A.A Fateev

Study of the statistical properties of the radiation from a VUV SASE FEL operating in the femtosecond regime

The Free-Electron Laser (FEL) at the TESLA Test Facility at DESY operates in the self-amplified spontaneous emission mode and generates sub-100-fs radiation pulses in the vacuum ultraviolet spectral region. During operation in the saturation regime, radiation pulses with GW peak power are produced. The statistical properties of the FEL radiation have been studied for different amplification regimes as well as behind a narrow-band monochromator and found to be in good agreement with the results of numerical simulations. Information about the spectral and temporal structure of the FEL radiation has been deduced from the statistical properties. The pulse duration of the FEL radiation can be varied by tailoring the electron bunch that drives the FEL.

Development of a pump-probe facility combining a far-infrared source with laser-like characteristics and a VUV free electron laser

Abstract The TESLA Test Facility (TTF) at DESY is a facility producing sub-picosecond electron pulses for the generation of VUV or soft X-ray radiation in a free electron laser (FEL). The same electron pulses would also allow the direct production of high-power coherent radiation by passing the electron beam through an undulator. Intense, coherent far-infrared (FIR) undulator radiation can be produced from electron bunches at wavelengths longer than or equal to the bunch length. The source described in this paper provides, in the wavelength range 50– 300 μm , a train of about 1– 10 ps long radiation pulses, with about 1 mJ of optical energy per pulse radiated into the central cone. The average output power can exceed 50 W . In this conceptual design, we intend to use a conventional electromagnetic undulator with a 60 cm period length and a maximum field of 1.5 T . The FIR source will use the spent electron beam coming from the VUV FEL which allows one to significantly extend the scientific potential of the TTF without interfering with the main option of the TTF FEL operation. The pulses of the coherent FIR radiation are naturally synchronized with the VUV pulses from the main TTF FEL, enabling pump-probe techniques using either the FEL pulse as a pump or the FIR pulse as a probe, or vice versa.

Alignment of the optical feedback system of VUV regenerative FEL amplifier at the TESLA test facility at DESY

In this paper, we describe optical feedback system of VUV Regenerative FEL Amplifier (RAFEL) at the TESLA test facility at DESY. The aim of the RAFEL experiment is to construct fully coherent, tunable VUV radiation source by means of applyingnarrow-band optical feedback in the VUV SASE FEL operatingcurrently at DESY. One of the problem of the realization of the RAFEL is severe requirements for the angular stability of the optical elements (about few microradians). This problem has been solved by means of installation of active alignment system with reference laser. Another problem is alignment of optical elements separated by 65 m within complicated experimental conditions connected with aperture limitations (down to 6 mmÞ: This problem has been solved in two steps. Preliminary alignment with an accuracy of about 80 mrad has been performed with laser alignment system and OTR screens used at the TTF accelerator for electron beam diagnostics. Final alignment has been performed with VUV SASE FEL radiation. Measured feedback coefficient is about 1 percent and is in agreement with the designed value. r 2002 Elsevier Science B.V. All rights reserved. PACS: 41.60.Cr; 52.75.M; 42.62.Cf

A CONCEPT OF A WIDE APERTURE KLYSTRON WITH RF ABSORBING DRIFT TUBES FOR A LINEAR COLLIDER

Abstract This paper is devoted to a problem of the optimal design of the electrodynamic structure of the X-band klystron for a linear collider. It is shown that the optimal design should provide a large aperture and a high power gain, about 80 dB. The most severe problem arising here is that of parasitic self-excitation of the klystron, which becomes more complicated at increasing aperture and power gain. Our investigations have shown that traditional methods for suppressing the self-excitation become ineffective at the desired technical parameters of the klystron. In this paper we present a novel concept of a wide aperture klystron with distributed suppression of parasitic oscillations. Results of an experimental study of the wide-aperture relativistic klystron for VLEPP are presented. Investigations have been performed using the driving beam of the JINR LIA-3000 induction accelerator ( E = 1 MeV, I = 250 A, τ = 250 ns). To suppress self-excitation parasitic modes we have used the technique of RF absorbing drift tubes. As a result, we have obtained design output parameters of the klystron and achieved a level of 100 MW output power.

