4D transverse and 2D longitudinal phase space characterization of high brightness electron beams at PITZ

Abstract

In the scope of this thesis work, the existing diagnostic setups for the transverse and longitudinal phase space characterization at the Photo Injector Test facility at DESY in Zeuthen (PITZ) have been utilized to obtain detailed and reliable results. PITZ, being a test facility for European XFEL and FLASH, needs to do detailed characterization of electron beams to ensure that they meet the requirements of the FELs, i.e., small transverse emittance and energy spread as well as high peak current. For the reconstruction of the horizontal and vertical phase spaces, PITZ utilizes a slit scan technique as a standard tool because of its space charge dominated electron beams. A novel method for 4 dimensional transverse phase space characterization, known as virtual pepper pot, is proposed that can give insight to the transverse beam phase space coupling. It utilizes the horizontal and vertical single slit scan data to form pepper pot like beamlets. The systematic error of the methodology is explored and the loss of signal at the halo of the horizontal and vertical beamlets due to low signal to noise ratio is considered in the algorithm. To reconstruct the Longitudinal Phase Space (LPS) before the booster accelerating structure, a tomographic reconstruction method called algebraic reconstruction technique was utilized, but the LPS results showed many artefacts. In this thesis, methodical studies were done to improve the existing LPS tomography technique. Some core concerns were addressed e.g. booster phase range, space charge effects and noisy artefacts in results. The reconstruction method adopted was an image space reconstruction algorithm which showed promising results owing to assurance of non-negative solution. Moreover, the initial guess of LPS for iterations was established from low energy section momentum measurements to give a unique solution.