  Long pulse modulators are used to produce high-voltage, high-power pulses
with durations of several hundred microseconds up to some milliseconds. The
loads are one or more klystrons for producing RF power to accelerate the
particle beam in superconducting cavities. After years of development and
improvements in different institutes a variety of topologies exist, and are
presented. The basics of modulators, pulse requirements and klystrons are
explained. Additionally, the charging of internal energy storage will be
addressed. The outlook for future developments is given.
