In an accelerator magnet, magnetic fields are used to steer and focus charged particle beams. What tools does Opera have to rapidly assess field quality? And can I see how the particle beams behave?
Opera’s post-processor includes tools for characterizing field homogeneity or gradients in free-space volumes. For dipole, quadrupole and higher order multi-pole magnets, characteristics are usually calcu-lated as a set of Fourier coefficients on a circle or part circle. Similar functions are also available to display field homogene¬ity on spherical surfaces. Field values can be calculated at any point and Opera can directly track individual charged particles or systems of particles through or beyond the magnetic aperture. Results can be displayed in various ways, including: • 3D track lines through the geometry • projections onto the major coordinate planes • intersection points on any 2d plane • current or power density maps
Can Opera model pulsed magnets, especially the redistribution of currents in the conductors? And how does it deal with laminations?
Opera can perform transient simulations with a user-defined pulse for either the current in, or the voltage across the winding. The simulation is able to capture skin-effects and proximity effects. For magnets built using laminations, Opera has a material model that can treat a bulk volume – such as the magnet yoke - as a “packed” structure, thereby removing the need to model the individual laminations. The designer only needs to specify the packing factor of the lamination stack and the orientation of the plane of the laminations.
What physics can Opera capture in the superconducting windings of my magnet?
In most cases superconducting magnets can be accurately represented using stand¬ard coil models. However, Opera includes comprehensive facilities for modelling the detailed physics of superconductors when it is necessary to do so, for exam¬ple shielding produced by super-currents under Meissner effect conditions, or the hysteretic behaviour as a magnet current is ramped up and down. Opera’s most sophisticated model for superconducting windings is to simulate a quench. The Opera-3d quench simulator solves the time-transient coupled thermal and electromagnetic equations. The tool is able to model complete coils connected to supply/protection circuits and evaluate the effectiveness of the protection. Simulations can include heating from eddy currents in formers and support structures. Whilst Opera can simulate quench in a complete coil or system of coils, it can also model individual superconducting wires of both LT and HT superconductors.
How accurate is Opera for simulating NMR/MRI magnets?
Superconducting NMR/MRI magnets are usually represented by a proprietary coil model that is capable of producing highly accurate results for field homogeneity in the imaging region, measured in parts per million. This level of accuracy is essential for this application which relies on magnetically sensitive high-Q NMR resonances. Opera’s track-record for achieving such high accuracy has made it the premier simulation software for designing superconducting NMR/MRI magnets worldwide.
I’m designing superconducting solenoid MRI magnets and need to assess the small effect of the shielded room and the steel reinforcing on the magnet’s homogeneity?
The formulation used in Opera-3d’s magnetostatic solver (previously known as TOSCA) allows the field from this type of perturbation problem to be computed very accurately. The field from unshielded solenoids can be calculated using the Biot-Savart expression to one part in 100 million. The shield and the reinforcing structure will make a small perturbation to the central field, usually in the order of one part in one thousand which is well within the accuracy of Opera.
Can I assess how effective the shielding is for my proposed MRI facility?
Yes, Opera computes relatively small residual fields in shielded space very accurately, even if fields elsewhere in the model are much higher. Isosurfaces can be easily displayed in the Post-processor, allowing a 3D visualisation of the 5 Gauss limit.