High power microwave system for 10 MeV LINAC

The microwave (MW) system has been designed to energize the accelerator and generate the required electric field for acceleration of electrons. The block diagram of the MW system is of shown in Fig. 1. It consists of klystron amplifier, high voltage DC charging power supply, and pulse modulator for klystron, solid state driver amplifier, waveguide transmission line with vacuum isolation microwave window and control and protection circuits.

Figure1 : Functional block diagram of microwave system of the 10 MeV LINAC

Microwave power to the LINAC is provided by a peak power pulsed klystron amplifier. Klystron is a vacuum tube microwave/RF amplifier. This klystron has a power gain of ~50 dB (105) and requires a pulsed high voltage of ~55kV. The input RF drive power of ~60W to klystron is provided by a pulsed RF solid state power amplifier developed in house at RRCAT. The output of the klystron which is ~ 6 MW peak is fed to the LINAC through a waveguide transmission system.

Pulse Modulator
A line type modulator of 15MW peak power capability has been developed indigenously at RRCAT. This modulator consists of gullemein E type pulse forming network, command charging scheme consisting of two thyratrons is used for charging and discharging of the PFN. 1:4 ratio high voltage pulse transformer is used to feed the high voltage pulse to the Klystron. Microwave system is one of the challenging tasks for development. The microwave system is in operation with 10MeV LINAC.

Figure 2: Left 6 MW klystron with lead shield mounted on Pulse transformer tank, right Pulse modulator system switching thyratron.
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