Design calculations of the CLIC transfer structure

The power required for acceleration in the main linac of CLIC (CERN Linear Collider) is generated by a high current, moderate energy drive beam. The transfer structure will extract this power at 30 GHz from the the drive beam. A design under study consists simply of a circular cylindrical beam tube of relatively large diameter (16 mm) which is coupled to the wide side of one or more rectangular output waveguides through rows of coupling holes. Output waveguide cutoff and coupling hole spacing are chosen such that the beam is synchronous with the backward TE/sub 10/ wave of the output waveguide at 30 GHz. The RF pulse length is controlled by the length of coupling sections. By placing output waveguides on both sides of the beam tube, 160 MW/m can be extracted with section lengths of 35 cm. Numerical studies show that the desired power level can be reached with small coupling holes.<>