Formation of high-brightness REB to generate THz radiation in beam-plasma system

Summary form only given. Terahertz emission from plasma with strong Langmuir turbulence excited by high current relativistic electron beam (REB) is experimentally studied at the GOL-3 facility (BINP). The typical parameters of the beam used in the experiments, were the following: 0.6÷0.8 MeV/20 kA/10 μs. In recent experiments the beam current density was about 1÷2 kA/cm² in a plasma column with the density ~ 2·10¹⁴ cm^-3 that allowed us to get sub THz-emission with a power of a few kW/cm³ in the frequency range 100÷400 GHz. To extend our experiments on emission to the range of 1 THz we have to inject the beam into the plasma column of higher density 1÷2·1015 cm^-3. This level of the plasma density requires the substantial increase of the beam brightness in the plasma. To solve this problem we have performed 2-D self-consistent simulations by numerical code POISSON-2 for the beam formation at different geometries of a magnetically insulated ribbon diode. In addition, the transformation of the generated ribbon beam to a circular one and its compression to the radius ~2 cm in the magnetic field ~4 T in which the plasma column is placed, were also considered in the computer simulations. To determine the brightness of the beam we have measured the beam current density and the angular spread of the beam electrons after the transformation and compression of the beam cross-section. The comparison of the experimental and simulation data has been done. The obtained results are used for the design of a new diode configuration with high brightness of the beam.