TechnoSoft

The Opera electromagnetic simulation software from Cobham Technical Services is helping scientists at CERN to design the magnets needed for the forthcoming upgrade of the Large Hadron Collider (LHC) in preparation for its high luminosity operation.

Both the two-dimensional (2d) and three-dimensional (3d) versions of Opera are being used to model a wide variety of the LHC injectors’ normal conducting (NC) electromagnets and permanent magnets, starting with the magnets of the new 160 MeV H- linear accelerator and including upgrades of the magnets used in the transfer lines and other accelerators on the way to the LHC.

Several tens of different magnet types and variants are presently being analysed using Opera-2d; these are then re-modelled in Opera-3d. By accurately simulating end effects, the Opera-3d tool facilitates design of more efficient magnets and allows local effects such as saturation and field harmonics due to non-planar symmetry to be taken into account early-on in the design process.

CERN’s Technology Department is also using Opera to design NC particle accelerator magnets for numerous other projects, including, for example, the ELENA (Extra Low Energy Antiproton) ring and the HIE-ISOLDE (HIgh Energy Isotope mass Separator On-Line) facility.

According to Daniel Schoerling, Project Engineer for NC magnets in CERN’s Technology Department, “With most of our magnet designs, we require very high prediction accuracy of the magnetic field quality in the good field region, typically of the order of 1/10,000 or better. Over the years we have gained confidence in Opera’s magnetostatic simulation performance for solid and laminated yoke magnets, supported by the effective correlation between simulation results and magnetic measurements obtained from manufactured units. When we observe differences higher than a few parts in 10000 we can usually attribute them to factors such as mechanical error or uncertainty of the BH curve of the material used for the magnet’s manufacture. In fact, because of the accuracy of the software’s magnetic length and field quality predictions, with many of our magnet designs we no longer need to incorporate any means of performing post-production field quality correction."

The core finite element analysis technology behind Opera was developed originally to support the design of particle accelerator magnets, starting with a project in the 1970s by scientists at the UK’s Rutherford Appleton Laboratory. At that time, the software required a mainframe computer and was intended principally to help solve design problems with the move towards superconducting magnets for higher energy particle accelerators. Today, the software addresses multiple types of physics – including electromagnetic, thermal and stress – and offers 2d and 3d design, simulation, analysis and optimisation facilities to anyone with access to a standard PC. Used by universities, engineering companies and research organisations worldwide, it is also the design tool of choice of CERN’s Technology Department for all normal-conducting (NC) magnets.

Faster simulation software for analysing charged particle devices has been released by the electromagnetic design tool supplier Cobham Technical Services. The new parallel processing software accelerates one of the major electromagnetic simulation solver options for Cobham’s renowned Opera-3d suite of electromagnetic and multi-physics design tools – which use finite element (FE) analysis to compute the physical interaction of charged particles with electrostatic or magnetostatic fields. The effects of space charge, self-magnetic fields and relativistic particle flow are included in the analysis.

Developed from the sequential processing version of Opera's space charge solver, also known as SCALA, the newly parallelised 3D Space Charge module uses code that is optimised for the shared memory architecture of standard PCs and workstations with multi-core processors. Although the speed benefit of parallel processing depends on model complexity, highly iterative and computationally-intensive analysis tasks can be greatly accelerated by the technique. By parallelising the solve process, including the existing efficient particle tracking algorithms, the parallel processing version of the 3D Space Charge module can shorten simulation run-times significantly.

Cobham's 3D Space Charge module will be of particular interest to engineers and scientists seeking to reduce the development costs and programme timescales of devices such as electron or ion guns. Application areas include X-ray machines, electron microscopes, field emission displays, mass spectrometers, electron beam lithography equipment, ion-beam sources and magnetron sputter coaters.

The space charge solver fully integrates with Opera-3d’s Modeller and Post-Processor, giving access to Opera’s full range of model creation and results analysis tools. Models of complex geometry emitters can be constructed easily and accurately within the 3D Modeller, or imported from CAD systems via industry-standard interfaces such as STEP and IGES, and proprietary formats such as SAT (Standard ACIS Text) and Pro/Engineer. In preparation for FE analysis, the Modeller performs mesh generation, using tetrahedral, prismatic or hexahedral elements, or a user-defined mix of two or more element types. In addition to the use of parallel processing, further increases in simulation speed can be gained by the Space Charge module’s ability to exploit model symmetry.

Opera’s Space Charge module incorporates a comprehensive set of surface and volume emission models. These include a range of formulations for thermionic and field effect surface emission, secondary emission from surfaces and from within volumes, and magnetised plasma emission – the last of these being a specialised plasma emission module designed for the efficient analysis of magnetron sputter coating systems. In addition, user-defined emission models are supported, allowing, for example, measured emission data to be used. Multiple emission models and particle species can be accommodated by a single model, allowing systems of essentially arbitrary complexity to be simulated.

The method used in Opera’s Space Charge solver calculates emission and the subsequent trajectories of particles in the presence of electric and applied magnetic fields. The charged particles themselves contribute to the space charge, and so affect the electric field; this is accounted for self-consistently by iterating the trajectory and field solutions until convergence is reached. Additionally, dielectric materials, if present in the model, can become charged by particle incidence, and produce leakage current flow. These further influence the particle trajectories and can also be included in the simulation. Although the effect of the modified space charge is often the dominant factor in determining particle trajectories, in high intensity beams the self-magnetic field generated by the beam current can also be important, and can optionally be included in the simulation.

The comprehensive and powerful post processing facilities available in the Opera-3d Post-Processor enable a designer to extract the maximum information from an analysis. 3D visualisation allows models and the analysis results to be viewed from any perspective, together with full colour field overlays and contour maps. Particle trajectories may be displayed, colour-coded by metrics such as energy, current or time-of-flight. Intersections of the trajectories with model surfaces may be determined and processed to give, for example, the distributions of beam and deposited current and power density.

The Space Charge solver is compatible with Opera-3d’s powerful multi-physics capabilities, which support simulations that involve more than one physical effect. For example, the temperature rise caused by particles bombarding a surface can be computed, together with the resultant deformation and stress induced by thermal expansion. The deformed structure can subsequently be analysed to determine the effect on the electromagnetic solution – the cycle continuing until a converged solution is reached.