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The five-dimensional finite-orbit Monte Carlo code ORBIT-RF [M. Choi et al., Phys. Plasmas 12, 1 (2005)] is successfully coupled with the two-dimensional full-wave code all-orders spectral algorithm (AORSA) [E. F. Jaeger et al., Phys. Plasmas 13, 056101 (2006)] in a self-consistent way to achieve improved predictive modeling for ion cyclotron resonance frequency (ICRF) wave heating experiments in present fusion devices and future ITER [R. Aymar et al., Nucl. Fusion 41, 1301 (2001)]. The ORBIT-RF/AORSA simulations reproduce fast-ion spectra and spatial profiles qualitatively consistent with fast ion D-alpha [W. W. Heidbrink et al., Plasma Phys. Controlled Fusion 49, 1457 (2007)] spectroscopic data in both DIII-D [J. L. Luxon, Nucl. Fusion 42, 614 (2002)] and National Spherical Torus Experiment [M. Ono et al., Nucl. Fusion 41, 1435 (2001)] high harmonic ICRF heating experiments. This work verifies that both finite-orbit width effect of fast-ion due to its drift motion along the torus and iterations between fast-ion distribution and wave fields are important in modeling ICRF heating experiments. [ABSTRACT FROM AUTHOR]

To fully account for the wave-particle interaction physics in ion cyclotron resonant frequency (ICRF) heating experiment, finite orbit effects and non-Maxwellian distribution have to be self-consistently coupled with full-wave solutions. For this purpose, the five-dimensional Monte Carlo code ORBIT-RF [M. Choi et al., Phys. Plasmas 12, 1 (2005)] is being coupled with the two-dimensional full-wave code AORSA [E. F. Jaeger et al., Phys. Plasmas 13, 056101 (2006)] to iteratively evolve the ion distribution in four-dimensional spatial velocity space that is used to update the dielectric tensor in AORSA for evaluating the full-wave fields. In this paper, it is demonstrated that using the full-wave fields from a Maxwellian dielectric tensor in AORSA and confining the resonant ions to their initial orbits in ORBIT-RF, ORBIT-RF largely reproduces the AORSA linear wave absorption profiles for fundamental and higher harmonic ICRF heating. An exception is an observed inward shift in the ORBIT-RF absorption peak for high harmonics near the magnetic axis compared with that of AORSA, which can be attributed to a finite orbit width effect. The success of this verification supports the validity of the Monte Carlo wave-particle interaction model and the readiness of the iterative coupling between ORBIT-RF and AORSA for an improved modeling of ICRF heating experiments. [ABSTRACT FROM AUTHOR]

A class of very high poloidal beta (β[sub p]) equilibria is exhibited in which εβ[sub p] (ε is the inverse aspect ratio) exceeds analytic equilibrium limits previously anticipated from simplified large aspect ratio models, as well as previous experimental equilibrium limits. The extension in these limits is shown to be due to a combination of finite aspect ratio effects and strong cross section shaping. In a conventional aspect ratio configuration, equilibria with εβ[sub p] = 3 exist, which is 50% higher than both the previously observed record and the analytically predicted limit. For very low aspect ratio with ε[sup -1] = 1.4, typical of spherical tori, values of εβ[sub p] = 5 are possible. [ABSTRACT FROM AUTHOR]

When electron cyclotron wave propagation can be treated by geometric optics, the local current drive efficiency can be expressed as an integral. A kernel for the integral that takes into account important neoclassical effects such as particle trapping and orbit modification is derived using a momentum-conserving collision operator. For absorption at the low field side of a tokamak, trapping effects reduce the efficiency significantly, while for absorption at the high field side, modification of passing particle orbits also diminishes the driven current, although to a lesser extent. [ABSTRACT FROM AUTHOR]

The poloidal electric field generated by electron heating in a collision dominated tokamak plasma is calculated by the adjoint method. The physical mechanism is elucidated as due to a combination of the Doppler shifted cyclotron resonance and magnetic field inhomogeneity. For uniform rf field on a flux surface, the normalized electrostatic potential is found to be much smaller than the inverse aspect ratio for realistic power levels. [ABSTRACT FROM AUTHOR]

Runaway effects on lower-hybrid current ramp-up are studied numerically using a twodimensional Fokker-Planck analysis and a nonlinear circuit equation. Runaway contribution to the inductance is shown to be important in limiting the magnitude of the induced electric field. This tends to reduce the current ramp-up efficiency. However, for a range of ω[sub p]/Ω, the anomalous Doppler instability can be excited and the runaway production rate as well as the associated inductance is significantly reduced when that happens. This allows the ramp-up efficiency to be further increased. [ABSTRACT FROM AUTHOR]

The effects of scattering by density fluctuations on the single pass lower-hybrid propagation in tokamaks for current drive are analyzed in a cylindrical plasma model with sheared magnetic field. Even for the launched N[sub ] spectrum peaked around 2, the turbulent scattering and propagation in the sheared field significantly modifies the N[sub ] spectrum so that the waves can effectively couple to slower electrons. At low densities, a small amount of the incident energy experiences a large N[sub ] upshift and creates a high-energy electron tail which interacts with the main part of the wave energy. At higher densities, the bulk of the wave energy is shifted in Nil before damping resulting in lower current drive efficiencies. [ABSTRACT FROM AUTHOR]

Studies the confinement and the stability of properties of the DIII-D tokamak high-performance discharges in terms of rotational and magnetic shear. Experimental results obtained from the negative central magnetic shear (NCS); Core transport barrier that forms inside the NCS region; Performance of NCS discharges with strongly peaked pressure profiles.