WEOL06  ビームダイナミクス・加速器理論  8月5日 大ホール 17:00 - 17:20
A Two Particle Model for Study of Effects of Space-Charge Force on Beam Instabilities.
○陳 栄浩(高エネルギー加速器研究機構),Chao Alexander(SLAC),Blaskiewicz Michael(BNL)
○Yong Ho Chin (High Energy Accelerator Research Organization), Alexander Chao (SLAC), Michael Blaskiewicz (BNL)
In this report, we present a new two particle model for study of beam instabilities in the presence of the space-charge force. It is a simple expansion of the well-known two particle model for a strong head-tail instability and is still analytically solvable. It leads to a formula for the growth rate as a function of the two dimensionless parameters: the space charge tune shift (normalized by the synchrotron tune) and the wake field strength, . The 3-dimensional contour plot of the growth rate as a function of those two dimensionless parameters reveals stopband structures. Many simulation results generally indicate that beam instability can be damped by a weak space-charge force, but the beam becomes unstable again when the space charge force is further increased. The new two particle model indicates a similar behavior. The damping of beam instabilities in weak space-charge regions and its loss in strong space-charge regions are explained by a combination of linearized coherent kicks between the space-charge force and the wake fields, not by an incoherent tune spread due to the non-linearity of the space-charge force.