A numerical study of confinement scaling in the advanced reversed-field pinch (RFP) is presented. In the advanced RFP, the tearing mode activity that dominates conventional RFP plasma fluctuations is reduced by current profile control (CPC). In this work, theoretical limits for confinement in the advanced RFP are explored, modelling a CPC with internally applied electric fields. The obtained scalings of ion temperature, poloidal beta value, energy confinement time and magnetic field fluctuations indicate strongly improved confinement as compared with the conventional RFP. Reactor relevant on-axis temperatures are obtained using ohmic heating alone. Pressure driven modes persist within the present 3D nonlinear, resistive, single-fluid MHD model, but may be reduced by non-ideal effects.

Density fluctuation measurements by far-forward collective scattering in the MST reversed-field pincha) Rev. Sci. Instrum. 83, 10E302 (2012); 10.1063/1.4728098Control of ideal and resistive magnetohydrodynamic modes in reversed field pinches with a resistive wall

A self-consistent zero-dimensional model of a Magnetized Target Fusion MTF configuration is presented. The plasma target is a Field Reversed Configuration (FRC). Model parameters were scanned using a Monte Carlo routine in order to determine an operating point that would correspond to reactor conditions. Albeit the model being intrinsically optimistic, the highest Q-values found only slightly exceed unity. The limited performance is due to the short dwell time of the liner, preventing a large portion of the fuel to burn.

In the reversed-field pinch (RFP), tearing modes associated with the dynamo are responsible for reduced energyand particle confinement. In this study, it is observed that by implementing current profile control (CPC) in the RFP, a dynamo-free state can be achieved. The effect of CPC in the RFP is examined by the use of numerical simulations, and scaling laws are presented for confinement parameters. The model is nonlinear MHD in 3D including finite resistivity and pressure. A linear regression analysis is performed on simulation data from a series of computer runs for a set of initial parameter values. Scaling laws are determined for radial magnetic field, energy confinement time, poloidal beta and temperature. Confinement is improved substantially as compared with the conventional RFP-the temperature reaches reactor relevant levels by ohmic heating alone. It is observed that the configuration spontaneously develops into a quasi single helicity state. The CPC scheme is designed to eliminate the fluctuating electric dynamo field E f = − v × B , using feedback of an externally imposed electric field. The focus of this study is on obtaining principal theoretical optimization of confinement in the RFP by implementing CPC and to formulate scaling laws for confinement parameters, thus investigating the reactor viability of the concept.

In the advanced reversed-field pinch (RFP), current profile control (CPC) enables energy confinement time and poloidal beta to increase substantially as compared with the conventional RFP due to reduced magnetic field stochasticity. Numerical simulations using the three-dimensional non-linear resistive MHD-code DEBSP are performed showing that the poloidal beta is not limited to the m = 0 stability criterion βθ < 1/2. Instead, as tearing modes are diminished, it may approach unity. The beta criterion is theoretically analysed and a new, more general, criterion is derived. Analytic estimates of the resistive tearing and g-mode growth rates are derived for m = 0, and it is shown that both tearing and g-mode growth rates decrease significantly as CPC is employed. Furthermore, quasi-steady state operation with increased confinement due to active control of the current profile is numerically demonstrated for the advanced RFP for a scenario with βθ < 1/2.