Christophe Trophime

Magnet calculations at the Grenoble High Magnetic Field Laboratory

An axisymmetrical constrained semi-analytic optimization process is our basic tool for designing magnets. Developments of 3-D numerical models are undertaken to complement this approach. Such models are needed to investigate the overall behavior of our magnets. They are likely to provide suitable insights to solve the design problems arising from the demand for high magnetic field with both great spatial homogeneity and temporal stability.

SMES Optimization for High Energy Densities

High critical temperature superconductors (HTS) bring a lot of opportunities for SMES (Superconducting Magnetic Energy Storage). The large current densities under very high fields and the mechanical strength of IBAD route ReBaCuO coated conductors are very favorable characteristics. Electricity storage still is an issue in general and SMES bring a very interesting solution for pulse current supplies especially if its energy density increases. The record for SC magnet is 13.4 kJ/kg today. We study how to enhance this value. One of the main limitations for the SMES energy density is the mechanical stress as shown i.a. by the viriel theorem, which links simply stress and energy. The current density is another limitation not only the critical characteristic. Indeed protection also plays an important part and often is the real limitation for LTS magnets. We optimized solenoids with mechanical stress and current density constraints. 20 kJ/kg requires current densities of the order of 400 and stresses of about 400 MPa. These values are compatible with YBCO data but pose protection difficulties, which should be perhaps rethought. The design and these protection issues are discussed.

SEISM: a 60 GHz cusp electron cyclotron resonance ion source.

LPSC has been involved for several years in a challenging research and development program on the production of pulsed ions beams with high ionization efficiency primarily dedicated to radioactive ion beams. The generation of the high magnetic field requires the use of helix techniques developed at Laboratoire National des Champs Magnétiques Intenses. As a first approach, a cusp structure has been chosen. 3D simulations were used to define the geometry of the helices. The computer aided design of the mechanical parts of the magnetic structure has been performed at LPSC and was optimized to decrease the total volume of the source. The first 60 GHz magnetic structure (helices coils in their tanks, electrical, and water cooling environment) should be available before the end of 2009.

DC High Field Magnets at the LNCMI

The Laboratoire National des Champs Magnétiques Intenses (LNCMI) is a French large scale facility enabling researchers to perform experiments in the highest possible magnetic field. DC magnetic fields up to 35 T are provided at the Grenoble site and pulsed fields up to 80 T at Toulouse. We focus in this paper on the latest developments of the polyhelix technologies which is used for the most constrained parts of the dc high field magnets. In November 2010, LNCMI has achieved the standardization of its three 24 MW magnets sites (which includes the site for the new 42 T+ hybrid magnet); longitudinally cooled polyhelix inserts are now systematically used as the innermost part of these magnets. The on-going developments aim at developing “hybrid” polyhelix inserts incorporating radially cooled helices in the center to decrease the thermal constraints and to reach higher magnetic fields with the maximal power presently available on the Grenoble site (24 MW). We give an overview of these developments which combine both numerical and experimental approaches.

Quench Considerations and Protection Scheme of a High Field HTS Dipole Insert Coil

The large scale particle accelerators of the future in the 20 T regime are enabled by high temperature superconducting magnets. The dipole magnets needed in new high-field accelerators can be constructed with an YBCO insert and a Nb3Sn outsert. Such a configuration makes the quench analysis and magnet protection challenging because the quench behavior in both of these coils is different and there is very strong inductive coupling between the coils. The Nb3Sn coil is characterized by high energy and current and relatively fast quench propagation velocity. However, quench propagates slowly in YBCO coils because of typically wide spread large temperature margin. Currently, in the EuCARD project, a European collaboration is targeting to construct a small-scale high field YBCO-Nb3Sn hybrid magnet. In this paper, we scrutinize quench in the YBCO insert. We utilized an approach based on a solution of the heat diffusion equation with the finite element method. Additionally, we present a protection scheme for the coil.

Progress Report on the 43 T Hybrid Magnet of the LNCMI-Grenoble

A CEA-CNRS French collaboration is currently developing a new hybrid magnet to produce in a first step a continuous magnetic field of 43 T in a 34-mm warm bore aperture. This magnet combines a resistive insert, composed of Bitter and polyhelix coils, and a large bore superconducting “outsert.” The superconducting coil is based on the novel development of a Nb-Ti/Cu Rutherford Cable On Conduit Conductor (RCOCC) cooled down to 1.8 K by a bath of superfluid helium at atmospheric pressure. It aims at producing a nominal magnetic field of 8.5 T in a 1.1-m cold bore diameter. The specifications of the RCOCC will be presented together with the design and parameters of the cryogenic system. The solution to reduce the coupling between resistive and superconducting coils will be recalled as well as the constraints for designing the mechanical structure. The design study phase is coming to an end. The status of the conductor production and the next steps of the project are presented.

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.

Design Study of High Field Resistive Magnets for Diffraction Experiments

The European Synchrotron Radiation Facility (ESRF), and the Institut Laue Langevin neutron facility (ILL) in collaboration with the Laboratoire National des Champs Magne¿tiques Intenses (LNCMI-CNRS) have performed during 2008 a design study for the implementation of continuous high magnetic fields suitable for diffraction studies. Two main designs have been studied: a horizontal field magnet suitable for back scattering and absorption experiments and a split magnet.

Magnetic Field Homogeneity Optimization of the Giga-NMR Resistive Insert

The development of a Polyhelix resistive insert for high-resolution, solids NMR experiment is quite challenging. The targeted magnetic field homogeneity in a 1 cm diameter sphere volume is 1000 times less than what is observed with traditional Polyhelix magnets. The Polyhelix insert design is derived from our high field magnet optimization process to which we add some more constraints to enforce the field homogeneity. NMR measurements of the Giga-NMR resistive insert show that the achieved homogeneity is improved by an order of magnitude compared to High Field insert. Numerical investigations are carried out to analyze the observed inhomogeneity. Computations suggested a better configuration of the insert, which reduces the observed strong linear term. The expected behavior is confirmed experimentally