Study of self-modulation of an electron beam in plasma

The acceleration of electron beams in plasma wakefields driven by charged particlebeams is among the most promising candidates for future TeV-scale compact electronaccelerators. Currently available high energy proton beams that could serve as driverbeams in a plasma wakefeld accelerator (PWFA) are much longer than what is requiredfor efficient excitation of high-amplitude wakefields and thus for generating the desiredhigh acceleration gradients. The self-modulation instability (SMI) is a phenomenonwhich enables the transformation of a long charged particle beam into a train ofequidistant short bunches when passing through a plasma. Such bunch trains canresonantly drive wakefields in plasma and generate multi-GV=m acceleration gradients.The proof-of-principle experiment AWAKE was started at CERN to demonstrateacceleration of electrons in plasma wakefields driven by self-modulated proton beams.Since the underlying physics of the SMI is the same for any charged particle beam,the use of electron beams for studying the SMI is an appealing option, as the electronbeams are easier to handle. The Photo Injector Test facility at DESY in Zeuthen (PITZ)offers a unique possibility to study and experimentally demonstrate the self-modulationof long electron beams in plasma: it is capable of generating long electron beams, andit possesses a variety of diagnostic devices for the electron beam characterization. Forthe SMI studies, measurements of the longitudinal phase space are of main importance,as they reflect characteristic features of the SMI.This work is devoted to the first experimental demonstration of the SMI by usinglong electron beams passing through a plasma. Preparations for the self-modulationexperiment, including the development of a plasma source, are described. Results ofthe first longitudinal phase space measurements of the SMI at PITZ and supportingbeam dynamics simulations are presented