Using Drive Rods in Induction Cells to Reduce the Beam Break Up Instability

Abstract

The beam breakup instability is an effect that must be heavily suppressed for optimum operation of high current induction accelerators. The RF modes generated inside the induction cells can deflect or degrade subsequent beam traversing the cell. Significant effort has been invested in minimizing the effect over several decades. One mechanism that is known to reduce the transverse impedance, the main observable experimentally which directly relates to the BBU amplitude, is to introduce ferrites to absorb the fields. Another, less investigated mechanism, is to disturb the modes symmetry by inserting the drive rods at the proper locations in the cell. This paper will show that the drive rods can dramatically reduce the transverse impedance and will show that simulations are maturing towards predicting this effect.