Barrel Toroid Research Articles

Fast Dump of the ATLAS Toroids

The toroidal magnet system of the ATLAS Detector at CERN consists of a Barrel Toroid (BT) and two End Cap Toroids (ECT-A and ECT-C). Each toroid is built up from eight racetrack coils wound with an aluminum stabilized NbTi conductor and indirectly cooled by forced flow liquid helium. The three toroids operate in series at 20.5 kA with a total stored energy of 1.5 GJ. In order to verify the reliability and effectiveness of the quench protection system, series of fast dump tests have been performed first of the single toroids and finally of the entire toroidal magnet system. In this paper a model to simulate the fast dump of the ATLAS toroids in single mode operation and in full system configuration is presented. The model is validated through comparison with measured data extracted from the ramp-and-quench runs. The calculated energy dissipation in the various coils is in very good agreement (within 1-2%) with the enthalpy changes estimated from the temperature measurements of the different parts of the cold masses. The results confirm the safe operation of such a gigantic and complicated magnet system which is now ready for continuous running of the ATLAS Detector.

Cryogenic Characteristics of the ATLAS Barrel Toroid Superconducting Magnet

ATLAS, one of the experiments of the LHC accelerator under commissioning at CERN, is equipped with a large superconducting magnet the Barrel Toroid (BT) that has been tested at nominal current (20500 A). The BT is composed of eight race-track superconducting coils (each one weights about 45 tons) forming the biggest air core toroidal magnet ever built. By means of a large throughput centrifugal pump, a forced flow (about 10 liter/second at 4.5 K) provides the indirect cooling of the coils in parallel. The paper describes the results of the measurements carried out on the complete cryogenic system assembled in the ATLAS cavern situated 100 m below the ground level. The measurements include, among other ones, the static heat loads, i.e., with no or constant current in the magnet, and the dynamic ones, since additional heat losses are produced, during the current ramp-up or slow dump, by eddy currents induced on the coil casing.

First Cool-Down and Test at 4.5 K of the ATLAS Superconducting Barrel Toroid Assembled in the LHC Experimental Cavern

The large ATLAS superconducting magnets system consists of the Barrel, two End-Caps Toroids and the Central Solenoid. The eight separate coils making the Barrel Toroid (BT) have been individually tested with success in a dedicated surface test facility in 2004 and 2005 and afterwards assembled in the underground cavern of the ATLAS experiment. In order to fulfill all the cryogenic scenarios foreseen for these magnets with a cold mass of 370 tons, two separate helium refrigerators and a complex helium distribution system have been used. This paper describes the results of the first cool-down, steady-state operation at 4.5 K and quench recovery of the BT in its final configuration.

Assembly Concept and Technology of the ATLAS Barrel Toroid

The ATLAS detector for the LHC collider at CERN requires a large superconducting Barrel Toroid (BT) with overall dimensions of 25 m length, 22 m diameter which is installed in the ATLAS cavern 100 m underground. The Barrel Toroid provides the magnetic field for the muon detector. The toroid is assembled from 8 flat race track coils of dimensions 25 m times 5 m. Following the on-surface acceptance test of the 8 BT coils, they are successively inserted in the underground cavern and assembled as a full toroid by using 16 supporting rings of struts that link the 8 coils to form a rigid and stable structure. The total mass of the toroid is 850 t. Particular issues are that the axis of the toroid has to be horizontal and the final shape of the toroid cylindrical with a tolerance of +/-10 mm with respect to an overall system diameter of 22 m. The desired shape of the toroid can only be controlled by installing the 8 coils in calculated positions in space (forming an elliptic shaped structure), and by linking them using bolted struts linking the coils. The final release of the structure is done under its self weight hydraulically. This required very large tooling essentially to support all the 8 coils in space in a nearly stress free condition until the toroid supporting rings have been closed. The theoretical positions are found by performing detailed 3-D Finite Element Calculations that predict the shape of the toroid under its operational load. The assembly of this huge toroid is unique and no experience basis exists. This paper presents the concept and technology required for the assembly of the toroid as well as the cryogenic supply lines, highlights the FEA mechanical calculations performed to predict the shape, summarizes the tooling required and reviews the experience gained during the installation

