New technology based on clamping for high gradient radio frequency photogun

High gradient rf photoguns have been a key development to enable several applications of high quality electron beams. They allow the generation of beams with very high peak current and low transverse emittance, satisfying the tight demands for free-electron lasers, energy recovery linacs, Compton/Thomson sources and high-energy linear colliders. In the present paper we present the design of a new rf photogun recently developed in the framework of the SPARC_LAB photoinjector activities at the laboratories of the National Institute of Nuclear Physics in Frascati (LNF-INFN, Italy). This design implements several new features from the electromagnetic point of view and, more important, a novel technology for its realization that does not involve any brazing process. From the electromagnetic point of view the gun presents high mode separation, low peak surface electric field at the iris and minimized pulsed heating on the coupler. For the realization, we have implemented a novel fabrication design that, avoiding brazing, strongly reduces the cost, the realization time and the risk of failure. Details on the electromagnetic design, low power rf measurements and high power radiofrequency and beam tests performed at the University of California in Los Angeles (UCLA) are discussed in the paper

Design of high gradient, high repetition rate damped C-band rf structures

The gamma beam system of the European Extreme Light Infrastructure–Nuclear Physics project foresees the use of a multibunch train colliding with a high intensity recirculated laser pulse. The linac energy booster is composed of 12 traveling wave C-band structures, 1.8 m long with a field phase advance per cell of 2π=3 and a repetition rate of 100 Hz. Because of the multibunch operation, the structures have been designed with a dipole higher order mode (HOM) damping system to avoid beam breakup (BBU). They are quasiconstant gradient structures with symmetric input couplers and a very effective damping of the HOMs in each cell based on silicon carbide (SiC) rf absorbers coupled to each cell through waveguides. An optimization of the electromagnetic and mechanical design has been done to simplify the fabrication and to reduce the cost of the structures. In the paper, after a review of the beam dynamics issues related to the BBU effects, we discuss the electromagnetic and thermomechanic design criteria of the structures. We also illustrate the criteria to compensate the beam loading and the rf measurements that show the effectiveness of the HOM damping

Design, realization, and high power test of high gradient, high repetition rate brazing-free S -band photogun

In this paper, we address the energy spread and slice energy spread of an externally injected electron beam in plasma wakefield accelerators operating in the linear or quasilinear regime. The energy spread is first derived taking into account the phase dependence of the wakefield along the finite-length bunch together with the dephasing during acceleration and found to be strongly dependent on the bunch length. This could be compensated by the beam loading effect, the energy spread from which is then derived and found to be nearly independent of the bunch length. However, the transverse dependence of the beam loading effect also makes the particles at the same longitudinal position experience different accelerating fields, introducing a significant slice energy spread. To estimate the slice energy spread, a theoretical analysis was conducted by taking the transverse betatron motion into account. As a study case, 3D simulations for the 5 GeV laser-plasma acceleration stage of the European Plasma Research Accelerator with eXcellence in Applications project have been performed. Careful optimization of the parameters allows one to obtain an energy spread of ≤1% and a slice energy spread of ≤0.1%, with good agreement between theories and simulations

Initial performance of the CUORE-0 experiment

CUORE-0 is a cryogenic detector that uses an array of tellurium dioxide bolometers to search for neutrinoless double-beta decay of ^{130}Te. We present the first data analysis with 7.1 kg y of total TeO_2 exposure focusing on background measurements and energy resolution. The background rates in the neutrinoless double-beta decay region of interest (2.47 to 2.57 MeV) and in the {\alpha} background-dominated region (2.70 to 3.90 MeV) have been measured to be 0.071 \pm 0.011 and 0.019 \pm 0.002 counts/keV/kg/y, respectively. The latter result represents a factor of 6 improvement from a predecessor experiment, Cuoricino. The results verify our understanding of the background sources in CUORE-0, which is the basis of extrapolations to the full CUORE detector. The obtained energy resolution (full width at half maximum) in the region of interest is 5.7 keV. Based on the measured background rate and energy resolution in the region of interest, CUORE-0 half-life sensitivity is expected to surpass the observed lower bound of Cuoricino with one year of live time.Comment: 8 pages, 5 figures, version 2 as published in Eur. Phys. J.

