In this paper, we study a possible microbunching instability in the TESLA Test Facility linac. A longitudinal space charge is found to be the main effect driving the instability. Analytical estimates ...show that initial perturbations of beam current in the range 0.5–
1
mm
are amplified by a factor of a few hundred when the beam passes two bunch compressors. A method to suppress the instability is discussed.
Klystron instability of a relativistic electron beam in a bunch compressor Saldin, E.L.; Schneidmiller, E.A.; Yurkov, M.V.
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
09/2002, Letnik:
490, Številka:
1
Journal Article
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In this paper, we consider a klystron-like mechanism of amplification of parasitic density modulations in an electron bunch passing a magnetic bunch compressor. Analytical expressions are derived for ...the small-signal gain. The effect of wakefields in front of the bunch compressor is analyzed by using a model of linear compression which assumes linear correlated energy chirp and linear dependence of a path length on energy deviation. Analysis of the density modulation growth due to coherent synchrotron radiation inside bends of the magnetic bunch compressor is done for the simplified case of no correlated energy chirp (no compression). Analytical results of this paper can be used for benchmarking numerical simulation codes.
In this paper we propose a new method for measurements of the longitudinal profile of 100
fs electron bunches for X-ray Free Electron Lasers (XFELs). The method is simply the combination of two ...well-known techniques, which where not previously combined to our knowledge. We use seed 10-ps 1047
nm quantum laser to produce exact optical replica of ultrafast electron bunches. The replica is generated in an apparatus which consists of an input undulator (energy modulator), and the short output undulator (radiator) separated by a dispersion section. The radiation in the output undulator is excited by the electron bunch modulated at the optical wavelength and rapidly reaches 100
MW-level peak power. We then use the now-standard method of ultrashort laser pulse-shape measurement, a tandem combination of autocorrelator and spectrum (FROG—frequency resolved optical gating). The FROG trace of the optical replica of electron bunch gives accurate and rapid electron bunch shape measurements in a way similar to a femtosecond oscilloscope. Real-time single-shot measurements of the electron bunch structure could provide significant information about physical mechanisms responsible for generation ultrashort electron bunches in bunch compressors. The big advantage of proposed technique is that it can be used to determine the slice energy spread and emittance in multishot measurements. It is possible to measure bunch structure completely, that is to measure current, energy spread and transverse emittance as a function of time. We illustrate with numerical examples the potential of the proposed method for electron beam diagnostics at the European XFEL.
We propose a scheme for generation of single 100 GW 300-as pulse in the X-ray free electron laser with the use of a few cycles optical pulse from Ti:sapphire laser system. Femtosecond optical pulse ...interacts with the electron beam in the two-period undulator resonant to 800 nm wavelength and produces energy modulation within a slice of the electron bunch. Following the energy modulator the electron beam enters the first part of the baseline gap-adjustable X-ray undulator and produces SASE radiation with 100 MW-level power. Due to energy modulation the frequency is correlated to the longitudinal position within the few-cycle-driven slice of the SASE radiation pulse. The largest frequency offset corresponds to a single-spike pulse in the time domain which is confined to one half-oscillation period near the central peak electron energy. After the first undulator the electron beam is guided through a magnetic delay which we use to position the X-ray spike with the largest frequency offset at the “fresh” part of the electron bunch. After the chicane the electron beam and the radiation produced in the first undulator enter the second undulator which is resonant with the offset frequency. In the second undulator the seed radiation at reference frequency plays no role, and only a single (300 as duration) spike grows rapidly. The final part of the undulator is a tapered section allowing to achieve maximum output power 100–150 GW in 0.15 nm wavelength range. Attosecond X-ray pulse is naturally synchronized with its fs optical pulse which reveals unique perspective for pump–probe experiments with sub-femtosecond resolution.
The paper presents a comprehensive analysis of the statistical properties of the radiation from a self-amplified spontaneous emission (SASE) free electron laser operating in linear and nonlinear ...mode. The investigation has been performed in a one-dimensional approximation assuming the electron pulse length to be much larger than a coherence length of the radiation. The following statistical properties of the SASE FEL radiation have been studied in detail: time and spectral field correlations, distribution of the fluctuations of the instantaneous radiation power, distribution of the energy in the electron bunch, distribution of the radiation energy after the monochromator installed at the FEL amplifier exit and radiation spectrum. The linear high gain limit is studied analytically. It is shown that the radiation from a SASE FEL operating in the linear regime possesses all the features corresponding to completely chaotic polarized radiation. A detailed study of statistical properties of the radiation from a SASE FEL operating in linear and nonlinear regime has been performed by means of time-dependent simulation codes. All numerical results presented in the paper have been calculated for the 70 nm SASE FEL at the TESLA Test Facility being under construction at DESY.
