L. L. Ma

Properties and performance of two wide field of view Cherenkov/fluorescence telescope array prototypes

A wide field of view Cherenkov/fluorescence telescope array is one of the main components of the Large High Altitude Air Shower Observatory project. To serve as Cherenkov and fluorescence detectors, a flexible and mobile design is adopted for easy reconfiguring of the telescope array. Two prototype telescopes have been constructed and successfully run at the site of the ARGO-YBJ experiment in Tibet. The features and performance of the telescopes are presented

Argo-ybj Observation of the Large-scale Cosmic ray Anisotropy During the Solar Minimum Between Cycles 23 and 24

This paper reports on the measurement of the large-scale anisotropy in the distribution of cosmic-ray arrival directions using the data collected by the air shower detector ARGO-YBJ from 2008 January to 2009 December, during the minimum of solar activity between cycles 23 and 24. In this period, more than 2 × 10 11 showers were recorded with energies between ∼1 and 30 TeV. The observed two-dimensional distribution of cosmic rays is characterized by two wide regions of excess and deficit, respectively, both of relative intensity ∼10 −3 with respect to a uniform flux, superimposed on smaller size structures. The harmonic analysis shows that the large-scale cosmic-ray relative intensity as a function of R.A. can be described by the first and second terms of a Fouries series. The high event statistics allow the study of the energy dependence of the anistropy, showing that the amplitude increases with energy, with a maximum intensity at ∼10 TeV, and then decreases while the phase slowly shifts toward lower values of R.A. with increasing energy. The ARGO-YBJ data provide accurate observations over more than a decade of energy around this feature of the anisotropy spectrum.

Prototype of the Superferric Dipoles for the Super-FRS of the FAIR-Project

The FAIR China Group (FCG), consisting of the Institute of Modern Physics (IMP Lanzhou), the Institute of Plasma Physics (ASIPP, Hefei) and the Institute of Electric Engineering (IEE, Beijing) developed and manufactured in cooperation with GSI, Germany a prototype of a superferric dipole for the Super-Fragment-Separator of the FAIR-project. The dipole magnets of the separator will have a deflection radius of 12.5 m, a field up to 1.6 T, a gap of at least 170 mm and an effective length of more than 2 meters to bend ion beams with a rigidity from 2 T · m up to 20 T · m. The magnets operate at DC mode. These requirements led to a superferric design with a yoke weight of more than 50 tons and a maximum stored energy of more than 400 kJ. The principles of yoke, coil and cryostat construction will be presented. We will also show first results of tests and measurements realized at ASIPP and at IMP.

Strain-based quench detection for a solenoid superconducting magnet

In this paper, we present a non-electric quench detection method based on the strain gauge measurement of a superconducting solenoid magnet at cryogenic temperature under an intense magnetic field. Unlike the traditional voltage measurement of quench detection, the strain-based detection method utilizes low-temperature strain gauges, which evidently reduce electromagnetic noise and breakdown, to measure the magneto/thermo-mechanical behavior of the superconducting magnet during excitation. The magnet excitation, quench tests and trainings were performed on a prototype 5 T superconducting solenoid magnet. The transient strains and their abrupt changes were compared with the current, magnetic field and temperature signals collected during excitation and quench tests to indicate that the strain gauge measurements can detect the quench feature of the superconducting magnet. The proposed method is expected to be able to detect the quench of a superconducting coil independently or utilized together with other electrical methods. In addition, the axial quench propagation velocity of the solenoid is evaluated by the quench time lags among different localized strains. The propagation velocity is enhanced after repeated quench trainings.

A 3 Tesla Superconducting Magnet for Hall Sensor Calibration

A 3 T superconducting magnet with a 70 mm diameter warm bore and energy storage of 47 kJ has been successfully fabricated and tested, which can be used to calibrate Hall sensors in high magnetic field as well as conduct superconducting experiments. The magnet consists of three solenoid coils and an iron yoke. The homogeneity of the magnetic field in the region of interest (ROI) is . The coils of the magnet were fabricated with NbTi-Cu superconducting wire and the stray magnetic field is shielded by an iron yoke. The coils and yoke are fully immersed in a helium vessel. The optimized structural design, stress and quench simulation, fabrication and test results are presented in this paper.

