BINP SB RAS, Novosibirsk
The startup from noise problem in SASE FELs is usually treated in linear approximation. In this case amplification of initial density fluctuations may be calculated and averaging over initial conditions may be fulfilled explicitly. In general nonlinear case the direct averaging is not applicable. During last years we developed the approach based on the BBGKY hierarchy for the n-particle distribution functions. The interaction of particles in FEL is time-dependent (retarded). Nevertheless, using special time-coordinate transformation, it is possible to make interaction “time-independent” and then to write down the BBGKI equations. Similar to plasma physics, the equations may be truncated after the second one (for the two-particle correlation function). Using this approach we consider several particular cases which illustrate some peculiar features of the SASE FEL operation.
BINP SB RAS, Novosibirsk
The projected electron RF gun of 10 MeV L-band injector for FEL employs a commercial thermionic cathode-grid assembly with 0.08 mm gap that conventionally used in metal-ceramic RF tubes. Three-dimensional (3D) computer simulations have been performed that use the mesh refinement capability of the both Microwave Studio (MWS) and 2D SAM codes to examine the whole region of the real cathode-grid assembly in static fields in order to illustrate the beam quality that can result from such a gridded structure. These simulations have been found to reproduce the beam current dependency on applied potentials that are observed experimentally. Based on it ASTRA RF beam simulations also predict a complicated time-dependent response to the waveform applied to the grid during the current turn-on, calculation of the dissipated power by electrons at the grid, and particle tracking downstream of the grid into RF gun cavity and further on. These simulations may be representative in other sources, such as BINP Microtron-Recuperator 180 MHz injector and other RF injectors for industrial and scientific applications.
BINP SB RAS, Novosibirsk
Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Elektronen-Speicherring BESSY II, Berlin
The first stage of Novosibirsk high power free electron laser (FEL) provides electromagnetic radiation in the wavelength range 120 - 230 micron. The maximum average power is 500 W. Five user stations are in operation now. Novosibirsk ERL has rather complicated magnetic system. One orbit for 11-MeV energy with terahertz FEL lies in vertical plane. Other four orbits lie in the horizontal plane. The beam is directed to these orbits by switching on of two round magnets. In this case electrons pass four times through accelerating RF cavities, obtaining 40-MeV energy. Then, (at fourth orbit) the beam is used in FEL, and then is decelerated four times. At the second orbit (20 MeV) we have bypass with third FEL. Last year two of four horizontal orbits are assembled and commissioned. The electron beam was accelerated twice and then decelerated down to low injection energy. First multi-orbit ERL operation was demonstrated successfully. In 2009 the first lasing at the second FEL, installed on the bypass of the second track, was achieved. The wavelength tunability range lays near 50 micron. Energy recovery of a high energy spread used electron beam was optimized.