BMBF-project „E-CUBE“ (HHU/DESY/Uni Jena)

Electron bunches with extreme emittance – realization of “Trojan Horse Injection” and simulation of accelerators with ultra-small emittance

The Federal Ministry of Education and Research is funding another cooperation between the HHU and the University of Jena together with DESY in Hamburg as a follow-up to the successful network project “Plasma-Photocathode – electron bunches of highest brilliance at FLASH” from 2016-2019. Our main focus is the practical implementation of the “Trojan Horse Injection” which has been suggested by us based on simulations. This scheme describes a special acceleration method which generates electron bunches with an ultra-small emittance.

The concept is based on Plasma Wakefield Acceleration (PFWA). The relativistic electron bunch accelerated by FLASH at DESY is the perfect driver for our method. This electron beam is focused into a pre-ionized plasma in the FLASHForward-beamline, which creates a co-propagating plasma wave, a so-called wakefield. The electric fields within the wakefield structure are many orders of magnitude higher than those in current state-of-the-art accelerator cavities. The concept of “Trojan Horse Injection” starts at that point: A laser pulse is focused into the wakefield, and additional atoms are ionized in the focus. The released electrons with their precisely defined initial conditions are then accelerated and keep their ultra-small initial emittance.

The properties of these novel electron bunches are troubling for currently used diagnostics because they do not provide the required resolution. For this reason one part of the project deals only with the investigation of new methods to test the emittance.

The work in our group is focused on the exact control of the ionization laser and, especially, the temporal and spatial parameters of the ultra-small focus spot, which is used as electron source by ionization of a gas. This includes developing a novel optical beamline, but also the exact control of timing and jitter between the laser pulse and the driving FLASH-electron bunch – with an accuracy of about a few femtoseconds.

All experimental projects are supported by our university-internal cooperation with the group of Prof. Alexander Pukhov, who is doing a theoretical description of PWFA on the basis of Particle-in-Cell simulations and is able to pre-test various parameters.