Magneto-Mechanical Coupling Analysis of a Superconducting Solenoid Magnet in Self-Magnetic Field

For high-precision scientific instruments, the accuracy and sensitivity of the magnet system and the quality of field generated strongly depend upon the disturbance of structures. Since the superconducting structural devices with high transport current are often exposed to large Lorentz forces, which lead to the unavoidable deformation inside superconducting coils, the deformation and configuration change will affect the accurate operation of the magnet system and even its stability. For simplicity, the linear theory is commonly utilized for the stress/strain evaluation of the superconducting coils arising from electromagnetic forces. The aim of the present work is to formulate the equations governing the magneto-mechanical characteristics of a superconducting solenoid system. Due to the axisymmetry, 2-D numerical modeling for the superconducting solenoid is performed to calculate the hoop stress/strain and magnetic field. Maxwells equations and the equilibrium equations for mechanical deformation have been simultaneously solved by means of coupled finite element method. The numerical results have good agreement with the experimental observations and show the magneto-mechanical coupling of the solenoid superconducting magnet in the self-magnetic field is remarkable especially for a high field or large transport current in the coils.

Design of a superconducting magnet for CADS

This paper describes a superconducting magnet system for the China Accelerator Driven System (CADS). The magnetic field is provided by one main, two bucking and four racetrack coils. The main coil produces a central field of up to 7 T and the effective length is more than 140 mm, the two bucking coils can shield most of the fringe field, and the four racetrack superconducting coils produce the steering magnetic field. Its leakage field in the cavity zone is about 5 × 10−5 T when the shielding material Niobium and cryogenic permalloy are used as the Meissner shielding and passive shielding respectively. The quench calculations and protection system are also discussed.

Quench Protection Design and Simulation of a 7 Tesla Superconducting Magnet

A 7 Tesla superconducting magnet with a clear warm bore of 156 mm in diameter has been developed for Lanzhou Penning Trap at the Institute of Modern Physics for high precision mass measurement. The magnet is comprised of 9 solenoid coils and operates in persistent mode with a total energy of 2.3 MJ. Due to the considerable amount of energy stored during persistent mode operation, the quench protection system is very important when designing and operating the magnet. A passive protection system based on a subdivided scheme is adopted to protect the superconducting magnet from damage caused by quenching. Cold diodes and resistors are put across the subdivision to reduce both the voltage and temperature hot spots. Computational simulations have been carried in Opera-quench. The designed quench protection circuit and the finite element method model for quench simulations are described; the time changing of temperature, voltage and current decay during the quench process is also analysed.

The Main Dipole Magnets Design and Test of HIMM Project

In the project of Heavy Ion Medical Machine, there are eight dipole magnets in the synchrotron and ten dipole magnets in the high-energy beam line used for beam bending. Both types of dipole magnets have the same bending radius and bending angle, but the gaps are different. The maximum magnetic field of synchrotron dipole is 1.66 T, and the high beam line dipole is 1.6 T. The magnetic field calculation and the structure design are presented in this paper; the trim slot in the pole and the removable pole ends are used in order to reach the required field homogeneity. The magnetic field measurement results, which include field homogeneity and reproducibility, are also shown in details. The test results show that the dipole magnet design could satisfy the major specified physical requirements.

A Criterion of the Strain-Based Quench Decision for a Low-Temperature Superconducting Solenoid

It is important to pursue an efficacious way of detecting the quench in superconducting magnets as soon as possible so that the large magnetic energy stored in the magnets can be discharged duly. By means of strain measurement during the spontaneous quench, we recently proposed a quench-detection method for low-temperature superconducting solenoid magnets. By examining the leap character of strain-rate recorded, we further extended the strain-based quench-detection method. An appropriate criterion for the spontaneous quench was suggested and utilized for two liquid helium-cooled superconducting solenoids with different sizes and coil configurations. It was shown that the proposed method is capable of providing a safe criterion for the quench detection/protection within a short period of time, and it is a simple process comparing with the rate of quench development. The experimental data from the two different solenoids under excitation and quench tests supported the new strain-based detection method.