Electron cyclotron emission detection of neoclassical tearing modes for control for ITER.

Successful operation of ITER requires control of magnetic instabilities including neoclassical tearing modes (NTMs) that can degrade confinement and lead to disruption. Low latency detection by electron cyclotron emission (ECE) diagnostics has been demonstrated in a few current experiments. Using a synthetic diagnostic, we demonstrate low latency NTM detection for ITER with plasmas described by ITER IMAS database scenarios and with realistic limitations imposed on the instrumentation by these high temperature scenarios.

Natural velocity of magnetic islands.

The phase velocity of magnetic islands is calculated in the semicollisional regime with cold ions. Two solution branches arise, corresponding to islands propagating with the ions and with the electrons. For the ion branch the phase velocity and the polarization current are small.

Analytic solution for low-frequency rf sheaths in pulsed discharges.

The equations governing the evolution of rf-driven sheaths are solved analytically in the regime where the rf frequency is small compared to both the ionic plasma frequency and the ion transit time in the sheaths. Poincaré's map of first return is used to gain geometric insight into the dynamics of the circuit-sheath system. The requirements of minimizing wall bombardment while maximizing the efficiency of the coupling to the substrate sheath are shown to lead to an optimum value for the blocking capacitance in asymmetric discharges.

Finite Larmor-radius theory of magnetic island evolution.

Gyrokinetic theory is used to investigate the effect of the polarization drift on magnetic island evolution. Three regimes are found. For island phase velocities between the ion- and electric-drift velocities, the polarization current is shown to be stabilizing.