Search

In 2017, the OSQAR-CHASE experiment dedicated to the search of chameleon particles has been run with one spare LHC dipoles installed and re-commissioned on its dedicated cryogenic bench at CERN-SM18. High vacuum condition has been reached within the magnet aperture using cryo-pumping. A 18 W CW laser working at 532 nm and a state-of-the art CCD detector have been installed, aligned and operated searching for a phosphorescent signal of the vacuum permeated by the magnetic field coming from Chameleons. The analysis of the data is ongoing. In parallel, a new analysis of the OSQAR-LSW data recorded during the 2014 experimental run is being pursued. It is based on the cross-correlation method and will allow further improvement of the present reference exclusion limits obtained by OSQAR-LSW for scalar and pseudoscalar sub-eV axion like particle search. Additional gains in the sensitivity of OSQAR-LSW can be obtained by using more than 2 LHC dipoles and by developing dedicated Fabry-Perot cavities. A new French-German proposal has been submitted in 2017 to the ANR-DFG funding agencies to support these developments. Concerning OSQAR-VMB, the first phase is coming to an end. The next one requires the development of a long Fabry-Perot cavity and a revision of the optical detection scheme. An extended European initiative is being prepared within the scope of the Physic Beyond Collider (PBC) working group to measure the vacuum magnetic birefringence at CERN.

Recent intensive theoretical and experimental studies highlight the possibility of new fundamental particle physics beyond the standard model that can be probed by sub-eV energy experiments. The OSQAR photon regeneration experiment looks for Light Shining through a Wall (LSW) from the quantum oscillation of optical photons into Weakly Interacting Sub-eV Particles (WISPs), like axion or axion-like particles (ALPs), in a 9 T transverse magnetic field over the unprecedented length of 2 x 14.3 m. No excess of events has been detected over the background. The di-photon couplings of possible new light scalar and pseudo-scalar particles can be constrained in the massless limit to be less than 8.0 x 10-8 GeV-1. These results are very close to the most stringent laboratory constraints obtained for the coupling of WISPs to two photons. Plans for further improving the sensitivity of the OSQAR experiment are presented.

Recent intensive theoretical and experimental studies highlight the possibility of new fundamental particle physics beyond the standard model that can be probed by sub-eV energy experiments. The OSQAR photon regeneration experiment looks for Light Shining through a Wall (LSW) from the quantum oscillation of optical photons into Weakly Interacting Sub-eV Particles (WISPs), like axion or axion-like particles (ALPs), in a 9 T transverse magnetic field over the unprecedented length of 2 x 14.3 m. No excess of events has been detected over the background. The di-photon couplings of possible new light scalar and pseudo-scalar particles can be constrained in the massless limit to be less than 8.0 x 10-8 GeV-1. These results are very close to the most stringent laboratory constraints obtained for the coupling of WISPs to two photons. Plans for further improving the sensitivity of the OSQAR experiment are presented. Recent theoretical and experimental studies highlight the possibility of new fundamental particle physics beyond the Standard Model that can be probed by sub-eV energy experiments. The OSQAR photon regeneration experiment looks for “Light Shining through a Wall” from the quantum oscillation of optical photons into “Weakly Interacting Sub-eV Particles”, like axion or axion-like particles (ALPs), in a 9 T transverse magnetic field over the unprecedented length of $2 \times 14.3$ m. No excess of events has been detected over the background. The di-photon couplings of possible new light scalar and pseudo-scalar particles can be constrained in the massless limit to be less than $8.0\times 10^{-8}$ GeV$^{-1}$ . These results are very close to the most stringent laboratory constraints obtained for the coupling of ALPs to two photons. Plans for further improving the sensitivity of the OSQAR experiment are presented. Recent theoretical and experimental studies highlight the possibility of new fundamental particle physics beyond the Standard Model that can be probed by sub-eV energy experiments. The OSQAR photon regeneration experiment looks for "Light Shining through a Wall" (LSW) from the quantum oscillation of optical photons into "Weakly Interacting Sub-eV Particles" (WISPs), like axion or axion-like particles (ALPs), in a 9 T transverse magnetic field over the unprecedented length of $2 \times 14.3$ m. No excess of events has been detected over the background. The di-photon couplings of possible new light scalar and pseudo-scalar particles can be constrained in the massless limit to be less than $8.0\times10^{-8}$ GeV$^{-1}$. These results are very close to the most stringent laboratory constraints obtained for the coupling of ALPs to two photons. Plans for further improving the sensitivity of the OSQAR experiment are presented.

