Jan-Patrick Schwinkendorf

The FLASHForward facility at DESY

The FLASHForward project at DESY is a pioneering plasma-wakefield acceleration experiment that aims to produce, in a few centimetres of ionised hydrogen, beams with energy of order GeV that are of quality sufficient to be used in a free-electron laser. The plasma is created by ionising a gas in a gas cell with a multi-TW laser system. The plasma wave will be driven by high-current-density electron beams from the FLASH linear accelerator. The laser system can also be used to provide optical diagnostics of the plasma and electron beams due to the <30 fs synchronisation between the laser and the driving electron beam. The project will explore both external and internal witness-beam injection techniques. The operation parameters of the experiment are discussed, as well as the scientific programme.

Calibration and cross-laboratory implementation of scintillating screens for electron bunch charge determination

We revise the calibration of scintillating screens commonly used to detect relativistic electron beams with low average current, e.g., from laser-plasma accelerators, based on new and expanded measurements that include higher charge density and different types of screens than previous work [Buck et al., Rev. Sci. Instrum. 81, 033301 (2010)]. Electron peak charge densities up to 10 nC/mm2 were provided by focused picosecond-long electron beams delivered by the Electron Linac for beams with high Brilliance and low Emittance (ELBE) at the Helmholtz-Zentrum Dresden-Rossendorf. At low charge densities, a linear scintillation response was found, followed by the onset of saturation in the range of nC/mm2. The absolute calibration factor (photons/sr/pC) in this linear regime was measured to be almost a factor of 2 lower than that reported by Buck et al. retrospectively implying a higher charge in the charge measurements performed with the former calibration. A good agreement was found with the results provided by Glinec et al. [Rev. Sci. Instrum. 77, 103301 (2006)]. Furthermore long-term irradiation tests with an integrated dose of approximately 50 nC/mm2 indicate a significant decrease of the scintillation efficiency over time. Finally, in order to enable the transfer of the absolute calibration between laboratories, a new constant reference light source has been developed.

FLASHForward: DOOCS Control System for a Beam-Driven Plasma-Wakefield Acceleration Experiment

The FLASHForward project at DESY is an innovative beam-driven plasma-wakefield acceleration experiment integrated in the FLASH facility, aiming to accelerate electron beams to GeV energies over a few centimeters of ionised gas. These accelerated beams are tested for their capability to demonstrate exponential free-electron laser gain; achievable only through rigorous analysis of both the driver and witness beams phase space. The thematic priority covered in here the control system part of FLASHForward. To be able to control, read out and save data from the diagnostics into DAQ, the DOOCS control system has been integrated into FLASH Forward. Laser beam control, over 70 cameras, ADCs, timing system and motorised stages are combined into the one DOOCS control system as well as vacuum and magnet controls. Micro TCA for Physics (MTCA.4) is the solid basic computing system, supported from high power workstations for camera readout and normal Linux computers. FLASH FLASH [1], a soft X-ray free-electron laser, is available to the photon science user community for experiments since 2005. Ultra-short X-ray pulses, shorter than 30 femtoseconds, are produced using the SASE process. The FLASH facility operates two SASE beamlines in parallel: FLASH1 & FLASH2 and as third beamline FLASHForward (see Fig. 1). Pulses of FLASH come in bursts of several hundred pulses with a repetition rate of 10 Hz. Figure 1: FLASH layout. DOOCS INSIDE FLASHFORWARD As FLASHForward is part of FLASH, it is obvious to us also the FLASH control system infrastructure DOOCS. The whole server architecture as existing hardware and software is a big advantage to integrate the needed detector hardware for FLASHForward. As most of the FLASHForward part is a laser system, diagnostic is slightly different as in FLASH. Laser alignment can be detected with chip cameras. Hence the amount of cameras is increasing easily to more than 70. Other components, like the timing system must be adapted in FLASHForward to get a synchronization to FLASH, which is necessary for all data taking. In the following chapters a short description of the most important components and systems are made. DOOCS CONTROL SYSTEM DOOCS, the Distributed Object Oriented Control System [2] was designed for FLASH. Currently it is extended to control the European XFEL accelerator (see Fig. 2). Recent developments for the client side applications are written in JAVA to allow them to be used on many computer platforms. This object oriented abstraction model helps for clean programming interfaces and in the overall system design including the hardware for a machine and is a significant step forward in the goal to improve software productivity and quality. Figure 2: DOOCS structure. COMPUTING HARDWARE MicroTCA.4, is a new standard form the PICMG to extend the applications of the existing μTCA crate system. This extension was developed in an international collaboration of High Energy Physics laboratories and many industrial partners within the PICMG organization. It is fully ___________________________________________ † sven.karstensen@desy.de Proceedings of IPAC2018, Vancouver, BC, Canada Pre-Release Snapshot 27-May-2018 12:00 UTC