Self-modulation experiments of an electron beam for beam-driven plasma wakefield acceleration. Final report

The main goal of the project was the development and setup of an experiment to demonstrate the self-modulation of long electron beams. The following was achieved: - The self-modulation of the PITZ electron beam was simulated with the HiPACE software to support the development process of a plasma cell. It was found that the plasma density should be about ${10}^{15}$ cm${}^{-3}$, and that the rms size of the electron beam in the plasma channel must be below 100 $\mu$m to give a strong signal produce. - A novel plasma cell with an innovative cross-shaped geometry was developed, manufactured and characterized for use at PITZ. Among other things, this included the measurement of the temperature curve in the cell (the temperature on the axis is higher than 600 °C for about 20 cm - enough for the required plasma channel length of 10 cm) and the lithium vapor density ($4\times$10${}^{13}$ cm${}^{-3}$ - this is to be improved). For the first time in the world, it was possible to demonstrate a plasma in a cell with a cross-shaped geometry. - Several preparatory experiments were carried out with the accelerator: The scattering of the electron beam at the windows, which separates the gas atmosphere inside the plasma cell from the vacuum in the accelerator, has been thoroughly investigated. The best candidate was a polymer film with a measured scattering angle below the target of 0.2mrad. All other components of the plasma cell were also characterized. - The plasma cell was integrated into the accelerator, thus conducting initial self-modulation experiments. So far, no signature of self-modulation has been measured, but enough information has been gathered to identify all deficits, so that after upgrading the components in question, a successful experiment is very likely. This will be pursued at its own expense.