On a possibility to Suppress Microwave Instability

The microwave instability appears to be main limiting factor in both longitudinal brightness of electron beam and achievement of very short bunches. It causes anomalous bunch lengthening and energy spread growth. The 6D brightness of electron beam is the main figure of merit for their applications for generation of coherent X-rays. In this paper a possibility to suppress or to eliminate the microwave instability using advanced RF system based on inverse sub-mm FEL is discussed [1]. We present the theoretical developments of strong focusing in longitudinal direction and discuss results of computer simulations. A possibility of storage ring operating with femtosecond high peak current electron bunches and natural energy spread is discussed. This beams can be used to generate both coherent and spontaneous X-ray beams with femtosecond duration. We discuss a possibility of the storage ring based FEL X-ray light source with average spectral brightness of 1027-1028 ph/sec/mm2/mrad2/0.01%BW. This value exceeds existing 3rd generation light sources by 6-9 orders of magnitude, making it a 5th generation light source.