S. Mizumaki

Progress in ATLAS central solenoid magnet

The ATLAS central solenoid magnet is being developed to provide a magnetic field of 2 Tesla in the central tracking volume of the ATLAS detector under construction at the CERN/LHC project. The solenoid coil design features high-strength aluminum stabilized superconductor to make the coil thinnest while maintaining its stability and the pure-aluminum strip technique for quench protection and safety. The solenoid coil is installed in a common cryostat with the LAr calorimeter in order to minimize the cryostat wall. A transparency of 0.66 radiation length is achieved with these integrated efforts. The progress in the solenoid coil fabrication is reported.

Development of a thin-wall superconducting magnet for the positron spectrometer in the MEG experiment

A thin-wall superconducting magnet was developed for the positron spectrometer in the MEG experiment. The magnet is specially designed to provide a gradient magnetic field to achieve good features of the spectrometer such as constant projected bending radius for monochromatic positrons and much quicker sweep of positrons than in the conventional uniform solenoidal field, which allows a stable operation of the spectrometer in a high rate muon beam. A high-strength aluminum-stabilized conductor was developed so as to minimize the thickness of the coil between the target and photon detector. A pair of compensation coils is implemented in the magnet to cancel stray field around the photon detector to be placed closely to the magnet. Design of the magnet and results from the excitation tests to measure performance of the magnet will be presented here.

Ultimate Performance of the ATLAS Superconducting Solenoid

A 2 tesla, 7730 ampere, 39 MJ, 45 mm thin superconducting solenoid with a 2.3 meters warm bore and 5.3 meters length, is installed in the center of the ATLAS detector and successfully commissioned. The solenoid shares its cryostat with one of the detectors calorimeters and provides the magnetic field required for the inner detectors to accurately track collision products from the LHC at CERN. After several years of a stepwise construction and test program, the solenoid integration 100 meters underground in the ATLAS cavern is completed. Following the on-surface acceptance test, the solenoid is now operated with its final cryogenic, powering and control system. A re-validation of all essential operating parameters is completed. The performance and test results of underground operation are reported and compared to those previously measured.

Quench protection and safety of the ATLAS central solenoid

Fabrication of the ATLAS central solenoid was completed and the performance test has been carried out. The solenoid was successfully charged up to 8.4 kA, which is 10% higher than the normal operational current of 7.6 kA. Two methods for quench protection, pure aluminum strips accelerating quench propagation and quench protection heaters distributing normal zones, are applied in order to safely dissipate the stored energy. In this paper, quench characteristics and protection methods of the ATLAS central solenoid are described.

ATLAS superconducting solenoid on-surface test

The ATLAS detector is presently under construction as one of the five LHC experiment set-ups. It relies on a sophisticated magnet system for the momentum measurement of charged particle tracks. The superconducting solenoid is at the center of the detector, the magnet system part nearest to the proton-proton collision point. It is designed for a 2 Tesla strong axial magnetic field at the collision point, while its thin-walled construction of 0.66 radiation lengths avoids degradation of energy measurements in the outer calorimeters. The solenoid and calorimeter have been integrated in their common cryostat, cooled down and tested on-surface. We review the on-surface set-up and report the performance test results.

The BESS-Polar Ultra-Thin Superconducting Solenoid Magnet and Its Operational Characteristics During Long-Duration Scientific Ballooning Over Antarctica

An ultra-thin superconducting solenoid has been developed for a cosmic-ray spectrometer ballooning over Antarctica, which is named BESS-Polar II. The coil with a diameter of 0.9 m, a length of 1.4 m and a thickness of 3.5 mm, is wound with high-strength aluminum stabilized superconductor and provides 0.8 T in the spectrometer. Based on the experience at the BESS-Polar-I solenoid flight for nine days in 2004, the BESS-Polar-II solenoid, which was cryogenically improved, realized a persistent current mode operation for 25 days in the second flight campaign in December 2007 though January 2008. It has contributed to accumulate the cosmic-ray observation data with 4700 million events and 16 terabyte in a hard disk unit. This report will describe the second solenoid performance during the flight.

Quench Characteristics of the ATLAS Central Solenoid

A thin superconducting solenoid has been constructed for ATLAS, one of the four LHC experiments at CERN. The single layer coil wound with an Al stabilized NbTi superconductor, with overall dimensions of 5.3 m length and 2.6 m diameter and operating at 7.6 kA provides the 2 T magnetic field for the inner detector. The coil was successfully tested at the company before shipment and re-tested at CERN on surface in its final configuration before commencing the installation in the ATLAS cavern 100 m underground. The tests include an extensive study of the quench evolution and in particular the normal zone propagation through the coil windings and in the superconducting bus-lines. A special feature of this coil is the use of aluminum quench propagation strips glued to the windings inner surface. This design enhances the turn-to-turn normal zone propagation velocity, reaching up to 0.8 m/s, and limits the hot spot temperature to 110 K. Along the conductor, normal zone propagation reaches velocities up to 14 m/s at nominal current

On-surface integration and test of the ATLAS central solenoid and its proximity cryogenics

The ATLAS detector for the LHC at CERN requires a superconducting solenoid, which provides the magnetic field for the inner detector. The ATLAS central solenoid and its associated proximity cryogenics system has been designed by KEK in collaboration with CERN. Following construction and preliminary tests at Toshiba in Japan the equipment has been shipped to CERN. The system is being prepared for the integration in the common cryostat with the LAr calorimeter, whereafter a full on-surface test has to be completed before its final installation 100 m underground in the ATLAS cavern. For this purpose a provisional set-up for commissioning of the final proximity cryogenics, the connecting chimney and the solenoid has been established. A number of tests and simulations have been conducted in applying a new process control system to validate the cryogenics functionalities, the electrical powering scheme as well as the magnet control and safety systems. The present status of the solenoid project and the results of the various cryogenic and electrical tests are reported.

Mechanical characteristics of a coil support system for the ATLAS central superconducting solenoid magnet

Mechanical characteristics of the support system for the ATLAS (A Toroidal LHC Apparatus) central superconducting solenoid magnet have been investigated. The coil support system was designed with a unique triangular-shape configuration made of GFRP and with spherical bearings at the joints. A mechanical performance test has been carried out to simulate various operational conditions. This paper describes the mechanical design and test results.

The chimney and superconducting bus lines for the ATLAS central solenoid

A thin superconducting solenoid magnet for the ATLAS detector in the CERN-LHC project is under construction as a cooperative work between KEK and CERN. A control dewar at the top of the detector is connected with a coil through a long chimney placed in the gap of the outer detectors and toroidal magnets. A set of superconducting bus lines and cooling tubes is arranged in the chimney. The fabrication of the chimney and the control dewar has been completed and the performance test was carried out. The current leads in the control dewar and the superconducting bus lines in the chimney were successfully tested with a current of 10 kA including 2 kA contingency. Quench characteristics of the bus was measured and also analyzed. A superconducting quench detector worked well to pick up quenches.