Physics Design for ARIES-CS

Novel stellarator configurations have been developed for ARIES-CS. These configurations are optimized to provide good plasma confinement and flux surface integrity at high beta. Modular coils have been designed for them in which the space needed for the breeding blanket and radiation shielding was specifically targeted such that reactors generating GW electrical powers would require only moderate major radii (<10 m). These configurations are quasi-axially symmetric in the magnetic field topology and have small number of field periods (≤3) and low aspect ratios (≤6). The baseline design chosen for detailed systems and power plant studies has 3 field periods, aspect ratio 4.5 and major radius 7.5 m operating at β~6.5% to yield 1 GW electric power. The shaping of the plasma accounts for ≥75% of the rotational transform. The effective helical ripples are very small (< 0.6% everywhere) and the energy loss of alpha particles is calculated to be ≤5% when operating in high density regimes. An interesting feature in this configuration is that instead of minimizing all residues in the magnetic spectrum, we preferentially retained a small amount of the non-axisymmetric mirror field. The presence of this mirror and its associated helical field alters the ripple distribution, resulting in the reduced ripple-trapped loss of alpha particles despite the long connection length in a tokamak-like field structure. Additionally, we discuss two other potentially attractive classes of configurations, both quasi-axisymmetric: one with only two field periods, very low aspect ratios (~2.5), and less complex coils, and the other with the plasma shaping designed to produce low shear rotational transform so as to assure the robustness and integrity of flux surfaces when operating at high β

Role of alpha particle damping in fast wave current drive and heating

The impact of energetic alpha particle wave absorption on the range of frequencies for efficient fast wave current drive and heating in a fusion reactor is investigated. The energetic alpha damping decrement is calculated, using a slowing down distribution function, and compared to electron and fuel ion damping over a wide range of frequencies. A combination of strong alpha damping and edge electron absorption in the higher ion harmonic regime limits core fast wave current drive to the lower harmonics (1 = 2,3). 4 refs., 4 figs

Fast wave current drive on ITER in the presence of energetic alphas

The impact of energetic alpha particle wave absorption on the range of frequencies for efficient fast wave current drive in an ITER-like fusion reactor core is investigated. The energetic alpha damping decrement is calculated, using an exact slowing down distribution function, and compared to electron and fuel ion damping over a wide range of frequencies. A combination of strong alpha damping and edge electron absorption in the higher ion harmonic regime limits efficient core fast wave current drive to the lower harmonics (1=2.3). However, high frequency fast waves may be employed to generate current in the outer plasma region. 11 refs., 7 figs

Advanced Tokamak Scenarios for the FIRE Burning Plasma Experiment

The advanced tokamak (AT) capability of the Fusion Ignition Research Experiment (FIRE) burning plasma experiment is examined with 0-D systems analysis, equilibrium and ideal-MHD stability, radio-frequency current-drive analysis, and full discharge dynamic simulations. These analyses have identified the required parameters for attractive burning advanced tokamak plasmas, and indicate that these are feasible with the present progress on existing experimental tokamaks

Fractional power operation of tokamak reactors: issues and prospects

The capability of a power plant to operate at a wide range of output power is essential for initial commissioning and normal maintenance. In this work, we explore critical physics issues related to operating a tokamak fusion reactor at fractions of its rated power and identify methods for power control. Analysis is carried out with a steady-state, profile-dependent, zero-dimensional power balance model of the plasma in which several empirical transport scalings appropriate to tokamaks are used. It is found that reactor operation depends strongly on the confinement model, plasma ..beta.. limit, and the effect of alpha power on transport. Parametric calculations indicate that density, auxiliary heating power and an effective external confinement control mechanism are the key control elements, and burn control is required in most cases. Transition between power plateaus is facilitated by operating, in the hybrid transformer mode. In general, the impact of fractional power operation on full power reactor designs appears to be small

Turbulence Scattering of High Harmonic Fast Waves

Effect of scattering of high-harmonic fast-magnetosonic waves (HHFW) by low-frequency plasma turbulence is investigated. Due to the similarity of the wavelength of HHFW to that of the expected low-frequency turbulence in the plasma edge region, the scattering of HHFW can become significant under some conditions. The scattering probability increases with the launched wave parallel-phase-velocity as the location of the wave cut-off layer shifts toward the lower density edge. The scattering probability can be reduced significantly with higher edge plasma temperature, steeper edge density gradient, and magnetic field. The theoretical model could explain some of the HHFW heating observations on the National Spherical Torus Experiment (NSTX)