The new design of the THz streak camera at PSI

SwissFEL is the Free Electron Laser (FEL) facility under construction at the Paul Scherrer institute (PSI), aiming to provide users with X-ray pulses of lengths down to 2 femtoseconds at standard operation. The measurement of the length of the FEL pulses and their arrival time relative to the experimental laser is crucial for the pump-probe experiments carried out in such facilities. This work presents a new device that measures hard X-ray FEL pulses based on the THz streak camera concept. It describes the prototype setup called pulse arrival and length monitor (PALM) developed at PSI and tested in Spring-8 Angstrom Compact Free Electron Laser (SACLA) in Japan. Based on the first results obtained from the measurements, we introduce the new improved design of the second generation PALM setup that is currently under construction and will be used in SwissFEL photon diagnostics

Femtosecond pulse length and arrival time measurement of hard X-Ray FELs

The ultra-bright short-pulsed radiation provided by the free electron lasers (FEL) is used for many new discoveries in different fields of science and industry. The advancement of the FEL technologies allows the generation of shorter photon pulses with higher photon energies or shorter radiation wavelengths that open new horizons for the new research. In order to better understand the measurements using the free electron laser pulses, it is important to know the properties of these pulses. Particularly, for the time-resolved experiments the temporal properties of the photon pulses such as their relative arrival times and the temporal durations, are of utmost importance. One of the techniques to measure these parameters of the FEL pulses is the THz streaking method. Thus far, this method has been used only for the photon pulses in ultraviolet and soft X-ray regions. This thesis provides a full characterization of the method and demonstrates its applicability in the hard X-ray photon energy range, measuring FEL pulses with photon energies of up to 10000 electronvolts. Measurement accuracies of sub-10 femtoseconds were achieved for both the arrival time and the pulse length measurements. Furthermore, it is shown here that the THz streaking method is able to simultaneously measure two FEL pulses of different energies. The results from some measurements were also compared to other independent measurement techniques. In addition to the performed measurements, simulation of the THz streaking effect was performed to better understand the measurement method. The simulations showed the ways of achieving higher accuracies with the THz streaking techniques. The results obtained from the experiments were consistent with the results provided by the simulations. The results obtained in this thesis provide new possibilities for the applications of the THz streaking method. They enable temporal diagnostics for photon pulses with a wide range of wavelengths and temporal durations. Such diagnostics can contribute largely to the success of the experiments performed at free electron laser sources

Simulation of FEL pulse length calculation with THz streaking method

Having accurate and comprehensive photon diagnostics for the X-ray pulses delivered by free-electron laser (FEL) facilities is of utmost importance. Along with various parameters of the photon beam (such as photon energy, beam intensity, etc.), the pulse length measurements are particularly useful both for the machine operators to measure the beam parameters and monitor the stability of the machine performance, and for the users carrying out pump– probe experiments at such facilities to better understand their measurement results. One of the most promising pulse length measurement techniques used for photon diagnostics is the THz streak camera which is capable of simultaneously measuring the lengths of the photon pulses and their arrival times with respect to the pump laser. This work presents simulations of a THz streak camera performance. The simulation procedure utilizes FEL pulses with two different photon energies in hard and soft X-ray regions, respectively. It recreates the energy spectra of the photoelectrons produced by the photon pulses and streaks them by a single-cycle THz pulse. Following the pulseretrieval procedure of the THz streak camera, the lengths were calculated from the streaked spectra. To validate the pulse length calculation procedure, the precision and the accuracy of the method were estimated for streaking configuration corresponding to previously performed experiments. The obtained results show that for the discussed setup the method is capable of measuring FEL pulses with about a femtosecond accuracy and precision

Upgrade of the two-screen measurement setup in the AWAKE experiment

The AWAKE project at CERN uses a self-modulated 400 GeV/c proton bunch to drive GV/m wakefields in a 10 m long plasma with an electron density of $n_{pe} = 7 \times 10^{14}$ electrons/cm$^3$. We present the upgrade of a proton beam diagnostic to indirectly prove that the bunch self-modulated by imaging defocused protons with two screens downstream the end of the plasma. The two-screen diagnostic has been installed, commissioned and tested in autumn 2016 and limitations were identified. We plan to install an upgraded diagnostics to overcome these limitations.The AWAKE project at CERN uses a self-modulated \SI{400}{GeV/c} proton bunch to drive GV/m wakefields in a \SI{10}{m} long plasma with an electron density of $n_{pe} = 7 \times 10^{14}\,\rm{electrons/cm}^3$. We present the upgrade of a proton beam diagnostic to indirectly prove that the bunch self-modulated by imaging defocused protons with two screens downstream the end of the plasma. The two-screen diagnostic has been installed, commissioned and tested in autumn 2016 and limitations were identified. We plan to install an upgraded diagnostics to overcome these limitations

