The Λp\bf{\Lambda p} interaction studied via femtoscopy in p + Nb reactions at sNN=3.18 GeV\mathbf{\sqrt{s_{NN}}=3.18} ~\mathrm{\bf{GeV}}

We report on the first measurement of $p\Lambda$ and $pp$ correlations via the femtoscopy method in p+Nb reactions at $\mathrm{\sqrt{s_{NN}}=3.18} ~\mathrm{GeV}$, studied with the High Acceptance Di-Electron Spectrometer (HADES). By comparing the experimental correlation function to model calculations, a source size for $pp$ pairs of $r_{0,pp}=2.02 \pm 0.01(\mathrm{stat})^{+0.11}_{-0.12} (\mathrm{sys}) ~\mathrm{fm}$ and a slightly smaller value for $p\Lambda$ of $r_{0,\Lambda p}=1.62 \pm 0.02(\mathrm{stat})^{+0.19}_{-0.08}(\mathrm{sys}) ~\mathrm{fm}$ is extracted. Using the geometrical extent of the particle emitting region, determined experimentally with $pp$ correlations as reference together with a source function from a transport model, it is possible to study different sets of scattering parameters. The $p\Lambda$ correlation is proven sensitive to predicted scattering length values from chiral effective field theory. We demonstrate that the femtoscopy technique can be used as valid alternative to the analysis of scattering data to study the hyperon-nucleon interaction.Comment: 12 pages, 11 figure

Strange hadron production at SIS energies: an update from HADES

We present and discuss recent experimental activities of the HADES collaboration on open and hidden strangeness production close or below the elementary NN threshold. Special emphasis is put on the feed-down from ϕ mesons to antikaons, the presence of the Ξ(-) excess in cold nuclear matter and the comparison of statistical model rates to elementary p+p data. The implications for the interpretation of heavy-ion data are discussed as well

Impact of the Coulomb field on charged-pion spectra in few-GeV heavy-ion collisions

In nuclear collisions the incident protons generate a Coulomb field which acts on produced charged particles. The impact of these interactions on charged-pion transverse-mass and rapidity spectra, as well as on pion–pion momentum correlations is investigated in Au + Au collisions at $\sqrt{^{S}NN}$ = 2.4 GeV. We show that the low-m$_{t}$ region (m$_{t}$ < 0.2 GeV / c$^{2}$) can be well described with a Coulomb-modified Boltzmann distribution that also takes changes of the Coulomb field during the expansion of the fireball into account. The observed centrality dependence of the fitted mean Coulomb potential energy deviates strongly from a $A_{part}^{2/3}$ scaling, indicating that, next to the fireball, the non-interacting charged spectators have to be taken into account. For the most central collisions, the Coulomb modifications of the HBT source radii are found to be consistent with the potential extracted from the single-pion transverse-mass distributions. This finding suggests that the region of homogeneity obtained from two-pion correlations coincides with the region in which the pions freeze-out. Using the inferred mean-square radius of the charge distribution at freeze-out, we have deduced a baryon density, in fair agreement with values obtained from statistical hadronization model fits to the particle yields

Quench propagation in Nb3_{3}Sn cos-theta 11 T dipole model magnets in high stress areas

A large number of training quenches at various currents, temperatures, and ramp rates, have been performed on six 11 T dipole model magnets. Quenches in the midplane of these magnets were of special interest, since the quench current in the last three models measured in 2016 was limited to between 84% and 92% of the magnets short sample limit. Measurements of quench propagation velocity, based on both voltage taps and quench antennas, yield a high propagation velocity of 50 to 80 m/s. Due to the high magnetic field gradient over the width of the midplane turn such a high propagation speed cannot be explained by propagation in longitudinal direction of the strand following the twist pitch. In these cases, current and heat sharing at the thin cable edge (where the field, stress, and cable compaction are high) are likely to provoke strand-to-strand quench propagation at higher velocities than along the strands. This investigation is focused on analyzing the quench propagation along the strands and strand-to-strand of various measured cases

Curved-Canted-Cosine-Theta (CCCT) Dipole Prototype Development at CERN

Due to its flexibility in generating advanced field harmonic corrections and potential for low cost compared to traditional designs, the Canted Cosine Theta (CCT) configuration is particularly interesting for compact particle accelerators and gantries for medical applications. This article presents the design of a curved demonstrator named Fusillo, a Canted Cosine Theta Nb-Ti dipole magnet that is being developed at CERN, featuring a large aperture of 236 mm, a small bending radius of 1 m, a bending angle of 90$^{\circ }$, and multi-harmonic field correction, with a 3.61 T conductor peak field. We detail the magnetic coil design, incorporating high-order magnetic field correction of the errors produced by the heavily curved coil, peak field reduction at the coil ends, the development of a new rope type cable, and the mechanical design and the development of the former that supports the coil and provides the curved shape. We also present the first results of a subscale model used to qualify the coil's former manufacturing process, the rope cable, the coil winding optimization, and the coil impregnation system

Fabrication and Test of the Fourth Prototype of the D2 Orbit Corrector Dipole for HL-LHC

