In the
frame of the R&D activity foreseen for the first phase of the SPARX
project,the SPARXINO test facility is meant to provide an ultra-high
electron beam at 1.2-1.5 GeV,able to drive SASE and seeded FEL experiments
in the 10- 3 nm range. The proposed layout is analyzed regarding its
sensitivity to laser pulse jitter effects and microbunching instability
limitations. First simulation results are presente.