New method to design electron beam shaping passive devices

Electrons accelerated to an energy between a few and several MeV find numerous applications in industry, medicine and research. Beam shaping passive devices are used in many of those applications in order to get an uniform distribution of the beam-deposited dose across a large area. Such devices are conceptually simple and have been in use for several decades, nevertheless designing them is still a time-consuming, often painful job. The so-far used engineering methods are based on severely simplified analytical models of beam-device interaction and reveal more and more limitations in view of ever growing requirements. Two negative consequences follow: it takes significant resources to construct a properly working device, and it is practically impossible to tell if the obtained final result is really optimal in some given conditions.

A new method to make engineering calculations of beam shaping devices has been developed by the speaker and will be presented during the seminar. The method uses Monte Carlo techniques applied at some realistic assumptions. Not restricted by many weaknesses of the previously applied methods it makes possible to quite quickly optimize the circuit under development. Multi-dimensional optimizations are possible, and the engineer may knowledgably take into account many requirements, which frequently contradict each other to some extent. The method is also capable to directly show how actual values of key beam parameters (dose distribution uniformity, transmission, loss of energy, beam contamination with X-rays etc.) are far away from optimal values; other so-far used methods do not offer that capability.

The new method is much more computing-intensive than other so-far used methods. However, computing power of modern computers (e.g. the CIS cluster in Świerk) is so high, and modern Monte Carlo software libraries (e.g. Geant4) are so rich that this obstacle is more and more easy to overcome. An example of application of the new method to compute beam shaping devices for an accelerator currently under development in NCBJ Division of Nuclear Equipment for Wroclaw Technology Park Non-destructive Testing Lab will be presented.

Detailed discussion of topics presented during the seminar may be found in the following recently published papers:

• P. Adrich, Nucl. Instrum. Methods Phys. Res. A 817 (2016) 93-99,
• P. Adrich, Nucl. Instrum. Methods Phys. Res. A 817 (2016) 100-108,
• P. Adrich et al., Acta Phys. Pol. B 47 (2016) 267-277.

All interested persons are invited

Dr. Agnieszka Syntfeld-Każuch, Dr. Jacek Rzadkiewicz, Associate Professor Sławomir Wronka