P. Fazilleau

Status of the construction of the CMS magnet

CMS (compact muon solenoid) is a general-purpose detector designed to run at the highest luminosity at the CERN Large Hadron Collider (LHC). Its distinctive features include a 4 T superconducting solenoid with 6 m diameter by 12.5 m long free bore, enclosed inside a 10,000-ton return yoke. The stored magnetic energy is 2.6 GJ. The magnet is being assembled in a surface hall and will be tested at the beginning of 2005 before being transferred to an experimental hall 90 m below ground level. The design and construction of the magnet is a common project of the CMS Collaboration. The task is organized by a CERN based group with strong technical and contractual participation of CEA Saclay, ETH Zurich, Fermilab, INFN Genova, ITEP Moscow, University of Wisconsin and CERN. The return yoke, 21 m long and 14 m in diameter, is equivalent to a thickness of 1.5 m of saturated iron interleaved with four muon stations. Manufacture of the yoke and vacuum tank is completed and the first sub-detectors have been installed. The indirectly-cooled, pure-aluminum-stabilized coil is made up from five modules internally wound with four layers of a 20 kA mechanically-reinforced conductor. The manufacture of the conductor is completed and winding is in progress for a final assembly in 2004. All ancillaries are delivered or under contract. The magnet project is described, with emphasis on the present status of the fabrication.

HTS Insert Magnet Design Study

Future accelerator magnets will need to reach higher field in the range of 20 T. This field level is very difficult to reach using only Low Temperature Superconductor materials whereas High Temperature Superconductors (HTS) provide interesting opportunities. High current densities and stress levels are needed to design such magnets. YBCO superconductor indeed carries large current densities under high magnetic field and provides good mechanical properties especially when produced using the IBAD approach. The HFM EUCARD program studies the design and the realization of an HTS insert of 6 T inside a dipole of 13 T at 4.2 K. In the HTS insert, engineering current densities higher than 250 under 19 T are required to fulfill the specifications. The stress level is also very severe. YBCO IBAD tapes theoretically meet these challenges from presented measurements. The insert protection is also a critical because HTS materials show low quench propagation velocities and the coupling with the magnet makes the problem even more challenging. The magnetic and mechanical designs of the HTS insert as well as some protection investigation ways will be presented.

HTS Dipole Insert Developments

Future accelerator magnets will need to reach a magnetic field in the 20 T range. Reaching such a magnetic field is a challenge only reachable using high temperature superconductor (HTS) material. The high current densities and stress levels needed to satisfy the design criterion of such magnets make YBaCuO superconductor the most appropriate candidate especially when produced using the IBAD route. The HFM EUCARD program is aimed at designing and manufacturing a dipole insert made of HTS material generating 6 T inside a Nb3Sn dipole of 13 T at 4.2 K. In the HTS insert, engineering current densities higher than 250 MA/m2 under 19 T are required to reach the performances. The stress level is consequently very high. The insert protection is also a critical issue as HTS shows low quench propagation velocity. The coupling with the Nb3Sn dipole makes the problem even more difficult. The magnetic and mechanical designs of the HTS insert will be presented as well as the technological developments underway to realize this compact dipole insert.

Study and Development of the Superconducting Conductor for the Grenoble Hybrid Magnet

To produce a continuous magnetic field of at least 8.5 T in a 1.1 m cold bore diameter, the superconducting outsert of the Grenoble Hybrid magnet is based on the novel development of a Nb-Ti/Cu Rutherford Cable On Conduit Conductor (RCOCC) cooled to 1.8 K by a bath of superfluid helium pressurized at atmospheric pressure. The main results of the conductor studies and development are presented after a brief introduction to the specificity of hybrid magnets, namely the electromagnetic couplings between resistive and superconducting coils. Results obtained with short samples of conductor are reviewed including the measurements of the elastic limit, AC losses, stability and critical current. The final specification of the RCOCC is presented highlighting the proposed method for the industrialization of the insertion process of the Rutherford cable on the hollow Cu-Ag stabilizer as well as its validation phase on short samples.

Commissioning of the CMS Magnet

CMS (compact muon solenoid) is one of the large experiments for the LHC at CERN. The superconducting magnet for CMS has been designed to reach a 4 T field in a free bore of 6 m diameter and 12.5 m length with a stored energy of 2.6 GJ at full current. The flux is returned through a 10 000 t yoke comprising of five wheels and two end caps composed of three disks each. The magnet was designed to be assembled and tested in a surface hall, prior to be lowered at 90 m below ground, to its final position in the experimental cavern. The distinctive feature of the cold mass is the four-layer winding, made from a reinforced and stabilized NbTi conductor. The design and construction was carried out by CMS participating institutes through technical and contractual endeavors. Among them CEA Saclay, INFN Genova, ETH Zurich, Fermilab, ITEP Moscow, University of Wisconsin and CERN. The construction of the CMS Magnet, and of the coil in particular, has been completed last year. The magnet has just been powered to full field achieving electrical commissioning. After a brief reminder of the design and construction the first results of the commissioning are reported in this paper.

Design Status of the R3B-GLAD Magnet: Large Acceptance Superconducting Dipole With Active Shielding, Graded Coils, Large Forces and Indirect Cooling by Thermosiphon

The R3B-Glad superconducting Magnet provides the field required for a large acceptance spectrometer, dedicated to the analysis of Reactions with Relativistic Radioactive ions Beams. In the framework of the FAIR Project to GSI and within NUSTAR physics program, the technical study started in 2006, and the engineering design is undertaken. One main feature of this butterfly-like magnet with graded, tilted and trapezoidal racetrack coils is the active shielding. It makes it possible to decreasing the field by two orders of magnitude within a 1.2 m length, despite the large opening on the outlet side of the magnet (around 0.8 square meters). The fringe field is lower than 20 mT in the target area beside the entry, while the main field is larger than 2 teslas, out of 2 m length. The other principal characteristics are as follows: first, a high level of magnetic forces (300 to 400 tons per meter), with little place to block the coils, requiring a very specific mechanical structure; then, the magnet protection system that is based on an external dump resistor, coupled to a strong quenchback effect, to prevent any damage of the coils which could be caused by the 24 MJ of stored energy; lastly, the indirect cooling of the cold mass with a two-phase helium thermosiphon. The overall size of the conical cryostat will be around 3.5 m long, 3.8 m high and 7 m broad.

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.

Development of the EuCARD Nb3Sn Dipole Magnet FRESCA2

The key objective of the superconducting high field magnet work package of the European Project EuCARD, and specifically of the high field model task, is to design and fabricate the Nb3Sn dipole magnet FRESCA2. With an aperture of 100 mm and a target bore field of 13 T, the magnet is aimed at upgrading the FRESCA cable test facility at CERN. The design features four 1.5-m-long double-layer coils wound with a 21-mm-wide cable. The windings are contained in a support structure based on a 65-mm-thick aluminum shell pretensioned with bladders. In order to qualify the assembly and loading procedure and to validate the finite element stress computations, the structure will be assembled around aluminum blocks, which replace the superconducting coils, and instrumented with strain gauges. In this paper, we report on the status of the assembly and we update on the progress on design and fabrication of tooling and coils.

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.