  The RF part of the new high current injector-linac HSI consists of five
cavities with the new operating frequency of 36 MHz instead of 27 MHz of the
removed Wideroe type injector. The calculated power requirements of the
cavities including beam load in three structures were between 110 kW for a
rebuncher and 1.75 MW pulse-power for the two IH-cavities. The beam load is up
to 150 kW for the RFQ and up to 750 kW for the two drift tube tanks. An
additional 36 MHz debuncher in the transfer line to the Synchrotron (SIS) will
need 120 kW pulse power. We decided to fulfil these demands with amplifiers of
only two power classes, namely three amplifiers with 2 MW and six amplifiers
with 200 kW pulse output power. The latter ones are also used as drivers for
the 2 MW stages. The 200 kW amplifiers were specified in detail by GSI and
ordered in the industry. The three 2 MW final amplifiers were designed,
constructed and built by GSI. The paper gives an overview of the complete RF
system and the operating performance of amplitude and phase control with beam
load. It further describes some specialities of the new 2 MW amplifiers like
the simplicity of the anode circuit, a very sophisticated socket for a cathode
driven amplifier with cathode on dc ground, the parasitic mode-suppression,
shielding and filtering of unallowable RF-radiation and operating experience
since October 1999.
