Investigation of subterhaertz emission from turbulent plasma heated by powerful REB at multimirror trap GOL-3 (2009)

Summary forn only given. Study of Langmuir turbulence (LT) in plasma and LT-induced nonlinear phenomena remains an important topic of the fundamental plasma science. A distinctive LT's feature is possibility of electromagnetic radiation emission on plasma frequency (v <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> ) and dual plasma frequency (2v <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> ) due to processes of plasmon conversion on plasma density fluctuations and plasmon-plasmon merging respectively. Well-identified in solar radio-flares, these processes remained weakly studied in laboratory plasmas. In this report we present the first results on experimental investigation of 100-550GHz-emission from hot (Tc~1 keV) and dense (n~10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sup> -10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">15</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> ) plasma at the GOL-3 multi- mirror open magnetic trap operating in conditions of turbulent heating by a powerful high-current relativistic electron beam (E <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> ~0.8 MeV, I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> ~30 kA, j <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> ~2 kA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , tau~12 mus, Q~130kJ). An original multi-channel quasi- optical radiometric diagnostics developed for spectral measurements at frequencies 100-550GHz corresponding to aforementioned v <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> - and 2v <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</sub> -emission processes is described. The diagnostics includes fast Shottky-diode-based receivers with internal preamplifiers for registering 1muW-10 mW radiation at integration time < 5 ns, and a set of quasi-optical band-pass metal mesh filters for selecting spectral bands at typical FWHM 20-60GHz and out-of-band rejection 20-40dB. The performed REB-plasma interaction experiments revealed a significant level of subterahertz emission with duration 7-10mus, which in some cases exceeded a saturation level of Shottky-detectors at "plasma-receiver" distance 2-3 m. It was observed a strong correlation of emission spectra with dynamics of plasma density, as well as spectra broadening and high-frequency shifting during REB-injection. The data of radiometric diagnostics are compared with combined data of laser scattering and other GOL-3 diagnostics for detailed analysis of LT-physics and verification of theoretical models.