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The m = 2, n = 1 (where m and n are the poloidal and toroidal mode numbers, respectively) neoclassical tearing mode (NTM) has been proposed as a candidate to explain the larger than expected losses of high energy ions produced by neutral beam injection observed in several experiments. Although the numerical simulations performed so far to study the effect of NTMs on energetic ions have reproduced several features observed in experiments, the agreement is not completely satisfactory. In particular, it has been difficult to reproduce the total amount of losses, which are affected by the details of the perturbation in the edge region. In this work, we study the effect of NTMs on the confinement of energetic ions produced by NBI injection using FOCUS, a full orbit code that runs in graphical processing units. This allows us to follow the evolution of a large number of ions with modest resources. A reconstruction technique that includes the experimental information available is employed to calculate the perturbed magnetic field. The main result of this study is that when the frequency of the NTM matches the toroidal precession frequency ω tp of the trapped ions ( ω t p ∼ E , where E is the energy of the ion), the losses increase significantly. [ABSTRACT FROM AUTHOR]

The collisionless electron temperature gradient-driven instability is studied in the parameter regime relevant for field-reversed configurations. Perturbations in the electrostatic potential and all three components of the vector potential are considered and fully magnetized models, which include finite beta orbit modifications, are used for electrons and ions. It is shown that the electron temperature gradient can drive unstable modes over a wide range of values of β and η[sub e]. These modes require a finite (but small) k[sub z] and propagate in the direction opposite to the lower hybrid drift. [ABSTRACT FROM AUTHOR]

The effect of finite parallel wavenumber and electron temperature gradients on the lower hybrid drift instability is studied in the parameter regime corresponding to the TRX-2 device [Fusion Technol. 9, 48 (1986)]. Perturbations in the electrostatic potential and all three components of the vector potential are considered and finite beta electron orbit modifications are included. The electron temperature gradient decreases the growth rate of the instability but, for kz=0, unstable modes exist for ηe(=T’en0/Ten0)>6. Since finite kz effects completely stabilize the mode at small values of kz/ky([bar_over_tilde:_approx._equal_to]5×10-3), magnetic shear could be responsible for stabilizing the lower hybrid drift instability in field-reversed configurations. [ABSTRACT FROM AUTHOR]

The high beta regime of the lower hybrid drift instability is studied using a fully electromagnetic dispersion relation in the local approximation. The electrons are described using a kinetic model that includes the effect of finite beta orbit modifications and three different models (unmagnetized, magnetized without VB drifts, and magnetized with VB drifts) are used for the ions. It is found that when magnetized ions without VB drifts are considered, the modes remain unstable for larger values of beta and the spectrum is very different from the unmagnetized ion case. When VB drift effects are included, the results became very similar to the unmagnetized ion case and some arguments are provided to explain this behavior. [ABSTRACT FROM AUTHOR]

Currents flowing parallel to a magnetic field with a gradient in the perpendicular direction are present in many interesting situations in plasma physics. In Ohmic heated experiments the current gradient is accompanied by a temperature gradient, and it is shown that both gradients can drive unstable, low-frequency, localized modes. These modes are studied using various models for the electron and ion dynamics (including an integral formalism that retains finite ion gyroradius effects) and considering the effects of density gradients and collisions. A detailed numerical study of the parametric dependence of the mode frequency and structure and a mechanism for anomalous current penetration are presented. [ABSTRACT FROM AUTHOR]

Low-frequency drift dissipative modes are studied in the parameter regime relevant to field-reversed configurations. It is shown that previous theories [Phys. Fluids 30, 878 (1987)] are not accurate in that the effect of collisions was not properly included. Analytic and numerical studies with a dispersion relation that correctly includes the effect of collisions and uses the same approximations as in the above-mentioned reference have yielded no unstable modes. [ABSTRACT FROM AUTHOR]