Abstract
The Grenoble Hybrid magnet is a modular platform using resistive and superconducting technologies to produce various continuous high magnetic field and flux configurations for the scientific ...community. They range from 43 T in 34 mm diameter with 24 MW electrical power to 9 T in 800 mm diameter when the superconducting coil is used alone. Thanks to the ongoing upgrade of the electrical power installation of LNCMI-Grenoble up to 30 MW and possibly to 36 MW, the possibility to increase the total field up to 45-46 T in the near future is foresee and deeply studied. The key design parameters will be briefly recalled including the specifically developed Nb-Ti/Cu conductor, the large bore outsert superconducting coil, the magnet cryostat with its structure including the eddy-current shield, the cryogenic line for the interconnection with the cryogenic satellite and the fully dedicated 150 l/h He liquefaction plant. All components of the hybrid magnet platform have been built, tested and delivered to LNCMI-Grenoble, where integration and assembly are ongoing. The status of the project will be given with focus to the recent commissioning tests of the cryogenic satellite producing the pressurized superfluid He at 1.8 K as well as to the successful powering tests of the specially developed current leads at ultimate current and under fully degraded cooling conditions simulating the worst-case accidental scenario.
In the framework of the series tests of superconducting magnets for the LHC, a special procedure was developed at CERN to perform conductor limited quenches at temperatures around 4.4 K. All results ...obtained on pre-series and series main dipoles tested to date will be presented with their analysis. These quenches allow fine diagnostics concerning the electrical integrity of the conductors and of the splices. They also allow the determination for each magnet of the temperature margin at nominal operating conditions of the LHC at superfluid helium. The comparison between the quench current and the critical current directly measured on short samples of superconducting cables used for the winding is discussed.
The Short Straight Section (SSS) for the Large Hadron Collider arcs, containing in a common cryostat the lattice quadrupoles and correction magnets, have now entered series production. The foremost ...features of the lattice quadrupole magnets are a two-in-one structure containing two 56 mm aperture, two-layers coils wound from 15.1 mm wide NbTi cables, enclosed by the stainless steel collars and ferromagnetic yoke, and inserted into the inertia tube. Systematic cryogenic tests are performed at CERN in order to qualify these magnets with respect to their cryogenic and electrical integrity, the quench performance and the field quality in all operating conditions. This paper reports the main results obtained during tests and measurements in superfluid helium. The electrical characteristics, the insulation measurements and the quench performance are compared to the specifications and expected performances for these magnets. The field in the main quadrupole is measured using three independent systems: 10-m long twin rotating coils, an automatic scanner, and single stretched wire. A particular emphasis is given to the integrated transfer function which has a spread of around 12 units rms in the production and is a critical issue. The dodecapole harmonic component, which required trimming through a change in coil shims, is also discussed. Finally, the magnetic axis measurements at room temperature and at 1.9 K, providing the nominal vertical shift for installation are reported
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.
The windings of high-field accelerator magnets are usually made of Rutherford-type superconducting cables. The magnetic field distribution along the axis of such magnets exhibits a periodic ...modulation with a wavelength equal to the twist pitch length of the cable used in the winding. This effect, resulting from quasipersistent currents, was investigated with a Hall probe array inserted inside the aperture of the LHC superconducting dipoles, both in short models and full-scale prototypes. The amplitude and the time dependence of this periodic field oscillation have been studied as a function of the magnet current history. The origin and, the impact on the LHC dipole stability of the nonuniform current redistribution producing such a field modulation are discussed.
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.
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.
The main superconducting dipoles for the LHC are being stored outdoors for periods from a few weeks to several years after conditioning with dry nitrogen gas. Such a storage before installation in ...the 27 km circumference tunnel may affect not only the mechanical and cryogenic functionality of the cryodipoles but also their quench and field performance. A dedicated task force was established to study all aspects of long term behavior of the stored cryodipoles, with particular emphasis on electrical and vacuum integrity, quench training behavior, magnetic field quality, performance of the thermal insulation, mechanical stability of magnet shape and of the interface between cold mass and cryostat, degradation of materials and welds. In particular, one specifically selected cryodipole stored outdoors for more than one year, was re-tested at cold. In addition, various tests have been carried out on the cryodipole assembly and on the most critical subcomponents to study aspects such as the hygrothermal behavior of the supporting system and the possible oxidation of the Multi Layer Insulation reflective films. This paper summarizes the main investigations carried out and their results
The series testing at 1.9 K of the 360 Short Straight Sections (SSS) for the Large Hadron Collider have started at CERN in September 2003. The SSS contain the lattice quadrupoles and correction ...magnets in a common cryostat. The lattice quadrupoles feature two collared coils with 56 mm bore assembled in a common yoke. The coils are wound in two-layers from 15.1 mm wide NbTi cable, insulated with polyimide tape. The paper reviews the main test results performed in superfluid helium. The magnetic field and magnetic center position of the quadrupoles and associated correctors were measured with two independent systems, namely an automated scanner and a single stretched wire technique. The quench training, the field quality and the magnetic alignment measurements are presented and discussed in terms of the specifications and expected performances of these magnets in the LHC. We discuss in detail the field quality in terms of multipole errors measured at injection and nominal field and decomposed into geometric and persistent current magnetization errors. Warm/cold correlation for the geometric multipoles and the magnetic axis is also presented.
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