|Double Bunch X-ray Free Electron Laser for High-intensity Two Color X-rays
|Two color x-ray pulses have been the subject of intense research at fourth generation light sources, as they enable a wide range of new applications, from anomalous diffraction imaging to ultra-fast x-ray pump x-ray probe experiments. To extend the two color capabilities of the LCLS, double bunch operation has been recently demonstrated and successfully delivered to user experiments. In this scheme two closely spaced bunches are generated in the injector and accelerated off-crest to two different energies. The resulting bunch train radiates a two-color x-ray pulse in the undulator. The relative time delay and energy difference of the two pulses are tunable independently, by taking advantage of the LCLS two stage compression system. The distinct advantage of this approach is the possibility of using the entire undulator length on both colors, thus allowing applications that require high-intensity and/or self-seeding with a large spectral separation (up to ~1-2%). We review the experimental results and discuss our operational experience with user experiments.
|Slides THC01 [2.156 MB]
|Thermal Emittance Measurements at the SwissFEL Injector Test Facility
|In a laser-driven RF-gun the ultimate limit of the beam emittance is the transverse momentum of the electrons as they exit the cathode, the so-called intrinsic or thermal emittance. In this contribution we present measurements of the thermal emittance at the SwissFEL Injector Test Facility for electron beam charges down to a few tens of fC. We have studied the thermal emittance and QE dependence on the laser wavelength, the RF-gun gradient and the cathode material (Cu and Cs2Te).
|Slides THC02 [1.063 MB]
|Suppression of the CSR-induced Emittance Growth in Achromats using Two-dimensional point-kick Analysis
|Coherent synchrotron radiation (CSR) effect causes transverse emittance dilution in high-brightness light sources and linear colliders. Suppression of the emittance growth induced by CSR is essential and critical to preserve the beam quality and to help improve the machine performance. To evaluate the CSR effect analytically, we propose a novel method, named “two-dimensional point-kick analysis”. In this method, the CSR-induced emittance growth in an n-dipole achromat can be evaluated with the analysis of only the motion of particle in (x, x') two-dimensional plane with n-point kicks, which can be, to a large extent, counted separately. To demonstrate the effectiveness of this method, the CSR effect in a two-diople achromat and a symmetric TBA is studied, and generic conditions of suppressing the CSR-induced emittance growth, which are independent of concrete element parameters and are robust against the variation of initial beam distribution, are found. These conditions are verified with the ELEGANT simulations and can be rather easily applied to real machines.
|Slides THC03 [1.941 MB]
|Beam Simulations of High Brightness Photocathode DC Gun and Injector for High Repetition FEL Light Source
|As a next generation FEL light source based on linac, high repetition rate operation to increase average FEL power has been proposed, e.g. LCLS-II project. The injector, which generates high brightness and high average current beam, is one of key components. A photocathode DC gun and superconducting RF cavities, which are developed for ERL light source, can be employed for the high repetition rate injector. For high repetition rate operation of FEL light source, injector simulations were carried out based on ERL injector with demonstrated hardware performance by the cERL beam operation in KEK. The optimization results show that the gun voltage of 500 kV is helpful to achieve low emittance. In addition, to estimate optimum gun voltage and cavity acceleration gradient for the FEL operation, two optimizations with different injector layouts were carried out. The results show that the both different layouts have potential to achieve target emittance for FEL operation. Under the realistic operation condition, the transverse normalized rms emittance of 0.8 mm mrad with the rms bunch length of 3 ps, the bunch charge of 325 pC, and the beam energy of 10 MeV is obtained from the optimizations.
|Slides THC04 [3.796 MB]