• A. Raghavi
  pnum, Mashhad
• N. Mahdizadeh
  PPRC, Tehran

A combination of two planar magnetic wigglers with orthogonal fields and a shared electron beam is proposed for energy transfer between two different electromagnetic waves. It is shown that one of the wigglers can acts as an IFEL accelerator by extracting energy from a seed wave while simultaneously another wiggler works as a FEL and amplifies its corresponding resonant frequency. The equation of motion in the small signal gain (SSG) regime for this FEL-IFEL structure is studied. It is shown that the bunching process occurs for the electron beam in two different scales, corresponding to two different ponderomotive waves. It is concluded finally that, in principle, it is possible to use a FEL-IFEL scheme for energy exchange between two electromagnetic waves and retain an electron beam in resonance with two different electromagnetic waves simultaneously.

• V. Petrillo, C. Maroli
  Universita' degli Studi di Milano, Milano
• M. Ferrario
  INFN/LNF, Frascati (Roma)
• L. Giannessi
  ENEA C.R. Frascati, Frascati (Roma)

We have written and numerically solved a set of 1-d FEL equations for electrons and radiation without the need of the slowly varying envelope approximation (SVEA). The equations, which take into account both forward and backward waves, have been applied to the case of a very short beam, as long as few wavelenghts, and to the case of long beams with short density modulations.

• E. Schneidmiller, M.V. Yurkov
  DESY, Hamburg

With the present undulator (planar, period 2.73 cm, peak field 0.486 T) the minimum wavelength of 4.5 nm at FLASH is determined by the maximum electron beam energy of approximately 1.2 GeV. On the other hand, many perspective user applications require shorter wavelength radiation and circular polarization. In this paper we perform analysis of a helical afterburner for generation of short wavelength, helically polarized radiation. We consider two options, operation of the afterburner at the second (frequency doubler), and the fourth (frequency quadrupler) harmonics. Since even harmonic of the SASE FEL radiation are suppressed, there is no linearly polarized background radiation from the main undulator. Our simulations show that relatively high level of the radiation power can be achieved in the afterburner, about 60 MW in the frequency doubler, and about 5 MW in the frequency quadrupler.

• M. Takasaki, M. A. Bakr, Y.W. Choi, K. Ishida, T. Kii, N. Kimura, R. Kinjo, K. Masuda, K. Nagasaki, H. Ohgaki, T. Sonobe, S. Ueda, K. Yoshida
  Kyoto IAE, Kyoto

A triode rf gun has been developed aiming at drastic reduction of back-streaming electrons at the thermionic cathode. Thermionic rf gun shows some advantages over photocathode gun such as low cost, easy operation and high average current, which are suitable for oscillator FELs. However, use of thermionic rf gun leads to inherent back-bombardment effect, which not only limits the macro-pulse duration, but also degrades the electron beam quality. In order to reduce the back-streaming electrons, we developed a thermionic triode rf gun which employs coaxial rf cavity much shorter than rf wavelength as the first cell. The phase and amplitude of the electric field for the first cell are independently controlled from successive cells. The results from simulations showed that the back-bombardment power was expected to be reduced by more than 80% without loss of beam brightness. The coaxial rf cavity to be installed in the rf gun for KU-FEL has been developed and a cold test has been performed. In this paper, we will report on the cold test results and comparison of them with the designed performance as well.

• T. Denis, K.-J. Boller, P.J.M. van der Slot
  Mesa+, Enschede

Compact, slow-wave, low energy electron beam radiation sources, like Cerenkov free-electron lasers (FELs), emit high power microwaves. However, they seriously degrade in output power, when scaled towards the THz range (0.1-10 THz). This prevents industry from applying THz radiation, although it would allow many new applications, like chemical selective security surveillance. The photonic free-electron laser (pFEL) is a promising concept for a handheld, tunable and Watt-level THz laser. In a pFEL several electron beams stream through a photonic crystal (PhC) leading to the emission of coherent Cerenkov radiation. The beams emit phase-locked due to the transverse scattering inside the PhC, which allows increasing the output power by increasing the number of beams streaming through the PhC. Therefore, scaling the pFEL’s operating frequency towards THz frequencies can be done without loss in output power. Furthermore, compact, low energy electron sources (< 15 keV) can drive the laser, due to the strong deceleration of the light by PhC’s. As a proof of principle, we developed the setup for a pFEL operating at 20 GHz to study the interaction between a single electron beam and the PhC.