title: Exponential energy growth in a Fermi accelerator.
abstract: An unbounded energy growth of particles bouncing off two-dimensional (2D) smoothly oscillating polygons is observed. Notably, such billiards have zero Lyapunov exponents in the static case. For a special 2D polygon geometry--a rectangle with a vertically oscillating horizontal bar--we show that this energy growth is not only unbounded but also exponential in time. For the energy averaged over an ensemble of initial conditions, we derive an a priori expression for the rate of the exponential growth as a function of the geometry and the ensemble type. We demonstrate numerically that the ensemble averaged energy indeed grows exponentially, at a close to the analytically predicted rate-namely, the process is controllable.
authors.affiliation: Faculty of Mathematics and Computer Science, Weizmann Institute of Science, PO Box 26, Rehovot 76100, Israel. kushal.shah@weizmann.ac.il
authors.forename: Kushal
authors.initials: K
authors.lastname: Shah
authors.forename: Dmitry
authors.initials: D
authors.lastname: Turaev
authors.forename: Vered
authors.initials: V
authors.lastname: Rom-Kedar