Research activities at the Photo Injector Test facility at DESY, Zeuthen site, (PITZ) aim to develop and optimize high brightness electron sources for Free Electron Lasers (FELs) like FLASH and the European XFEL. To demon- strate the XFEL operation, an electron bunch train contain- ing 3250 pulses of 1 nC charge at 10 Hz repetition rate is required. The spectrometers and related equipments for studying the longitudinal phase space for such long pulse trains do not yet exist at PITZ. Design and construction of a new high energy dispersive arm (HEDA2) is currently in progress. Besides the requirement to handle long electron bunch trains, the HEDA2 setup is designed to allow high resolution measurements of momentum distribution up to 40 MeV/c, a longitudinal phase space measurement with slice momentum spread down to 1 keV/c and transverse slice emittance measurements at off-crest booster phases. The status of the physics design and technical considera- tions of this dispersive section will be presented.