Search

Experimental and theoretical investigations of lower hybrid (LH) turbulence in the W7-AS stellarator are presented. The turbulence is excited by an ion beam, which is generated by a weak neutral hydrogen beam injected transversely to the confining magnetic field. The instability is detected by collective Thomson scattering of powerful gyrotron radiation. From the measured density dependence of the frequency it was identified as an LH type of instability. The spectrum is characterized by a narrow bandwidth in spite of the inherently poor radial resolution of the backscattering geometry. The theoretical model of an LH instability driven by a transverse fast ion component under the double resonance condition (coincidence of the LH frequency with a high cyclotron harmonic of the fast ions) is developed. The instability growth rate is derived. The stabilizing effect of high bulk ion temperatures was observed experimentally, in accordance with theoretical modelling. An instability saturation mechanism similar to the well known stochastic ion heating is proposed.

Calculation of the thermal regime and radiation of the Moon has been made, taking into account the temperature dependence of the specific heat, thermal conductivity, and absorption coefficient of the material. It is shown that the temperature dependence of the specific heat, typical of silicates, leads to a decrease of the calculated nighttime temperature of the Moon by 5–6°K. When the thermal conductivity varies 1.5 time in the interval 0–300°K, the temperature dependence of the thermal conductivity increases the nighttime temperature by 3–4°K and that during the shade phase of eclipse by 5–6°K. The only one considerable effect caused by the temperature dependence of the thermal conductivity is the growth of the constant component of the temperature up to the depth of 10–15 cm. As a result of it, the constant component of radiation increases with the growth of wavelenght up to λ = 1.5−2 cm. The linear temperature dependence of the absorption coefficient which is typical of silicates produces an increase of the constant component of radiation with the maximum 10–20° at 0.1–0.2 cm wavelenghts. It is concluded that precision measurements of the constant component of radiation on 2–3 cm, 0.1–0.2 cm wavelenghts and infrared waves are needed for determining the temperature dependence of the thermal conductivity and absorption coefficient.