Abstract:The undulator system in the European X-ray Free Electron Laser is mainly comprised of 5-m long undulator segments and 1.1 m long intersections in between. The longitudinal component of the electrons' velocity is reduced when traveling inside an undulator due to the wiggle motion. Therefore the optical phase is detuned. The detune effect is also from the undulator fringe field where electron longitudinal speed also deviates from the oscillation condition. The total detune effect is compensated by a magnetic dev… Show more
“…Therefore, to obtain balanced two-color spectral peaks, we have to identify the optimal around as discussed in the next section. This expected two-color feature was also discussed by Li and Pflueger 18 . Figure 2 Spectra of spontaneous radiation (Eq.…”
Section: Generation Mechanism Of Two-color Xfel Pulsessupporting
confidence: 73%
“…However, the side spectrum can survive and grow along the undulator line, resulting in time-synchronized two-color XFEL pulses. Although this phenomenon has been discussed in other studies on phase-matching strategies 17 , 18 , the out-of-phase condition is seldom explored, because it does not maximize the XFEL intensity at the resonance frequency. Notably, unlike other methods, this out-of-phase condition is advantageous for generating time-synchronized two-color XFEL pulses, and thus, warrants a detailed investigation.…”
To optimize the intensity of X-ray free-electron lasers (XFELs), phase shifters, oriented in phase with the phases of the XFEL pulse and electron beam, are typically installed at undulator lines. Although a π-offset between the phases (i.e., an “out-of-phase” configuration) can suppress the XFEL intensity at resonant frequencies, it can also generate a side-band spectrum, which results in a two-color XFEL pulse; the dynamics of such a pulse can be described using the spontaneous radiation or low gain theory. This attributes of this two-color XFEL pulse can be amplified (log-scale amplification) through an undulator line with out-of-phase phase shifters. In this study, the features of two-color XFEL pulses were evaluated through theory, simulations and experiments performed at Pohang Accelerator Laboratory X-ray Free Electron Laser. The XFEL gain slope and energy separation between the two-color spectral peaks were consistent through theoretical expectation, and the results of simulation and experiment. The experimentally determined two-color XFEL pulse energy was 250 μJ at a photon energy of 12.38 keV with a separation of 60 eV.
“…Therefore, to obtain balanced two-color spectral peaks, we have to identify the optimal around as discussed in the next section. This expected two-color feature was also discussed by Li and Pflueger 18 . Figure 2 Spectra of spontaneous radiation (Eq.…”
Section: Generation Mechanism Of Two-color Xfel Pulsessupporting
confidence: 73%
“…However, the side spectrum can survive and grow along the undulator line, resulting in time-synchronized two-color XFEL pulses. Although this phenomenon has been discussed in other studies on phase-matching strategies 17 , 18 , the out-of-phase condition is seldom explored, because it does not maximize the XFEL intensity at the resonance frequency. Notably, unlike other methods, this out-of-phase condition is advantageous for generating time-synchronized two-color XFEL pulses, and thus, warrants a detailed investigation.…”
To optimize the intensity of X-ray free-electron lasers (XFELs), phase shifters, oriented in phase with the phases of the XFEL pulse and electron beam, are typically installed at undulator lines. Although a π-offset between the phases (i.e., an “out-of-phase” configuration) can suppress the XFEL intensity at resonant frequencies, it can also generate a side-band spectrum, which results in a two-color XFEL pulse; the dynamics of such a pulse can be described using the spontaneous radiation or low gain theory. This attributes of this two-color XFEL pulse can be amplified (log-scale amplification) through an undulator line with out-of-phase phase shifters. In this study, the features of two-color XFEL pulses were evaluated through theory, simulations and experiments performed at Pohang Accelerator Laboratory X-ray Free Electron Laser. The XFEL gain slope and energy separation between the two-color spectral peaks were consistent through theoretical expectation, and the results of simulation and experiment. The experimentally determined two-color XFEL pulse energy was 250 μJ at a photon energy of 12.38 keV with a separation of 60 eV.
“…where L C is the length of the undulator cell (6.05m for PAL-XFEL), and n is the phase number representing the phase advance in multiples of 2π [17]. PI u and PI ps are the phase integral of the undulator and phase-shifter, respectively.…”
Section: Phase-shifter To Compensate For the Slippagementioning
confidence: 99%
“…For European XFEL, an appropriately large tuning range for the phase integral was chosen to avoid this discontinuity over the wavelength range: the phase number ≥14 was chosen to scan K from 1.5 to 3.9 [16,17]. The PAL-XFEL adopted the European-XFEL phase-shifter design as well [18].…”
Section: Introductionmentioning
confidence: 99%
“…The PAL-XFEL adopted the European-XFEL phase-shifter design as well [18]. This large tuning range phase shifter allows a smooth change line of the phase-shifter gap enabling a wide range scan of photon energy (see Figure 8 in ref [17]). A phase-shifter with a relatively large phase integral allows at least a total slippage of 13 times the radiation wavelength at PAL-XFEL.…”
Variable gap undulator widely used in X-ray free-electron laser (XFEL) enables the photon energy scan by changing its gap. A phase-shifter should be incorporated to compensate for the phase mismatch between the electron bunches and X-ray pulses arising while those traverse the drift space between undulator segments. The uncertainties in both the undulator parameter and the drift space distance introduce an error in calculating the optimum gap distance of the phase-shifter for the different undulator K. The phase-shifter gap needs to be set where the error is within the tolerable range. The control scheme we propose can maintain full FEL intensity over the scanned photon energies.
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