P. Pugnat

Results from the OSQAR photon-regeneration experiment : No light shining through a wall

A new method to amplify the photon-axion conversions in a magnetic field is proposed using a buffer gas at a specific pressure in a photon-regeneration experiment. As a first result, new bounds for mass and coupling constant for laboratory experiments aiming to detect any hypothetical scalars and pseudoscalars, which can couple to photons were obtained, excluding with 95% confidence level, the recently withdrawn PVLAS result.

Axion searches in the past, at present, and in the near future

Theoretical axion models state that axions are very weakly-interacting particles. In order to experimentally detect them, the use of colorful and inspired techniques become mandatory. There are a wide variety of experimental approaches that were developed during the last 30 years; most of them make use of the Primakoff effect, by which axions convert into photons in the presence of an electromagnetic field. We review the experimental techniques used to search for axions and will give an outlook on experiments planned for the near future.

Performance of the LHC final design full scale superconducting dipole prototypes

Within the LHC magnet program, a series of six, final design, full-scale superconducting dipole prototypes are presently being built in industry and tested at CERN. The main features of these magnets are: two-in-one structure, 56 mm aperture, six-block two layer coils wound from 15.1 mm wide graded NbTi cables, and all-polyimide insulation. This paper reviews the main test results of magnets tested at 4.2 K and 1.8 K. The results of the quench training, conductor performance, magnet protection, sensitivity to ramp rate and field quality are presented and discussed in terms of the design parameters and the aims of the full scale dipole prototype program.

Statistical diagnosis method of conductor motions in superconducting magnets to predict their quench performance

Premature training quenches are usually caused by the transient energy released within the magnet coil as it is energised. Two distinct varieties of disturbances exist. They are thought to be electrical and mechanical in origin. The first type of disturbance comes from nonuniform current distribution in superconducting cables whereas the second one usually originates from conductor motions or micro-fractures of insulating materials under the action of Lorentz forces. All of these mechanical events produce in general a rapid variation of the voltages in the so-called quench antennas and across the magnet coil, called spikes. A statistical method to treat the spatial localisation and the time occurrence of spikes is presented. It allows identification of the mechanical weak points in the magnet without need to increase the current to provoke a quench. The prediction of the quench level from detailed analysis of the spike statistics can be expected.

Feasibility study of an experiment to measure the vacuum magnetic birefringence

The use of a recently decommissioned 15-meters long twin aperture LHC supercon-ducting magnet prototype having a transverse magnetic fieldB ≈ 9.5 T provides the unique opportunity for the construction of a new powerful experiment to measure the Vacuum Magnetic Birefringence (VMB). The values or the limit values of the mass and of the coupling constant to two photons of possible dark matter candidates such as axions are aimed to be deduced from such an experiment. In this article, the technical feasibility study of a new setup to measure the VMB will be presented. It is based on a linear optical resonant cavity house in the LHC superconducting dipole prototype. The mechanical integrations of the optical components inside the magnet aperture as well as the optical detection principles will be presented. A comparison of the expected performances with respect to the present reference results for this type of experiment will also be given.

Review of Quench Performance of LHC Main Superconducting Magnets

The regular lattice of the large Hadron collider (LHC) will make use of more than 1600 main magnets and about 7600 corrector magnets, all superconducting and working in pressurized superfluid helium bath. This complex magnet system will fill more than 20 km of the LHC underground tunnel. In this paper an overview of the cold test program and quality assurance plan to qualify all LHC superconducting magnets will be presented. The quench training performance of more than 1100 LHC main dipoles and about 300 main quadrupoles, cold tested to date, will be reviewed. From these results an estimate of the number of quenches that will be required to start operation of the whole machine at nominal energy will be discussed. The energy level at which the machine could be operated at the early phase of the commissioning without being disturbed by training quenches will be addressed. The LHC magnet program required the development of many new tools and techniques for the testing of superconducting magnet coils, magnet protection systems, cryogenics, and instrumentation. This paper will also present a summary of this development work and the results achieved.

Final Design of the New Grenoble Hybrid Magnet

A CEA-CNRS French collaboration is currently developing a new hybrid magnet; this magnet combines a resistive insert composed of Bitter and polyhelix coils and a new large bore superconductor outsert to create an overall continuous magnetic field of 42+ T in a 34 mm warm aperture. The design of the superconducting coil outsert has been completed after thorough studies and successful experimental validation phases. Based on the novel development of a Nb-Ti/Cu Rutherford Cable On Conduit Conductor (RCOCC) cooled down to 1.8 K by the mean of a bath of superfluid helium at atmospheric pressure, the superconducting coil aims to produce a continuous magnetic field of 8.5 T in a 1.1 m cold bore diameter. The main results of the final design studies of the superconducting coil are presented including the 2D and 3D mechanical stress analysis, the conductor and coil specifications, the coil protection system as well as the required cryogenics infrastructure. The final design of the resistive insert coils is also described.

A New Design for the Superconducting Outsert of the GHMFL 42+ T Hybrid Magnet Project

A new superconducting coil outsert has been designed to be integrated within the existing infrastructure of the GHMFL hybrid project. Based on the novel development of a Nb-Ti Rutherford Cable On Conduit Conductor (RCOCC) cooled at 1.8 K by a bath of superfluid helium at atmospheric pressure, the superconducting coil aims to produce a continuous magnetic field of 8.5 T in a 1.1 m bore diameter. Combined with resistive insert coils, an overall continuous magnetic field of 42+ T will be produced in a 34 mm warm aperture. The main results of the conceptual study are reported including the conductor and coil specifications, the mechanical stress analysis, the coil protection scheme as well as the required cryogenics infrastructure. First developments and tests regarding the RCOCC are also presented.

Dynamical Response of Hybrid Magnet Structure Featuring Eddy-Current Shield During Transient Failure Mode

Hybrid magnets enable to achieve very high magnetic fields by combining resistive insert magnets with a large bore superconducting outer coil. In order to reduce the electromagnetic coupling between the coils, we introduce an eddy-current shield between the resistive and superconducting magnet. This additional shield is responsible for heat loads. To limit the degradation of the thermal behavior of the cold mass, an innovative support ferrule has been designed. It allows rigid connection of the eddy-current shield to the magnet structure. In this paper, the worst magnetic failure scenario is identified and modeled. It results in large transient forces applying to the structure. Transient mechanical analysis of the hybrid magnet structure featuring innovative support ferrule is presented. Simulations show that the proposed configuration leads to lower mechanical stresses than a configuration featuring a suspended shield.

Quench performance and field quality of the LHC preseries superconducting dipoles

The preseries production of the LHC main superconducting dipoles is presently being tested at CERN. The foremost features of these magnets are: twin structure, six block two layer coils wound from 15.1 mm wide graded NbTi cables, 56 mm aperture, polyimide insulation and stainless steel collars. The paper reviews the main test results of magnets tested to day in both normal and superfluid helium. The results of training performance, magnet protection, electrical integrity and the field quality are presented in terms of the specifications and expected performance of these magnets in the future accelerator.