A 50-MHz, 12-MW INDUCTION LINAC CURRENT MODULATOR

This paper describes a scheme to control the intrapulse energy variations of long pulse bursts of an induction linac. Analog control over the electron beam injector current is exercised in such a way that accelerator beam load variations compensate for thermal impedance variations of the accelerator cell ferrites. Circuit topology and test data are presented. The circuit uses 64 planar triodes to modulate the shunt impedance of two induction cells of the electron beam injector. Delayed feedback is used to apply a control signal to the modulator that varies the injector current to null the interpulse beam energy sweep at the linac output. The modulator exerts analog control over the top 5% of the beam current. It operates at a 60-ns pulse width and at up to a 0.1% duty factor.