FAST: a three-dimensional time-dependent FEL simulation code Saldin, E.L.; Schneidmiller, E.A.; Yurkov, M.V.
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
1999, Letnik:
429, Številka:
1
Journal Article
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In this report we briefly describe the three-dimensional, time-dependent FEL simulation code FAST. The equations of motion of the particles and Maxwell's equations are solved simultaneously taking ...into account the slippage effect. Radiation fields are calculated using an integral solution of Maxwell's equations. A special technique has been developed for fast calculations of the radiation field, drastically reducing the required CPU time. As a result, the developed code allows one to use a personal computer for time-dependent simulations. The code allows one to simulate the radiation from the electron bunch of any transverse and longitudinal bunch shape; to simulate simultaneously an external seed with superimposed noise in the electron beam; to take into account energy spread in the electron beam and the space charge fields; and to simulate a high-gain, high-efficiency FEL amplifier with a tapered undulator. It is important to note that there are no significant memory limitations in the developed code and an electron bunch of any length can be simulated.
We propose a technique for the production of attosecond X-ray pulses which is based on the use of X-ray SASE FEL combined with a femtosecond laser system. A few-cycle optical pulse from a Ti:sapphire ...laser interacts with the electron beam in a two-period undulator resonant to 800 nm wavelength and produces energy modulation within a slice of the electron bunch. Following the energy modulator the electron beam enters the X-ray undulator and produces SASE radiation. Due to energy modulation the frequency is correlated to the longitudinal position within the few-cycle-driven slice of SASE radiation pulse. The largest frequency offset corresponds to a single-spike pulse in the time domain which is confined to one half-oscillation period near the central peak electron energy. The selection of single-spike pulses is achieved by using a crystal monochromator after the X-ray undulator. Our studies show that the proposed technique is capable to produce 300-as long single pulses with GW-level output power in the 0.1 nm wavelength range, and is applicable to the European X-Ray Laser Project XFEL and the Linac Coherent Light Source at SLAC.
In this paper we consider a possible mechanism of strong distortions of longitudinal phase space due to collective effects in an electron bunch passing a bunch compressor. Analytical expressions are ...derived for the case of a linear compression. Estimates for the TESLA Test Facility at DESY are presented.
On the coherent radiation of an electron bunch moving in an arc of a circle Saldin, E.L.; Schneidmiller, E.A.; Yurkov, M.V.
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
10/1997, Letnik:
398, Številka:
2
Journal Article
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Existing theories of coherent synchrotron radiation (CSR) are developed for the motion of an electron bunch on a circular orbit and do not describe the case of finite magnet length. In this paper we ...present the CSR theory for a bunch of any length moving in an arc of a finite angle. The radiative interaction of the electrons in the bunch is analyzed for a line charge distribution using an ultrarelativistic approximation. It is shown in particular that this interaction is important not only inside the magnet but also on the straight part of the trajectory after the magnet.
Detailed analytical study of the CSR effects in the electron bunch with a stepped distribution of the charge density has been performed. The simple analytical technique of the radiative force calculation has been developed. The analytical solutions in the form of elementary functions are obtained for the radiative interaction force, for the energy loss distribution along the bunch and for the total energy loss of the bunch. The latter result is confirmed with calculation of the energy of coherent radiation in the far zone. The criterium for the applicable region of the existing theories to the case of a finite magnet length is obtained.
A new design for a single pass X-ray Self-Amplified Spontaneous Emission (SASE) FEL is proposed. The scheme consists of two undulators and an X-ray monochromator located between them. The first stage ...of the FEL amplifier operates in the SASE linear regime. After the exit of the first undulator the electron bunch is guided through a non-isochronous bypass and the X-ray beam enters the monochromator. The main function of the bypass is to suppress the modulation of the electron beam induced in the first undulator. This is possible because of the finite value of the natural energy spread in the beam. At the entrance to the second undulator the radiation power from the monochromator dominates significantly over the shot noise and the residual electron bunching. As a result the second stage of the FEL amplifier operates in the steady-state regime when the input signal bandwidth is small with respect to that of the FEL amplifier. Integral losses of the radiation power in the monochromator are relatively small because grazing incidence optics can be used. The proposed scheme is illustrated for the example of the 6 nm option SASE FEL at the TESLA Test Facility under construction at DESY. As shown in this paper the spectral bandwidth of such a two-stage SASE FEL (Δλ/λ⋍ 5 × 10−5) is close to the limit defined by the finite duration of the radiation pulse. The average brilliance is equal to 7 × 1024photons/(s × mrad2 × mm2 × 0.1% bandw.) which is by two orders of magnitude higher than the value which could be reached by the conventional SASE FEL. The monochromatization of the radiation is performed at a low level of radiation power (about 500 times less than the saturation level) which allows one to use conventional X-ray optical elements (grazing incidence grating and mirrors) for the monochromator design.
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