Experience Report of the Manufacture of the 25Meter Long Double Pancakes for the ATLAS Barrel Toroidal Magnet

The magnet system of the ATLAS detector, which presently is being installed in the LHC accelerator at CERN, consists of four components: the inner Solenoid, two End Cap Toroids and the Barrel Toroid (BT). The Barrel Toroid is composed by 8 separated superconducting coils, race-track shaped, 25 m long and 5 m large, each containing two superconducting windings referred as double pancakes. At the present time all the 8 coils have been completed and independently tested on surface under nominal conditions, and the final assembly of the toroid in the ATLAS cavern is in progress. The construction of double pancakes of unprecedented size has required a great effort in order to match the tight design dimensional tolerances and to obtain a good impregnation quality. In this paper we summarize the most relevant features of the manufacturing process of the double pancakes and the results of the measurements performed to guarantee the geometrical, impregnation and electrical quality. These data can be now considered as the "status of the art" for large size superconducting coils

On-Surface Test of the ATLAS Barrel Toroid Coils: Overview

The Barrel Toroid (BT) provides the magnetic field for the muon detectors in the ATLAS experiment at CERN. The Toroid is built up from eight superconducting coils. Each coil consists of two 25 m times 5 m racetrack shape double pancakes impregnated and pre-stressed inside an aluminum coil casing. The 42-tons cold mass is cooled by forced-flow liquid helium circulating in aluminum pipes glued to its surface. The coils are tested on surface prior to their underground installation. The test program has started in September 2004 and finished in June 2005. This paper describes the test set up and various commissioning tests performed at the ATLAS Magnet Test Facility. It includes the aspects of test preparation, vacuum pumping, leak testing, cooling down, powering and warming up. The 8 coils have passed the tests successfully and have been assembled into the Toroid in the ATLAS cavern. The testing completes the production of the so far largest racetrack coils in the world

Design, Manufacture, and Test of the ATLAS Magnet System Run Down Units

The ATLAS Experiment at the LHC (CERN) has a Magnet System composed by one Barrel Toroid (BT) and two End Cap Toroids (ECT's) powered in series at 20.5 kA with an overall stored energy of 1.5 GJ, and one Central Solenoid, operated at 7,600 A with a stored energy of 39 MJ. During the normal discharge the stored energy is dissipated inside external resistors and diodes (globally referred as Run Down Unit, RDU). Being critical for magnet safety the RDU was designed so as to operate also in case of severe fault conditions. This paper presents the details of the design and the tests performed to develop each component and to assess their behavior under normal and fault conditions. The final test for commissioning inside ATLAS underground cavern are in progress

Electromagnetic Behavior and Stress Analysis of BT Thermal Shields

The ATLAS detector is one of the huge detectors used on the future LHC at CERN. Its magnet system is composed of a barrel toroid (BT) and two end-cap toroids (ECT) inserted at the ends of the BT, of an inner solenoid and of an iron shield close to the inner bore of the BT. The coil cryogenic system is designed to cool down the thermal shields by helium gas at 80 K. In the event of any variation of the magnetic flux, eddy currents are induced in these shields. This paper presents the computations of eddy currents in the shields using a variational formulation of the problem in terms of the electric vector potential and a finite element method. The worst case - fast discharge into dump diodes and resistors - is presented in the electrical behavior section. The evolution of eddy currents is computed using this method. Finally, anchor points are determined in the mechanical analysis in order to minimize the mechanical stresses on the shields.

