Cascaded Longitudinal Space Charge Amplifier
The longitudinal space-charge amplifier (LSCA) has been recently proposed as an alternative to the free-electron laser instability for the generation of intense broadband radiation pulses. In a LSCA, a relativistic electron beam becomes modulated in density (i.e., microbunched) by the interaction with its own collective space-charge forces, combined with longitudinal dispersion in transport. The process can be initiated by noise in the beam alone, and can be optimized and cascaded through several amplification stages to yield strong microbunching for the emission of intense pulses down to the attosecond level. Compared to an FEL, the LSCA has certain advantages, particularly in terms of compactness and robustness to non-ideal beam conditions.
At NLCTA, we experimentally demonstrated a cascaded longitudinal space-charge amplifier at optical wavelengths, wherein multiple LSCAs are placed in series. The distinct advantage of the cascaded arrangement is the potential for much larger gain for the same total dispersion. Although seeded by electron beam shot noise, strong compression of the electron beam along the three amplification stages leads to emission of coherent undulator radiation pulses exhibiting a single spectral spike and a single transverse mode. The on-axis gain in radiation intensity is about four orders of magnitude larger than the spontaneous emission.
For more details, see the paper published in Physical Review Letters:PhysRevLett.110.264802.pdf