Systematic optics studies for the commissioning of the AWAKE electron beamline

The commissioning of the AWAKE electron beam line was successfully completed in 2018. Despite a modest length of about 15 m, this low-energy line is quite complex and several iterations were needed before finding satisfactory agreement between the model and the measurements. The work allowed to precisely predict the size and positioning of the electron beam at the merging point with the protons inside the plasma cell, where no direct measurement is possible. All the key aspects and corrections which had to be included in the model, precautions and systematic checks to apply for the correct setup of the line are presented. The sensitivity of the ∼18 MeV electron beam to various perturbations, like different initial optics parameters and beam conditions, energy jitters and drifts, earth’s magnetic field etc., is described

The AWAKE Electron Spectrometer

The AWAKE experiment at CERN aims to use a proton driven plasma wakefield to accelerate electrons from 10–20 MeV up to GeV energies in a 10 m plasma cell. We present the design of the magnetic spectrometer which will measure the electron energy distribution. Results from the calibration of the spectrometer's scintillator and optical system are presented, along with a study of the backgrounds generated by the 400 GeV SPS proton beam

Development of Electron Bunch Compression Monitors for SwissFEL

SwissFEL will be a hard x-ray fourth generation light source to be built at Paul Scherrer Institut (PSI), Switzerland. In SwissFEL the electron bunches will be produced with a length of 3ps and will then be compressed by a factor of more than 1000 down to a few fs in order to generate ultra short x-ray pulses. Therefore reliable, accurate and noninvasive longitudinal diagnostic is essential after each compressing stage. In order to meet the requirements of this machine, new monitors have to be developed. We will present recent results of setups that measure electro-magnetic radiation, namely edge, synchrotron and diffraction radiation, emitted by the electron bunches (far field, spectral domain). These monitors are tested in the SwissFEL Injector Test Facility. A state of the art S-band Transverse Deflecting Cavity together with a Screen Monitor is used for calibration

Fast, automated, continuous energy scans for experimental phasing at the BioMAX beamline

In X-ray macromolecular crystallography (MX), single-wavelength anomalous dispersion (SAD) and multi-wavelength anomalous dispersion (MAD) techniques are commonly used for obtaining experimental phases. For an MX synchrotron beamline to support SAD and MAD techniques it is a prerequisite to have a reliable, fast and well automated energy scan routine. This work reports on a continuous energy scan procedure newly implemented at the BioMAX MX beamline at MAX IV Laboratory. The continuous energy scan is fully automated, capable of measuring accurate fluorescence counts over the absorption edge of interest while minimizing the sample exposure to X-rays, and is about a factor of five faster compared with a conventional step scan previously operational at BioMAX. The implementation of the continuous energy scan facilitates the prompt access to the anomalous scattering data, required for the SAD and MAD experiments

Beam Dynamics Studies and Instrumentation Tests for Bunch Length Measurements at CLEAR

International audienceA new CERN Linear Electron Accelerator for Research (named CLEAR) has been installed as a general-purpose user facility to study novel accelerating techniques, high-gradient structures, instrumentation and irradiation experiments. CLEAR is a flexible accelerator that can provide high quality bunched electron beams with a wide range of beam parameters up to an energy of 220 MeV, offering several testing capabilities. Among all the potential applications, novel accelerating techniques, such as plasma acceleration and THz generation are considered. These applications require shorter bunches, down to the 100 fs level. This paper reports on beam dynamics studies and instrumentation tests to establish a bunch length of this order in CLEAR. The short bunches are generated using adiabatic bunching in the first accelerating structure. For bunch length diagnostic CLEAR is equipped with a streak camera and a transverse deflecting cavity. Alternatively a phase-scan of the last accelerating structure could be used as well to estimate the bunch length. The experimental results with respect to these different techniques are presented and compared with simulations