Heat Load Measurements on a Large Superconducting Magnet: An Application of a Void Fraction Meter

ATLAS is one of the two major experiments of the LHC project at CERN using cryogenics. The superconducting magnet system of ATLAS is composed of the barrel toroid (BT), two end caps toroids and the Central Solenoid. The BT is formed of 8 race-track superconducting dipoles, each one 25 m long and 5 m wide. A reduced scale prototype (named B0) of one of the 8 dipoles, about one third of the length, has been constructed and tested in a dedicated cryogenic facility at CERN. To simulate the final thermal and hydraulic operating conditions, the B0 was cooled by a forced flow of 4.5 K saturated liquid helium provided by a centrifugal pump of 80 g/s nominal capacity. Both static and dynamic heat loads, generated by the induced currents on the B0 casing during a slow dump or a ramp up, have been measured to verify the expected thermal budget of the entire BT. The instrument used for the heat load measurements was a void fraction meter (VFM) installed on the magnet return line. The instrument constructed at CERN was calibrated in order to provide direct readings of heat loads. An example of application of the VFM measuring method to a large-scale apparatus cooled at liquid helium temperature.

Production and qualification of 40 km of Al-stabilized NbTi cable for the ATLAS experiment at CERN

The production of the conductor for the superconducting toroids of the ATLAS experiment at LHC (CERN) is now in progress. The toroid system, composed of one barrel toroid (BT) and two end cap toroids (ECTs), exploits aluminum-clad Rutherford-type NbTi conductors of large size (57 /spl times/ 12 mm for BT, 42 /spl times/ 12 mm for ECTs) and high critical current (Ic) (58 kA for BT and 60 kA for ECTs @ 4.2 K, 5 T). Some 55 km of conductor are required for the BT and 26 km for the ECTs, respectively. An Italian-Swiss (ETH Zurich and INFN) consortium is in charge of the delivery of half of the whole amount. This paper describes the results of this production with particular emphasis to the quality control system developed to monitor the production with both on-line controls and the post-production quality assessment protocols. The main result is the confirmation that the technologies selected and the whole process are reliable and reproducible over large production quantities. The overall degradation due to the cabling and the co-extrusion, was rather moderate, 34% in total, and did not change significantly along the production. An ultrasonic system was developed to assess the quality of the bonding between the Rutherford and the aluminum matrix over the whole length, and its results were combined with the quantitative results from pull-out tests at the conductor's extremities: in all the cases the 20 MPa limit for the BT and 15 MPa for the ECTs, respectively was largely exceeded, and no relevant change was detected among the lengths.

Manufacturing aspects of the ATLAS barrel toroid double pancakes

In 1999 INFN (Istituto Nazionale di Fisica Nucleare) ordered to ANSALDO the manufacturing of 16 double pancakes for the ATLAS BARREL TOROID. In July 2001 four Double Pancakes have already been completed and shipped to the integration site. In this paper the main aspects of the manufacturing of the largest superconducting coils ever built (5/spl times/25 m) are described. The main phases of the manufacturing procedure are reviewed starting from the conductor preparation to the VPI impregnation, including references to the materials used as well as to the relevant customer's requirements. In particular the special winding form and the winding technique are treated. For each phase the most critical aspects and the relevant solutions are pointed out. Particular details about the technical solutions adopted for the impregnation and curing of the Double Pancake, which could not be performed inside an autoclave due to the huge dimension of the coil itself, are reported. Finally the methods used for the dimensional and electrical tests are described and the results obtained on the first double pancakes are analyzed.

Mechanical characterization of the tie rods for the ATLAS B0 model coil

The ATLAS Barrel Toroid (BT) consists of 8 superconducting coils of 25 m length and 5 m width. Each coil is equipped with eight titanium alloy tie rods acting as support for the magnetic forces, the intensity of which will be up to 180 t for the most loaded one. The B0 model coil is about 1/3 length scale of the BT, equipped with three tie rods. In order to simulate the behavior of the coil supports, a test facility has been built to test individual tie rods at cryogenic temperature. The initial aim was to verify the amount of stick and slip, the possibility of it occurring during the excitation and the flexion of the support at the anchoring point on the magnet. This was achieved by inducing in the support the same movements foreseen during the cool-down and the excitation of the magnet and loading with the same forces. Following the evolution of the project it was decided to test the tie rod simply in traction at 250 tons, without displacements. In this paper the test facility is described and the data of the tests of the B0 tie rods are reported.

