RF Linac

Linac

Upper photo shows complete prototype linac section less than 40 cm long.  It consists of 20 standing wave RF cells, each fed individually.  This is a departure from the more common traveling wave structure.  Two of these structures will be used to reach 20 MeV energy in less than 1 m.
 

The linac design has been designed by S. Tantawi of SLAC.  A prototype shown in the figure has been constructed and is undergoing high power tests at SLAC.  Its novel design distributes the coupling individually to each cell of a standing-wave accelerator structure. The idea of feeding each cavity has existed for some time ; however, until now there has been no practical electron linac implementation that allows such a topology to exist. What this invention provides is a practical implementation of a microwave circuit that is capable of feeding individual or multiple cavities separately. This circuit is designed in such a way that the coupling between cavities is minimized. Hence, individual cavities can be optimized without the constraint usually applied from the coupling between adjacent cavities. This has the benefit of more efficient designs that consume less rf power. Therefore, the overall cost of building a linear accelerator system for any application is substantially reduced. 

The overall performance of the device allows for an extremely high repetition rate well above 10 kHz for short pulses on the order of 500 ns. With an operational gradient of  20 MV/m the maximum temperature rise is roughly 15 degrees C. The peak power requirement to achieve this gradient is 1.6 MW, which leaves plenty of power from the 6 MW klystron to account for beam loading and the photoinjector.