Electromagnetic modeling package speeds design of active electron optic X-ray tubes for Philips Medical Systems

The three-dimensional version of Vector Fields’ specialized electromagnetic modeling algorithm for charged particle beams is playing a key role in the development cycle of Philips Medical Systems’ first commercial X-ray imaging systems with ‘active optics’. Active beam technology supports dynamic focusing and positioning of the electron beam during investigation procedures, greatly improving the resolution and quality of imaging in CT (computer tomography) and cardiovascular scanning equipment.

Vector Fields’ solver for charged particle beams – which runs as part of the Opera toolsuite – has helped Philips Medical Systems to overcome the enormous design challenge of actively focusing an X-ray tube, which is subject to complex space-charge effects. Space charge impacts emission efficiency and distorts beam trajectory, and its effects are exacerbated as emission current increases – which itself is highly desirable in X-ray equipment for both speed of operation and the ability to image denser material.

x-ray tube filament beam trajectories

Beam trajectories from an X-ray tube filament calculated by Opera, with 2D and 3D plots of the intensity distribution of the focal spot

Vector Fields’ Opera electromagnetic modeling suite is being used by Philips to help design the emitting elements and an ‘electromagnetic lens’ beam focusing system. The software has been particularly useful in understanding focusing at higher beam current levels, as distortion from the space charge effect is non linear and very hard to predict. The software allows users to model performance using a combination of emission effects including the Langmuir-Fry current limits.

“The active optics design problem has a lot of variables, and it would be extremely difficult to bring a system to market without the aid of an accurate modeling tool,” notes Dr Wolfram Maring of Philips Medical Systems. “Opera’s 3D charged particle beam solver has saved a great deal of development time and cost. It’s helped us prove our basic active optics concept, and eliminated several prototype iterations of the focusing system – keeping this major investment project on track.”

This is the second major project where Philips has had the benefit of the 3D version of the particle beam solver. Before receiving this iteration of the software from Vector Fields, engineers typically had to fabricate one or two more physical prototypes than they do today, as the 2D package they had previously used could not simulate all of the characteristics of the final X-ray tube design. Opera also makes it easy to study layout tolerances, helping Philips to investigate lifecycle aftercare issues for the new product.

Philips Medical Systems is a long-standing user of Opera, and the company’s support has played a key role in the development of the charged particle beam solver. This solver uses finite element techniques to analyse the electromagnetic fields coupled with the space charge effects on high current (charged particle) beams. The software supports the import of models created by standard CAD systems for easy and fast modeling.

Space charge is a net electrical charge in a region of space. A negative space charge often occurs near a metal object in a low electrical field when heated to incandescence in a vacuum. The effect was first observed by Thomas Edison in light bulb filaments, where it is sometimes called the Edison Effect. Opera users can calculate the current emitted by thermionic cathodes. Simulation of the electromagnetic effects in particle beam trajectories, space charge distribution and electrostatic field stress, then provides detailed information and visualization of the system, giving the basis for design improvements.