Modeling of the microbunching instability

We show that, through careful control of noise sources, it is possible to determine the microbunching gain curve for the FERMI@ELETTRA linac using the particle tracking code elegant. In addition to using a sufficiently large number of particles (60×10⁶), use of a low-pass filter is very helpful in controlling noise and providing convenient intrabin interpolation. Gains of up to 1500 are seen for modulation wavelengths down to 25  μm. Because of the high gain, very small initial modulations are needed to avoid saturation, which further motivates the use of a large number of particles. We also show, for the first time, how the density modulation evolves in detail inside the dipoles of a multichicane system.