Moiseyenko V. Radio-frequency plasma discharges in fusion devices

A new numerically stable method of weighted residuals and a model for Maxwell's equations in cylindrical geometry are developed, where all components of the electric field are represented by means of identical finite elements. It is more effective than Galerkin method when stiffness takes place in Maxwell's equations. An original numerically stable model for the calculation of electromagnetic fields in the plasma of axisymmetric open traps without taking into account slow waves has been developed. It is implemented in the new upgraded PLFEM-S code, which differs in the possibility of numerically stable calculation of azimuthal-asymmetric modes. The new method is proposed, and the model for calculation of electromagnetic fields in plasma of non-axisymmetric open traps without taking into account slow waves is developed. A new numerical model for calculating the distribution and absorption of radio frequency fields by sloshing ions (splashing ions). An original and effective method for calculations with strongly oscillating solutions has been developed. It allows one to use a sparse grid and thereby significantly reduce computational costs. Lower hybrid resonance in cold plasma leads to singular solutions of Maxwell's equations. The application of the penalty method allows one to bypass these difficulties without the large additional costs associated with the complexity of the calculation algorithm. The comparative analysis of methods of radio-frequency heating of plasma in mirrors is given. Simulation of ion-cyclotron heating of sloshing ions in an open trap with straight lines of force was performed. For large traps, heating of the minority is effective in a wide range of minority concentrations and plasma densities. An efficient scenario of heating sloshing ions on the second cyclotron harmonic in an open trap with straight lines of force is substantiated and proposed. A detailed analysis of the invented scenario of rapid plasma heating during its creation in a mirror showed its significant efficiency. The calculations indicate its prospects for pulse modes of operation. A theoretical study of the penetration of an electrostatic field through a Faraday screen of a half-turn antenna for the first time showed a significant advantage of a two-layer screen. Experiments on the Uragan -3M demonstrated the success of the Alfven heating scenario with high k||, which was implemented using a compact three-half-turn antenna. The analysis of the features of discharges in the Uragan -3M torsatron showed the high efficiency of radio-frequency plasma heating together with defects in the magnetic configuration of the Uragan -3M. There are several options to change the configuration to make the area of the embedded magnetic surfaces wider. An inwardly shifted magnetic configuration is a promising choice in this regard. Radio-frequency plasma heating was first introduced and studied in Uragan -2M. The new crankshaft antenna heats the plasma at frequencies below the ion-cyclotron frequency. The discharge supported by this antenna becomes "hot" for a few milliseconds, and then fades under a strong influx of impurities into the plasma. The scenario of high-frequency cleaning of inner vacuum surfaces with the help of continuous VHF discharge, proposed, implemented and studied at Uragan -2M, showed a high cleaning speed. Numerical simulations indicate the insufficient suitability of the initially used loop antenna for VHF discharge: its load resistance is too small for good electrical matching. Instead of a frame, a T-shaped antenna was proposed, which can be used during continuous cleaning of walls in toroidal magnetic traps. The scenario of high-frequency cleaning of inner vacuum surfaces in the mode of ultrashort pulses of electron-cyclotron heating in a hydrogen atmosphere was introduced and studied on the Wendelstein7-X stelarator. A detailed study of Uragan -3M pulsed high-frequency cleaning in a small magnetic field. The cleaning discharge with excitation of fast magnetosonic wave is convenient that it can be carried out, using the same antenna devices and RF generators which are used for creation and heating of plasma in working modes, and without any change of frequency of antenna and generator RF circuits. An original concept of a stelarator-mirror nuclear-thermonuclear hybrid has been developed and estimates of energy balance have been made. Modeling was performed on the concept of stelarator-mirror hybrid with injection of neutral atoms. Injection of the neutral beam can be used to create a population of hot tritium ions in the mirror part of the stelarator- mirror thermonuclear-fission hybrid. The results of power balance calculations are close to the results obtained for a system with radio-frequency heating. The calculated thermonuclear Q is within the required range. Also, a study of the motion of fast ions created by high-frequency heating in the stelarator-mirror mode of Uragan -2M operation was performed.