PPT-Numerical Analysis of Gradient-Induced Eddy Current in a Superconducting MRI Magnet

Institute of Electrical Engineering Chinese Academy of Sciences Beijing 100190 China College of Electrical and Information Engineering Hunan University Changsha 410082 China Chaoqun Niu. . Caspi. and Lucas . Brouwer. *. Lawrence Berkeley National Laboratory, Berkeley, CA. USA. December 11. th. 2012. The . Canted-Cosine-Theta Dipole . (CCT). For LBNL High Field Magnet Program. * . PhD student UC Berkeley. mechanical vibrations in superconducting magnets for quench detection and diagnostics. M. . Marchevsky. ,. Lawrence Berkeley National Laboratory. Credits: . P. . Roy, X. Wang, G. . Sabbi. , S. . Prestemon. . Lenz's law . Induced current produces a secondary magnetic field that is always opposed to the primary magnetic field that induced it, an effect called . Lenz’s law. .. Self-inductance (L). The alternating current in the coil generates an alternating magnetic field that induces an . pp 793 - 820. Essential Questions. How can current be produced without a power source?. How do motors work?. How is mechanical energy converted to electrical energy?. Objective(s. ): We will . be able to…. Santosh Kumar Sahu. INTER UNIVERSITY ACCELERATOR CENTER, INDIA. C. ryogenics & Applied . S. uperconductivity Lab. CONTENTS. Short description of Superconducting Quadrupole magnet cryostat at IUAC.. magnetism. Faraday’s Law of Electromagnetic Induction. induced currents. electric generator. eddy currents. Electromagnetic Waves (Maxwell & Hertz). 1. Basic facts of Magnetism. Oersted. . discovered that a compass needle responded to the a current in a loop of wire. EDDY CURRENTS SEPARATOR. Eddy . currents. are . an. . electrical. . phenomenon. . that. . occurs. . when. a conductor . goes. . through. a variable . magnetic. . field. . . This. . relative. Eddy current inspection is one of several NDT methods that use the principal of “electromagnetism” as the basis for conducting examinations. .. Eddy currents are created through a process called electromagnetic induction. When alternating current is applied to the conductor, such as copper wire, a magnetic field develops in and around the conductor. This magnetic field expands as the alternating current rises to maximum and collapses as the current is reduced to zero. If another electrical conductor is brought into the close proximity to this changing magnetic field, current will be induced in this second conductor. Eddy currents are induced electrical currents that flow in a circular path. They get their name from “eddies” that are formed when a liquid or gas flows in a circular path around obstacles when conditions are right.. magnetism. Faraday’s Law of Electromagnetic Induction. induced currents. electric generator. eddy currents. Electromagnetic Waves (Maxwell & Hertz). 1. Basic facts of Magnetism. Oersted. . discovered that a compass needle responded to the a current in a loop of wire. Quench Propagation and Protection. Herman ten Kate. CERN Accelerator School on Superconductivity for Accelerators, . Erice. 2013. . 3. Quench Protection, what for?. Superconducting coil running at 2 or 4 K, what can go wrong ?. . Gijs de Rijk. CERN. 10. th. April 2019. Magnet types: field. 1.5 - 2T resistive (Cu or Al coils, steel yoke, all warm), ramp rates 10 . th. T/s, ~40kCHF/m. 2 - 3 T . Superferric. (Superconducting, . Magnetic Field. While MRI is considered to be a safe imaging technique, it is not without hazards. The magnet field will attract many ferromagnetic metals in an uncontrolled fashion and cause them to fly towards the magnets bore and turning them into high velocity projectiles. The bore of the magnet is where the fringe field is strongest, as all the lines of force are constricted and their relative strengths heightened. Various objects can be considered projectiles. is connected to an ammeter. A . primary coil. is connected . to a . battery. A current can be produced by a . changing magnetic field. First shown in an experiment by Michael Faraday. Faraday’s Experiment. Quadrupole. Dipole magnets. A dipole magnet gives a constant B-field.. The field lines in a magnet run from North to South. . The field shown at right is positive in the vertical direction.. Symbol convention:.