Positive topological entropy for multi-bump magnetic fields
  We study the dynamics of a charged particle in a planar magnetic field which consists of $n\geq 2$ disjoint localized peaks. We show that, under mild geometric conditions, this system is semi-conjugated to the full shift on $n$ symbols and, hence, carries positive topological entropy. 
Andreas Knauf, Frank Schulz, Karl Friedrich Siburg
math.DS math-ph math.MP