A new measurement system, based on a large-diameter search-coil rotating in the superfluid helium, a fast digital integrator, a motor drive unit with slip rings, and a flexible software environment was developed at CERN for the measurement of dynamic effects in superconducting magnets. This system has made it possible the measure, with a resolution of up to 1 Hz, the multipole field errors due to superconductor magnetization and interstrand coupling currents. In this paper we present the development and calibration of the measurement system, its installation in the vertical cryostat of CERN’s recently refurbished test station, and its application to the US-LARP built, 120-mm aperture Nb$_{3}$Sn quadrupole magnet (HQ01e) for the upgrade of the LHC insertion regions.

This document gives a brief description of the Local Quench Antennas (LQA) with the goal to help understanding the mechanism used to record and localize a quench in the LHC dipole magnets. The analysis of the signals of the main voltage taps is reported in detail. This analysis is necessary to get the information about the approximate quench location of the quench: aperture, and pole. It gives also the range of time in which the quench started and developed allowing filtering the LQA data. A readable display of the signals is presented. The principle to obtain the longitudinal location of the quench starting point along the magnet head is explained. It is presented how to work out the origin of the quench, based on the information, between sides and blocks of the same pole. A criterion, based on the quench propagation velocity, provides the information about the quenched layer based on probability calculations. Finally the method is applied to investigate the quench origin of the magnet MB2420 and the results are reported at the end of this document.

To eliminate the risk of thermal runaways in LHC interconnections a consolidation by placing shunts on the main bus bar interconnections is proposed by the Task Force Splices Consolidation. To validate the design two special SSS magnet spares are placed on a test bench in SM-18 to measure the interconnection in between with conditions as close as possible to the LHC conditions. Two dipole interconnections are instrumented and prepared with worst-case-conditions to study the thermo-electric stability limits. Two quadrupole interconnections are instrumented and prepared for studying the effect of current cycling on the mechanical stability of the consolidation design. All 4 shunted interconnections showed very stable behaviour, well beyond the LHC design current cycle.

The status of the OSQAR experiments is presented highlighting the progress achieved in 2010. For the photon regeneration part, three experimental runs have been performed after thorough preparatory phases in the CERN SM18 test hall. For the first time, this experiment has been successfully conducted with two aligned LHC dipoles and the expected sensitivity was achieved for the search of light scalar and pseudoscalar particles. Concerning the measurement of the Vacuum Magnetic Birefringence (VMB), dedicated studies to integrate within a LHC dipole the newly developed ultra-fine ellipsometry techniques have been performed in collaborating Institutes.

In order to reduce the burden on the beam-based feedback, the Large Hadron Collider control system is equipped with the Field Description for the LHC (FiDeL) which provides a forecast of the magnetic field and the multipole field errors. FiDeL has recently been extensively tested at CERN to determine main field tracking, multipole forecasting and compensation accuracy. This paper describes the rationale behind the tests, the procedures employed to power the main magnets and their correctors, and finally, we present the results obtained. We also give an indication of the prediction accuracy that the system can deliver during the operation of the LHC and we discuss the implications that these will have on the machine performance.

A dedicated measurement campaign was set up to test the FiDeL concept and its LSA implementation. The test was performed by demonstrating the tracking of B1 and B2 for two LHC main dipoles and one LHC main quadrupole. It also included the compensation of the b3 and b5 harmonics in the dipole magnets using the sextupole and decapole corrector magnets. In this report we present the techniques developed to power the magnets for these tests during the current ramps; the instrumentation and data acquisition setup used to perform the tracking experiments; the calibration procedure and data corrections employed; and finally the main results obtained., peer-reviewed

This paper contains a summary of the results of the magnetic and mechanical alignment tests performed at CERN on the first 111 arc Short Straight Sections. These include the mechanical axis of the Cold Bore Tube at room temperature, the magnetic axis of main quadrupoles and correctors at both room and cryogenic temperature, and the field direction of the main quadrupoles. The measurements show that the quality of the assemblies is generally within the requirements for the machine.