In this paper, we propose a scheme to generate tunable coherent X-rayradiation for future light source applications. This scheme uses an energychirped electron beam, a laser modulator, a laser chirper and two bunchcompressors to generate a prebunched kilo-Ampere current electron beam from afew tens Ampere electron beam out of a linac. The initial modulation energywavelength can be compressed by a factor of $1+h_b R_{56}^a$ in phase space,where $h_b$ is the energy bunch length chirp introduced by the laser chirper,$R_{56}^a$ is the momentum compaction factor of the first bunch compressor. Asan illustration, we present an example to generate more than 400 MW, 170attoseconds pulse, 1 nm coherent X-ray radiation using a 60 Ampere electronbeam out of the linac and 200 nm laser seed. Both the final wavelength and theradiation pulse length in the proposed scheme are tunable by adjusting thecompression factor and the laser parameters.
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