Start-to-end simulations for bunch compressor and THz SASE FEL at PITZ

Abstract

The magnetic bunch compressor was designed as part of a THz accelerator source being developed at the Photo Injector Test facility at DESY in Zeuthen (PITZ) as a prototype for pump-probe experiments at the European XFEL. As an electron bunch is compressed to achieve higher bunch currents for the THz source, the beam dynamics in the bunch compressor was studied by numerical simulations. A start-to-end simulation optimizer including coherent synchrotron radiation (CSR) effects has been developed by combining the use of ASTRA, OCELOT, and GENESIS to support the design of the THz source prototype. In this paper, we present simulation results to explore the possibility of improving the performance of the THz FEL at PITZ by using the developed bunch compressor.

Numerical Simulation of an Electron Beam for Magnetic Bunch Compressor Commissioning at PITZ

“…Firstly, it can be used to compress an 2-4 nC electron bunch to have a full width at half maximum (FWHM) length longer than >5 ps and to have a peak current of up to 400 A, which is suitable for SASE FEL production [8]. Secondly, it can be used to compress an electron bunch with a bunch charges lower than 400 pC to have a bunch length shorter than 1 ps FWHM for a super-radiant radiation [9]. Lastly, it can be used to manipulate the longitudinal phase space for getting high radiation energy in the case of seeding FEL production [10].…”

“…The shifts of the magnets in (z, y) coordinates in a millimeter unit are as follows: CHICANE.D1 (-4.2, +25), CHICANE.D2 (+4.2, -25), CHICANE.D3 (-4.2, -25), and CHICANE.D4 (+4.2, +25). These shifts deriver an effective length of 327 mm for each dipole magnet [9]. The designed parameters including geometric parameters and magnet specifications are listed in table 1.…”

Commissioning of Bunch Compressor to Compress Space Charge-Dominated Electron Beams for THz Applications

“…Furthermore, such collective effects-both space charge and CSR effects-introduce dispersion leakage due to the imbalance in the longitudinal dynamics of particles [7,8]. According to our previous study via the particle tracking simulation [2], the compression performance (compression ratio of bunch length) is dropped, and projected vertical emittance is increased drastically when increasing bunch charge. While the beam is fully compressed and the beam current is increased, space charge and CSR effects limit the bunch compressor performance and distort the current profile.…”

“…However, the bunch compressor was installed downstream of a longitudinal bunch profile measurement station, and the bunch profile after compression cannot be directly measured. In order to predict the bunch compression outcome via the start-to-end simulation results, both beam momentum chirps dp/dt upstream and coherent transition radiation (CTR) downstream of the chicane are measured to benchmark the simulation results in [2].…”

“…Furthermore, the bunch compressor has been foreseen and assigned as a part of the prototype for various applications such as the SASE FEL, seeded FEL, superradiant radiation, etc. [2].…”