Stability condition for the drive bunch in a collinear wakefield accelerator

The beam breakup instability of the drive bunch in the structure-based collinear wakefield accel- erator is considered and a stabilizing method is proposed. The method includes using the specially designed beam focusing channel, applying the energy chirp along the electron bunch, and keeping energy chirp constant during the drive bunch deceleration. A stability condition is derived that defines the limit on the accelerating field for the witness bunch.Comment: 10 pages, 6 figure

Hamiltonian preserving nonlinear optics

In this paper we present a method of constructing a nonlinear accelerator lattice that has an approximate integral of motion that is given upfront. The integral under consideration is a Hamiltonian in normalized (canonical) coordinates that is preserved by a lattice with a given accuracy. We establish a connection between the integrator of a Hamiltonian in normalized coordinates and a real lens arrangement. We apply known algorithms of high-order symplectic integrators, to produce several nonlinear lattices and show that this approach could improve the design of the nonlinear insert considered at the IOTA and UMER facilities. We also suggest new lattice design based on the Yoshida integrator.Comment: 14 pages, 13 figure

Flat bubble regime and laminar plasma flow in a plasma wake field accelerator

A simple 2D model of the bubble formation in a plasma wakefield accelerator is developed and investigated. It is shown that in the case of a flat driver the bubble may consist of two parts that correspond to two different types of the plasma flow: a laminar flow where plasma electron streams do not cross and a two-stream (turbulent) flow. The laminar flow turns out to be robust to the symmetry breaking. Building-of of the developed model we demonstrate that in the case of the laminar flow and non-relativistic plasma electrons the transverse wake field is absent inside the bubble even in the case of a transversely nonuniform plasma.Comment: 9 pages 5 Figure