On the symmetry of cylindrical implosions driven by a rotating beam of fast ions

Cylindrical implosions driven by intense beams of heavy ions are one of the promising ways to create high energy density states in matter. To ensure the needed azimuthal symmetry of the beam energy deposition, it was proposed [Sharkov et al., Nucl. Instrum. Methods Phys. Res. A 464, 1 (2001)] to rotate the ion beam around the target axis. Combining analytical calculations with two-dimensional hydrodynamic simulations, a lower limit is established on the frequency ν of the beam rotation dictated by the target hydrodynamics. This limit is shown to be directly proportional to the desired radial convergence ratio Cr for stepwise beam power profiles, and to Cr1/2 for smooth pulses. With a smooth pulse, 6-10 beam revolutions per pulse should be sufficient to reach Cr≅30, while a stepwise pulse requires ≅100 revolutions. Also, the upper bound on the asymmetry of the elliptical focal spot of a rotating ion beam is calculated