Abstract
Transverse deflecting structures (TDS) are widely used in accelerator physics to measure the longitudinal density of particle bunches. When used in combination with a dispersive section, the whole longitudinal phase space density can be imaged. At the Linac Coherent Light Source (LCLS), the installation of such a device downstream of the undulators enables the reconstruction of the X-ray temporal intensity profile by comparing longitudinal phase space distributions with lasing on and lasing off [1]. However, the resolution of this TDS is limited to around 1 fs rms (root mean square), and therefore, in most cases, it is not possible to resolve single self-amplified spontaneous emission (SASE) spikes within one photon pulse.By combining the intensity spectrum from a high resolution photon spectrometer [2] and the temporal structure from the TDS, the overall resolution is enhanced, thus allowing the observation of temporal, single SASE spikes. The combined data from the spectrometer and the TDS is analyzed using an iterative algorithm to obtain the actual intensity profile.In this paper, we present the reconstruction algorithm as well as analyzed data obtained from simulations which shows the reliability of this method. Real data will be published at a later stage.
Highlights
The longitudinal phase space distribution of electron bunches can be mapped to transverse coordinates by streaking them using a transverse deflecting radio frequency (RF) structure (TDS) in one direction and combining that streak with a dipole magnet which serves as an energy spectrometer in the other direction
When the TDS is installed downstream of the undulators at a Free-Electron Laser (FEL) the X-ray temporal profile can be obtained by comparing images where the FEL process is suppressed to images where it is enabled [1, 4]
For a typical TDS used at an FEL, such as the Linac Coherent Light Source (LCLS), the resolution is limited to the order of 1 fs rms
Summary
The longitudinal phase space distribution of electron bunches can be mapped to transverse coordinates by streaking them using a transverse deflecting radio frequency (RF) structure (TDS) in one direction and combining that streak with a dipole magnet which serves as an energy spectrometer in the other direction. The combined data from the spectrometer and the TDS is analyzed using an iterative algorithm to obtain the actual intensity profile. We present the reconstruction algorithm as well as analyzed data obtained from simulations which shows the reliability of this method.
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