2019, Gross, M., Qian, H.J., Boonpornprasert, P., Chen, Y., Good, J.D., Huck, H., Isaev, I., Koschitzki, C., Krasilnikov, M., Lal, S., Li, X., Lishilin, O., Loisch, G., Melkumyan, D., Mohanty, S.K., Niemczyk, R., Oppelt, A., Shaker, H., Shu, G., Stephan, F., Vashchenko, G., Will, I.

Laser pulse shaping is one of the key elements to generate low emittance electron beams with RF photoinjectors. Ultimately high performance can be achieved with ellipsoidal laser pulses, but 3-dimensional shaping is challenging. High beam quality can also be reached by simple transverse pulse shaping, which has demonstrated improved beam emittance compared to a transversely uniform laser in the 'pancake' photoemission regime. In this contribution we present the truncation of a Gaussian laser at a radius of approximately one sigma in the intermediate (electron bunch length directly after emission about the same as radius) photoemission regime with high acceleration gradients (up to 60 MV/m). This type of electron bunch is used e.g. at the European XFEL and FLASH free electron lasers at DESY, Hamburg site and is being investigated in detail at the Photoinjector Test facility at DESY in Zeuthen (PITZ). Here we present ray-tracing simulations and experimental data of a laser beamline upgrade enabling variable transverse truncation. Initial projected emittance measurements taken with help of this setup are shown, as well as supporting beam dynamics simulations. Additional simulations show the potential for substantial reduction of slice emittance at PITZ. © Published under licence by IOP Publishing Ltd.

2018, Gross, M., Lishilin, O., Loisch, G., Boonpornprasert, P., Chen, Y., Engel, J., Good, J., Huck, H., Isaev, I., Krasilnikov, M., Li, X., Niemczyk, R., Oppelt, A., Qian, H., Renier, Y., Stephan, F., Zhao, Q., Brinkmann, R., Martinez de la Ossa, A., Osterhoff, J., Grüner, F.J., Mehrling, T., Schroeder, C.B., Will, I.

The self-modulation instability is fundamental for the plasma wakefield acceleration experiment of the AWAKE (Advanced Wakefield Experiment) collaboration at CERN where this effect is used to generate proton bunches for the resonant excitation of high acceleration fields. Utilizing the availability of flexible electron beam shaping together with excellent diagnostics including an RF deflector, a supporting experiment was set up at the electron accelerator PITZ (Photo Injector Test facility at DESY, Zeuthen site), given that the underlying physics is the same. After demonstrating the effect [1] the next goal is to investigate in detail the self-modulation of long (with respect to the plasma wavelength) electron beams. In this contribution we describe parameter studies on self-modulation of a long electron bunch in an argon plasma. The plasma was generated with a discharge cell with densities in the 1013 cm-3 to 1015 cm-3 range. The plasma density was deduced from the plasma wavelength as indicated by the self-modulation period. Parameter scans were conducted with variable plasma density and electron bunch focusing.

2018, Loisch, G., Good, J., Gross, M., Huck, H., Isaev, I., Krasilnikov, M., Lishilin, O., Oppelt, A., Renier, Y., Stephan, F., Brinkmann, R., Grüner, F., Will, I.

Beam driven plasma acceleration is one of the most promising candidates for future compact particle accelerator technologies. In this scheme a particle bunch drives a wake in a plasma medium. The fields inside of the wake can be used to accelerate a trailing witness bunch. To maximise the ratio between acceleration of the witness to deceleration of the drive bunch, the so called transformer ratio, several methods have been proposed. The ones yielding the most favorable results are based on shaped drive bunches that are long in terms of the plasma wavelength. We present here methods to create such drive bunches employing temporally shaped UV-laser pulses for the extraction of electron bunches from a photo-electron gun. Theoretical considerations, experimental results and possibilities for further improvements are discussed.