Collins and Sivers asymmetries in muonproduction of pions and kaons off transversely polarised protons

Measurements of the Collins and Sivers asymmetries for charged pions and charged and neutral kaons produced in semi-inclusive deep-inelastic scattering of high energy muons off transversely polarised protons are presented. The results were obtained using all the available COMPASS proton data, which were taken in the years 2007 and 2010. The Collins asymmetries exhibit in the valence region a non-zero signal for pions and there are hints of non-zero signal also for kaons. The Sivers asymmetries are found to be positive for positive pions and kaons and compatible with zero otherwise. © 2015

Novel Ways of Heat Removal from Highly Irradiated Superconducting Windings in Accelerator Magnets

Novel ideas of heat removal from superconducting windings in accelerator type magnets are investigated with the help of a recently developed and validated thermal model of a magnet cold mass implemented in COMSOL Multiphysics. Here the focus is on how to improve heat removal from the midplane of a superconducting quadrupole magnet, the area exposed to the highest radiation heat load. In addition, this part of the coil windings has the longest thermal path towards the heat sink and several thermal design improvements proposed in the past are not very effective here. It is shown that with minor changes in the geometrical design, the cooling of the midplane conductors can be strongly increase

Conceptual Development of a Novel Ultra-Thin and Transparent 2 T Superconducting Detector Solenoid for the Future Circular Collider

In the frame of the ongoing Future Circular Collider (FCC) Study, a novel ultra-thin and maximum radiation transparent solenoid for next generation particle detectors is under development. Actually, two versions providing 2 T and 3 T for the FCC-ee and FCC-hh detectors, respectively, are engineered, but here we report on the 2 T version only. Essential aspects of the design are presented. The mechanical and thermal stability of the cold mass is investigated. New, very high-yield stress Al-stabilized NbTi/Cu conductors are required to allow a 0.4 ∗ X 0 radiation thickness. For conductor production, welding of dissimilar aluminum alloys will be necessary. Electron beam and friction stir welding techniques were tested to connect the Ni-doped pure Aluminum stabilizer to the very high-yield strength Al-7068 alloy. The welding results and their applicability are presented and discussed. The proposed conduction-based cold mass cooling scheme using heat drains, and quench protection were analyzed and results are presented

Progress in the FCC-ee Interaction Region Magnet Design

The design of the region close to the interaction point of the FCC-ee experiments is especially challenging. The beams collide at an angle (±15mrad) in a region where the detector solenoid magnetic field is large. Moreover, the very low vertical β^{*} of the machine necessitates that the final focusing quadrupoles are also inside this high field region. The beams should be screened from the effect of the detector solenoid field, and the emittance blow-up due to vertical dispersion in the interaction region should be minimized while leaving enough space for detector components. Crosstalk between the two final focus quadrupoles, only about 6 cm apart at the tip, should also be minimized. We present an update on the subject

Operational experience with the combined solenoid/dipole magnet system of the COMPASS Experiment at CERN

The first ever polarized Drell-Yan measurements were performed at the COMPASS experiment at CERN in 2015, making use of a transversely polarized ammonia target using Dynamic Nuclear Polarization (DNP). A 2.5T longitudinal field is generated with a superconducting solenoid coil carrying a nominal current of 650A, while high homogeneity is obtained by using additional shim - and compensation coils. A superconducting dipole coil encloses the solenoid and together they are integrated in a common cryostat. To obtain transverse polarization, the target material is first polarized in the stronger longitudinal solenoid field and after that, it is rotated to the less strong transverse dipole field (0.63T at 590A). The absolute field strength is never allowed to drop below 0.48T to guarantee a high polarization percentage. In the meantime the forces between the coils should be limited and therefore, the coils cannot both be carrying the nominal operational current, since this will destroy the system. The magnetic field rotation procedure is therefore uniquely developed for this system. The total system is slightly over 2m in length and the stored energy of the system is 2.58MJ for the solenoid at 650A and 0.468MJ for the dipole at 590A.Polarized Drell–Yan measurements require a strong homogeneous magnetic field. A 2.5 T longitudinal field is generated with a superconducting solenoid carrying a nominal current of 650 A, while high homogeneity is obtained by using additional shim—and compensation coils. Since the target needs to be transversely polarized, a second main coil is required. A superconducting dipole coil encloses the solenoid and together they are integrated in a common cryostat. Field rotation, from longitudinal to transverse and vice versa, is possible by simultaneously powering both coils. During the complete procedure, the absolute field strength is never allowed to drop below 0.48 T to guarantee a high polarization percentage. In the meantime, the forces between the coils need to be controlled, and therefore the coils cannot both be carrying the nominal operational current, since this will destroy the system. The magnetic field rotation procedure is therefore uniquely developed for this system. In this paper, the magnet system is described and a summary of the operational experience gained during data taking is provided

Superconducting detector magnets baseline designs for particle physics experiments at the Future Circular Collider

International audienceIn early 2014 a design study started at CERN for a Future Circular Collider. A new tunnel with a circumference of about 100 km for the collider magnets is foreseen as well as new general-purpose particle detectors to probe electron-positron (e$^-$e$^+$), electron-hadron (eh), and hadron-hadron (hh) collisions, housed in large underground caverns. In the last four years baseline designs for the various detector magnets were developed. For the FCC-ee detector two magnet variants were defined: a 7.6-m bore and 7.9-m-long classical 2 T solenoid with 600 MJ stored energy, surrounding the calorimeters, and also a very challenging 4-m bore, 6-m-long, some 100-mm-thick ultrathin and radiation transparent 2 T solenoid with a stored energy of some 170 MJ, that surrounds only the inner tracker of the detectors. For the FCC-eh detector, the detector solenoid is combined with forward and backward dipole magnets required to guide the electron beam in and out of the collision point. This detector requires a 3.5 T solenoid, 2.6-m free bore and 9.2-m length with about 230 MJ of stored energy. Most demanding is the FCC-hh detector with a 14 GJ stored energy magnet system comprising three series connected solenoids, requiring 4 T in the main solenoid with 10-m free bore and a length of 20 m, in line with two 3.2 T forward solenoids with 5.1-m free bore and 4-m length. A quite challenging series of detector magnets is proposed, that needs to be further engineered in the coming years. The superconductor technology though is essentially the same in all the solenoids proposed: conductors comprising Rutherford type cables made of NbTi/Cu strands, stabilized by nickel doped pure aluminum and structurally reinforced with a high yield strength aluminum alloy. The cold masses are conduction cooled through helium cooling pipes welded to their outer support cylinder. The designs of the various baseline magnets as well as their engineering are presented