The kinetic approximation was used to obtain an expression for the bilinear component of the nonlinear charge density, which is used to describe the parametric decay of a microwave with ordinary polarization whose frequency corresponds to the second harmonic of the electron cyclotron resonance. As a result of the decay, an upper hybrid wave and a lower hybrid wave are excited.

The nonlinear theory of radial correlation reflectometry (RCR) predicts that the cross correlation function of a signal follows a Gaussian distribution with a cutoff separation, where the correlation length is determined by both the turbulence amplitude and its radial correlation length. In contrast, phase spectrum analysis provides information solely on the turbulence amplitude. This work describes the possibility of applying both signal analysis methods and demonstrates that turbulence amplitude and radial correlation length can be simultaneously measured using RCR diagnostics in the nonlinear regime.

The saturation level of the two Upper-Hybrid-plasmon low-threshold parametric decay instability (PDI) depends on the pump wave beam width. The edge plasma turbulence may lead to drastic distortion of the pump beam, thus generating PDI characteristic changes. Numerical evaluations of the PDI process are provided in this work for different turbulence scenarios. The average PDI characteristics are evaluated and compared to the simulation results for the pump beam unperturbed by the edge plasma turbulence. It is shown that up to the intermediate turbulence level, the PDI characteristics are only gently modified. But at high edge turbulence level, which can happen in tokamaks, the threshold increases and the growth rate reduces. It is important to note that the anomalous absorption keeps a little reduction value, whatever the edge turbulence regimes.

Plasma turbulence can result in significant distortion of probing and receiving microwave beams, and this effect can modify the registered spectrum in a collective Thomson scattering (CTS) experiment. An analytical description of the CTS experiment is provided in this paper for the probing beam distortion due to the plasma edge turbulence. The effect of the registered frequency spectrum distortion by the turbulence is evaluated for different turbulence levels for plasma parameters similar to those excepted in ITER.

It is shown that plasma turbulence at the edge of a fusion machine can lead to significant broadening of an X-mode microwave beam, which also impacts the performance of the heating systems and diagnostics. Based on a similar method developed for O-mode polarization, the expression for the mean microwave power distribution after the beam passes through the plasma edge turbulence is obtained, and its spatial and probabilistic distributions are analyzed. As this polarization is used for collective Thomson scattering (CTS) on ITER and for electron cyclotron resonance heating (ECRH) on ASDEX Upgrade, numerical simulations of beam broadening due to the edge turbulence are performed for the two conditions of plasma parameters, related to the planned CTS experiments on ITER and to ECRH experiments on ASDEX Upgrade. Ideas to reduce the beam broadening induced by the edge turbulence in the CTS case have been tested and are summarized in the conclusion.

— In this paper, we obtain an expression for the high-frequency quadratic susceptibility of strongly inhomogeneous magnetoactive plasma, which describes the nonlinear coupling of an ordinary wave with longitudinal oscillations.

Получено выражение для высокочастотной квадратичной восприимчивости сильно неоднородной магнитоактивной плазмы, которое описывает нелинейную связь волны обыкновенной поляризации с продольными колебаниями.

The expression is obtained for the high-frequency quadratic susceptibility of the strongly inhomogeneous magnetoactive plasma, which describes the nonlinear coupling between the extraordinary polarized wave and the longitudinal vibrations and makes it possible to explain the strong anomalous absorption of the pump wave observed in the model experiments.

The possibility of the anomalous electromagnetic emission in the ECRH experiments at both half the gyrotron frequency and the 3/2 harmonic of it associated with excitation of low-threshold two-upper hybrid-plasmon parametric decay instability is predicted. The experimental conditions when this emission can be detected are analyzed. A measurable level of the corresponding radiance temperature is demonstrated. The general consideration is accompanied by the numerical analysis performed under the experimental conditions typical of the off-axis X2-mode ECRH experiments.

Recent research at three small tokamaks with different parameters located at the Ioffe Institute—the spherical tokamak Globus-M, the large aspect ratio tokamak FT-2 and the compact tokamak TUMAN-3M—are reviewed. This overview covers energy confinement (Globus-M and FT-2), L–H transition (TUMAN-3M and FT-2), Alfvén waves (Globus-M and TUMAN-3M), ion cyclotron emission (TUMAN-3M), major plasma discharge disruption (Globus-M) and scrape-off layer (Globus-M) studies. A full-f global gyrokinetic modeling benchmark using synthetic diagnostics in FT-2 is described. Anomalous absorption and emission in electron cyclotron resonance heating experiments due to the parametric excitation of localized upper hybrid waves are analyzed theoretically. Progress in the development of the neutral particle analysis, gamma-ray spectrometry and divertor Thomson scattering combined with laser-induced fluorescence diagnostics for ITER is discussed. The status of the new Globus-M2 spherical tokamak is reported.

We revisit the problem of a resonant interaction between the electromagnetic extraordinary and two electrostatic waves in uniform plasmas. Starting from analysis of the kinetic equation, we eventually get the formal integral representation of the coupling coefficients describing this nonlinear phenomenon and simplify it substantially. The final expressions for the coupling coefficients are obtained in the form convenient for numerical analysis. We prove them to obey the Manley–Rowe symmetry and compare the derived formula to the one obtained within the cold-fluid model.

The bilinear plasma susceptibility describing the nonlinear coupling of electromagnetic and two electrostatic waves in strongly non-uniform magnetized plasmas is derived using both the distribution function moments equations and the kinetic approach. The possibility of the drastic enhancement of nonlinear coupling leading to a decrease of the two-plasmon decay instability threshold in strongly inhomogeneous plasmas is demonstrated.

It has been shown that plasma inhomogeneity reduces the threshold of the parametric instability of two-plasmon decay and, in particular, allows the excitation of plasmons with the same frequency by a spatially uniform pump field.

Показано, что неоднородность плазмы снижает порог параметрической неустойчивости двухплазмонного распада и, в частности, делает возможным возбуждение плазмонов одинаковой частоты пространственно однородным полем накачки.