33 research outputs found
Generation of powerful terahertz emission in a beam-driven strong plasma turbulence
Generation of terahertz electromagnetic radiation due to coalescence of
upper-hybrid waves in the long-wavelength region of strong plasma turbulence
driven by a high-current relativistic electron beam in a magnetized plasma is
investigated. The width of frequency spectrum as well as angular
characteristics of this radiation for various values of plasma density and
turbulence energy are calculated using the simple theoretical model adequately
describing beam-plasma experiments at mirror traps. It is shown that the power
density of electromagnetic emission at the second harmonic of plasma frequency
in the terahertz range for these laboratory experiments can reach the level of
1 with 1% conversion efficiency of beam energy losses to
electromagnetic emission
Detection of high k turbulence using two dimensional phase contrast imaging on LHD
High k turbulence, up to 30 cm(-1), can be measured using the two dimensional COâ‚‚ laser phase contrast imaging system on LHD. Recent hardware improvements and experimental results are presented. Precise control over the lens positions in the detection system is necessary because of the short depth of focus for high k modes. Remote controllable motors to move optical elements were installed, which, combined with measurements of the response to ultrasound injection, allowed experimental verification and shot-to-shot adjustment of the object plane. Strong high k signals are observed within the first 100-200 ms after the initial electron cyclotron heating (ECH) breakdown, in agreement with gyrotron scattering. During later times in the discharge, the entire k spectrum shifts to lower values (although the total amplitude does not change significantly), and the weaker high k signals are obscured by leakage of low k components at low frequency, and detector noise, at high frequency