New 2BPM-1K scheme and resistive wall instability

Abstract

One of the main goals of a transverse damping feedback system for the Superconducting Super Collider (SSC) is to control the transverse multibunch instabilities. These instabilities arise due to the interaction of the bunches with the wake field left by previous bunches traveling in the ring. The wake field is the electromagnetic field resulting from the interaction of charged particles in the bunch with the surrounding conductors elements, and it can also be characterized by the associated impedance. The instability that arises due to the resistive beam pipe is called resistive wall instability. Since the SSC Collider machine the injection time is higher than one hour and the storage time at high energy (20 TeV) must be at least 20 hours, the control of the resistive wall instability is of fundamental importance for the Collider to be operational. The most dangerous mode of the beam oscillation is the dipole one which has an estimated growth time between 56 msec and 150 msec. Reference 3 shows that the traditional feedback scheme was not good enough to control (with low gain) the Dipole Mode Multibunch Instability (DMMI) due to the resistive wall impedance. Consequently, a novel two BPM-two kickers transverse feedback systemmore » was proposed to control the DMMI much better (the gain could be one order of magnitude lower). This novel system was optimized later on, and it is still under study. Since this system has two kickers, one would like to reduce the cost of the system by looking for the possibility of using one single kicker with other correction scheme. In this paper, a new scheme is shown, using two BPM`s and a single kicker, which allows excellent control of the DMMI due to resistive wall impedance and allows a complete cancellation of the coherent oscillations within two turns, when the gain is equal to one and there is no other perturbations.« less