Neutrinoless double-beta decay search with CUORE and CUORE-0 experiments

The Cryogenic Underground Observatory for Rare Events (CUORE) is an upcoming experiment designed to search for the neutrinoless double-beta decays. Observation of the process would unambiguously establish that neutrinos are Majorana particles and provide information on their absolute mass scale hierarchy. CUORE is now under construction and will consist of an array of 988 TeO2 crystal bolometers operated at 10 mK, but the first tower (CUORE-0) is already taking data. The experimental techniques used will be presented as well as the preliminary CUORE-0 results. The current status of the full-mass experiment and its expected sensitivity will then be discussed

The CMS ECAL Enfourneur: a gigantic machine with a soft touch

The electromagnetic calorimeter (ECAL) of the CMS experiment at the LHC is composed of 75848 scintillating lead tungstate crystals arranged in a barrel section and two endcaps. The barrel part is made of 36 supermodules (SM), 2.7 tons each, and is installed inside the CMS magnet. There are 18 SMs on each side of CMS, with each SM containing 1700 crystals. During Long Shutdown 3, all ECAL SMs must be extracted to refurbish the electronics in preparation for HL-LHC. A dedicated machine called the Enfourneur is used to extract and re-insert the SMs inside CMS, with a required accuracy of about 1 mm. In order to speed up the extraction and insertion process, two Enfourneurs will be employed, operating in parallel on both sides. In view of the purchase of the second Enfourneur, the design has been improved, starting from the feedback of past operations. The improvements to the new Enfourneur design include: increased space for the operators, optimization of the operations and the controls with the use of electric motors, and an updated alignment system. Handling plans inside the CMS cavern have been defined in order to be compliant with the rest of CMS structures and procedures

Design, realization, and high power test of high gradient, high repetition rate brazing-free S-band photogun

rf photoguns find several types of applications as high brightness electron sources for free-electron lasers, energy recovery linacs, Compton and Thomson sources, and high-energy linear colliders. The high peak current and low transverse emittance of the generated beam are obtained with the combination of a high peak electric field (>100  MV/m) at the cathode surface, a proper choice of the solenoid field around, or immediately after, the gun, and special fabrication and treatments of the cathode itself. On the other hand, to increase the average electron current, a high repetition rate (>100  Hz) and/or a multibunch rf gun have to be developed. These types of devices are, in general, fabricated by brazing processes of copper machined parts. The brazing processes require a large vacuum furnace, are very expensive, and pose a not negligible risk of failure. A new fabrication technique for this type of structure has been recently developed and implemented at the Laboratories of Frascati of the National Institute of Nuclear Physics (INFN-LNF, Italy) and already applied to an rf gun now operating at a relatively low cathode peak field and low repetition rate [D. Alesini et al., Phys. Rev. Accel. Beams 18, 092001 (2015)]. It is based on the use of special rf-vacuum gaskets that allow a brazing-free realization process. The S-band gun of the Extreme Light Infrastructure-Nuclear Physics Gamma Beam System, under construction in Magurele (Bucharest, Romania), has been realized with this new technique and represents a further and fundamental step toward the consolidation of this technology for high gradient particle accelerator fabrication. It operates at 100 Hz with a 120  MV/m cathode peak field and 1.5-μs-long rf pulses to house the 32 bunches necessary to reach the target gamma flux. High gradient tests, performed at full power and a full repetition rate, have shown the extremely good performances of the structure in terms of the breakdown rate and conditioning time and definitively demonstrated the reliability and suitability of such fabrication process for high gradient structure realization. In this paper, we report and discuss the electromagnetic and thermomechanical design, the realization process, and all the experimental results at low and high power at a full repetition rate

First muon-neutrino disappearance study with an off-axis beam

We report a measurement of muon-neutrino disappearance in the T2K experiment. The 295-km muon-neutrino beam from Tokai to Kamioka is the first implementation of the off-axis technique in a long-baseline neutrino oscillation experiment. With data corresponding to 1.43 × 10(20) protons on target, we observe 31 fully-contained single μ-like ring events in Super-Kamiokande, compared with an expectation of 104 ± 14(syst) events without neutrino oscillations. The best-fit point for two-flavor νμ → ντ oscillations is sin 2(2θ(23)) = 0.98 and |Δm(2)(32)| = 2.65 × 10(−3) eV2. The boundary of the 90% confidence region includes the points (sin2 (2θ(23)), |Δm(2)(32)|) = (1.0, 3.1 × 10(−3) eV2), (0.84, 2.65 × 10(−3) eV2) and (1.0, 2.2 × 10(−3) eV2).ISSN:1550-7998ISSN:0556-2821ISSN:1550-236