POSSIBLE ENHANCEMENT OF SASE FEL OUTPUT FIELD INTENSITY INDUCED BY LOCAL PHASE JUMP

A possible influence on the FEL dynamics of a locally induced phase ju mp between the FEL radiation and electron beam is considered. A numeri cal study has been made for the SASE mode FEL supposing that the phase jumps are introduced at different depths inside the undulator. The FE L evolution starting from a small input signal was studied in 1D high gain approach. It was shown that the FEL radiation output is sensitive to the phase jump value if it is introduced at the depth where satura tion of output power takes places. In the steady state regime, the pha se displacement of order similar to pi provides enhancement of the pea k output power up to 50%. Some kind of optical tapering is also possib le giving further FEL efficiency enhancement. (C) 1998 Elsevier Scienc e B.V. All rights reserved.