• Z. Liu
  IUCF, Bloomington, Indiana
• S.M. Cousineau, V.V. Danilov, J. Galambos, J.A. Holmes, M.A. Plum
  ORNL, Oak Ridge, Tennessee

The instability caused by the electron cloud effect (ECE) may set an upper limit to beam intensity in proton storage rings. This instability is potentially a major obstacle to the full intensity operation, at 1.5·10¹⁴ protons per pulse, of the Spallation Neutron Source (SNS). High intensity experiments have been done with different sets of parameters that affect the electron-proton (e-p) instability, of which bunch intensity and bunch shape are considered as two main factors. In the experiment, the phase and amplitude of the second harmonic RF cavity are used to modify the bunch shape. Simulation with the beam dynamics code ORBIT has been carried out to compare with experimental results and to understand the impact of bunch shape on electron cloud build-up and beam stability. We have also attempted to benchmark the e-p model to predict the frequency spectrum and the RF buncher voltage threshold values against experimental results. Details and discussion will be reported in this conference.

* M.T.F. Pivi and M.A. Furman, PRSTAB 6, 034201 (2003)
** V. Danilov et. al, 39th ICFA Advanced Beam Dynamics Workshop, 2006
*** B. Macek et. al, PAC 2003

• R.A. Hardin
  ORNL RAD, Oak Ridge, Tennessee
• V.V. Danilov, C. Deibele
  ORNL, Oak Ridge, Tennessee

The prototype of an analog transverse (vertical and horizontal) feedback system to actively damp the electron-proton (e-p) instability has been developed and tested on the ORNL Spallation Neutron Source (SNS). We will describe the principle components, system configuration, and review several experimental studies geared towards understanding the current performance and limitations of the system.

• S. Nagaitsev
  Fermilab, Batavia
• V.V. Danilov
  ORNL, Oak Ridge, Tennessee

Integrable nonlinear motion in accelerators has the potential to introduce a large betatron tune spread to suppress instabilities and to mitigate the effects of space charge and magnetic field errors. To create such an accelerator lattice one has to find magnetic and/or electrtic field combinations leading to a stable integrable motion. This paper presents families of lattices with one invariant where bounded motion can be easily created in large volumes of the phase space. In addition, it presents two examples of integrable nonlinear accelerator lattices, realizable with longitudinal-coordinate-dependent magnetic or electric fields with the stable nonlinear motion, which can be solved in terms of separable variables.