Controlling a new plasma regime.

Success of the UK's Spherical Tokamak for Energy Production (STEP) programme requires a robust plasma control system. This system has to guide the plasma from initiation to the burning phase, maintain it there, produce the desired fusion power for the desired duration and then terminate the plasma safely. This has to be done in a challenging environment with limited sensors and without overloading plasma-facing components.

Evidence of Electron Heating by Alpha Particles in JET Deuterium-Tritium Plasmas.

The fusion-born alpha particle heating in magnetically confined fusion machines is a high priority subject for studies. The self-heating of thermonuclear fusion plasma by alpha particles was observed in recent deuterium-tritium (D-T) experiments on the joint European torus. This observation was possible by conducting so-called "afterglow" experiments where transient high fusion yield was achieved with neutral beam injection as the only external heating source, and then termination of the heating at peak performance.

Control of magnetohydrodynamic stability by phase space engineering of energetic ions in tokamak plasmas.

Virtually collisionless magnetic mirror-trapped energetic ion populations often partially stabilize internally driven magnetohydrodynamic disturbances in the magnetosphere and in toroidal laboratory plasma devices such as the tokamak. This results in less frequent but dangerously enlarged plasma reorganization. Unique to the toroidal magnetic configuration are confined 'circulating' energetic particles that are not mirror trapped.

Demonstration of effective control of fast-ion-stabilized sawteeth by electron-cyclotron current drive.

In a tokamak plasma, sawtooth oscillations in the central temperature, caused by a magnetohydrodynamic instability, can be partially stabilized by fast ions. The resulting less frequent sawtooth crashes can trigger unwanted magnetohydrodynamic activity. This Letter reports on experiments showing that modest electron-cyclotron current drive power, with the deposition positioned by feedback control of the injection angle, can reliably shorten the sawtooth period in the presence of ions with energies >or=0.

Synergy of electron-cyclotron and lower-hybrid current drive in steady-state plasmas.

Improvement (up to a factor of approximately 4) of the electron-cyclotron (EC) current drive efficiency in plasmas sustained by lower-hybrid (LH) current drive has been demonstrated in stationary conditions on the Tore Supra tokamak. This was made possible by feedback controlled discharges at zero loop voltage, constant plasma current, and constant density. This effect, predicted by kinetic theory, results from a favorable interplay of the velocity space diffusions induced by the two waves: the EC wave pulling low-energy electrons out of the Maxwellian bulk, and the LH wave driving them to high parallel velocities.