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Contribution Oral

SR and FEL sources and centers

Inter-cavity scattering schemes of planar THz-band FELs based on parallel intense moderately-relativistic sheet electron beams


  • Prof. Nikolai PESKOV

Primary authors


Up to now free-electron lasers are much powerful generators in THz-band able to operate at multi-megawatt power level. Such devices are driven by relativistic electron beams (REBs) of ~ 5 - 10 MeV oscillating in magnetostatic undulators and, thus, are rather bulky and costly. At the same time, generation of powerful THz radiation can be realized when using moderately-relativistic (0.5 - 1.5 MeV) high-current (1 - 3 kA) electron beams together with intense mm wave to pump transverse oscillations of the electrons (so-called RF-undulator), which could possesses much shorter period (wavelength) in comparison with “traditional” magnetostatic undulators (with additional twice higher Doppler up-conversion in counter scattering scheme). In FEL of such type (FEL-scattron) it is attractive to exploit an inter-cavity scattering regimes when pumping wave is generated by the same or parallel electron beam and, thus, no additional powerful microwave sources is needed.

Original project of multi-MW long-pulse two-stage FEL-oscillator based on two parallel sheet REBs is under development at the high-current accelerator ELMI in collaboration between BINP RAS (Novosibirsk) and IAP RAS (N.Novgorod). The basis for this project is 75 GHz planar FEM with two-dimensional distributed feedback, which was elaborated currently with a record-level output power (~ 50 MW) and narrow-band spectrum. In the two-stage scheme, this 75 GHz FEM module is used as a driver (i.e. the first stage of the oscillator). This 75 GHz radiation is transported by special waveguide (set of the Bragg deflectors) to the second channel and used as a pumping wave. At the second stage this wave undergoes stimulated scattering at the supplementary REB to produce THz radiation.

According to simulation, proposed scheme allows THz radiation pulses of ~ 10 - 20 kW power to be obtained in the so-called SASE-regime. Installation in the FEL-scattron section of advanced Bragg resonator to provide feedback loop for THz radiation, would result in increase of the output power of the THz channel up to a multi-megawatt level. As a result, energy content of up to 1 - 10 J in the THz-band pulses of hundreds nanoseconds to microsecond pulse duration can be achieved.

Key components of the electrodynamical system for two-stage FEM were manufactured and good coincidence of their “cold” tests with results of simulations was demonstrated. Experimental studies of this FEM scheme is in progress currently.