Effect of Multiple Scattering on the Compton Recoil Current Generated in an EMP, Revisited

• Published in: IEEE transactions on nuclear science Vol. 62; no. 4; pp. 1695 - 1706
• Main Authors: Farmer, William A., Friedman, Alex
• Format: Journal Article
• Language: English
• Published: United States IEEE 01.08.2015
• Subjects: CLASSICAL AND QUANTUMM MECHANICS, GENERAL PHYSICS; Computational modeling; Conductivity; Current density; EM analysis; EMP radiation effects; high altitude electromagnetic pulse (HEMP); Mathematical model; MILITARY TECHNOLOGY, WEAPONRY, AND NATIONAL DEFENSE; Monte Carlo methods; nuclear explosions; Observers; radiative interference; Scattering
• ISSN: 0018-9499; 1558-1578
• DOI: 10.1109/TNS.2015.2431683

Multiple scattering has historically been treated in EMP modeling through the obliquity factor. The validity of this approach is examined here. A simplified model problem, which correctly captures cyclotron motion, Doppler shifting due to the electron motion, and multiple scattering is first considered. The simplified problem is solved three ways: the obliquity factor, Monte-Carlo, and Fokker-Planck finite-difference. Because of the Doppler effect, skewness occurs in the distribution. It is demonstrated that the obliquity factor does not correctly capture this skewness, but the Monte-Carlo and Fokker-Planck finite-difference approaches do. The obliquity factor and Fokker-Planck finite-difference approaches are then compared in a fuller treatment, which includes the initial Klein-Nishina distribution of the electrons, and the momentum dependence of both drag and scattering. It is found that, in general, the obliquity factor is adequate for most situations. However, as the gamma energy increases and the Klein-Nishina becomes more peaked in the forward direction, skewness in the distribution causes greater disagreement between the obliquity factor and a more accurate model of multiple scattering.