Study of 14 GHz VLEPP klystrons with 11 and 15 mm aperture

Results of experimental study of two variants of relativistic klystron for VLEPP are presented. Investigations have been performed using the driving beam of the JINR LIA‐3000 induction accelerator (E=1 MeV, I=300 A, τ=250 ns). The main emphasis is put on the study of the self‐excitation parasitic modes and their temporal evolution. A concept of relativistic klystron with RF absorbing drift tubes is proposed to solve the problem of the parasitic oscillations suppression. The results of preliminary experiments with such a klystron are presented, too.

JINR test facility for studies FEL bunching technique for CLIC driving beam

Abstract SILUND-21 linear induction accelerator (energy up to 10 MeV, peak current about of 1 kA, pulse duration 50–70 ns) is constructed at JINR in the framework of an experimental program to study free electron laser physics, a problem of two-beam acceleration and microwave electronics. In this paper we present the project of an experiment to adopt the FEL bunching technique for generation of the CLIC driving beam.

Study of 14 GHz VLEPP klystron with RF absorbing drift tubes

Results of experimental study of a wide-aperture relativistic klystron for VLEPP are presented. Investigations have been performed using the driving beam of the JINR LIA-3000 induction accelerator. To suppress self-excitation parasitic modes we have used technique of RF absorbing drift tubes. We have obtained 75 MW of output power in a long pulse (250 ns) and 100 MW in a short pulse (50 ns).

Development of a pump-probe facility with sub-picosecond time resolution combining a high-power ultraviolet regenerative FEL amplifier and a soft X-ray SASE FEL

This paper presents the conceptual design of a high power radiation source with laser-like characteristics in the ultraviolet spectral range at the TESLA Test Facility (TTF). The concept is based on the generation of radiation in a regenerative FEL amplifier (RAFEL). The RAFEL described in this paper covers a wavelength range of 200–400 nm and provides 200 fs pulses with 2 mJ of optical energy per pulse. The linac operates at 1% duty factor and the average output radiation power exceeds 100 W. The RAFEL will be driven by the spent electron beam leaving the soft X-ray FEL, thus providing minimal interference between these two devices. The RAFEL output radiation has the same time structure as the X-ray FEL and the UV pulses are naturally synchronized with the soft X-ray pulses from the TTF FEL. Therefore, it should be possible to achieve synchronization close to the duration of the radiation pulses (200 fs) for pump-probe techniques using either an UV pulse as a pump and soft X-ray pulse as a probe, or vice versa. r 2001 Elsevier Science B.V. All rights reserved.

Development of a facility for probing the structural dynamics of materials with femtosecond X-ray pulses

We propose to use Thomson backscattering of far-infrared (FIR) pulses (100–300 μm wavelength range) by a 500 MeV electron beam to generate femtosecond X-rays at the TESLA Test Facility (TTF) at DESY. Using the parameters of the photocathode rf gun and the magnetic bunch compressors of the TESLA Test Facility (TTF), it is shown that electron pulses of 100-fs (FWHM) duration can be generated. Passing the short electron bunches through an undulator (after the conversion point) can provide a FIR high-power source with laser-like characteristics. On the basis of the TTF parameters we expect to produce X-ray pulses with 100-fs duration, an average brilliance of nearly 1013 photons s−1 mrad−2 mm−2 per 0.1% BW at a photon energy 50 keV. The total number of Thomson backscattered photons, produced by a single passage of the electron bunch through the mirror focus, can exceed 107 photons/pulse. We also describe the basic ideas for an upgrade to shorter X-ray pulse duration. It is demonstrated that the TTF has the ca...

Powerful nanosecond pulsed generators for linear induction accelerators at JINR

The paper presents a review of nanosecond pulse generator schemes for LIA developed at the JINR. The main feature of these schemes consists in the use of relatively low-voltage generators (V∼20−50 kV) with low-resistance output impedance (R∼0.5 Ω). A high power in nanosecond pulses (W∼1 GW) is produced by nonlinear compression schemes with distributed parameters which compress electromagnetic energy in time.