Low-level RF system design for the Next Linear Collider damping rings

The design current for the Next Linear Collider (NLC) damping rings is an order of magnitude higher than existing damping rings. As opposed to storage rings, damping rings are required to operate at a high repetition frequency. Transient beam loading is therefore particularly severe. The NLC design calls for a full current fill pattern consisting of up to 4 trains of 90 bunches for a total DC current of 1.2 A. However, using conventional filling techniques, with a rapid current ramp the ring energy acceptance could decrease due to transient loading and the beam might not be captured. In this paper we describe two features of the low-level RF system design. The first avoids any reduction of duty cycle while the second ensures beam capture and regulation of the cavity voltages and beam phase