The ELTEST Experiment - Infn

ELTEST 2Introduction• A key question in electron beam physics is the convective evolution (alongthe beam) of small non uniformities (due, e.g. to the emitting cathode or tothe presence of grids or small errors in the alignment of the system) inspace charge regime and their effects on the beam emittance (e.g.wavebreaking due to transverse plasma oscillations, longitudinal expansionleading to debunching and reduction of the peak current). Thesephenomena are important up to energies of about 150 MeV in photoinjectorproduced beams with pulse duration of few ps and current of somehundreds A [Serafini and Rosenzweig(1997)], and can limit the achievablebrightness in photoinjectors [Fraser et al.(1986)], and the performance ofinteresting applications as X ray FEL’s and plasma based accelerators (seee.g. [Ferrario et al.(1999)]). Direct experimental investigation of thecharacteristics of such beams is very difficult due to the small beam width(some hundreds microns) and limited flexibility of the overall apparatus.It is possible to investigate the same space charge phenomena in beamswith lower energy (few keV) which can exhibit a similar behavior as theINFN Gr V, Napoli 19/09/05