As part of the High-Luminosity upgrade project (HL-LHC) for the Large Hadron Collider (LHC) at CERN, new double-aperture beam orbit corrector magnets will be installed near the recombination dipole (D2). These magnets are 2.2 m long Nb–Ti dipoles based on the Canted Cosine-Theta (CCT) design. They provide an in bore magnetic field of 2.60 T at 394 A in a 105 mm aperture with an integrated field of 5 Tm. The fourth full-length prototype was built and tested at CERN. Its design is based on the best engineering practices from previous prototypes. In this paper we first report on recent improvements in the manufacturing process, focusing on the feedback from winding and on the optimization of the impregnation phase. The magnetic measurements carried out at warm and cold temperatures are then reported. Finally, the results of powering tests at 1.9 K and 4.5 K are presented. The magnet meets the dimensional, electrical and magnetic requirements, and is a valid reference for the HL-LHC series production that is currently being carried out in collaboration between CERN and Institute of High Energy Physics (IHEP)

Hi-Lumi LHC Twin Aperture Orbit Correctors 0.5-m Model Magnet Development and Cold Test

The large hadron collider (LHC) upgrade, called high-luminosity LHC is planned for the next decade. A wide range of magnets and new technologies are currently under development. One of these systems will be a set of twin aperture beam orbit correctors positioned on the approaches to the ATLAS and CMS experiments. This twin aperture magnet system comprising 16 magnets, approximately 2 m long, with large 105-mm clear aperture coils. Each aperture will independently deliver 5-T⋅m integral field, between apertures the field vectors are rotated by 90° from each other, and individually powered. This paper presents the sequence of component developments to produce a cost-effective canted cosine theta model magnet. We describe the challenges encountered during the manufacture of the coil formers with their helical canted coil winding process which places a number of insulated wires into the 2-mm-wide 5-mm-deep slot. We describe the: pressurized impregnation process, multiple jointing to connect inner and outer sets of wires within the confines of the coil assembly, and magnet assembly into support structure and yoke. Finally, we present the quench performance and initial test results of this novel coil configuration

Assessment of MQXF Quench Heater Insulation Strength and Test of Modified Design

The HL-LHC interaction region magnet triplets (Q1,Q2, and Q3) will be composed of superconducting Nb3Sn quadru-poles. The MQXF quadrupole protection system is based on CLIQ (Coupling-Loss Induced Quench system) and outer layer quench heaters.This paper reports a summary of quench heaters to coil high voltage tests performed on MQXF short and long coils in air after fabrication, and in air and He gas after magnet training. Breakdown voltage values demonstrate good marginwith respect to the Electrical design criteria for the HL-LHC inner triplet mag-nets. A modification in thequench heater installation-with an ex-tra layer of fiber glass between the coil and the quench heater trace-has been proposed and tested in a mirror magnet to further increase electrical margins. Results demonstrated improvements of high voltage margin at the expense of a clear increase of hot spot temperature.Thebaseline heater to coil insulation was assessed to be able to guarantee safe operation for the Nb3Sn quadrupole mag-nets for the interaction regions of HL-LHC.The HL-LHC interaction region magnet triplets (Q1, Q2, and Q3) will be composed of superconducting Nb3Sn quadrupoles. The MQXF quadrupole protection system is based on CLIQ (Coupling-Loss Induced Quench system) and outer layer quench heaters. This paper reports a summary of quench heaters to coil high voltage tests performed on MQXF short and long coils in air after fabrication, and in air and He gas after magnet training. Breakdown voltage values demonstrate good margin with respect to the Electrical design criteria for the HL-LHC inner triplet magnets. A modification in the quench heater installation- with an extra layer of fiber glass between the coil and the quench heater trace- has been proposed and tested in a mirror magnet to further increase electrical margins. Results demonstrated improvements of high voltage margin at the expense of a clear increase of hot spot temperature. The baseline heater to coil insulation was assessed to be able to guarantee safe operation for the Nb3Sn quadrupole magnets for the interaction regions of HL-LHC

Powering Performance and Endurance Beyond Design Limits of HL-LHC Low-Beta Quadrupole Model Magnets

For the High Luminosity Upgrade project (HL-LHC) of the CERN Large Hadron Collider (LHC), lower β* quadrupole magnets based on advanced Nb 3 Sn conductors will be installed on each side of the ATLAS and CMS interaction points. To quantify the endurance and technological limits of these magnets, beyond their maximum operational conditions, two short length model magnets have been extensively tested at the CERN SM18 test facility. Both magnets were subjected to eight thermal cycles. One of them was trained beyond its ultimate current (17.89 kA, corresponding to 143 T/m field gradient and 12.2 T peak field), reaching a maximum of 19.57 kA at 1.9 K (corresponding to 155 T/m, 13.4 T peak field and 95.4% of the short sample limit) in a 150 mm diameter bore. This magnet currently has the record highest field gradient of this quadrupole magnet class. The second short model had zero re-training quenches up to nominal (16.47 kA) and ultimate current at 1.9 K during the thermal cycles; more than 1000 current cycles to nominal current; and provoked quenches to simulate the most severe failure scenarios of the protection system. After all these tests, both magnets continue to perform beyond requirements for operating current and temperature. In this paper, the tests performed on the two magnets are discussed