may perform a distributed energy measurement along the machine. Furthermore, a single shot energy measurement can be useful in plasma accelerators to measure shot to shot energy variations after the plasma interaction. Preliminary measurements of OTR angular distribution of about 100 MeV electrons have been performed at the SPARC_LAB facility. In this paper, we discuss the sensitivity of this measurement to beam divergence and others parameters, as well as the resolution required and the needed upgrades of conventional OTR diagnostics, using as an example the data collected at SPARC_LAB.
R\&D activity on Cu photocathodes is under development at the SPARC\_LAB test facility to fully characterize each stage of the photocathode "life" and to have a complete overview of the photoemission properties in high brightness photo-injectors. The nano(n)-machining process presented here consists in diamond milling, and blowing with dry nitrogen. This procedure reduces the roughness of the cathode surface and prevents surface contamination introduced by other techniques, such as polishing with diamond paste or the machining with oil. Both high roughness and surface contamination cause an increase of intrinsic emittance and consequently a reduction of the overall electron beam brightness. To quantify these effects, we have characterized the photocathode surface in terms of roughness measurement, and morphology and chemical composition analysis by means of Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS), and Atomic Force Microscopy (AFM) techniques. The effects of n-machining on the electron beam quality have been also investigated through emittance measurements before and after the surface processing technique. Finally, we present preliminary emittance studies of yttrium thin film on Cu photocathodes.
The machine described in this document is an advanced Source of up to 20 MeV Gamma Rays based on Compton back-scattering, i.e. collision of an intense high power laser beam and a high brightness electron beam with maximum kinetic energy of about 720 MeV. Fully equipped with collimation and characterization systems, in order to generate, form and fully measure the physical characteristics of the produced Gamma Ray beam. The quality, i.e. phase space density, of the two colliding beams will be such that the emitted Gamma ray beam is characterized by energy tunability, spectral density, bandwidth, polarization, divergence and brilliance compatible with the requested performances of the ELI-NP user facility, to be built in Romania as the Nuclear Physics oriented Pillar of the European Extreme Light Infrastructure. This document illustrates the Technical Design finally produced by the EuroGammaS Collaboration, after a thorough investigation of the machine expected performances within the constraints imposed by the ELI-NP tender for the Gamma Beam System (ELI-NP-GBS), in terms of available budget, deadlines for machine completion and performance achievement, compatibility with lay-out and characteristics of the planned civil engineering.
The present Report concerns the current status of the Italian Tau/Charm accelerator project and in particular discusses the issues related to the lattice design, to the accelerators systems and to the associated conventional facilities. The project aims at realizing a variable energy Flavor Factory between 1 and 4.6 GeV in the center of mass, and succeeds to the SuperB project from which it inherits most of the solutions proposed in this document. The work comes from a cooperation involving the INFN Frascati National Laboratories accelerator experts, the young newcomers, mostly engineers, of the Cabibbo Lab consortium and key collaborators from external laboratories.
During the current run of an electron-positron collider DAFNE special electrodes for electron cloud suppression have been inserted in all dipole and wiggler magnets of the positron ring. In this paper we discuss the impact of these electrodes on beam dynamics and overall collider performance. In particular we report results of measurements such as e-cloud instabilities growth rate, transverse beam size variation, tune shifts along the bunch train etc. with the electrodes switched on and off that clearly indicate the effectiveness of the electrodes for e-cloud suppression.
Recently the peak luminosity achieved on the DAΦNE collider has been improved by almost a factor three by implementing a novel collision scheme based on large Piwinski angle and Crab-Waist. This encouraging result opened new perspectives for physics research and a new run with the KLOE-2 detector has been scheduled to start by spring 2010. The KLOE-2 installation is a complex operation requiring a careful design effort and a several months long shutdown. The high luminosity interaction region has been deeply revised in order to take into account the effect on the beam caused by the solenoidal field of the experimental detector and to ensure background rejection. The shutdown has been also used to implement several other modifications aimed at improving beam dynamics: the wiggler poles have been displaced from the magnet axis in order to cancel high order terms in the field, the feedback systems have been equipped with stronger power supplies and more efficient kickers and electrodes have been inserted inside the wiggler and the dipole vacuum chambers, in the positron ring, to avoid the e-cloud formation. A low level RF feedback has been added to the cavity control in both rings.
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 using for a long time for ion clearing purposes in the DAFNE electron ring. Theoretical considerations and experimental measurements at DAFNE 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 DAFNE 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.
There are several potential advantages for a collider operation with a lattice with negative momentum compaction factor (alfa). Since the lattice of the Frascati e+e- Phi-factory DAFNE is flexible enough to provide collider operation even with alfa < 0, we have exploited this possibility for an experimental study of the beam dynamics. The negative momentum compaction lattices have been successfully implemented and stable 1 A currents have been stored in both electron and positron rings without any problem for RF cavities and feedback systems operation. First collisions have been tested at low currents. In this paper we describe the experimental results and compare them with expectations and numerical simulations. Present limitations to DAFNE operation with alfa < 0 and ways to overcome them are also discussed.
The Frascati F-Factory DAFNE has been delivering luminosity to the KLOE, DEAR and FINUDA experiments since year 2000. Since April 2004 the KLOE run has been resumed and recently peak luminosity of 1.0x1032 cm-2s-1 and integrated luminosity of 6.2 pb-1/day have been achieved. The scientific program of the three high-energy experiments sharing DAFNE operation will be completed approximately by the end of year 2006. A scientific program for DAFNE beyond that date has not been defined yet and it is matter of discussion in the high-energy physics and accelerator physics communities. In this paper we present some future scenarios for DAFNE, discussing the expected ultimate performances of the machine as it is now and addressing the design for an energy and/or luminosity upgrade. The options presented in the following are not exhaustive and they are intended to give a glance of what is doable using the existing infrastructures.
DAFNE operation restarted in September 2003, after a six month shut-down for the installation of FINUDA, a magnetic detector dedicated to the study of hypernuclear physics. FINUDA is the third experiment running on DAFNE and operates while keeping on place the other detector KLOE. During the shut-down both Interaction Regions have been equipped with remotely controlled quadrupoles in order to operate at different solenoid fields. Among many other hardware upgrades one of the most significant is the reshaping of the wiggler pole profile to improve the field quality and the machine dynamic aperture. Commissioning of the collider in the new configuration has been completed in short time. The peak luminosity delivered to FINUDA has reached 6 10^31 s-1cm-2, with a daily integrated value close to 4 pb-1.
We analyze in some detail a recently proposed transfer matrix mean field approximation which yields the exact critical point for several two dimensional nearest neighbor Ising models. For the square lattice model we show explicitly that this approximation yields not only the exact critical point, but also the exact boundary magnetization of a semi--infinite Ising model, independent of the size of the strips used. Then we develop a new mean field renormalization group strategy based on this approximation and make connections with finite size scaling. Applying our strategy to the quadratic Ising and three--state Potts models we obtain results for the critical exponents which are in excellent agreement with the exact ones. In this way we also clarify some advantages and limitations of the mean field renormalization group approach.