Self-consistent modeling of radio-frequency plasma generation in stellarators
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SelfConsistent Modeling of RadioFrequency Plasma Generation in Stellarators V. E. Moiseenkoa, Yu. S. Stadnika, A. I. Lysoivanb, and V. B. Korovina a
National Science Center Kharkov Institute of Physics and Technology, National Academy of Sciences of Ukraine, Akademicheskaya ul. 1, Kharkov, 61108 Ukraine email: [email protected], [email protected] b Laboratory for Plasma Physics, Royal Military Academy, EURATOM–Belgian State Association, Avenue de la Renaissance 30, B1000 Brussels, Belgium email: a.lyssoivan@fzjuelich.de Received April 20, 2011; in final form, May 16, 2013
Abstract—A selfconsistent model of radiofrequency (RF) plasma generation in stellarators in the ion cyclotron frequency range is described. The model includes equations for the particle and energy balance and boundary conditions for Maxwell’s equations. The equation of charged particle balance takes into account the influx of particles due to ionization and their loss via diffusion and convection. The equation of electron energy balance takes into account the RF heating power source, as well as energy losses due to the excitation and electronimpact ionization of gas atoms, energy exchange via Coulomb collisions, and plasma heat con duction. The deposited RF power is calculated by solving the boundary problem for Maxwell’s equations. When describing the dissipation of the energy of the RF field, collisional absorption and Landau damping are taken into account. At each time step, Maxwell’s equations are solved for the current profiles of the plasma density and plasma temperature. The calculations are performed for a cylindrical plasma. The plasma is assumed to be axisymmetric and homogeneous along the plasma column. The system of balance equations is solved using the Crank–Nicholson scheme. Maxwell’s equations are solved in a onedimensional approxi mation by using the Fourier transformation along the azimuthal and longitudinal coordinates. Results of sim ulations of RF plasma generation in the Uragan2M stellarator by using a frame antenna operating at fre quencies lower than the ion cyclotron frequency are presented. The calculations show that the slow wave gen erated by the antenna is efficiently absorbed at the periphery of the plasma column, due to which only a small fraction of the input power reaches the confinement region. As a result, the temperature on the axis of the plasma column remains low, whereas at the periphery it is substantially higher. This leads to strong absorption of the RF field at the periphery via the Landau mechanism. DOI: 10.1134/S1063780X1311007X
1. INTRODUCTION The physical basis for plasma production is elec tronimpact ionization of neutral particles. The ion ization crosssection reaches its maximum value at electron energies several times higher than the thresh old energy εH (ε H = 13.6 eV for hydrogen atoms). The 1 time of plasma production is τ ~ , where naa0 ε H / me a0 is the Bohr radius, na is the neutral atom density, and me is the electron mass. In thermonuclear devi
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