CERN Plans on High Field magnets development

The talk covered a short status of the LHC installation, an overview of R&D directions on superconducting magnets beyond the start of the LHC specifically addressing high field magnets, and an overlook of already on-going activities at CERN

Is 3 T peak, 3T/S ramp, a dream?

Experience with AC superconducting magnets for accelerators has still to be gained. So far, few experiments were carried out typically in pulsed mode (one or few ramps). The design and manufacture of an AC dipole providing 3 T in the aperture ramped at 3 T/s ramp shall take into account many aspects resulting in a balanced compromise between the different contributions of magnet losses, temperature/field margin, lifetime under the cyclic operation in a radioactive environment. This note recalls some aspects to be considered for designing and manufacturing such a dipole, pointing out the still open issues which need R&D

Dielectric insulation and high-voltage issues

Electrical faults are in most cases dramatic events for magnets, due to the large stored energy which is potentially available to be dissipated at the fault location. After a reminder of the principles of electrostatics in Section 1, the basic mechanisms of conduction and breakdown in dielectrics are summarized in Section 2. Section 3 introduces the types and function of the electrical insulation in magnets, and Section 4 its relevant failure mechanisms. Section 5 deals with ageing and, finally, Section 6 gives some principles for testing. Though the School specifically dealt with warm magnets, for completeness some principles of dielectric insulation for superconducting accelerator magnets are briefly summarized in a dedicated appendix.Comment: 21 pages, presented at the CERN Accelerator School CAS 2009: Specialised Course on Magnets, Bruges, 16-25 June 200

A Feasibility Study of Superconducting Dipole for the Early Separation Scheme of SLHC

In the framework of the LHC luminosity upgrade an early separation scheme is being studied for the final phase ($L\approx 10^{35} cm^{-2} s^{-1}$ with substantial changes in the IR). In this paper we compare a Nb$_{3}$Sn and a Nb-Ti cos($\theta$) design: the aim is to explore the benefits and the limits of a compact solution with respect to the detector's constraints and the energy deposition issues. We propose to put the dipole system (cryostat and magnet) at a location starting at 6.8 m from the IP. The preliminary cross section, the achievable integrated field, the energy deposition on the magnet are presented and discusse

Detecting photon-photon scattering in vacuum at exawatt lasers

In a recent paper, we have shown that the QED nonlinear corrections imply a phase correction to the linear evolution of crossing electromagnetic waves in vacuum. Here, we provide a more complete analysis, including a full numerical solution of the QED nonlinear wave equations for short-distance propagation in a symmetric configuration. The excellent agreement of such a solution with the result that we obtain using our perturbatively-motivated Variational Approach is then used to justify an analytical approximation that can be applied in a more general case. This allows us to find the most promising configuration for the search of photon-photon scattering in optics experiments. In particular, we show that our previous requirement of phase coherence between the two crossing beams can be released. We then propose a very simple experiment that can be performed at future exawatt laser facilities, such as ELI, by bombarding a low power laser beam with the exawatt bump.Comment: 8 pages, 6 figure

Cable Insulation Scheme to Improve Heat Transfer to Superfluid Helium in Nb-Ti Accelerator Magnets

In superconducting magnets operating at high heat loads as the ones for interaction region of particle colliders or for fast cycling synchrotrons, the limited heat transfer capability of state-of-the-art electrical insulation may constitute a heavy limitation to performance. In the LHC main magnets, Nb-Ti epoxy-free insulation, composed of polyimide tapes, has proved to be permeable to superfluid helium, however the heat flux is rather limited. After a review of the standard insulation scheme for Nb-Ti and of the associated heat transfer mechanisms, we show the existence of a large margin available to improve insulation permeability.We propose a possible way to profit of such a margin in order to increase significantly the maximum heat flux drainable from an all polyimide insulated Nb-Ti coil, as it is used in modern accelerator magnets

Comparative Study of Heat Transfer from Nb-Ti and Nb3_3Sn coils to He II

In superconducting magnets, the energy deposited or generated in the coil must be evacuated to prevent temperature rise and consequent transition of the superconductor to the resistive state. The main barrier to heat extraction is represented by the electric insulation wrapped around superconducting cables. In the LHC, insulation improvement is a key point in the development of interaction region magnets and injector chain fast-pulsed magnets for luminosity upgrade; the high heat load of these magnets, in fact, is not compatible with the use of current insulation schemes. We review the standard insulation schemes for Nb-Ti and Nb$_{3}$Sn technology from the thermal point of view. We implement, in an analytical model, the strongly nonlinear thermal resistances of the different coil components including the permeability to superfluid helium of Nb-Ti insulations, measured during the LHC main dipole development. We use such a model to compare Nb-Ti and Nb$_{3}$Sn technologies by taking into account their specific operating margin in different working conditions. Finally, we propose an insulation scheme to enhance the heat transfer capability of Nb-Ti coils

Localization of Electrical Insulation Failures in Superconducting Collared Coils by Analysis of the Distortion of a Pulsed Magnetic Field

The localization of possible electrical faults in superconducting accelerator magnets may, in most cases, be a complex, expensive and time-consuming process. In particular, inter-turn short circuits and failures of the ground insulation are well detectable when the magnet is collared, but often disappear after disassembly for repair due to the release of the pre-stress in the coils. The fault localization method presented in this paper is based on the measurement and analysis of the magnetic field generated inside the magnet aperture by a high voltage pulse. The presence of the fault modifies the distribution of the current in the coils and produces a distortion of the magnetic field. The described method aims at locating both the longitudinal and azimuthal position of the fault-affected area. The test method, the transient case FEM models and the implemented experimental set-up are presented and discussed for the LHC dipole models

Logistics of LHC cryodipoles from simulation to storage management

The main families of LHC superconducting cryomagnets consist of 1232 cryodipoles and 488 quadrupoles. The different contracts, which are constraining the production and installation of these cryomagnets, have been initially rated according to the baseline schedule, based on a "just in time" scheme. However the complexity of the construction and the time needed to fully test the cryomagnets require that each contract is decoupled as much as possible from the others' evolutions and impose temporary storage between different assembly and test activities. In this paper the organisation of cryomagnet flow and the main challenges of logistics are analysed on the basis of the planning of each main step before installation in the LHC. Finally, the solutions implemented for storage, handling and transport are presented and discussed