The thermal and magnetic stress analyses of the ATLAS Barrel Toroid-B0 coil

The B0 coil is a test-model of the ATLAS Barrel Toroid (BT) coils. It has been installed in the test station at CERN. One important item of the B0 test is the strain/stress measurements. In order to determine the expected stress values at the strain gage locations on the coil casing and the tie rods, detailed thermal and magnetic stress analyses of the B0 coil have been carried out. The analysis results are prepared for a later one-to-one comparison with the measurement results.

The superconducting magnet system for the ATLAS detector at CERN

The ATLAS superconducting magnet system for the ATLAS detector in the LHC at CERN comprises a barrel toroid (BT), two end cap toroids and a central solenoid, with overall dimensions of 20-m diameter by 26-m length. Though this magnet system is used for a particle detector, its size, geometrical arrangement and coil technology is comparable to what is usual for fusion machines. The manufacturing has started in the industry and integration of the magnets will start in the year 2002. Assembly in the cavern will start at the end of the year 2003, starting with BT installation. In this paper, the magnet system is presented as well as the common infrastructure and services.

The ATLAS magnet test facility at CERN

The ATLAS magnet system consists of a barrel toroid (BT), two end-cap toroids (ECT) and a central solenoid (CS). The BT with overall dimensions of 20 m diameter by 26 m length is made of 8 coils placed in their individual cryostats and symmetrically assembled around the central axis. The ATLAS magnet test facility is being completed at CERN and will host in the next years to come pairs of BT coils at the same time as well as the ECT and the CS systems already fully assembled. Two model coils will be tested in the years 2000-2001, the B00 model coil and the B0 model coil, a 9 m short version of the BT coil built to verify the functionality and the construction concepts of the BT.

Mechanical measurements on the race-track prototype for the ATLAS B0 and barrel toroid magnet

The ATLAS Barrel Toroid (BT) consist of 8 superconducting coils 25 m long and 5 m large, In order to check the stability of the magnets and the technical solutions for the construction a scaled magnet, called B0, is under construction. A race-track coil 2.7 m long and 0.7 m large has been built, to verify the characteristic of the superconducting conductor. As a matter of fact this race-track magnet is the first multi-turn superconducting magnet, with indirect cooling, built with fully bonded aluminum coil. The mechanical deformations of the magnet during the energization and the induced quenches are monitored in 12 points. The overall transverse deformation of the magnet is measured by 6 strain gages placed on measuring clamps connecting the two arms of the magnets, 3 on the upper side, and 3 on the lower side of the magnet. The other sensors are placed on one arm, on the casing of the magnet: 5 on the external part and 1 in the inner part in order to see the bending of the arm. Removable reinforcing clamps are present between the arms. The mechanical measurements obtained with and without the reinforcing clamps are presented.

Progress on the conductor for the superconducting toroids of the ATLAS experiment

The production of the conductor for the superconducting toroids of the ATLAS experiment at LHC (CERN) is under way. The conductor is obtained by coextruding a big Rutherford cable with very pure aluminium. All toroids, one Barrel Toroid (BT) and two End Cap Toroids (ECT), require a conductor with a critical current of about 60 kA at 5 T, 4.2 K and a RRR in excess of 800 (at zero field), together with a very good bonding between cable and aluminum: 20 MPa for the BT and 15 MPa for the ECT. So far four long lengths, approximately 7 km out of the 90 km of the total need, have been successfully produced, thus demonstrating the feasibility of the process. The paper describes the results of the R&D phases and the results obtained in this first production. The critical current degradation due to cabling and coextrusion was found quite moderate (7-8% in total), despite the low copper content of the strands (Cu:NbTi=1.09-1.18). The bonding was also very good with values well in excess of the specification. A special control system based on continuous ultrasonic inspection was used in the coextrusion line to monitor the bonding quality in real time during production.

The ATLAS magnets test facility at CERN

The magnet system for the ATLAS detector at CERN consists of a Barrel Toroid (BT), two End-Cap Toroids (ECT) and a Central Solenoid (CS). The overall dimensions of the system are 20 m in diameter by 26 m in length. Before underground installation all coils will be tested on surface in a magnet test facility which is under construction. Moreover two model coils are tested as well as subsystems. In this paper the design and construction of the test facility is presented.